Report Version 7 - Final
An investigation of clopyralid and
aminopyralid in commercial
composting systems
A review of existing research on the occurrence, fate and management of residual risks from the herbicides clopyralid and aminopyralid during PAS 100 green waste composting processes and subsequent application of composts to susceptible agricultural crops.
Project code: OAV031-002 Research date: June 2009 to May 2010
Date: October 2010
WRAP helps individuals, businesses and
local authorities to reduce waste and
recycle more, making better use of
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Document reference: WRAP, 2009, An investigation of clopyralid and aminopyralid in composting systems. Project OAV031-
002. Report prepared by Dr E Jane Gilbert, Josef Barth, Enzo Favoino and Dr Robert Rynk. .
Written by: Dr E Jane Gilbert, Josef Barth, Enzo Favoino and Dr Robert Rynk
Front cover photography: Harvesting grass for silage
WRAP, Dr E Jane Gilbert, Josef Barth, Enzo Favoino and Dr Robert Rynk believe the content of this report to be correct as at the date of writing. However, factors such as
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An investigation of clopyralid and aminopyralid in commercial composting
systems 3
Executive summary
Clopyralid and aminopyralid are herbicides that retard the growth of some plants by mimicking natural plant
hormones (auxins). They have been licensed internationally to control annual and perennial broadleaf weeds in
certain crops, turf and pastureland. When the manufacturers‘ guidelines are followed, herbicide residues should
not be present in materials destined for composting, and the resulting composts will present no risks to crops.
However, there have been a number of reported incidences in the USA and New Zealand where herbicide
residues have been identified in composting feedstocks and composted products. When present in these
products, the residues have been associated with phytotoxic effects in susceptible plants, including commercially-
grown crops such as tomatoes.
The objectives of this project were to: Review existing research on the occurrence, fate and management of
residual risks from the herbicides clopyralid and aminopyralid during BSI PAS 100: 2005 green waste composting
processes and subsequent application of composts to susceptible agricultural crops; To review previous examples
where residual risks from these herbicides had been realised and managed elsewhere in the world; To collate this
information and identify options for managing any identified residual risks from these herbicides to sensitive
crops.
Based on the information gathered during this study, risks from persistent herbicide contamination of composts
are thought to be low.
Clopyralid is sold for both amateur and professional use in the UK, either singly, or in conjunction with other
herbicides. A total of 34,344 kg (34.3 tonnes) of clopyralid was applied to agricultural land in 2006 over an area
of 304,738 ha across Great Britain. During 2009 a total of 867 kg was sold in amateur products, equivalent to
2.5% of the 2006 agricultural application estimate. Data on quantities of aminopyralid sold for professional use
during these periods were not available – no formulations of this compound are currently available for amateur
use. Neither compound presents a risk to human health, animal health, crops or the wider environment if used
according to their manufacturers‘ instructions.
The difficulty for compost site operators is that clopyralid and aminopyralid are effective at very low
concentrations, and that treated plant material may accidentally enter composting feedstocks from a variety of
diffuse (non-point) sources, which means that standard HACCP procedures may not be sufficient to prevent
unsuitable material from being processed. The feedstocks of concern are grass and animal manures. However,
for herbicide residues in the finished composts to be present at a sufficient dose to impact upon sensitive crops
when those composts are used, a significant quantity of herbicide-contaminated material must be composted
together for a sufficiently short time and the composts be applied to sufficiently sensitive crops at sufficiently high
rates. Such coincidences of circumstance are known to have occurred in the USA and New Zealand, and although
uncommon they do prompt questions about the suitability of composts for particularly sensitive end uses.
Clopyralid degradation during composting is highly variable: degradation appears to be biphasic (i.e. degradation
occurs in two separate phases); the composting temperature appears to affect the rate of degradation (it is faster
at higher temperatures); the initial concentration of clopyralid affects its rate of degradation (it is slower at higher
initial concentrations); and, the rate of degradation is faster during the active phase of composting compared
with the maturation phase. Once applied to soil, the rate of degradation of clopyralid appears to be dependent
upon moisture, temperature, the application rate, the extent of aerobicity in the soil and the amount of organic
matter. Notably clopyralid binds to organic matter, which appears to slow degradation. Clopyralid is stable in
anaerobic environments and has a high leachability potential.
In a number of studies increases in clopyralid concentrations during the early phases of composting were noted,
due to the faster rate of degradation of organic matter. Half-lives of between 10 to 30 days were reported,
although in one experiment degradation was not observed even after 112 days. These studies indicate that short
composting periods may not be sufficient to degrade clopyralid should it be present in composting feedstocks.
However, as most compost applied to fields would be ploughed prior to planting crops, it seems likely that
potential contamination would present a minimal risk. Where compost has been used as a mulch (for example, in
the growth of top fruit) no incidences of herbicide effects have been documented.
Aminopyralid displays many similar properties to clopyralid: it is stable in water, is stable to anaerobic
degradation and is highly mobile in the soil. Aminopyralid is rapidly degraded via photolysis, whereas clopyralid is
An investigation of clopyralid and aminopyralid in commercial composting
systems 4
stable to light. The main routes of dissipation of aminopyralid appear to be through mineralisation and soil
leaching. Aminopyralid appears to be more stable than clopyralid in soil (half-life of 103.5 days compared with 25
days, respectively). It has been suggested that aminopyralid has a greater biological activity than clopyralid.
The review did not identify any research assessing the degradation of aminopyralid during composting.
Based on the information gathered during this study, risks from persistent herbicide contamination of composts
are thought to be low, particularly from aminopyralid, use of which is now more strictly controlled. However, we
have set out a number of recommendations aimed at either preventing or reducing the possible risks of clopyralid
contamination in compost.
The extent to which there is potential for contaminated grass (or other green wastes) to enter a commercial
composting facility through a municipal waste collection service and to cause problems is currently unquantified,
however, the most robust long term strategy to ensure compost quality is to eliminate the potential for
contamination to occur at source. As long as these products are sold for amateur use, the onus should remain on
herbicide manufacturers to provide clear, practical, easy-to-follow advice to householders for recycling grass and
other garden wastes following herbicide application – and for householders to follow this advice.
The challenges faced by local authorities in meeting their targets to divert biodegradable municipal waste from
landfill should not be underestimated; hence disposal of grass or other green wastes in residual (mixed or ‗black
bag‘) waste collections should not be encouraged.
Based on experience from other countries where herbicide residues are known to have impacted upon sensitive
crops through composts, appropriate bioassay testing is expected to give the most direct assurance of compost
quality. A suitable bioassay is already compulsory within the PAS 100 specification, but it is recommended that
the existing PAS 100 bioassay be validated:
Using compost containing concentrations of clopyralid known to adversely affect plant growth;
Against red clover (Trifolium pratense), as this has a high degree of sensitivity to clopyralid and ability to
produce observable results after 14 days; and
Against the test methods described by Brinton et al., 2005, and the Recycled Organics Unit, 2007c, as
these were developed specifically to identify low concentrations of herbicide in the growing medium.
The extent to which compost manufacturers can control clopyralid contamination in feedstocks is limited.
However, we recommend that compost site operators:
Remain vigilant to the potential for clopyralid contamination during late spring and summer when the
input of grass clippings is likely to be at its greatest, and ensure that this is adequately addressed in
HACCP plans (where appropriate);
Communicate with suppliers of feedstocks to highlight the potential for contamination through the use of
clopyralid-containing herbicides. This may take the form of a Contract of Supply with landscapers,
grounds maintenance and sports turf professionals to highlight the potential for contamination, and
ensure, as far as reasonably practicable, that feedstocks are not delivered for composting within a year
of clopyralid application. Information on the risks and safe management of treated feedstocks could be
developed for communication to professionals when they deliver feedstocks to a composting site. These
initiatives could usefully be achieved through a joint exercise between with the manufacturers of
clopyralid, the composting industry and in consultation with WRAP;
Consider increasing the frequency of bioassay testing for composts intended for use in growing media or
to raise protected crops, however, it is acknowledged that this will entail additional costs;
Ensure that high-risk composted animal manures be sent for use in non-sensitive applications. This
could be addressed through a contract of supply (which already exists for agricultural and field
horticultural crops through the Compost Quality Protocol in England and Wales). As a matter of course,
compost producers should make their customers aware of the suitability of their composts for different
end uses;
Adhere to the 2010 WRAP Guidelines for the Specification of Quality Compost for use in Growing Media
for all compost sold for use in either growing media or protected crops.
An investigation of clopyralid and aminopyralid in commercial composting
systems 5
Contents
1.0 Introduction ................................................................................................................................ 8 2.0 Methodology ............................................................................................................................... 8 3.0 Properties of clopyralid and aminopyralid ................................................................................. 9
3.1 Chemical and physical properties .......................................................................................... 9 3.2 Toxicology .......................................................................................................................... 9 3.3 Biological mode of action and target plants .......................................................................... 10 3.4 Licensed applications in the UK ........................................................................................... 11
3.4.1 Clopyralid ............................................................................................................. 11 3.4.2 Aminopyralid ........................................................................................................ 12
4.0 Herbicide dissipation and degradation pathways.................................................................... 13 5.0 Clopyralid dissipation and degradation ................................................................................... 14
5.1 Dissipation and degradation in soils .................................................................................... 14 5.2 Dissipation and degradation of clopyralid during composting ................................................. 15
5.2.1 Composting feedstocks .......................................................................................... 15 5.2.2 Fate during composting ......................................................................................... 15
5.3 Aminopyralid dissipation and degradation ............................................................................ 18 5.4 Composting feedstocks ...................................................................................................... 19
6.0 Compost contamination: an historical perspective ................................................................. 20 6.1 Clopyralid ......................................................................................................................... 20
6.1.1 Concentrations detected ........................................................................................ 20 6.1.2 The situation in Washington State, USA .................................................................. 21
6.2 Aminopyralid..................................................................................................................... 22 6.3 Picloram ........................................................................................................................... 22
7.0 Compost testing and bioassays ................................................................................................ 23 8.0 Effects of clopyralid and aminopyralid on plant growth ......................................................... 23
8.1 Application issues .............................................................................................................. 23 8.2 Effect of clopyralid on crop rotation .................................................................................... 23 8.3 Translocation in Canada thistle and biological activity ........................................................... 24 8.4 Translocation into tree leaves ............................................................................................. 24 8.5 Enclosed growing of crops in polytunnels and glasshouses .................................................... 24 8.6 Rainfall ............................................................................................................................. 24 8.7 Compost application rates .................................................................................................. 24
9.0 Managing the risks ................................................................................................................... 25 9.1 Composting feedstocks ...................................................................................................... 25 9.2 Compost use ..................................................................................................................... 27
9.2.1 Agriculture and field horticulture ............................................................................ 27 9.2.2 Growing media and protected crops ....................................................................... 27 9.2.3 Landscaping and grounds maintenance ................................................................... 27
10.0 Recommendations .................................................................................................................... 28 10.1 Municipal wastes ............................................................................................................... 28 10.2 Compost manufacturers ..................................................................................................... 28 10.3 Compost testing ................................................................................................................ 29
11.0 References ................................................................................................................................ 30 Appendix 1 ............................................................................................................................................ 33 Appendix 2 ............................................................................................................................................ 40 Literature review of garden waste composition .................................................................................. 40 12.0 Introduction .............................................................................................................................. 40
12.1 Results from England .................................................................................................... 40 12.1.1 Morpeth, Northumberland ...................................................................................... 40 12.1.2 Dogsthorpe, Peterborough ..................................................................................... 41 12.1.3 Nine English local authorities.................................................................................. 41
12.2 European data ............................................................................................................... 43 12.2.1 Hamburg, Germany ............................................................................................... 43 12.2.2 Aarhus, Denmark .................................................................................................. 43
12.3 Conclusions .................................................................................................................... 43
An investigation of clopyralid and aminopyralid in commercial composting
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Figures
Figure 1 – Clopyralid-induced damage in a tomato plant ................................................................................ 10 Figure 2 – Fates of pesticides in compost applied to soil ................................................................................ 13 Figure 3 – Seasonal variation in proportion of grass clippings collected in green / food waste co-collection at
Castle Morpeth in 1995/96 .......................................................................................................................... 41 Figure 4 – Variation in grass collected in a garden / food waste collection scheme in Hamburg, Germany .......... 43
Tables
Table 1 - Physico-chemical properties of clopyralid and aminopyralid ................................................................ 9 Table 2 - Summary toxicological properties of clopyralid and aminopyralid ........................................................ 9 Table 3 – Application of clopyralid to various crop types in 2006 (Great Britain) ............................................... 12 Table 4 – Environmental fates of clopyralid (soil and water) .......................................................................... 14 Table 5 - Measured half-lives of clopyralid in composting feedstocks .............................................................. 17 Table 6 – Degradation and fate of aminopyralid ............................................................................................ 18 Table 7 – Concentrations of aminopyralid in harvested crops in Canada and North America .............................. 19 Table 8 – Summary of compost contamination by clopyralid .......................................................................... 20 Table 9 – Composting feedstocks and their potential to be contaminated with clopyralid .................................. 26 Table 10 – Clopyralid-containing products sold in the UK for amateur use ....................................................... 33 Table 11 – Clopyralid-containing products sold in the UK for professional use .................................................. 34 Table 12 - Aminopyralid-containing products approved for use in November 2009 ........................................... 37 Table 13 - Aminopyralid-containing products approved for use before July 2008 .............................................. 37 Table 14 - Picloram containing products registered in the UK ......................................................................... 39 Table 15– Summary of green waste composition in the Morpeth trial .............................................................. 40 Table 16– Summary of green waste composition at Dogsthorpe ..................................................................... 42
An investigation of clopyralid and aminopyralid in commercial composting
systems 7
Glossary
a.e. Acid equivalent
Auxin Plant hormones that control plant growth and behaviour
Biphasic degradation Degradation occurring in two separate phases, usually with different decay rates
CAS Chemical Abstracts Service registry number
DAT Day(s) after treatment
DT 50 DT50 is the time required for the pesticide concentration under defined conditions to decline
to 50% of the amount at application.
