INFOTOX (Pty) Ltd · 2015-07-09 · Report No: 026-2010 Rev 2.0 Human Health Risk Assessment for...

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Human Health Risk Assessment for the

Proposed M14 Furnace at Metalloys

Document No 026-2010 Rev 2.0

Compiled by:

Willie van Niekerk PhD QEP(USA) Pr Sci Nat(Environmental Science)

5 September 2010

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INFOTOX (Pty) Ltd.

This report has been prepared by INFOTOX (Pty) Ltd with all reasonable skill, care and

diligence within the terms of the Agreement with the Client. The report is confidential to the

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their own risk.

WCA van Niekerk PhD QEP (USA) Pr Sci Nat (Environmental Science)

Managing Director

5 September 2010

Executive summary

Samancor Manganese (Pty) Ltd trading as Metalloys (“Metalloys”) is planning an expansion of its ferromanganese production by building another furnace as an expansion to the existing M12 operations. The proposed M14 Furnace was partially constructed several years ago and the furnace shell and raw materials handling plant building are in place. M14 is proposed to be constructed largely as a replica of M12 in capacity, but design improvements are being made, notably in the electrode system and secondary dust extraction equipment. Terra Pacis Environmental (Pty) Ltd (“Terra Pacis”) appointed Airshed Planning Professionals (Pty) Ltd (“Airshed”), a company specialising in air quality studies, to undertake an air quality impact assessment of the proposed operations. The primary objective of the Airshed study has been to determine potential impacts on the surrounding environment and human health. Subsequently, Terra Pacis appointed INFOTOX (Pty) Ltd (“INFOTOX”) to conduct a quantitative

human health risk assessment on the data produced by Airshed. This report presents the

findings of INFOTOX.

In the case of the criteria pollutants [particulate matter (PM10), sulphur dioxide (SO2), and

nitrogen oxides (represented by NO2)], mortality or hospitalisation rates for respiratory or

cardiovascular causes are the measure of associated illness that is mostly applied in

epidemiological studies. INFOTOX followed the approach of quantifying exposure to air

contaminants according to central tendency exposure (CTE) and reasonable maximum

exposure (RME) in the study area. CTE represents the most likely exposure scenario under

which conditions the majority of individuals would be subjected. The RME is the maximum

exposure that is reasonably expected to occur in the scenario under investigation.

Central tendency exposure (CTE) and reasonable maximum exposure (RME) estimates were

obtained from concentration isopleths of the criteria pollutants that were superimposed on a

map of the study area. Meyerton Park, which is directly adjacent to the Metalloys Site, was

identified as the residential area that receives the highest concentrations of airborne pollutants

from sources on the Metalloys Site. All other residential locations are under concentration

isopleths at much lower levels.

INFOTOX calculated the potential fractional increase in the incidences of mortality and

morbidity associated with increased concentrations of PM10 and SO2. Concentration estimates

of NO2 were too low to be of health significance. In the absence of baseline data on mortality

and emergency room visits or hospitalisation rates for specific health effects, it is not possible to

relate the fractional increases to actual numbers of cases. Considering the relatively small

residential area in which the CTE and RME have been determined, however, it is expected that

the number of cases based on excess mortality and morbidity relating to the modelled increase

in PM10 and SO2 concentrations would be small, if not insignificant. It is not possible to make a

more conclusive statement on the available information.

Meyerton Park has been identified as the residential area with the highest potential for adverse

health effects due to PM10 emissions from the Metalloys works. A more definitive statement on

health risks could be made if population numbers and estimates of age distribution for the area

were known. Furthermore, it will be helpful if concentration isopleths across Meyerton Park

were presented with a higher resolution. However, such additional information would not

change the overall conclusion that risks associated with emissions from the proposed

M14 Furnace would be small, if not insignificant.

In so far as exposure to manganese is concerned, it was concluded that it is unlikely that the

estimated CTE and RME exposures in Meyerton Park would lead to measurable adverse health

effects on chronic exposure under the concentrations that were predicted in air dispersion

estimates. The conclusion was based on credible interpretation of epidemiological data and is

presented with confidence. Exposure to manganese at other residential locations in the study

area was predicted to be lower than in Meyerton Park and associated health risks are thus likely

to be even more insignificant.

Table of contents

1 Introduction ............................................................................................................................ 1

2 The human health risk assessment paradigm ...................................................................... 1

3 Study area.............................................................................................................................. 3

4 Risk quantification for criteria pollutants................................................................................ 4

5 Risks associated with exposure to airborne manganese...................................................... 6

5.1 Manganese toxicity ................................................................................................................ 6

5.2 Selection of an appropriate guideline concentration in air .................................................... 7

5.3 Risk quantification methodology............................................................................................ 9

6 Methodology for quantification of exposure ........................................................................ 10

7 Quantitative human health risk assessment for criteria pollutants ..................................... 10

7.1 Particulate matter (PM10).................................................................................................... 10

7.2 Sulphur dioxide .................................................................................................................... 15

7.3 Nitrogen dioxide ................................................................................................................... 18

