New techniques for improved decision-making in contaminated land risk assessment
Brownfield & Contaminated Land
11th May 2017
Rebekka McIlwaine
Siobhan Cox
Historical development and its effect on soil contamination in urban areas
Rebekka McIlwaine Rory Doherty Siobhan Cox Mark Cave Society of Brownfield Risk Assessment (SoBRA) funded project
Historical development and its effect on soil contamination in urban areas
• Study areas: Belfast and Sheffield • Elements: Arsenic, Cobalt, Chromium, Copper,
Molybdenum, Nickel, Lead, Antimony, Tin, Vanadium, Zinc
• Source identification: data analysis • Historical development • ‘Typical’ concentrations
Study area: Belfast
• History of linen production (from early 18th Century) and ship building (late 18th Century)
• Varied bedrock geology, known to control PTE concentrations – Basalts to the north – Sherwood sandstone – Greywacke to the south
Belfast
Tellus geochemical soil samples
Inorganics 4 samples per km2
781 samples
Geochemical Datasets
Shallow sample at 5 - 20cm depth
Shallow sample at 5 - 20cm depth
Deep sample at 35 – 50cm depth
X-ray fluorescence Inductively coupled plasma following aqua regia digest Inductively coupled plasma following aqua regia digest
Source Identification
Data analysis
• Various analyses were carried out: SPATIAL – Interpolated maps
STATISTICAL – Inspection of contaminant distributions (skewness and kurtosis) – Depth ratio boxplots – Cluster analysis – Principal component analysis
Belfast: Depth comparison
• Anthropogenic – more likely to be
elevated at surface (ratio >1)
– Less likely to have lower outliers
– Wider distribution • Geogenic
– more likely to be elevated at depth (ratio <1)
– More likely to have lower outliers
Belfast: Principal Component Analysis
Source Identification: skewness and kurtosis
• Skewness measures symmetry in the data
• Kurtosis measures whether the data has a ‘tail’
• Generally geogenic contaminants in the bottom left corner
Less symmetry
and greater ‘tail’
Historical development
Historical development
• Boundaries taken from the extent of urbanised areas on OS mapping
• Belfast – 1858 – 1901 – 1919-1939 – Current
Historical development
• Spatial distribution of Pb in surface soils
• Relatively uncontaminated area in the centre of the city
• Halo of contamination around this
Historical development
Belfast: Pollution Indices
• PI = Uc/Rc (Uc = median urban conc., Rc = median rural conc.)
• Co, V, Cr & Ni – highest PI Current Belfast
• Pb – highest 1901
• All others – highest 1919-1939
• Pb and Sn show considerably higher enrichment
Typical concentrations
Can we calculate ‘typical’ values?
• ‘Typical’ or ‘background’ values • Do not assess risk – provide
‘typical’ concentrations of a compound or element
• UK approach defines background levels as both geogenic and diffuse anthropogenic in origin – ‘Normal Background Concentration’ (NBC)
• Finland - ‘Upper Limit of Geochemical Baseline Variation’ (ULBL)
Typical Threshold Values – Northern Ireland
• Example - Nickel • Identify domains
Ni (mg/kg) 1.45 – 3.55 3.56 – 10.47 10.48 – 25.12 25.13 – 44.67 44.68 – 112.2 112.21 – 165.96 165.97 – 234.42 234.43 – 372.2
Calculating Typical Threshold Values
NBC approach (Cave et al 2012) (needs at least 30 data points) 1. Assess skewness of data 2. Perform data transformation (log or box cox) 3. Determine percentiles (parametric, robust or empirical methods) 4. NBC: the upper 95th confidence limit of the 95% percentile
Calculating Typical Threshold Values
ULBL approach (Jarva et al 2010) • ULBL is the upper limit of the upper whisker line of the box and whisker plot
Typical Threshold Values – Northern Ireland
ULBLX =P75 + 1.5 × (P75−P25)
Upper limit of geochemical baseline variation
Nickel domain TTV (mg/kg) Basalt 250
Mournes 11 Peat 33
Principal 88
Calculating Typical Threshold Values - urban
NBC method ULBL method ‘MAD’ method (Reimann et al., 2005) • Uses the median and median absolute deviation (MAD) where:
Geochemical background = median + 2xMAD • Accepted in Gateshead by local authority as method by which to calculate ‘Normal Background Concentrations’