Ha Hectare
IUPAC International Union of Pure and Applied Chemistry reference
LOQ Limit of Quantitation
OM Organic matter
PHI Pre-harvest interval
Ppb Parts per billion i.e.
Ppm Parts per million i.e.
SOM Soil Organic Matter
t1/2 Half life, which is the time taken for the concentration to decrease by 50%
US EPA United States Environmental Protection Agency
Acknowledgements
The authors are grateful to the following individuals for providing information and insight:
Ron Alexander - Ron Alexander Associates, USA
Dr Will Brinton - Woods End Laboratory, USA
Dan Caldwell - CER-Compost, USA
Angus Campbell, Recycled Organics Unit, New South Wales, Australia
Jeff Gage - Compost Design Services, USA
Elaine Gotts – Scotts Ltd, UK
Steve Higginbotham - Stewardship Ltd, UK
Ruth Rogers – Chemicals Regulation Directorate, UK
David Senior – Vitax Ltd, UK
Anne Thompson and Andy Bailey - Dow AgroSciences, UK
Jennifer Thwaites – Horticultural Trades Association, UK
Chris Wild - Rigby Taylor Ltd, UK
An investigation of clopyralid and aminopyralid in commercial composting
systems 8
1.0 Introduction Clopyralid and aminopyralid are herbicides that retard the growth of some plants by mimicking natural plant
hormones (auxins). They have been licensed internationally to control annual and perennial broadleaf weeds in
certain crops, turf and pastureland. Although extremely effective in their intended uses, herbicide residues have
been identified in composting feedstocks and composted products in the USA and New Zealand, where they have
been associated with phytotoxic effects in susceptible plants, including commercially-grown crops such as
tomatoes.
Based on scientific literature, a risk assessment of the application of composted green wastes to agricultural land
by the Macaulay Land Use Research Institute (2009), suggested that clopyralid may present a risk to crop plants
following compost application. The objective of this work, therefore, was to review existing research on the
occurrence, fate and management of residual risks from the herbicides clopyralid and aminopyralid during BSI
PAS 100 green waste composting processes and subsequent application of composts to susceptible agricultural
crops. Specifically, this report:
Summarises the occurrence and fate during composting of the herbicides aminopyralid and clopyralid
within commercial composting systems;
Summarises the environmental fates of aminopyralid and clopyralid residues in soil; and
Provides options for managing any identified residual risk(s) to sensitive crops from aminopyralid and
clopyralid.
2.0 Methodology This study comprised a comprehensive literature review followed up by direct contact with relevant individuals
and organisations.
In conducting the literature review, search terms were established, including synonyms and spelling variations. A
number of on-line databases (e.g. PubMed and Agricola) and search engines e.g. Google Scholar and
www.ojose.com were interrogated using the standardised search terms. Hand searches of conference
proceedings (e.g. ORBIT proceedings) and grey literature held by the consortium partners were conducted.
Literature in German, Italian, Spanish and Swedish were also searched:
In Germany, the archive of the German Compost Quality Assurance Organisation (the BGK), databases
of the Environmental Information System of the State of Baden-Wuerttemberg UIS-BW (where most of
the research on organic pollutants in compost and soils is carried out) were reviewed;
In Sweden, Samsoek (which provides access to 41 Swedish Libraries at the Swedish Agricultural
University SLU) and the Biological Waste Treatment Working Group at the Swedish Waste Management
Association were contacted.
Information from the Chemicals Regulation Directorate (formerly the Pesticides Safety Directorate) and product
safety data sheets from licensed manufacturers of clopyralid and aminopyralid were obtained.
Each acquired document was assigned a unique reference number, then graded depending upon whether it was
peer reviewed, a technical or non-technical report, then catalogued in a database alongside a short summary.
This was used as the basis of a secondary literature screen, in which publications cited in reports obtained in the
initial screen were obtained. Search terms were expanded accordingly.
An investigation of clopyralid and aminopyralid in commercial composting
systems 9
3.0 Properties of clopyralid and aminopyralid Clopyralid and aminopyralid are herbicides that retard the growth of some plants by mimicking natural plant
hormones (auxins). They have been licensed internationally to control annual and perennial broadleaf weeds in
certain crops, turf and pastureland. Specific information about these herbicides is detailed below.
3.1 Chemical and physical properties Clopyralid and aminopyralid are both pyridine carboxylic acid compounds and their key properties are summarised
in Table 1 (Dow AgroSciences, 1998, and PPDB web site, 2009 a and b).
Table 1 - Physico-chemical properties of clopyralid and aminopyralid
Property Clopyralid Aminopyralid
Chemical name 3,6-dichloro-2-pyridinecarboxylic acid (CAS*)
3,6-dichloropyridine-2-carboxylic acid
(IUPAC**)
3,6-dichloropicolinic acid
4-amino-3,6-dichloro-2-pyridinecarboxylic
acid (CAS*)
4-amino-3,6-dichloropyridine-2-carboxylic
acid (IUPAC**)
Molecular mass 192.0 207.0
Empirical formula C6H3Cl2NO2 C6H4Cl2N2O2
Structural formula
Chemical family Pyridine carboxylic acid Pyridine carboxylic acid
Solubility in water High High
Volatility Low Low
Leachability Groundwater Ubiquity Score (indicator of
leachability) = 5.06 (high)
Groundwater Ubiquity Score (indicator of
leachability) = 4.78 (high)
Koc - Organic-
carbon sorption
constant (ml g-1)
***
5 (very mobile)
Decreases with increasing pH
8 (very mobile)
Decreases with increasing pH
* Chemical Abstracts Service registry number
** International Union of Pure and Applied Chemistry reference *** The Koc measures the affinity for pesticides to sorb to organic carbon: the higher the value, the stronger the tendency to attach to and move with carbon in soils. Koc values greater than 1000 indicate strong adsorption to soil, whilst chemicals with lower Koc values (less than 500) tend to move more with water than be adsorbed to sediment.
3.2 Toxicology Both clopyralid and aminopyralid appear to present a low risk to human health and exhibit low to moderate
ecotoxicity across a range of indicator species (Table 2; PPDB web site, 2009 a and b).
Table 2 - Summary toxicological properties of clopyralid and aminopyralid
Toxicity Clopyralid Aminopyralid
Eco toxicity Low to moderate, although may affect some
arthropods
Low bioaccumulation potential
Low to moderate
Low bioaccumulation potential
Human health Not acutely toxic
Unknown reproduction / development effects
Respiratory tract irritant
Not acutely toxic
Eye irritant
An investigation of clopyralid and aminopyralid in commercial composting
systems 10
3.3 Biological mode of action and target plants Clopyralid and aminopyralid are chemicals that mimic indole acetic acid (IAA), a plant growth hormone (auxin),
that induces cell elongation and division (Tu et al., 2001). They bind to the IAA receptor sites in plant cells,
thereby preventing the natural auxin from exerting its normal effect. As such, they impede the growth of certain
plants, resulting in stunted growth (see below), and ultimately death (Dow AgroSciences, 1998). They are used
as post-emergence herbicides (that is, they are applied after the weeds have started to grow; PPDB web site,
2009 a and b). Both clopyralid and aminopyralid are systemic, and enter plants through both the roots and
leaves; clopyralid is known to be translocated through the plant through both the xylem and phloem tissues,
effectively impacting all parts of the growing plant (Dow AgroSciences, 1998). Symptoms of clopyralid activity
have been documented as (Dow AgroSciences, 1998):
inhibited root and shoot growth;
thickened roots and inhibited root hair production;
thickened, curved, and twisted shoots, stems and leaves;
parallel venation (narrow leaves with callus tissue);
cupping and crinkling of leaves;
callus (hardened) growth on stems;
cracked stems; and
proliferated growth.
An example of clopyralid damage is shown in Figure 1.
Figure 1 – Clopyralid-induced damage in a tomato plant
An investigation of clopyralid and aminopyralid in commercial composting
systems 11
Clopyralid targets four major broadleaf families (Dow AgroSciences, 1998) namely:
Asteraceae, which is sometimes referred to as the Compositae (commonly known as the aster, daisy, or
sunflower family); includes plants such as sunflower, cocklebur, ragweed, chicory, scentless chamomile,
Canada thistle, knapweed, dandelion, and perennial sow-thistle;
Fabaceae, which is sometimes referred to as Leguminosae (commonly known as the legume, pea, bean
or pulse family); includes plants such as clover, black medic, vetch and mesquite;
Solanaceae, commonly known as the nightshade family or potato family; includes plants such as
nightshade, bryony, tomato and aubergine; and
Polygonaceae, commonly known as the knotweed family; includes plants such as fat hen and docks.
Aminopyralid is also effective against species in the Asteraceae (Compositae), Fabaceae (Leguminosae) and
Solanaceae families.
Both aminopyralid and clopyralid are used to control broadleaf weeds in grasslands (agricultural and amenity).
3.4 Licensed applications in the UK 3.4.1 Clopyralid Clopyralid is sold for both amateur (nine products) and professional (35 products) use in the UK (see Table 10
and Table 11 in Appendix 1), either singly, or in conjunction with other herbicides. Formulation and
concentrations vary between products and are dependent upon crop types, which influence application rates and
restrictions, such as timing of application before harvest or flowering.
Clopyralid is marketed by a number of companies, but sales data are limited. Agricultural application rates were
available from the Food and Environment Research Agency (Pesticides Usage Statistics web site, 2009) for 2006
(the latest year for which data were available), and are summarised in Table 3. A total of 34,344 kg (34.3
tonnes) of clopyralid was applied in 2006 to a treated area of 304,738 ha across Great Britain. By contrast, a total
of 867 kg was sold in amateur products in 2009 (David Senior and Elaine Gotts, Personal Communications),
equivalent to 2.5 % of the 2006 agricultural application estimate.
Labels on amateur products recommend use between April – September (Verdone), and April – October (Vitax),
which both coincide with the maximum quantities of grass clippings received at composting sites (see Appendix
2). Due to the complexities of retail supply chains, data were not available to assess variability of sales
throughout the year; however, data supplied by the Horticultural Trades Association indicated that perceived
sales of lawn care fertilizers1 peaked during April and May (Jennifer Thwaites, Personal Communication; data not
shown). Collectively 89 % of perceived sales were made between April and October, again coinciding with the
period during which grass clippings could be received at composting sites.
Sales data were only available from a minority of suppliers providing clopyralid formulations for professional (lawn
care) applications. These data indicate that 367 kg were sold into this market during 2009 (David Senior and
Chris Wild, Personal Communications), but the true figure is thought to be significantly higher than this.
1 As specific sales data for clopyralid containing products were unavailable, we obtained data on sales of lawn care fertilizers on the assumption that purchasing trends and use of these products would likely mirror those of lawn care herbicides. Data were supplied by the Horticultural Trades Association as part of their Garden Industry Monitor and are based on consumer perceived spend rather than actual sales.
An investigation of clopyralid and aminopyralid in commercial composting
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Table 3 – Application of clopyralid to various crop types in 2006 (Great Britain)
Crop
Total area treated*
(ha)
Total mass applied
(kg)
Cereals 1,779 366
Oil seeds 67,430 5,422
Peas and beans 440 40
Potatoes 7.7 <1
Set aside 11,203 1,335
Beet crops** 93,536 7,098
Other arable crops 4,544 411
Vegetable brassicas 1,337 155
Lettuce and other leafy salad ND ND
Onions and leeks 1,845 113
Carrots and parsnips ND ND
Other root vegetables 50 4.7
Other outdoor vegetables 852 65
Maize and sweetcorn 1,716 188
Other fodder crops 274 34
Grassland 123,026 19,357
Top fruit and hops 12 1.7
Strawberries 790 93
Other soft fruit 79 10
Outdoor ornamental crops 808 102
Protected edible crops ND ND
Protected ornamental crops*** <1 <1
Mushrooms ND ND
* Area treated refers to the active substance treated area. This is the basic area treated by each active
substance, multiplied by the number of times the area was treated e.g. A field of 3 ha is treated 4 times with
active X. Therefore, the area treated is 12 ha (3x4)
** This includes sugar beet and beetroot, as well as fodder beet and mangels
*** This includes edible plants for propagation
ND No data were available, either for 2006 or the preceding years, suggesting that clopyralid was not recorded
as used on these crops.
The data in Table 3 suggest that animal feed crops and grassland are the largest recipient of
clopyralid in the agricultural sector.
3.4.2 Aminopyralid Aminopyralid is licensed for sale in the UK in nine products (as of November 2009) to control a range of weeds on
grassland for grazing by sheep and cattle. Use of the treated grass is restricted, with silage making or hay
harvesting from treated land not permitted within one year following application of the herbicide. Aminopyralid is
also available for professional use in amenity situations to control pernicious or invasive weeds (Chemicals
Regulation Directorate, 2009) (Table 12). Until July 2008 eight products were approved for a variety of
applications (Table 13), however, approvals for their sale, supply and use were suspended temporarily in 2008 by
the (former) Pesticides Safety Directorate (now the Chemicals Regulation Directorate; Pesticides Safety
Directorate, 2008a). Products were marketed by two companies, Dow AgroSciences Ltd and AgChemAccess Ltd
(a brokerage service for agrochemical products). Dow AgroSciences have stated that they are the sole
manufacturer globally (Dow, 2008).