8 Quantitative human health risk assessment for manganese.............................................. 20

9 Conclusions ......................................................................................................................... 23

9.1 Criteria pollutants ................................................................................................................. 23

9.2 Airborne manganese ........................................................................................................... 24

10 Uncertainty review ............................................................................................................... 25

11 Recommendations............................................................................................................... 25

12 References........................................................................................................................... 26

List of tables

Table 7.1.1: Highest daily and annual averaged ambient air concentrations of PM10 at

residential locations in the study area (M14 Operations, Scenario 1)

(Kornelius and Krause, 2010)........................................................................... 11

Table 7.1.2: Highest daily and annual averaged ambient air concentrations of PM10 at

residential locations in the study area (Scenario 2) (Kornelius and Krause,

2010). ................................................................................................................ 13

Table 7.1.3: Attributable fraction of cases due to exposure to PM10. ................................. 15

Table 7.2.1: Highest daily and annual averaged ambient air concentrations of sulphur

dioxide at residential locations in the study area (Kornelius and Krause,

2010). ................................................................................................................ 16

Table 7.2.2: Attributable fraction of cases due to exposure to sulphur dioxide. .................. 17

Table 7.3.1: Highest daily and annual averaged ambient air concentrations of nitrogen

dioxide (Kornelius and Krause, 2010). ............................................................. 19

Table 8.1: Highest annual averaged ambient air concentrations of manganese at

residential locations in the study area (Kornelius and Krause, 2010). ............ 21

Table 8.2: Estimates of the highest annual averaged manganese concentrations at

residential locations in the study area for CTE and RME levels...................... 21

List of figures

Figure 3.1: Map of the study area showing the Metalloys Site with red boundaries

(Kornelius and Krause, 2010)............................................................................. 3

Figure 7.1.1: Highest daily PM10 concentrations associated with the proposed M14

Furnace (Scenario 1) (Kornelius and Krause, 2010). ...................................... 12

Figure 7.1.2: Annual averaged PM10 concentrations associated with the proposed M14




Figure 7.1.4: Annual averaged PM10 concentrations associated with the proposed M14


Figure 7.2.1: Highest daily SO2 concentrations associated with the proposed M14

Furnace (Kornelius and Krause, 2010). ........................................................... 17

Figure 7.2.2: Annual averaged SO2 concentrations associated with the proposed M14


Figure 7.3.1: Highest daily NO2 concentrations associated with the proposed M14


Figure 7.3.2: Annual averaged NO2 concentrations associated with the proposed M14


Figure 8.1: Baseline annual averaged manganese concentrations after

implementation of the Metalloys Emissions Reduction Strategy (Kornelius

and Krause, 2010). ........................................................................................... 22

Figure 8.2: Annual averaged manganese concentrations associated only with the

proposed M14 Furnace (Kornelius and Krause, 2010).................................... 22

Figure 8.3: Annual averaged manganese concentrations cumulative for baseline and

the proposed M14 Furnace (Kornelius and Krause, 2010).............................. 23

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Proposed M14 Furnace at Metalloys Page 1 of 29

1 Introduction

Samancor Manganese (Pty) Ltd trading as Metalloys (“Metalloys”) is planning an expansion of

its ferromanganese production by building another furnace as an expansion to the existing M12

operations. The proposed M14 Furnace was partially constructed several years ago and the

furnace shell and raw materials handling plant building are in place. M14 is proposed to be

constructed largely as a replica of M12 in capacity, but design improvements are being made,

notably in the electrode system and secondary dust extraction equipment. Knights (2009)

published a comprehensive overview of the proposed M14 Furnace and auxiliary processes and

equipment.

Terra Pacis Environmental (Pty) Ltd appointed Airshed Planning Professionals (Pty) Ltd

(“Airshed”), a company specialising in air quality studies, to undertake an air quality impact

assessment of the proposed operations. The primary objective of the Airshed study has been

to determine potential impacts on the surrounding environment and human health. The report

was published in April 2010 (Kornelius and Krause 2010).

Subsequently, Terra Pacis appointed INFOTOX (Pty) Ltd to conduct a quantitative human

health risk assessment on the data produced by Airshed. This report presents the findings of

INFOTOX.

2 The human health risk assessment paradigm

The original paradigm for regulatory human health risk assessment (HHRA) in the USA was

developed by the USA National Research Council (NRC 1983). This model has been adopted

and refined by the US Environmental Protection Agency (USEPA) and other agencies in the

world as published under the International Programme on Chemical Safety (IPCS 1999) and is

widely used in the world for quantitative human health risk assessments. The elements of the

HHRA approach are described below.

Hazard assessment

Hazard assessment is the identification of chemical contaminants suspected to pose hazards

and a description of the types of toxicity that they may evoke. In an industrial area, generally

there are several substances of potential concern and in full risk assessments it is often

necessary to consider these substances together in terms of impacts on health and the

environment. In this M14 Furnace project, hazards were identified in the process assessment

conducted by Knights (2009) and Kornelius and Krause (2010) used emissions data from the

M12 Furnace to predict the additional environmental concentrations of the identified

contaminants that will be associated with the proposed M14 operations. Because the proposed

M14 Furnace will be largely a replica of M12 in capacity, but with better emissions controls, it

was used as a conservative surrogate for the M14 Furnace and its emissions.