Typical Threshold Values for Belfast’s development zones (mg/kg)
1858 1901 1919-1939 Modern
S4UL
Lowest
value
ULBL M
+2MAD NBC * ULBL
M
+2MAD NBC ULBL
M
+2MAD NBC ULBL
M
+2MAD NBC
As 18 13 - 21 15 BC 37 26 17 E 52 19 14 L 21 37 **
Cu 120 95 - 160 100 BC 210 200 120 BC 640 120 80 L 130 520 +
Mo 2.8 1.8 - 3.5 2.4 L 4.7 5.1 3.0 E 18 2.7 1.8 L 3.1 -
Pb 190 140 - 430 280 L 490 620 270 BC 1300 200 120 L 260 34 ++
Sb 2.7 1.9 - 4.3 3.1 L 10 7.2 3.7 BC 33 3.0 2.1 L 4.3 -
Sn 16 11 - 20 14 L 33 51 18 BC 1000 14 7.7 BC 24 -
Zn 240 210 - 310 220 L 470 510 290 BC 2100 240 170 L 290 620 +
• * Insufficient samples
• ** Residential with homegrown produce +Allotments ++pC4SL for allotments
(BC = box-cox transformation, L = log transformation and E = empirical)
Conclusions
• Potential sources of elements in soil can be identified using: – Depth ratios, cluster analysis and PCA (and also
skewness and kurtosis) • These methods could also be used to identify elements with
geogenic and anthropogenic sources in Sheffield • Historical development in Belfast and Sheffield is linked to
element contamination, with elevated levels of Pb, Sn and Sb in particular being associated with development in the early 20th Century
• Further work is needed to assess risks associated with this….
Further details
• The final report from this study is available on the SoBRA website
• McIlwaine, R., Doherty, R., Cox, S.F., Cave M. R. (2017) The relationship between historical development and potentially toxic element concentrations in urban soils. Environmental Pollution, 220(B): 1036-1049 http://dx.doi.org/10.1016/j.envpol.2016.11.040
What next?
Total versus Bioavailable Contamination
• McIlwaine et al. 2017 considered the total concentration of elements in soils
• Most risk assessment models assess exposure to total contamination through: – Inhalation – Ingestion – Dermal contact
• For many inorganic contaminants ingestion is the principal pathway • However, once ingested, contamination has to leave the soil and
enter the bloodstream to be able to cause toxic effects • It is less conservative to consider the bioavailable or bioaccessible
concentrations of elements in the soil
Bioavailability and bioaccessibililty
(Cave et al., 2011)
Bioavailability and bioaccessibililty
• Oral bioavailability: The degree to
which a substance is absorbed and becomes available to the target tissue (without first being metabolised) (CIEH, 2009).
• Oral bioaccessibility: The degree to which a chemical is released from soil into solution (and thereby becomes available for absorption) when that soil is ingested and undergoes digestion (CIEH, 2009). – Generally less than or equal to the
bioavailable fraction
Measured by: • In-vivo:
Juvenile swine
• In-vitro: in a test tube in the lab
Measuring bioaccessibility: The Unified BARGE Method (UBM)
• Bioaccessibility test developed by the BARGE group (including BGS)
• Simulates the gastric (G) and gastro-intestinal (GI) phase
• Undergone inter-laboratory trials (Wragg et al., 2011)
• Validated against in-vivo testing for Cd, Pb and As (Denys et al., 2012)
• ISO Technical Specification 17924 www.bgs.ac.uk/barge
What factors affect oral bioaccessibility
• Mineral form • Particle size • Encapsulation • Chemical species
• Also:
– pH – SOM
(Cave et al., 2011)
Oral bioaccessibility testing in Northern Ireland
• UBM testing of 91 soil samples across NI (Barsby et al. 2012)
• UBM testing of 145 samples (incl Barsby dataset) for Ni, V and Cr across NI (Palmer et al. 2014)
• Detailed investigations of Ni & Cr bioaccessibility in soils overlying the Antrim basalts (Cox et al. 2013 & Cox et al. 2017)
(Barsby et al., 2012)
What next? Oral bioaccessibility testing for Belfast
• Set up the UBM in QUB
• Selected 100 samples for UBM testing
• Includes different – land uses – geology – development
zones
How do we use bioaccessibility testing in Risk Assessment?
• Sets out – how to use
bioaccessibility testing in risk assessment
– Common misuses – Common myths
• However bear in mind it was
written before the UBM method was developed!!
How do we use bioaccessibility testing in Risk Assessment?