The previously licensed products are listed in Table 13 in the Appendix (Association for Organics Recycling web
site, 2009). Notably only one was licensed for amateur use, although this was never marketed (Anne Thompson,
Dow AgroSciences, Personal Communication), with the remainder licensed for use by professionals, principally to
control deep-rooted perennial weeds in grassland, including docks, thistles, nettles, and ragwort (Manure Matters
web site, 2009).
An investigation of clopyralid and aminopyralid in commercial composting
systems 13
Of the six million hectares of managed grassland2 in the UK, approximately 114,000 ha of agricultural grassland
were treated with a product containing aminopyralid during 2008 (Anne Thompson, Dow AgroSciences, Personal
Communication).
4.0 Herbicide dissipation and degradation pathways There are a number of different ways in which pesticides (including herbicides) may be either degraded or
dissipated in the environment. This has been summarised graphically in Figure 2 (derived from the Recycled
Organics Unit, 2007b).
Figure 2 – Fates of pesticides in compost applied to soil
Reproduced with permission of the Recycled Organics Unit in New South Wales, Australia.
Büyüksönmez et al. (1999 and 2000) reviewed the occurrence, fate and degradation of pesticides during
composting. Biological, chemical and physical mechanisms all play a role, and are dependent upon the pesticide‘s
properties and the environment in which it has been applied. The authors summarised the fates as:
Adsorption;
Leaching;
Volatilisation;
Abiotic transformation processes (hydrolysis, photolysis, advanced oxidation processes); and
Biological transformation (either complete or partial mineralisation).
Büyüksönmez et al. (1999) also noted that the degradation of pesticides during composting appears to be similar
to that in soil, therefore they concluded: ―the behaviour of a particular pesticide in soil should be a reasonable
approximation of what might occur during composting‖. However, they also noted that the high temperatures
occurring during composting, the high levels of organic matter and biological activity may affect degradation. In
particular, adsorption, humification, biologically-mediated transformation and volatilisation may play more
important roles. Fogarty and Tuovinen (1991) discussed the effects of composting parameters on pesticide
degradation, although the study did not specifically discuss clopyralid or aminopyralid.
2 This includes grass for grazing by any form of livestock or horses and grass intended for forage production i.e. silage, hay or haylage.
An investigation of clopyralid and aminopyralid in commercial composting
systems 14
5.0 Clopyralid dissipation and degradation Summary data of the fates of clopyralid in water and soil are summarised in Table 4 (Dow AgroSciences, 1998
and PPDB web site, 2009b).
Table 4 – Environmental fates of clopyralid (soil and water)
Environment Degradation mechanism and time scale
Aquatic Photolysis (DT50 = 271) – classed as stable
Dow states that there is no significant degradation from sunlight
t1/2 = 261 days at 25 °C
Stable to direct hydrolysis – classed as very persistent
Stable in aerobic and anaerobic water – no significant degradation
Soil Typical soil, average half-life = 25 days
Range = 8-250 days (19 soils)
Less than 69 days in 95% of the soils
Shorter half-life in warm, moist soils and lower application rates
DT50 in soil = 34 days (moderately persistent)
Anaerobic Soil Metabolism - no significant degradation
Major degradation occurs through microbial action, with CO2 being the only
significant metabolite.
Degradation is enhanced with lower application rates, higher soil moisture and
temperature.
Potential for particle bound transport index = low
Koc - Organic-carbon sorption constant (ml g-1) = 5 (very mobile). Binding to organic matter increases over time.
DT50 = is the time required for the pesticide concentration under defined conditions to decline to 50% of the
amount at application.
Hydrolysis = a chemical reaction in which a molecule is cleaved into two parts by the addition of a molecule of
water.
5.1 Dissipation and degradation in soils
Technical information published by Dow AgroSciences (1998) suggested that clopyralid degradation occurs via
aerobically-mediated microbial processes. Studies assessing its effect on soil microbial activity (five different soil
types) suggested that clopyralid (at 1 and 10 ppm) did not affect nitrification, nitrogen fixation or respiration.
Early studies investigating the fate of clopyralid in Canadian soils by Pik et al., 1977 indicated that:
Degradation was microbially mediated;
The rate of degradation was influenced by moisture content and was fastest in moist soils
(t1/2 = approximately 2 months);
The rate of degradation was inversely related to the soil organic matter content;
The rate of degradation was dependent upon season (being fastest during summer and slowest in
winter), suggesting temperature plays a role; and
Leaching was also inversely related to the soil organic matter (SOM) content – as adsorption was directly
related to the SOM.
The importance of soil micro-organisms was shown by Ahmad et al., (2003) who conducted laboratory-scale
experiments in sterilised and non-sterilised soils. Clopyralid concentrations decreased with a t1/2 of 7.3 days (at
20 °C) in the non-sterilised soil compared to a t1/2 of 57.8 days in the sterilised soil. Dissipation was also shown
to be temperature dependent (t1/2 of 4.1 days versus 46.2 days at 30 and 10 °C, respectively).
An investigation of clopyralid and aminopyralid in commercial composting
systems 15
Smith and Aubin (1989) measured the dissipation of clopyralid in three prairie soils (clay, clay loam and sandy
loam) at different temperatures. They found that dissipation increased as the temperature increased (from 10 to
30 °C), and showed first-order kinetics. Half lives ranged from 10 to 47 days, and were similar in the clay and
sandy loam soils, and greatest in the clay loam soil at higher temperatures. The authors did not disclose the
organic matter content of the test soils.
Clopyralid has a high leachability potential, which suggests it may leach into groundwater. However, Dow
AgroSciences (1998) and others (Tu et al., 2001) suggest that, in practice, this may not be as great as calculated
from its physico-chemical properties. Cox et al. (1996) measured the leaching and adsorption of clopyralid in
laboratory-based soil columns (one sandy and two silty clay soils). The experiments suggested that clopyralid
was poorly adsorbed to the soils. Notably these soils had low levels of organic matter (0.57 % sandy soil, and
1.29 % and 1.48 % in the silty clay soils), and in the experiments the greatest variation from predicted
adsorption to the soils occurred in the soil with the highest level of organic matter.
A number of researchers have suggested that light may also play a role, as dissipation in field-scale experiments
was slowest in shaded pasture and shaded bare ground compared to un-shaded plots (Ahmad et al., 2003). This
has been supported recently by bench-scale research by Abramović et al., (2007) who examined the
photocatalytic removal of clopyralid in water. They noted at a range of pH values (1 to 9) that clopyralid was
stable for at least two months, in the presence or absence of sunlight. However, they found that in the presence
of ultra violet light degradation was over 30-times faster than the rate of photocatalytic degradation under visible
light.
Notably, clopyralid does not appear to be degraded in anaerobic environments (either soil or water), which may
have implications for anaerobically treated materials (e.g. manures and slurries treated in an on-farm anaerobic
digester). Further research in this area is recommended, in particular, to assess whether post-aerobic treatment
of digestates (both the liquor and fibre) would subsequently reduce concentrations of the herbicide.
In summary, the rate of degradation of clopyralid in soil appears to be dependent upon the following variables:
Moisture – degradation is retarded in dry soils Temperature – degradation slows in cold soils
Clopyralid application rate – higher application rates appear to slow degradation Extent of aerobicity in the soil – degradation is slow in anaerobic soils
Amount of organic matter – binding to organic matter increases with time, which
appears to slow degradation
5.2 Dissipation and degradation of clopyralid during composting
5.2.1 Composting feedstocks There does not appear to be much evidence to suggest that clopyralid degrades in grassland or crops once it has
been applied. Dow notes that studies conducted on pasture grass, corn, spring wheat and cabbage indicated
that clopyralid was not metabolised or degraded by these crops (Dow AgroSciences, 1998). Clopyralid occurs in
plants as the unmetabolized parent acid, which might therefore be directly inputted to a composting process.
Metabolic studies in animals have suggested that in ruminants and poultry, clopyralid is excreted rapidly and
unchanged in the urine. In chickens, it was detected unchanged in the droppings. Whilst this is beneficial from a
toxicological point of view, it means that manures may be a potential source of contamination if subsequently
used as composting feedstocks.
5.2.2 Fate during composting A number of studies have been published, both in the peer-reviewed and grey literature, on the change in
concentrations of clopyralid during composting. These have been summarised below.
Vandervoort et al. (1997) conducted field studies of clopyralid dissipation on turf grass applied at a rate of 650 g
/ ha in conjunction with triclopyr (220 g ha-1). Grass was cut, then composted, with one pile turned regularly,
and one pile left unturned. Samples were taken from both the inside and outsides of the piles. Temperature and
moisture content were not monitored. Notably, the grass was not mixed with any other materials before
composting and the pile sizes were very small (approx. 0.5 m3): grass clippings do not compost well on their
An investigation of clopyralid and aminopyralid in commercial composting
systems 16
own, and could be expected to compost at lower temperatures and under less aerobic conditions than are
common in a commercial composting environment.
Clopyralid concentrations decreased from 32,000 ppb to 900 ppb in the outer samples of the turned piles and
from 1,560 ppb to 1,300 ppb in the inner samples of the turned piles after 365 days of composting (98% and
17% reductions, respectively). Concentrations in the unturned piles decreased from 7,200 ppb to 600 ppb and
6,800 ppb to 100 ppb, in the outer and inner samples after 365 days of composting (92% and 99% reductions,
respectively). This demonstrated a variable reduction in measured concentrations over a year. However, as
some crops may be sensitive to concentrations as low as 3 ppb (see Section 8.0), residual concentrations noted in
this study were still greatly (33 times) in excess of threshold concentrations for some crops, suggesting that
significant phytotoxic potential remained. The authors also noted that the pesticides studied, including clopyralid,
tended to show biphasic degradation: an initial fast rate of degradation (thought to be due to abiotic factors e.g.
volatilisation or photolysis), followed by a much slower rate (due to microbial degradation).
Brinton and Blewett (2004) tested levels of clopyralid in commercially-produced composts and investigated the
degradation of clopyralid in bench-scale laboratory reactors simulating garden leaf-waste composting. They
found that the rate of degradation of clopyralid was:
Dependent on temperature (greater at 35 °C than at 24 °C);
Dependent on the initial concentration of clopyralid – an inverse relationship was observed (the half-life
increased as the initial concentration increased); and
Approximately twice as fast during the active stage of composting (sanitisation) compared with
maturation (curing).
The researchers also noted an apparent increase in clopyralid concentrations during the early stages of
composting, which they attributed to a decrease in organic matter at a greater rate than clopyralid degradation.
They suggested that under typical composting conditions clopyralid exhibited a half-life of approximately 30 days.
The fact that clopyralid degradation was slower at higher concentrations is curious: it suggests an inhibitive
effect, however, clopyralid is known to exhibit low toxicity to micro-organisms (Dow AgroSciences, 1998). This
observation merits further investigation.
A study carried out in New South Wales, Australia, also showed that clopyralid (and a related herbicide, picloram)
did not decrease during composting (after 16 weeks) of shredded garden waste that had a moisture content of
between 55-65%. An increase in concentration of clopyralid was also observed during the study period (between
9 and 12 weeks) (Recycled Organics Unit, 2007a). This was observed both with low (approx. 17 ppb) and high
(50 ppb) initial clopyralid concentrations, however, the final concentration of clopyralid at both application rates
was still found to be greater at the end of the 16 week test period (approx 27 ppb and 53 ppb for the low and
high application rates, respectively).
These studies indicate that short composting periods may not be sufficient to degrade clopyralid should it be
present in composting feedstocks.
Brinton and Blewett (2004) also tested clopyralid-containing compost from the Spokane (Washington State, USA)
composting facility. They re-wetted then incubated samples at 35 °C and 24 °C, and observed that the decline in
concentration was greatest at 35 °C, with degradation occurring slowly at 24 °C (ambient). In all the tests,
clopyralid concentrations appeared to be dependent upon composting conditions. Maintaining composting
temperatures above ambient therefore appears to enhance the rate of degradation.
In an attempt to assess whether clopyralid formulation (granular vs. sprayable) and different mowing regimes
(mulching mower and clippings collected with a rotary mower) affected clopyralid concentrations, Washington
State University conducted a series of trials on turfgrass during 2002 (Miltner et al., 2003). There were some
differences in concentrations in the clippings between the two formulations (the concentration being greater
initially in the plot treated with the sprayable formulation). They found that, in general, the mowing regime did
not affect clopyralid concentrations in the collected grass clippings, which decreased logarithmically (t1/2 was
approximately 10 days). The authors concluded that, based on this rate of decrease, it would take over a year
for clopyralid concentrations to decrease to levels where the grass could be used as compost feedstock without
restriction.
An investigation of clopyralid and aminopyralid in commercial composting
systems 17
Researchers in Lithuania (Lubytė et al., 2007) assessed the effect of clopyralid dissipation in three substrates:
chopped straw, high moor peat and pine wood sawdust, and found that the half-life was 23 days in the straw and
peat, and 21 days in sawdust. They also investigated the effects of adding a mixture of humic acids (humate)
and a commercially available live microbial preparation used to treat septic tanks. They found that the additives
did not affect the rate of decrease of clopyralid concentrations. However, it was unclear from the results
presented how much loss was due to microbial degradation and how much was due to leaching losses. The
researchers did note that 64 – 73% of clopyralid was lost during the first 30 days. No residues of clopyralid were
detected 450 days after application.
The biphasic degradation noted by researchers (Vandervoort et al., 1997, and Lubytė et al., 2007) deserves
further research. It may be that the initial "disappearance" is partially due to adsorption to organic matter (OM)
and the latter phase is due to microbial decomposition/leaching of the adsorbed molecules as the OM
decomposes. (Concentrations of the pesticides are measured relative to dry matter content and not ash). This
attributed binding to organic matter is not expected based on clopyralid‘s low organic-carbon sorption constant
(Koc; Table 1). It has also been suggested that degradation appears to slow later in the composting process,
which may be attributed to increased humification of the organic matter (hence tighter binding to the herbicide).
These observations illustrate the complexity of the issue and highlight the need to ensure the active composting
process is carried out over a reasonable length of time, although this will also be dictated by feedstock types,
potential levels of contamination and composting method.
The measured half-lives of clopyralid in composting experiments vary between 10 and 30 days (summarised in
Table 5), depending upon composting conditions and feedstocks, although in one experiment, concentrations
were not found to decrease after 16 weeks (112 days) (Recycled Organics Unit, 2007a). Degradation rates
therefore appear to be highly variable and merit further investigation, for example, to assess whether there is a
relationship between the extent of humification or lignification in the substrates, and whether the carbon to
nitrogen ratio (and, more importantly, the available nitrogen) has any effect.
Table 5 - Measured half-lives of clopyralid in composting feedstocks
Feedstock Measured half-life
(Days)
Reference
Leaf-garden waste 30 Brinton and Blewett, 2004
Grass 10 Miltner et al., 2003
Straw 23 Lubytė et al., 2007
Peat 23 Lubytė et al., 2007
Sawdust 21 Lubytė et al., 2007
Although the half-life provides a useful measure of the time taken for the concentration to decrease by 50%, as
biphasic degradation has been noted in a number of experiments, the rate of degradation in the second (slower)
phase may well be the most important from both a composter‘s and end user‘s perspective.
Only one reference to the composting method was identified. When problems arose at the Spokane composting
facility in eastern Washington State, USA, composting site managers changed the composting method from that
of an open-air turned windrow to using an AgBag (enclosed composting system). This did not, however, affect
clopyralid concentrations (Bezdicek et al., 2001).
Clopyralid degradation appears to be variable. Key points to note include:
Biphasic degradation (i.e. degradation occurring in two separate phases) was noted by a
number of authors;
The composting temperature appears to affect degradation rates (faster degradation occurs
at higher temperatures);
The initial concentration of clopyralid affects its rate of degradation (it is slower at higher
concentrations);
The rate of degradation is faster during active composting compared with maturation;
An increase in clopyralid concentrations during the early phases of composting have been
noted, due to the faster rate of degradation of organic matter;
Half-lives of between 10 to 30 days were noted, although in one experiment no degradation
was observed after 112 days (Recycled Organics Unit, 2007);
An investigation of clopyralid and aminopyralid in commercial composting
systems 18
Clopyralid concentrations in grass clippings following application to turf were not affected
by mowing methods; and
No degradation in plants or animals following ingestion have been observed
5.3 Aminopyralid dissipation and degradation The literature review did not identify any studies that specifically assessed the concentration or fate of
aminopyralid during composting; instead, data based on environmental studies have been described below.
In reviewing the regulatory submission by Dow AgroSciences, the United States Office of Prevention, Pesticides
Environmental Protection and Toxic Substances Agency in 2005 (US OPPEPTC Agency, 2005) summarised the
fates of aminopyralid in a number of different environments. Data taken from this and two other sources (PMRA,
2007 and the PPDB web site, 2009a) are summarised in Table 6.
Table 6 – Degradation and fate of aminopyralid
Environment Degradation mechanism and time scale
Aquatic Photolysis is primary degradation mechanism (t1/2 = 0.6 days)
Photolysis – classed as fast
Stable to direct hydrolysis – classed as very persistent
Stable in anaerobic water sediments – DT50 = 712 days
Slow degradation in aerobic water (t1/2 = 462 to 990 days)
Soil Rate of degradation varied depending upon soil (types not stated) (t1/2 = 31.5 to
533.2 days in 5 soils)
The US EPA* used a half-life of 103.5 days
Health Canada states that biotransformation in aerobic soils is fast 6–39 days, but
was very slow in a clay loam soil (t1/2 = 330 days)
Photolysis on the soil surface was slow (t1/2 = 72 days)
Adsorption onto soil was weak
Two field dissipation studies suggested aminopyralid had a half-life (t1/2) of 20 and
32 days
Minimal leaching below 15 to 30 cm soil depth
Potential for particle bound transport index = low
Koc - Organic-carbon sorption constant (ml g-1) = 8 (very mobile)
* US EPA = United States Environmental Protection Agency
DT50 = is the time required for the pesticide concentration under defined conditions to decline to 50% of the
amount at application.
Aminopyralid thus displays many similar properties to clopyralid: both are stable in water, are stable to anaerobic
degradation and are highly mobile in the soil. Aminopyralid is rapidly degraded via photolysis under aquatic
conditions, whereas clopyralid is stable to light.
Notably, like clopyralid, aminopyralid appeared to be stable in anaerobic water sediments, which suggests that
biologically-mediated degradation proceeds via aerobically-mediated mechanisms. This is supported by a
statement on behalf of Dow AgroSciences on the Manure Matters web site, 2009: ―Residues in manure break
down if rotovated into the soil and turned frequently‖. This may have implications for materials treated in an
anaerobic digester, such as manures, if the digestate is subsequently applied to sensitive crops.
The main routes of dissipation of aminopyralid appear to be through mineralisation and soil leaching (PMRA,
2007). Aminopyralid appears to be more stable than clopyralid in soil (t1/2 of 103.5 days compared with 25 days,
respectively). Dow themselves have stated that: ―Based on laboratory test guidelines, aminopyralid cannot be
considered as readily biodegradable. However, field studies showed aminopyralid is likely to be non-persistent
An investigation of clopyralid and aminopyralid in commercial composting
systems 19
and relatively immobile‖ (Dow, 2008). The former Pesticides Safety Directorate (now the Chemicals Regulation
Directorate) has suggested that: ―Most of the aminopyralid residue in the soil should have been broken down
after 6 months if the manure been has fully incorporated (rotavated/mixed) into the soil to aid decomposition‖
(Pesticides Safety Directorate, 2008a). As with clopyralid, this suggests that the level of aerobicity in the soil will
affect the rate of degradation. Dow has suggested a period of one year before the soil is aminopyralid-free on
the Manure Matters web site (2009).
5.4 Composting feedstocks There are limited data in the public domain regarding potential concentrations of aminopyralid in feedstocks that
may enter a composting process. Regulatory data submitted in Canada suggests that concentrations were
detected in a number of crops in the parts per million (ppm) range (PMRA, 2007). These are summarised in
Table 7.
Table 7 – Concentrations of aminopyralid in harvested crops in Canada and North America
Crop Application
concentration
Time following
application
Concentration in
harvested crop
(ppm)
Wheat forage 10 g a.e. / ha 0 DAT 0.777
Hay 10 g a.e. / ha 0 DAT 2.377
Wheat grain 10 g a.e. / ha 49 - 56 PHI 0.026
Straw 10 g a.e. / ha 49 - 56 PHI 0.145
Grass forage TIPA salt at ~120 g
a.e./ha
0 DAT 14.03
Grass hay TIPA salt at ~120 g
a.e./ha
0 DAT 51.50
a.e. = acid equivalent: it is the portion of a formulation that can be converted back to the corresponding parent
acid, which is the active herbicide ingredient. It is a term used when a pesticide derivative is used in order to
assess its potential ‗active‘ concentration.
DAT = Day(s) after treatment
PHI = Pre-harvest interval
TIPA = triisopropanolamine
The high concentrations in harvested grass may well present problems if these feedstocks are composted or
digested.
The former Pesticides Safety Directorate also noted that aminopyralid ― ... remains tightly bound to the plant
material until it decomposes‖ (Pesticides Safety Directorate, 2008a) and that when ―manure breaks down it
releases the aminopyralid, which is likely to be at its highest level in the soil about 3 weeks after applying the
manure. However, soil bacteria then break down the aminopyralid so that susceptible plants may start to recover
and grow again.‖ Half-lives of aminopyralid were not quoted.
Ingested aminopyralid is thought to be excreted largely unchanged via the faeces and urine in goats (PMRA
(2007) and cattle (Pesticides Safety Directorate, 2008a), therefore this explains the presumed high levels found in
animal manures, and accounts for the problems experienced by allotment holders in the UK during 2008 (see
Section 6.2).
An investigation of clopyralid and aminopyralid in commercial composting
systems 20
6.0 Compost contamination: an historical perspective
6.1 Clopyralid Unexpected phytotoxic effects of some composts were described in the USA over ten years ago, which were
symptomatic of herbicide activity. Although initially unexplained, further analysis suggested that the effects were
due to clopyralid contaminating commercially-produced composts. Much has been written about this and is
documented on the Internet, so for the sake of brevity a brief history is set out in Table 8.
Table 8 – Summary of compost contamination by clopyralid
Date Documented contamination References
1999 Spokane, Washington, USA
Problems with contaminated compost identified
Symptoms noted on tomato plants grown in containers
Source of contamination identified as grass clippings
Concentrations 31 – 75 ppb detected in compost
Christchurch, New Zealand
Clopyralid detected in compost
Grass clippings identified as source
Bezdicek et al., 2001
CIWMB, 2003
Dow AgroSciences, 2001
Fietje, 2001
Rynk, 2000
2000 Washington State University, USA
Problems with contaminated compost identified, including
the herbicide picloram (an isolated incident)
Clopyralid concentrations from trace to over 200 ppb
detected
Contaminated grass hay and straw identified as the source
Pennsylvania State University
Problems identified during growing trials
Clopyralid at 10 – 75 ppb detected
Incidents in New Jersey also reported
Bezdicek et al., 2001
CIWMB, 2003
Houck and Burkhart, 2001
2001 Dow AgroSciences voluntarily withdrew sales of clopyralid in
Spokane County, WA.
Anon, 2001
2002 Washington State Department of Agriculture (WSDA)
Banned some uses of clopyralid (lawns and turf), except on
golf courses
California State
Restricted clopyralid sale to and use by qualified persons
Oregon State
Clopyralid detected in compost (up to 94 ppb)
Restrictions on clopyralid sales made except in agriculture,
forests, rights of way, cemeteries and golf courses
Anon, 2002
CIWMB, 2003
Musick, 2004
Roberts-Pillon, 2008
Rynk, 2002b
Rynk, 2003
State of Oregon, 2003
WSDA, 2002
2003 Washington State (East)
Increase in clopyralid concentrations in compost reported
Musick, 2004
2008 New Zealand
Clopyralid taken off retail market
Use restricted to agriculture and commercial turf
management
ERMA, 2007
6.1.1 Concentrations detected Initially, analytical test methods for clopyralid were only capable of detecting concentrations above about 50 ppb
(Bezdicek et al., 2001), which is about five-times the concentrations that can affect sensitive plants (below 10
ppb). Test methods therefore required some modification, and clopyralid residues as low as 1 ppb were
An investigation of clopyralid and aminopyralid in commercial composting
systems 21
subsequently detectable. This enabled researchers to identify clopyralid in a number of composts that had
damaged plants (Bezdicek et al., 2001).
Concentrations of clopyralid varied greatly. However, some were found to be well in excess of the levels known
to adversely affect plant growth. For example, in 2001 the Washington State Department of Agriculture (WSDA)
collected samples of feedstocks and finished compost, spanning a range of composting methods and feedstocks.
In one instance a concentration of 1,550 ppb clopyralid was detected in grass clippings, and 477 ppb in immature
compost (Rynk, 2002a).
Following the ban on the use of clopyralid for use on lawns and turf in Washington State in 2002, samples of
composts tested on behalf of WSDA showed a decrease in clopyralid concentrations in compost (by up to 80%),
suggesting the ban had had an effect (WSDA, 2004). In a similar move, the Oregon Department of Agriculture
reported a drop of 47% between 2003 and 2004 in clopyralid concentrations in Oregon‘s compost, although two
facilities did, unexpectedly, show an increase (Musick, 2004 and Roberts-Pillon, 2008).
It has been suggested that clopyralid contamination was more widespread than research data reported, because
many composting operations were not routinely testing for the herbicide (Dan Caldwell, Personal
Communication).
6.1.2 The situation in Washington State, USA The problems at Spokane in eastern Washington State, USA, were first identified in commercially-grown
tomatoes, raised in a glass house in 100% compost, in contrast to the problems at Pullman (also in Washington
State), which were identified outdoors following the application of compost to gardens (Rynk, 2000).
Spokane residents were served by a green waste kerbside collection scheme, which had a high participation rate.
Properties were characterised by a large proportion of lawns that were managed under professional contracts and
treated with Confront (a mixture of clopyralid and triclopyr sold by Dow AgroSciences). Clopyralid was used
heavily in the Spokane area; amounts were much greater than in other areas of Washington State (Rynk, 2002a,
Dow AgroSciences, 2001 and Dan Caldwell, Personal Communication).