• QUB deriving graphs of GACs for varying BAF for a variety of contaminants & land uses based on S4ULs
– Methodology adapted from Scott and Nathanail, 2011
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60 70 80 90 100
Arse
nic
GAC
(mg/
kg)
Arsenic BAF (%)
GAC for Inorganic Arsenic with changing oral bioaccessible fraction (BAF)
GAC Res with Produce S4UL Res with Produce
GAC Res without Produce S4UL Res without Produce
37 mg/kg 40 mg/kg
0
500
1000
1500
2000
2500
3000
0 10 20 30 40 50 60 70 80 90 100
Arse
nic
GAC
(mg/
kg)
Arsenic BAF (%)
GAC for Inorganic Arsenic with hanging oral bioaccessible fraction (BAF)
GAC POS resi S4UL POS res GAC POS park S4UL POS park
Acknowledgments
This research was funded by an Annual Scholarship from the Society of Brownfield Risk Assessment (SoBRA)
Bioaccessibility testing was undertaken as oart of the REMEDIATE project funded from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 643087
The Tellus project was funded by the Department of Enterprise Trade and Investment and by the Rural Development Programme through the Northern Ireland Programme for building sustainable prosperity.
References
• Cave, M.R., Wragg, J., Denys, S., Jondreville, C., Feidt, C., 2011. Oral Bioavailability, in: Swartjes, F.A. (Ed.), Dealing with Contaminated Sites. Springer Netherlands, pp. 287–324. doi:10.1007/978-90-481-9757-6_7
• Chartered Institute of Environmental Health (CIEH), 2009. Professional Practice Note: Reviewing human health risk assessment reports invoking contaminant oral bioavailability measurements or estimates.
• Denys, S., Caboche, J., Tack, K., Rychen, G., Wragg, J., Cave, M., Jondreville, C., Feidt, C., 2012. In vivo validation of the unified BARGE method to assess the bioaccessibility of arsenic, antimony, cadmium, and lead in soils. Environ. Sci. Technol. 46, 6252–60. doi:10.1021/es3006942
• Scott DI & Nathanail CP, 2011. Generic human-health assessment criteria for arsenic at former coking works sites. CL:AIRE Research Bulletin RB14. CL:AIRE, London, UK. ISSN 2047-6450
• Wragg, J., Cave, M., Basta, N., Brandon, E., Casteel, S., Denys, S., Gron, C., Oomen, A., Reimer, K., Tack, K., Van de Wiele, T., 2011. An inter-laboratory trial of the unified BARGE bioaccessibility method for arsenic, cadmium and lead in soil. Sci. Total Environ. 409, 4016–30. doi:10.1016/j.scitotenv.2011.05.019
References: Research about soil contamination and bioaccessibility in Northern Ireland
• Barsby, A., McKinley, J.M., Ofterdinger, U., Young, M., Cave, M.R., Wragg, J., 2012. Bioaccessibility of trace elements in soils in Northern Ireland. Sci. Total Environ. 433, 398–417. doi:10.1016/j.scitotenv.2012.05.099
• Cox, S.F., Chelliah, M.C.M., McKinley, J.M., Palmer, S., Ofterdinger, U., Young, M.E., Cave, M.R., Wragg, J., 2013. The importance of solid-phase distribution on the oral bioaccessibility of Ni and Cr in soils overlying Palaeogene basalt lavas, Northern Ireland. Environ. Geochem. Health 35, 553–567. doi:10.1007/s10653-013-9539-6
• Cox, S., McKinley, J. & Rollinson, G., 2017. Mineralogical Characterisation to improve understanding of oral bioaccessibility of Cr and Ni in Basaltic Soils in Northern Ireland. Journal of Geochemical Exploration. doi: 10.1016/j.gexplo.2017.02.006
• McIlwaine, R., Cox, S.F., Doherty, R., Palmer, S., Ofterdinger, U., McKinley, J.M., 2014. Comparison of methods used to calculate typical threshold values for potentially toxic elements in soil. Environ. Geochem. Health 36, 953–971. doi:10.1007/s10653-014-9611-x
• McIlwaine, R., Doherty, R., Cox, S.F., Cave M. R. (2017) The relationship between historical development and potentially toxic element concentrations in urban soils. Environmental Pollution, 220(B): 1036-1049 http://dx.doi.org/10.1016/j.envpol.2016.11.040
• Palmer, S., Cox, S.F., McKinley, J.M., Ofterdinger, U., 2014. Soil-geochemical factors controlling the distribution and oral bioaccessibility of nickel, vanadium and chromium in soil. Appl. Geochemistry 51, 255–267. doi:10.1016/j.apgeochem.2014.10.010
Top Related