It appeared that grass clippings were the principal feedstocks of concern (Rynk, 2003). Dow AgroSciences have
suggested that grass contributed up to 85% of the feedstocks at the Spokane composting facility (Dow
AgroSciences, 2001), and estimates by the former manager of two compositing sites in western Washington State
estimated that during the Spring grass volumes well above 50% by volume (over 80% by weight leading to
concentrations of between 70 to 150 ppb in the feedstocks) were received (Jeff Gage, Personal Communication).
In response to reported problems associated with clopyralid in the USA, Dow AgroSciences issued a paper
‗Clopyralid and Compost‘ in 2001 (Dow AgroSciences, 2001). They suggested that a number of factors came
together in Spokane that would not be expected to occur elsewhere; they stated that composting grass clippings
treated with Confront was off-label, and reiterated the need to follow the instructions on the label. However, the
US Composting Council (USCC) pointed out that the supply chain of compost feedstocks involves a number of
different parties, making it difficult to ensure that feedstocks aren‘t contaminated (Rynk, 2001), and have
stressed the need for effective and consistent communications among all participants.
The increase in clopyralid concentrations observed in Eastern Washington State suggested that labelling was not
the whole answer, as some contamination came from agricultural sources (Musick, 2004). Indeed, it has been
suggested that some Washington facilities have recently (in 2009) experienced contamination stemming from
animal feeds and straw for bedding (used as compost feedstocks), even with supplier contracts that stipulate no
clopyralid herbicide use in the crops. This has been enough to halt the sale of composts occasionally (Jeff Gage,
Personal Communication).
These problems indicate that voluntary controls and stewardship responsibilities by end users may not be
sufficient to prevent contamination arising. In a 2001 opinion article, Gabriella Uhlar-Heffner clearly stated that
responsibility should lie with manufacturers of the herbicide (Uhlar-Heffner, 2001). Based on these observations,
any risk management procedures adopted for the UK need to take account of unofficial off-label uses in both
amateur and professional applications.
An investigation of clopyralid and aminopyralid in commercial composting
systems 22
6.2 Aminopyralid Problems associated with the use of aminopyralid were reported in June 2008 in the UK, after allotment holders
experienced damage to sensitive plants following manure application (Davies, 2008 and RHS, 2008). This
appears to have been sourced from animals grazed on pastures or grassland previously treated with
aminopyralid-containing products, such as Forefront or Pharaoh (Manure Matters web site, 2009 and Pesticides
Safety Directorate, 2008a). Dow AgroSciences has suggested that the problems stemmed from farmers ignoring
label warnings about the management of manures, rather than inappropriate off-label application of aminopyralid
per se (Anne Thompson, Dow AgroSciences, Personal Communication). The unit price of aminopyralid was
probably sufficiently high to prevent casual off-label use.
In response to these problems and the high level of associated media attention, Dow AgroSciences voluntarily
requested that aminopyralid‘s approval be suspended. This was brought into effect on 24 July 2008 (Pesticides
Safety Directorate, 2008b).
Unfortunately, there has not been the level of reported research into this problem compared with the scrutiny
applied to clopyralid in the USA, therefore it has not been possible to ascertain the extent nor levels of
contamination experienced. Dow AgroSciences has stated that levels of aminopyralid in farm yard manures of
between 0.08 ppm to 0.48 ppm (80 to 480 ppb) were detected, whilst slurry concentrations of between < 0.01
ppm (Limit of Quantification) up to 0.19 ppm (10 to 190 ppb) were detected (Anne Thompson, Dow
AgroSciences, Personal Communication).
The Advisory Committee on Pesticides reviewed the suspension of aminopyralid during summer 2009. Nine
products containing aminopyralid (either singly or in conjunction with fluroxypyr or triclopyr) were subsequently
approved (November 2009; Table 12), subject to restricted use (compared with the previous products) and
increased stewardship. Products may be used either to:
Control a range of weeds on grassland for grazing (silage making or hay harvesting is not permitted
within one year following application). Products may only be applied to grassland on which cattle or
sheep (and not horses) may graze. The aim is to: ―prevent sale of manure from treated grassland being
supplied to gardeners and allotment holders, eliminating the risks involved‖ (Chemicals Regulation
Directorate, 2009). The restrictions will also mean that most of the manure produced will remain on the
treated grassland; manures collected when animals are housed (for example in milking parlours) may
only be spread onto grassland and must remain on the farm of origin; and
Control pernicious or invasive weeds in amenity situations. It must not be used on land where
vegetation will be cut for animal feed, fodder or bedding nor for composting or mulching within one year
of treatment. Additionally, it may not be used on land that will be grazed by livestock.
Notably, potential purchasers of aminopyralid must be trained by a British Agrochemicals Standards Inspection
Scheme (BASIS) certified advisor so that they are made aware of the potential risks, and checks will be made on
the proposed use.
6.3 Picloram Picloram is a pyridine herbicide, which is chemically similar and has similar modes of action to clopyralid and
aminopyralid. It is used to control the growth of woody plants, although it is also used to control a number of
broadleaved weeds.
Picloram was identified as the problematic herbicide in many of the situations experienced in Washington State
(Bezdicek et al., 2001), and apparently, more recently in North Carolina and perhaps Virginia (R. Rynk, Personal
Communication). Composts contaminated with picloram have not been reported in the literature in the UK to
date.
Sixteen products containing picloram as an active ingredient are licensed in the UK for professional use only, and
are listed in Table 14. Seven of these formulations also contain clopyralid. Picloram is used on oil seed rape
(winter) and land not intended for cropping. Agricultural residuals, including manures, may therefore represent
sources of this herbicide for composting or anaerobic digestion.
Research carried out by the Recycled Organics Unit in Australia suggested that picloram does not degrade during
the composting process (Recycled Organics Unit, 2007a).
An investigation of clopyralid and aminopyralid in commercial composting
systems 23
7.0 Compost testing and bioassays Testing composts in laboratories for low concentrations of herbicides is methodologically problematic, due to the
heterogeneous nature of the substrate, the presence of humic substances etc. (Recycled Organics Unit, 2007a).
As noted previously, laboratory test procedures were initially only able to detect clopyralid concentrations above
about 50 ppb (Bezdicek et al., 2001). Notwithstanding, analytical test methods are costly to perform and may
not provide a true picture of the bioavailability of the herbicide to plants. In the USA research by King County
and the City of Seattle in Washington State (King County, 2002) found that there was a wide variability in
analytical test results and bioassays.
Following reported problems in Washington State, USA, Washington State University published a bioassay test
method for gardeners and researchers to use (WSU, 2002). This adopted a two tier approach, describing a
simple test method for gardeners using peas, and a more scientifically robust method for researchers, which
involved employing a number of the USCC‘s Test Methods for the Examination of Composting and Compost.
Clopyralid damage of garden peas (variety not specified) was scored by referring to reference photographs as:
0 = ―No symptoms‖ – Leaves lie flat before opening. Leaves do not cup or curl upward at all.
1 = ―Slight damage‖ - Leaves of new growth are somewhat cupped. Leaves do not lie flat before
opening.
2 = ―Moderate damage‖ – Leaves are obviously cupped.
3 = ―Severe damage‖ – Most leaves are cupped. Stems are twisted.
However, the WSU bioassay employed high rates of compost, and the effects of other phytotoxic factors, such as
salinity (electrical conductivity) could not be disaggregated. Brinton et al. (2005 and 2006) investigated the
effects of electrical conductivity of composts on the growth of red clover (sensitive to clopyralid) and peas
(moderately sensitive to clopyralid). They found that by adjusting the quantity of compost in the test medium to
adjust for the level of electrical conductivity this allowed the effects of herbicide to be better identified. Notably,
this is similar to the bioassay specified in the UK‘s BSI PAS 100: 2005, which stipulates that compost samples be
diluted with sphagnum peat to obtain an electrical conductivity of 300 µS cm-1 (which is ten-times less than that
specified by Brinton) before testing using tomato plants.
Brinton et al., 2005 recommended the use of red clover (Trifolium pratense), which enabled phytotoxic effects at
low clopyralid concentrations to be detected. Similarly, the Recycled Organics Unit in New South Wales,
Australia, also developed a bioassay using red clover, as this plant produced observable effects at concentrations
as low as 1 – 2 ppb, and produced results within 14 days (Recycled Organics Unit, 2007c). (The PAS 100
bioassay method using tomatoes takes 28 days.)
Reference photos of auxin-like herbicide damage to red clover (Trifolium pratense) are available on-line, such as
those published by the Recycled Organics Unit in New South Wales, Australia (Recycled Organics Unit web site).
In the UK, Dow AgroSciences have suggested a simple bioassay for allotment holders and gardeners to use on its
manure matters web site. This involves a 50:50 mix of manure with multi-purpose compost and growing broad
beans as the test plant (variety not specified). It seems likely that this method would be susceptible to the
salinity issues discussed by Brinton et al., as well as phytotoxic effects due to high nutrients and substrate
instability.
It is recommended that the method described by either Brinton et al., or the Recycled Organics Unit (2007c) be
employed if clopyralid and/or aminopyralid damage is suspected.
8.0 Effects of clopyralid and aminopyralid on plant growth 8.1 Application issues There is a paucity of data in the public domain on the effects of clopyralid and aminopyralid on crops, dispersal
and degradation rates. The reports identified in the literature search are summarised below.
8.2 Effect of clopyralid on crop rotation Field-scale research looked into the effect of clopyralid applied at 70 to 560 g ae ha-1 (to wheat) and carryover in
the soil to crops planted a year after. Flax, potato, and safflower were not affected, however, growth of
sunflowers (at 280 and 560 g ha-1 clopyralid) and soybeans (at 560 g ha-1 clopyralid) were curtailed (exhibited in
reduced numbers of sunflower heads and yield, and reduced soybean height, stand and yield; Thorsness and
An investigation of clopyralid and aminopyralid in commercial composting
systems 24
Messersmith, 1991). The authors concluded that application rates of 280 g ha-1 or less, in silty clay, clay loam,
and silty clay loam soils would not affect crops sown 11 months or later3.
8.3 Translocation in Canada thistle and biological activity Bukun et al., (2009) investigated the translocation of both aminopyralid and clopyralid in Canada thistle (Cirsium
arvense; known in the UK as creeping thistle). They found that clopyralid was more readily absorbed by the test
plants and more readily translocated out leaf area where it was applied than aminopyralid. They also found that
more of the clopyralid translocated to above ground parts than in the roots, unlike aminopyralid which was found
at similar concentrations in above ground tissue and roots. Neither aminopyralid nor clopyralid were metabolised
by the plants eight days after treatment. The researchers suggest that aminopyralid has a greater biological
activity than clopyralid.
8.4 Translocation into tree leaves The contamination identified at Penn State University included fallen tree leaves vacuumed from the University‘s
lawns. In an attempt to ascertain whether clopyralid was translocated through the tree and was the source of
contamination, leaves from Elm, Oak and Maple trees in the campus grounds were handpicked and assayed for
clopyralid. In all samples, clopyralid could not be detected, suggesting that the herbicide was not translocated
through the tree and into the leaves (Burkhart and Davitt, 2002). However, although the leaves themselves were
eliminated as the source of contamination, that act of vacuum collection resulted in co-collection of treated grass.
This highlights the need for vigilance, as cross-contamination of clopyralid between feedstocks may occur.
8.5 Enclosed growing of crops in polytunnels and glasshouses Researchers at Penn State University (Burkhart and Davitt, 2002) investigated the effect of compost containing
clopyralid application in polytunnels. They observed that clopyralid could persist for more than two years under a
polytunnel. The authors suggested that clopyralid‘s persistence in polytunnels may be due to reduced moisture
content in soils (due to lack of natural precipitation and conservation of water due to irrigation methods), thereby
reducing soil microbial activity, bioavailability of the pesticide in the liquid-solid interface and reduced leaching
from the root zone. The authors suggested that organic matter may affect the solubility of clopyralid, with more
water required at greater organic matter levels to bring clopyralid into solution.
The researchers at Penn State University also noted that symptoms of clopyralid were only observed about four
weeks after transplanting crops (bell peppers) from glasshouse to field (Houck and Burkhart, 2001). This may
have been due changes in soil / substrate moisture levels, as a ‗wet / dry cycle‘ was thought to release clopyralid.
8.6 Rainfall The areas in eastern Washington State that were most plagued by clopyralid (and picloram) are dry climates
(Spokane, Pullman and the interior hay-producing regions). Although Western Washington State is moist it
obtains much of its manure feedstock from the dry region east of the mountains, and the compost is largely used
in the summer season, which is dry even on the west side. Being generally water soluble, sparse rainfall seems
to be a common element in at least some of the problem areas associated with these chemicals i.e. in regard to
the source of feedstocks, composting location and where the compost product is used. The effect of rainfall
throughout the cycle is a factor in the fate of these chemicals that seems to be overlooked in the literature.
The two key factors affecting clopyralid activity thus appear to be soil moisture and organic matter content. Crops grown in protective environments may therefore merit special attention.
8.7 Compost application rates Researchers at Washington State University (Cogger et al., 2002) investigated the effects of clopyralid containing
compost at high concentrations (82 ppb) and low (12 ppb) on the growth of tomatoes (three varieties), one
tomatillo, peas and beans. They applied compost to soil at two rates (1 and 3 inches depth of compost applied to
the soil surface before tilling), and incorporated the compost to a depth of six inches with a garden tiller. The
type of soil, and, in particular its organic matter content, was not disclosed. The test results suggested that only
at the high application rate (3 inches) in the high concentration compost were effects of clopyralid noted. The
plants appeared to grow normally at the lower application rates and with the lower clopyralid levels (high and low
application rates). Although this study was not scientifically rigorous, it does indicate that incorporating
3 UK application rates of clopyralid vary depending upon the crops to which it is applied. The maximum permitted annual rate of application of Dow Shield (18.02% w/w clopyralid as the monoethanolamine salt) is 400 g / ha.
An investigation of clopyralid and aminopyralid in commercial composting
systems 25
contaminated compost into soil could reduce the effects of clopyralid sufficiently to permit the growth of sensitive
plants.
Similar suggestions were also made by Woods End Laboratories (Brinton and Evans, 2002), who predicted that
crops grown in soils to which contaminated compost had been incorporated up to a depth of six inches, would
only occur at highly contaminated compost at high application rates and to crops such as peas, sunflower and
clover which are highly sensitive to clopyralid.
9.0 Managing the risks The UK composting sector has benefitted from the introduction of the (former) Composting Association‘s
standards and certification scheme in 2000, which, in conjunction with WRAP, led to the introduction of the BSI
PAS 100 specification for composted materials in 2002. These have been updated and superseded by a 2005
edition (BSI PAS 100:2005), augmented with the Compost Quality Protocol (CQP) in England and Wales in 2007
(WRAP and Environment Agency, 2007), and, more latterly, will be superseded again in 2010 by a new edition.
Collectively, these documents and the associated third-party certification scheme (now overseen but not run by
the Association for Organics Recycling) have required compost producers to implement a comprehensive Quality
Management System (QMS), coupled with an obligatory Hazard Analysis Critical Control Point (HACCP)
assessment. These set in place systems of control at every certified composting site, in contrast to the USA,
which does not have a nationally-based certification scheme of this sort.
Notably, the PAS 100 and the CQP mandate that an audit trail be maintained by the compost producer
throughout the composting process and that samples of compost routinely be tested at accredited laboratories for
contaminants and for phytotoxicity through a plant bioassay. A number of these principles have been suggested
by the Recycled Organics Unit in New South Wales, Australia, in developing its Risk Management Tools for the
Recycled Organics Industry (Recycled Organics Unit, 2007c).
A number of factors relating specifically to clopyralid contamination are discussed below.
As aminopyralid is now only licensed for use by professional users and is restricted to either grazing ground for
sheep and cattle (not horses) or amenity grassland to control invasive and pernicious weeds, the risks to
composting operations associated with its use have been significantly reduced. However, compost site operators
should be made aware that the compound is licensed for use in these applications and not accept feedstocks
from these sources when there is any doubt over their quality.
9.1 Composting feedstocks Pesticides, including clopyralid, may enter composting feedstocks from a variety of diffuse (non-point) sources.
This creates difficulties for composting site operators, especially when implementing their HACCP procedures.
The feedstocks of concern are detailed below in Table 9. Grass and animal manures (including animal feeds such
hay, silage, fodder crops, and animal bedding) present the greatest risk of clopyralid contamination.
An investigation of clopyralid and aminopyralid in commercial composting
systems 26
Table 9 – Composting feedstocks and their potential to be contaminated with clopyralid
Feedstock type Feedstock source Potential for contamination
Green waste (mixed) Municipal - household
(kerbside or HWRC
collection)
Variable.
Amateur use of clopyralid is only licensed for use on lawns
by householders.
It is likely that clopyralid contaminated grass would be
diluted by other green wastes in compost feedstocks,
although this may be less pronounced at certain times of
the year (e.g. late spring and summer when larger volumes
of grass clippings are composted [see Appendix 2]).
Additionally, due to its effect on certain plant species at
very low concentrations, dilution cannot be relied on as a
mitigation measure.
Composting at home of clopyralid contaminated materials
may be problematic, although this will be limited to
individual gardens depending on herbicide use.
Green waste (mixed) Municipal (non-household)
and non-municipal
Variable – possibly greater than household sources.
Greatest risk would be from grass clippings on
professionally managed lawns (e.g. golf courses) and
landscaped areas. However, the proportions of grass
clippings sent for commercial composting by landscapers
and other professional users are currently unknown,
although it is likely that the majority of such clippings will
remain at the site of production.
Contracts of Supply between compost site operators and
feedstock suppliers could address this issue, thereby
minimising risk.
Leaves and woody
wastes
Municipal - household Low, as clopyralid does not appear to transfer to woody
plant material, however, cross contamination from treated
grass has been documented.
Leaves and woody
wastes
Municipal (non-household)
and non-municipal
Variable – this will depend upon whether this material is
sourced from areas where clopyralid has been applied to
grass / turf. Contracts of supply would be helpful for this
scenario.
Crop by-products Agriculture Low to high, depending upon the feedstock crop.
Where crop residuals are composted on-farm and the
composted materials re-applied to the farmer‘s own land,
the farmer (or appointed third-party) can track feedstock
materials and ensure that the resulting compost is not
applied to sensitive crops.
Manures, including
straw and hay
All sources High risk.
Clopyralid is used principally on grassland and on crops
used as animal feed and fodder (Table 3). As clopyralid
passes through grazing animals unchanged, there is
potential for it to be ‗concentrated‘ in the faeces and urine.
Significant problems associated with manures have been
observed in the USA and in the UK (with aminopyralid).
An investigation of clopyralid and aminopyralid in commercial composting
systems 27
A literature review of the composition of garden waste collected for biological treatment is detailed in Appendix 2,
indicating a paucity of data. Grass clippings were, in general, found in the greatest proportions during the spring
and summer months, which coincides with the on-label use of lawn care products containing the herbicide
clopyralid. In one study (Morpeth, Northumberland) over 60% of the total garden waste collected in wheeled
bins was grass during May to September (1995/96).
Data on green waste compositions stemming from professional users (e.g. landscapers and lawn care specialists)
sent for commercial composting were not available.
In order to gain a better understanding of the potential risks associated with contaminants (e.g. clopyralid) that
may enter a commercial composting system through garden wastes, a better understanding of garden waste
composition and variation would be beneficial. This would need to accommodate differing collection systems
(bring and kerbside), housing types and local policies for residual waste collection.
9.2 Compost use
9.2.1 Agriculture and field horticulture It is hard to predict how long clopyralid residues will remain in the soil following either direct application of the
herbicide, or indirectly through contaminated compost. Soil organic matter, moisture, soil temperature and the
level of aerobicity (which will be dependent upon soil type) appear to be the main factors affecting dissipation
and degradation.
As most compost applied to fields would be ploughed prior to planting crops, it seems likely that potential
contamination would present a minimal risk (see, for example, Brinton and Evans, 2002), assuming the upstream
controls during processing and sourcing feedstocks (discussed above) are implemented. The potential for
problems could be highlighted in the compost producer‘s contract of supply, in particular, if contamination is
suspected. In this case, instructions based on the labelling requirements for clopyralid use could be followed.
Compost may also be used as a mulch in the growth of soft fruit (such as strawberries) and top fruit (see, for
example, Lock et al., 2008). It is not thought that clopyralid will translocate through trees into leaves (Burkhart
and Davitt, 2002), however, as its effects on top fruit production have not been documented, further research
would be beneficial. Clopyralid is licensed for use on strawberries, therefore it is not envisaged that restrictions
on compost use on this crop are warranted.
9.2.2 Growing media and protected crops Plants grown in containers and under protective cover (e.g. polytunnels) appear to be the most susceptible to
potential clopyralid contamination, due to the high levels of organic matter in the growth substrate, and the lower
rates of irrigation. The Guidelines for the Specification of Composted Green Materials used as a Growing Medium
Component (Waller, 2004) suggest that composted green material be incorporated up to a maximum of 33% by
volume with other suitable low nutrient substrates.
It is recommended that the Growing Media Specification be adhered to for all compost sold for use in either
growing media or protected crops. Additional bioassay testing of compost batches destined for incorporation into
growing media may provide assurance to growing media manufacturers, in particular at times of the year when
grass clippings would be at their greatest in compost feedstocks.
9.2.3 Landscaping and grounds maintenance Clopyralid is widely used on grass and turf in these sectors. There are popular landscape plants within the
Asteraceae family, including sunflowers, marigolds and dahlias that are used in these settings, therefore
landscapers and grounds maintenance professionals should be made aware of any suspected contamination
problems.
An investigation of clopyralid and aminopyralid in commercial composting
systems 28
10.0 Recommendations The predominant factor with clopyralid (and similar chemicals) in compost is not its rate of decomposition. In
general, clopyralid seems to decompose fairly well in the typical time frame of a composting process (although
the Australian studies apparently suggest otherwise). The dominant factor is concentration. Clopyralid (and like
chemicals) simply remain potent at very low concentrations, even after the original concentration decreases
substantially during composting (e.g. 99%).
The second dominant factor is the ultimate use of the compost. Clopyralid remains potent for only a few families
of plants; which unfortunately include important and popular food and landscape crops. High concentrations of
clopyralid in compost will go unnoticed for the many uses/plants for which clopyralid is quite acceptable.
Hence, ―clopyralid in compost‖ is a story about ―concentration and coincidence‖: Concentration because of
clopyralid potency at very low concentrations (and that of like products); coincidence because tainted compost
must coincide with particular uses to become a problem. Another important coincidence is that it takes a
somewhat unlikely combination of similar feedstocks, similarly treated with clopyralid, to establish a troublesome
clopyralid concentration to begin with. In most composting situations the feedstocks are diverse and/or come
from dispersed sources that do not have the same patterns of pesticide use. Important exceptions to this typical
situation occur, exemplified by the experience in Spokane, Washington State and by the use of ―single-source‖
feedstocks (e.g. manure obtained from one or two farms).
This review has provided background information to assist compost producers and end users in understanding
the sources and fate of clopyralid contamination. However, it has not provided a quantitative risk assessment,
and the potential for harm to plants from contaminated compost will depend upon a range of variables, such as
feedstock types, time of year, composting duration etc. Further research could usefully be undertaken to
quantify the risks of these products adversely affecting the UK composting sector, and we suggest that WRAP
and the composting industry engage with the manufacturers of clopyralid to identify an appropriate programme
of work.
Based on the information gathered during this study, we have set out a number of recommendations below
aimed at either preventing or reducing the risk of problems arising.
10.1 Municipal wastes There are a number of clopyralid-containing herbicide products available for amateur use (see Table 10) in the
UK. The extent to which contaminated grass (or other green wastes) entering a commercial composting facility
through a municipal waste collection service could create problems is unknown at present, however, the most
robust long term strategy to ensure compost quality is to eliminate the potential for contamination to occur at
source. As long as these products are sold for amateur use, the onus should therefore remain on herbicide
manufacturers to provide clear, practical advice to householders for recycling grass and other garden wastes
following herbicide application. This may include encouraging the practice of ―grasscycling4‖, where clippings are
left on the lawn, rather than removed during mowing.
The challenges faced by local authorities in meeting their targets to divert biodegradable municipal waste from
landfill should not be underestimated; hence disposal of grass or other green wastes in residual (mixed or ‗black
bag‘) waste collections should not be encouraged.
10.2 Compost manufacturers The extent to which compost manufacturers can control clopyralid contamination and ameliorate its effects is
limited. We therefore recommend that compost site operators:
Remain vigilant to the potential for clopyralid contamination during late spring and summer when the
input of grass clippings is likely to be at its greatest, and ensure that this is adequately addressed in
HACCP plans (where appropriate);
Communicate with suppliers of feedstocks to highlight the potential for contamination through the use of
clopyralid-containing herbicides. (This is particularly important where ―single source‖ feedstocks are
composted. Mixing feedstocks of different types or from different sources will lower the risk of starting
with a high concentration of clopyralid, and therefore ending up with unacceptably high concentrations.)
4 This practice has been widely adopted and promoted in the USA.
An investigation of clopyralid and aminopyralid in commercial composting
systems 29
This may take the form of a Contract of Supply with landscapers, grounds maintenance and sports turf
professionals to highlight the potential for contamination, and ensure, as far as reasonably practicable,
that feedstocks are not delivered for composting within a year of clopyralid application. A leaflet
explaining the risks and safe management of treated feedstocks could be developed; it is envisaged that
this could be handed to professionals when they deliver feedstocks to a composting site at the
weighbridge when waste transfer notes and other receipts are exchanged. These initiatives could
usefully be achieved through a joint exercise between with the manufacturers of clopyralid, WRAP and
the composting industry;
Consider increasing the frequency of bioassay testing for composts intended for use in growing media or
to raise protected crops, however, it is acknowledged that this will entail additional costs;
Where there is any doubt over their source, ensure that composted animal manures are sent for use in
non-sensitive applications. This could be addressed through a contract of supply (which already exists
for agricultural and field horticultural crops through the Compost Quality Protocol in England and Wales).
As a matter of course, compost producers should make their customers aware of the suitability of their
composts for different end uses; and
Adhere to the Growing Media Specification for all compost sold for use in either growing media or
protected crops.
Should clopyralid contamination be suspected, composts can still be used in a range of applications, such as: turf
topdressing, corn and cereal grains, soil amendment (where the compost is incorporated into soil used to grow
non-legume field crops) and topsoil manufacture. If clopyralid contamination is suspected, then crops and
applications to avoid include: growing media, growing beds under covers or in greenhouses, home vegetable
gardens and legumes.
10.3 Compost testing The BSI PAS 100 and the CQP require periodic testing of compost (at least once every 5000 m3 in PAS100:2005),
including the use of a plant bioassay which uses tomato as the indicator plant. Tomato is sensitive to low
concentrations of clopyralid (<1 ppb; Bezdicek et al., 2002). Based on experiences in the USA, plant bioassays
were shown to be the most appropriate test method for the routine evaluation of potential herbicide
contamination in composted materials, due to the cost and complexity of laboratory chemical analysis (see
Section 7.0). Brinton et al., 2005, and the Recycled Organics Unit, 2007c, however, suggested employing red
clover (Trifolium pratense) in place of tomato (Solanum esculentum).
Chapman et al., (2009) have recently reviewed the plant bioassay test method as specified in UK‘s PAS 100
specification against methods used elsewhere in the world. They concluded that the method specified in PAS 100
should be retained, but that additional validation be carried out. We also recommend that the existing PAS 100
bioassay be validated:
Using compost containing concentrations of clopyralid known to adversely affect plant growth;
Against red clover (Trifolium pratense), as this has a high degree of sensitivity to clopyralid and ability to
produce observable results after 14 days; and
Against the test methods described by Brinton et al., 2005, and the Recycled Organics Unit, 2007c, as
these were developed specifically to identify low concentrations of herbicide in the growing medium.
An investigation of clopyralid and aminopyralid in commercial composting
systems 30
11.0 References
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from water J. Serb. Chem. Soc. 72 (12): 1477–1486.
AEA Technology (2000) Monitoring the Production of Compost from Wastes on a Continuous Basis. Environment
Agency R&D Technical Report P355, pub. WRc, Swindon
Ahmad, R., James, T.K., Rahman, A. and Holland, P.T. (2003) Dissipation of the Herbicide Clopyralid in an
Allophanic Soil: Laboratory and Field Studies Journal of Environmental Science and Health Part B—Pesticides, Food
Contaminants, and Agricultural Wastes B38 (6): 683–695.
Aminopyralid. Pesticide Properties Database, University of Hertfordshire.
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Anon (2001) Chemical Company Pulls Herbicide Off Spokane Shelves BioCycle June: 6.
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http://www.recycledorganics.com/processing/risk/photos.htm [Accessed 16 June 2009]
Bezdicek, D., Fauci, M. Caldwell, D. and Finch, R. (2002) Proceedings of the International Symposium Composting
and Compost Utilization 933-939. Eds. Frederick C. Michel, Jr. Robert F. Rynk and Harry A. J. Hoitink.
Bezdicek, D., Fauci, M., Caldwell, D., Finch, R. and Lang, J. (2001). Persistent herbicides in compost. BioCycle
42(7), 25-30.
Boldrin, A. and Christensen, T.H. (2010) Seasonal generation and composition of garden waste in Aarhus
(Denmark) Waste Management 30, 551–557.
Brinton, W.F. and Blewett, T.C. (2004) Presence, Fate, and Effects of Clopyralid and Other Anthropogenic Residues
in Green Waste Composting. Paper 4A-21, in: A.R. Gavaskar and A.S.C. Chen (Eds.), Remediation of Chlorinated
and Recalcitrant Compounds—2004. Proceedings of the Fourth International Conference on Remediation of
Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2004). ISBN 1-57477-145-0, published by Battelle
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An investigation of clopyralid and aminopyralid in commercial composting
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Houck, N.J. and Burkhart, E.P. (2001) Penn State Research Uncovers Clopyralid In Compost BioCycle July: 32-33.
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An investigation of clopyralid and aminopyralid in commercial composting
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(2005) Pesticide Fact Sheet Aminopyralid
Vandervoort, C., Zabic, M.J. Branham, D. and Lickfeld, W. (1997) Fate of Selected Herbicides on Turfgrass: Effect of
Composting on Residues. Bull. Environ. Contam. Toxicol. 58: 38-45.
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Residues in Compost: Protocol for Gardeners and Researchers in Washington State. Information Sheet published
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WRAP and Environment Agency (2007) The Quality Protocol For The Production And Use Of Quality Compost From
Source-Segregated Biodegradable Waste.
An investigation of clopyralid and aminopyralid in commercial composting
systems 33
Appendix 1
Table 10 – Clopyralid-containing products sold in the UK for amateur use
Product
MAPP No
Product
Expiry Date
Marketing
Company
Crop(s) Active ingredients Maximum
application rate
Maximum
frequency
(per
year)
Evergreen
Lawn
Weedkiller
14530
31/12/2013 The Scotts
Company (UK)
Limited
lawn 5.400 g / l clopyralid
10.700 g / l fluroxypyr and
53.800 g / l MCPA
15 ml / 10 m2 1
Evergreen
Lawn
Weedkiller
Ready to Use
14531
31/12/2013 The Scotts
Company (UK)
Limited
lawn 0.160 g / l clopyralid,
0.320 g / l fluroxypyr and
1.600 g / l MCPA
500 ml / 10 m2 1
Verdone Extra
13113
31/12/2013 The Scotts
Company (UK)
Limited
lawn 5.400 g / l clopyralid,
10.700 g / l fluroxypyr and
53.800 g / l MCPA
15 ml product /10
square metres
1
Verdone Extra
Ready to use
11758
31/12/2013 The Scotts
Company (UK)
Limited
lawn 0.160 g / l clopyralid,
0.320 g / l fluroxypyr and
1.600 g / l MCPA
500 ml product /
10 m2
1
Verdone Extra
Spot Weeder
10834
31/12/2013 The Scotts
Company (UK)
Limited
lawn 0.160 g / l clopyralid,
0.320 g / l fluroxypyr and
1.600 g / l MCPA
500 ml product /
10 m2
1
Vitax
LawnClear 2
13508
30/04/2012 Vitax Limited lawn 27.000 g / l 2,4-D,
6.300 g / l clopyralid and
31.500 g / l MCPA
1.66 ml / m2 1
Vitax
LawnClear 2
Ready To Use
13509
31/12/2013 Vitax Limited lawn 1.130 g / l 2,4-D,
0.260 g / l clopyralid and
1.310 g / l MCPA
40 ml / m2 1 per year
Weedol Lawn
Weedkiller
14529
31/12/2013 The Scotts
Company (UK)
Limited
lawn 5.400 g / l clopyralid,
10.700 g / l fluroxypyr and
53.800 g / l MCPA
15 ml / 10 m2 1
Weedol Lawn
Weedkiller
Ready to Use
14532
31/12/2013 The Scotts
Company (UK)
Limited
lawn 0.160 g / l clopyralid,
0.320 g / l fluroxypyr and
1.600 g / l MCPA
500 ml / 10 m2 1 per year
An investigation of clopyralid and aminopyralid in commercial composting
systems 34
Table 11 – Clopyralid-containing products sold in the UK for professional use
Product
MAPP No
Product
Expiry Date
Marketing Company Crop(s) Active ingredients
Agrotech-Clopyralid
200 sl
12445
30/11/2009 Agrotech Trading
GmbH
barley, broccoli/calabrese, brussels
sprout, bulb onion, cabbage,
cauliflower, fodder beet, fodder rape,
forage maize, kale, linseed, mangel,
oats, oilseed rape (spring), oilseed
rape (winter), ornamental plant
production, permanent grassland, red
beet, rotational grass, salad onion,
strawberry, sugar beet, swede,
sweetcorn, turnip, wheat
clopyralid
Blaster 13267
31/12/2013 Headland Amenity Ltd amenity grassland clopyralid and triclopyr
Bofix FFC 13152
31/10/2012 Dow AgroSciences Ltd barley, oats, wheat clopyralid,florasulam and fluroxypyr
Bofix FFC 14179
31/12/2011 Dow AgroSciences Limited
barley (spring), barley (winter), oats, wheat (spring), wheat (winter)
clopyralid, florasulam and fluroxypyr
Charter 13908
31/12/2013 AgriGuard Ltd grassland clopyralid, fluroxypyr and triclopyr
Cliophar 13360
31/12/2013 Agriphar S.A barley (spring), barley (winter), maize, oats (spring), oats (winter), oilseed rape (spring), oilseed rape (winter), sugar beet, wheat (spring), wheat (winter)
clopyralid
Dow Shield 10988
31/12/2013 Dow AgroSciences Ltd barley, broccoli, brussels sprout, bulb onion, cabbage, calabrese, cauliflower, fodder beet, fodder rape, forage maize, kale, linseed, mangel, oats, oilseed rape (spring), oilseed rape (winter), ornamental plant production, permanent grassland, red beet, rotational grass, salad onion, strawberry, sugar beet, swede, sweetcorn, turnip, wheat
clopyralid
Esteem 12555
31/12/2013 Vitax Limited managed amenity turf 2,4-D, clopyralid and MCPA
Galaxy 13127
31/10/2012 Dow AgroSciences Limited
barley, oats, wheat clopyralid, florasulam and fluroxypyr
Galaxy 14085
31/12/2011 Dow AgroSciences Limited
barley (spring), barley (winter), oats, wheat (spring), wheat (winter)
clopyralid, florasulam and fluroxypyr
Galera 11961
31/12/2013 Dow AgroSciences Limited
oilseed rape (winter) clopyralid and picloram
An investigation of clopyralid and aminopyralid in commercial composting
systems 35
Glopyr 200 SL 10979
31/12/2013 Globachem NV barley, broccoli/calabrese, brussels sprout, cabbage, cauliflower, fodder beet, fodder rape, forage maize, grassland (established), kale, linseed, mangel, oats, oilseed rape (spring), oilseed rape (winter), onion, ornamental plant production (trees)(shrubs), red beet, strawberry, sugar beet, swede, sweetcorn, turnip, wheat
clopyralid
Grazon 90 13117
31/12/2013 Dow AgroSciences Ltd grassland clopyralid and triclopyr
Greencrop Champion 11755
30/11/2009 Greencrop Technology Ltd
barley, broccoli, brussels sprout, bulb onion, cabbage, calabrese, cauliflower, fodder beet, fodder rape, forage maize, kale, linseed, mangel, oats, oilseed rape (spring), oilseed rape (winter), ornamental plant production, permanent grassland, red beet, rotational grass, salad onion, strawberry, sugar beet, swede, sweetcorn, turnip, wheat
clopyralid
Greenor 10909
31/12/2013 Rigby Taylor Ltd managed amenity turf clopyralid, fluroxypyr and MCPA
Interfix 14386
31/12/2013 Iticon N.V. managed amenity turf clopyralid, fluroxypyr and MCPA
Landgold Clopyralid 200 12359
30/11/2009 Teliton Ltd barley, broccoli, brussels sprout, bulb onion, cabbage, calabrese, cauliflower, fodder beet, fodder rape, forage maize, grassland, kale, linseed, mangel, oats, oilseed rape (spring), oilseed rape (winter), red beet, salad onion, strawberry, sugar beet, swede, sweetcorn, turnip, wheat
clopyralid
Landgold Piccant 13770
30/11/2012 Goldengrass Limited oilseed rape (winter) clopyralid and picloram
Legara 13888
30/06/2013 AgChemAccess Limited oilseed rape (winter) clopyralid and picloram
Lonpar 08686
31/12/2013 Dow AgroSciences Ltd grassland 2,4-D, clopyralid and MCPA
LONTREL 200 11558
31/12/2013 Dow AgroSciences Ltd barley, broccoli, brussels sprout, bulb onion, cabbage, calabrese, cauliflower, fodder beet, fodder rape, forage maize, kale, linseed, mangel, oats, oilseed rape (spring), oilseed rape (winter), ornamental plant production, permanent grassland, red beet, rotational grass, salad onion, strawberry, sugar beet, swede, sweetcorn, turnip, wheat
clopyralid
Matrikerb 10806
31/12/2013 Dow AgroSciences Ltd (Contact PSD for approved crop/use information)
clopyralid and propyzamide
An investigation of clopyralid and aminopyralid in commercial composting
systems 36
Milentus Clopyralid 12448
30/11/2009 Milentus BV barley, broccoli/calabrese, brussels sprout, bulb onion, cabbage, cauliflower, fodder beet, fodder rape, forage maize, kale, linseed, mangel, oats, oilseed rape (spring), oilseed rape (winter) more
clopyralid
Nugget 13121
31/12/2013 AgriGuard Ltd oilseed rape (winter) clopyralid and picloram
Pastor 11168
31/12/2013 Dow AgroSciences Ltd permanent grassland, rotational grass clopyralid, fluroxypyr and triclopyr
Piccant 14294
31/12/2013 Goldengrass Limited oilseed rape (winter) clopyralid and picloram
Pirlid 11946
30/11/2009 Tronsan Ltd barley, broccoli/calabrese, brussels sprout, bulb onion, cabbage, cauliflower, fodder beet, fodder rape, forage maize, kale, linseed, mangel, oats, oilseed rape (spring), oilseed rape (winter), ornamental plant production, permanent grassland, red beet, rotational grass, salad onion, strawberry, sugar beet, swede, sweetcorn, turnip, wheat
clopyralid
Praxys 13912
31/12/2011 Dow AgroSciences Limited
amenity grassland, lawn, managed amenity turf
clopyralid, florasulam and fluroxypyr
Prevail 13205
31/12/2013 Dow AgroSciences Limited
oilseed rape (winter) clopyralid and picloram
Renegade 14507
31/12/2013 Chemsource Ltd oilseed rape (winter) clopyralid and picloram
Spearhead 09941
31/12/2013 Bayer Environmental Science
amenity turf (managed) clopyralid, diflufenican and MCPA
Thistlex 11533
31/12/2013 Dow AgroSciences Ltd permanent grassland, rotational grass clopyralid and triclopyr
Torate 12611
30/11/2009 AgriGuard Ltd barley, broccoli, brussels sprout, bulb onion, cabbage, calabrese, cauliflower, fodder beet, fodder rape, forage maize, grassland, kale, linseed, mangel, oats, oilseed rape (spring), oilseed rape (winter), ornamental plant production, red beet, strawberry, sugar beet, swede, sweetcorn, turnip, wheat
clopyralid
Trinity 12738
28/02/2012 AgriGuard Ltd grassland clopyralid, fluroxypyr and triclopyr
Vivendi 200 12782
31/12/2013 Agrichem BV barley, broccoli/calabrese, brussels sprout, bulb onion, cabbage, fodder beet, fodder rape, forage maize, kale, linseed, mangel, oats, oilseed rape, ornamental plant production, permanent grassland, red beet, salad onion, strawberry (outdoor use only), sugar beet, swede, sweetcorn, turnip, wheat
clopyralid
An investigation of clopyralid and aminopyralid in commercial composting
systems 37
Table 12 - Aminopyralid-containing products approved for use in November 2009
Product
MAPP No
Product
Expiry Date
Marketing Company Crop(s) Active ingredients
Forefront
14701
29/07/2011 Dow AgroSciences
Limited
grassland aminopyralid and
fluroxypyr
Halcyon
12749
29/07/2010 Dow AgroSciences
Limited
permanent grassland, rotational grass aminopyralid and
fluroxypyr
Halcyon
14709
29/07/2011 Dow AgroSciences
Limited
grassland aminopyralid and
fluroxypyr
Mileway
14702
29/07/2011 Dow AgroSciences
Limited
amenity grassland aminopyralid and
fluroxypyr
Pharaoh
13631
29/07/2010 Dow AgroSciences
Limited
grassland aminopyralid and
triclopyr
Pharaoh
14731
29/07/2011 Dow AgroSciences
Limited
grassland aminopyralid and
triclopyr
Pro-Banish
14730
29/07/2011 Dow AgroSciences
Limited
grassland aminopyralid
Synero
14059
29/07/2010 Dow AgroSciences
Limited
amenity grassland aminopyralid and
fluroxypyr
Synero
14708
29/07/2011 Dow AgroSciences
Limited
amenity grassland aminopyralid and
fluroxypyr
Table 13 - Aminopyralid-containing products approved for use before July 2008
Approved for amateur use
Product MAPP
No Marketing Company Crop(s) Active(s)
Banish5
Dow AgroSciences Ltd grassland 30 g / l Aminopyralid
13766
Approved for professional use
Forefront Dow AgroSciences Ltd
permanent grassland,
rotational grass 30 g / l Aminopyralid and 100 g / l fluroxypyr
12765
Halcyon Dow AgroSciences Ltd
permanent grassland,
rotational grass 30 g / l Aminopyralid and 100 g / l fluroxypyr
12749
Pharaoh Dow AgroSciences Ltd grassland 30 g / l Aminopyralid and 240 g / l triclopyr
13631
Pro-Banish Dow AgroSciences Ltd
permanent grassland,
rotational grass 30 g / l Aminopyralid
13767
Runway Dow AgroSciences Ltd amenity grassland 30 g / l Aminopyralid and 100 g / l fluroxypyr
14017
5 This was never marketed in the UK (Source DowAgroSciences)
An investigation of clopyralid and aminopyralid in commercial composting
systems 38
Synero Dow AgroSciences Ltd amenity grassland 30 g / l Aminopyralid and 100 g / l fluroxypyr
14059
Upfront
AgChemAccess Ltd permanent grassland,
rotational grass 30 g / l Aminopyralid and 100 g / l fluroxypyr
13782
An investigation of clopyralid and aminopyralid in commercial composting
systems 39
Table 14 - Picloram containing products registered in the UK
Product
MAPP No
Product
Expiry Date
Marketing Company Crop(s) Active ingredients
Atladox HI 05559
31/12/2010 Nomix Enviro Limited land not intended for cropping 2,4-D and picloram
Atladox Hi 13867
31/03/2013 Nomix Enviro, A Division of Frontier Agriculture Limited
land not intended for cropping 2,4-D and picloram
Galera 11961
31/12/2013 Dow AgroSciences Limited
oilseed rape (winter) clopyralid and picloram
Landgold Piccant 13770
30/11/2012 Goldengrass Limited oilseed rape (winter) clopyralid and picloram
Legara 13888
30/06/2013 AgChemAccess Limited oilseed rape (winter) clopyralid and picloram
Nugget 13121
31/12/2013 AgriGuard Ltd oilseed rape (winter) clopyralid and picloram
Pantheon 13695
31/12/2010 Pan Agriculture Limited
land not intended for cropping picloram
Pantheon 2 14052
31/12/2013 Pan Agriculture Limited
land not intended for cropping picloram
Piccant 14294
31/12/2013 Goldengrass Limited oilseed rape (winter) clopyralid and picloram
Prevail 13205
31/12/2013 Dow AgroSciences Limited
oilseed rape (winter) clopyralid and picloram
Renegade 14507
31/12/2013 Chemsource Ltd oilseed rape (winter) clopyralid and picloram
RouteOne Loram 24 13951
31/12/2013 Albaugh UK Limited land not intended for cropping picloram
Tordon 101 05816
31/12/2013 Dow AgroSciences Limited
land not intended for cropping 2,4-D and picloram
Tordon 22K 05083
31/12/2013 Dow AgroSciences Limited
land not intended for cropping picloram
Tordon 22K 05790
31/12/2010 Nomix Enviro Limited land not intended for cropping picloram
Tordon 22K 13869
31/03/2013 Nomix Enviro, A Division of Frontier Agriculture Limited
land not intended for cropping picloram
An investigation of clopyralid and aminopyralid in commercial composting
systems 40
Appendix 2
Literature review of garden waste composition
12.0 Introduction A short literature review was conducted to assess the composition of garden waste collected separately for
composting across the UK. The search was carried out on-line using a number of search engines and databases,
including Google Scholar, www.ojose.com, High Wire Press, and www.researchgate.net, in addition to the
author‘s own library. The search included studies assessing the composition of municipal waste in general, home
composting studies, WRAP‘s own research into separate organics collections and the variability of compost
quality.
12.1 Results from England The literature review indicated a paucity of data on the composition of green waste and how this varied
throughout the year. Most compositional studies sorted municipal waste into various categories, however,
‗garden waste‘ was nearly always classified into a single category. The data obtained are summarised below.
12.1.1 Morpeth, Northumberland The most comprehensive data set identified in this literature search was obtained by the Open University / HDRA
during research on behalf of the Environment Agency (HDRA & Open University, 1999). The trial assessed a
garden and food waste6 co-collection from 4,000 households in Castle Morpeth during 1995/96, where the waste
was collected fortnightly in a 240 litre wheeled bin. Households involved in the trial had, in general, large
gardens. Waste was sorted using the ‗cone and quarter‘ technique, and classified into six categories, namely:
grass cuttings, dried leaves, green leafy, woody brown, putrescibles and contaminants. The data are shown in
Table 15 and Figure 3.
Collectively they suggest that grass clippings comprised over 60% by mass of the total waste collected between
May and September, and illustrate the considerable seasonal variation in green waste composition throughout
the year. Not surprisingly, hardly any grass was collected during November and December.
Table 15– Summary of green waste composition in the Morpeth trial
(% Fresh weight ± SE)
June 1995
September 1995 December 1995 April 1996
Grass cuttings
84.4 ± 12.3
65.2 ± 4.5 1.2 ± 0.1 35.0 ± 5.0
Dried leaves
1.1 ± 1.1
0.5 ± 0 92.3 ± 3.8 33.4 ± 3.5
Green (leafy)
1.2 ± 0.9
15.5 ± 11.1 0.5 ± 1.0 6.3 ± 1.3
Brown (woody)
3.8 ± 2.7
15.5 ± 5.0 4.5 ± 0.1 22.0 ± 2.0
Putrescibles
1.8 ± 1.4
0.5 ± 1.0 0.7 ± 0.3 4.0 ± 1.0
Contaminants
7.7 ± 10.1
2.8 ± 0.5 0.8 ± 0.3 0.35 ± 0.15
Source: Environment Agency Technical Report P314; reproduced with permission
6 This scheme pre-dated the introduction of the Animal By-Products Regulation
An investigation of clopyralid and aminopyralid in commercial composting
systems 41
Figure 3 – Seasonal variation in proportion of grass clippings collected in green / food
waste co-collection at Castle Morpeth in 1995/96
Source: Ibid; reproduced with permission
12.1.2 Dogsthorpe, Peterborough The composition of green waste collected at the Dogsthorpe open windrow composting facility during 1995 / 96
was also determined as part of the above composting research programme funded by the Environment Agency
(AEA Technology, 2000). Researchers at AEA Technology categorised green waste collected at the city‘s
household waste recycling centres; samples were sorted into 13 categories on both bulk samples (i.e. pre-
shredding), or post-shredded material. The data, shown in Table 16, suggest that negligible quantities of grass
clippings were identified. Even though 1995 was a hot, dry summer, it is surprising the analyses didn‘t identify
grass during the autumn period. Rather, as the sampling methodology differed from that used in the Morpeth
trial, it is possible that grass was classified into the ‗fines‘ category, which averaged 29% (m/m) during the year
of the shredded samples. This illustrates the importance of using an appropriate sampling technique.
12.1.3 Nine English local authorities As part of a wider study funded by WRAP looking into home composting, garden waste from nine English local
authority areas was sampled during June and September 2004. (A variety of garden waste collection methods
were used across the sample authorities). During June, garden waste comprised approximately 21% (by mass),
whereas during September it fell to about 12%.
May Jul Aug Sept Nov Dec March Jun
An investigation of clopyralid and aminopyralid in commercial composting systems 42
Table 16– Summary of green waste composition at Dogsthorpe
Bulk Samples of
Feedstock received
(prior to shredding)
(% mass/ mass)
Shredded feedstocks (< 50 mm)
(% mass/ mass)
Delivery date August
1995
Jan 1996 August
1995
Sept 1995 Oct 1995 Nov 1995 Dec 1995 Jan 1996 Feb 1996 March
1996
Category
Grass Cuttings 1.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Green Foliage 19.4 20.66 2.80 2.81 42.31 1.13 1.4 51.46 41.8 36.46
Soft Prunings 7.73 0.08 11.2 11.2 0.00 0.00 0.00 0.00 0.00 2.00
Logs/Tree Trunks 7.49 27.79 5.6 5.6 4.83 3.87 3.77 12.05 13.3 12.8
Autumn Leaves 2.01 0.23 2.02 2.02 0.57 7.97 7.49 095 2.71 3.52
Soil 3.14 2.64 2.74 2.75 0 17.23 15.23 3.25 10.45 5.24
Allotment Waste 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.84
Fruit 2.01 0.04 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.9
Hard Prunings 9.47 14.65 14.79 14.78 7.6 24.87 23.14 18.23 19.14 18.16
Putrescibles 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Fines 22.8 30.78 46.47 46.47 43.98 28.73 32.79 14.04 12.6 10.2
Other readily degradables ND ND 13.26 13.26 0.00 14.69 14.55 0.00 0.00 0.00
Contaminants 24.9 3.15 1.12 1.11 0.67 1.52 1.63 0.00 0.00 6.89
Reproduced with permission.
An investigation of clopyralid and aminopyralid in commercial composting
systems 43
12.2 European data Given the lack of UK-based data, the literature search was expanded to include data published in peer reviewed
journals from within Europe.
12.2.1 Hamburg, Germany The most comprehensive study was reported by Krogmann (1999), who investigated the effects of season and
housing type on the composition of separately collected biowastes (garden and food wastes) from households in
Hamburg, Germany. The % grass (by mass) based on three housing types are shown in Figure 4. The data
presented were derived from Krogmann‘s and based on the % of the garden waste fraction only.
Figure 4 – Variation in grass collected in a garden / food waste collection scheme in
Hamburg, Germany
These data show that greatest proportion of grass clippings were collected during the spring and summer
months, with the single family and town houses presenting the greatest amount during the spring time. Notably,
in the downtown area, the greatest proportion of grass was obtained during summer, although these houses
were less likely to have large gardens.
12.2.2 Aarhus, Denmark Researchers in Denmark sampled garden waste eight times over a period of a year (twice in every season),
sorting into five different fractions (Boldrin & Christensen, 2010). Unfortunately grass clippings were classified in
the ―small stuff‖ category, which included grass, flowers, soil etc. This fraction was shown to comprise just over
50% (by mass) in January, rising to above 90% in September, with an annual weighted average of just over
75%.
12.3 Conclusions The results from this literature review indicate there is a paucity of data on the composition of garden waste
collected for biological treatment, with research at Morpeth, Northumberland, providing the most comprehensive
datasets. In general, the proportion of grass clippings was greatest during the spring months, although data
from Germany appeared to suggest this was influenced by housing type. In Morpeth, over 60% of the total
garden waste collected in wheeled bins was grass during May to September.
In order to gain a better understanding of the potential risks associated with contaminants (e.g. clopyralid) that
may enter a commercial composting system through garden wastes, a better understanding of garden waste
composition and variation would be beneficial. This would need to accommodate differing collection systems
(bring and kerbside), housing types and local policies for residual waste collection.
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