Dose-response assessment

Dose-response assessment (toxicological assessment) addresses the relationship between

levels of biological exposure and the manifestation of adverse health effects in humans, and/or

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how humans can be expected to respond to different doses or concentrations of contaminants.

The toxicological assessment follows a quantitative procedure that distinguishes between

carcinogens and noncarcinogens. Risk quantification for carcinogens uses a cancer slope

factor for each substance, whereas noncarcinogens are characterised by reference doses

(RfDs) and tolerable daily intakes (TDIs). Cancer potency is also expressed as a cancer unit

risk factor and noncancer effects are considered in terms of reference concentrations (RfCs) or

tolerable concentrations in air (TCAs). There were no carcinogens of potential concern

identified in this investigation.

The fundamental understanding in the assessment of exposure to noncarcinogens is that the

likelihood of adverse health effects occurring at exposures below the risk-based concentrations

is remote. In the case of noncarcinogenic contaminants that are relatively abundant in ambient

air, the use of RfCs or TCAs to assess potential impacts on human health has limitations,

because background concentrations (without considering the sources under investigation) may

already have adverse impacts on health. Risk assessment for criteria pollutants is discussed in

Section 4.

USEPA (IRIS 2010) defines a reference dose (RfD) as “an estimate of a daily oral exposure for

a given duration to the human population (including susceptible subgroups) that is likely to be

without an appreciable risk of adverse health effects over a lifetime.” It is derived from a

benchmark dose limit (BMDL), a no-observed-adverse-effect level (NOAEL), a lowest-observed-

adverse-effect level (LOAEL), or another suitable point of departure, with uncertainty/variability

factors applied to reflect limitations of the data used. The term tolerable daily intake (TDI) has a

meaning similar to the RfD, describing a threshold dose (IPCS 1999).

Exposure to noncarcinogens through inhalation is normally assessed against a reference

concentration in air (RfC). This may be converted to an inhaled dose by dividing by the body

weight (70 kg) and multiplying by the inhalation rate of 20 m3/day. The primary use of a RfD or

RfC is to evaluate increments of exposure from specific sources when background exposures

are low. Exceedence of the RfC is not a statement of risk. The term tolerable concentration in

air (TCA) has a meaning similar to the RfC, describing a threshold concentration (IPCS 1999).

Exposure assessment includes a description of the environmental pathways and distribution of

hazardous substances, identification of potentially exposed individuals or communities, the

routes of direct and indirect exposure, and an estimate of concentrations and duration of the

exposure. Exposure assessment in this study was limited to the air pathway of exposure, with

potential intake of air contaminants through inhalation.

Airshed Planning Professionals (Kornelius and Krause, 2010) conducted mathematical

dispersion modelling based on the emissions inventory for Metalloys to estimate ambient air

concentrations of the contaminants of interest at locations where members of the community

could be exposed. The ambient air levels of contaminants are presented as concentration

isopleths. These isopleths indicate ranges of concentrations across the area and should be

interpreted as a continuum, rather than discreet concentration intervals. The concentration

isopleths are shown in Section 7. Air concentrations are presented according to averaging

times. Meteorological conditions affect the dispersion of contaminants and it is possible to

select worst-case conditions. For assessment of acute health effects, the highest modelled

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concentrations over a period of 24 hours were selected. For chronic exposure to systemic

toxicants, annual averages of contaminants in air were used for health risk quantification.

Risk characterisation

Risk characterisation (quantification of health risks) involves the integration of the components

described above, with the purpose of determining whether specific exposures to an individual or

a community might lead to adverse health effects. If possible, the probabilities (risk) of

occurrences of these effects are estimated.

Assessment of health risks associated with exposure to carcinogens and systemic toxicants is

normally conducted on the basis of documented toxicological information on cancer slope

factors (or inhalation unit risk factors) and reference doses or reference concentrations in the

low exposure region.

3 Study area

Figure 3.1 shows a map of the study area with the Metalloys Site indicated with red boundaries.

Residential areas identified as potential receptor locations for air contamination from the

Metalloys process emissions are also indicated on the map.

Figure 3.1: Map of the study area showing the Metalloys Site with red boundaries

(Kornelius and Krause, 2010).

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4 Risk quantification for criteria pollutants

In the case of the criteria pollutants [particulate matter (PM10), sulphur dioxide (SO2), and

nitrogen oxides (represented by NO2)], mortality or hospitalisation rates for respiratory or

cardiovascular causes are the measure of associated illness that is mostly applied in

epidemiological studies. Air concentrations of compounds that exceed the ambient air quality

guidelines or standards indicate that adverse health conditions may develop, but simple

comparisons between exposure concentrations and ambient air quality guidelines are

inadequate to quantify health outcomes. In general, predicted or measured impacts of industrial

emissions on air quality are used as a basis to quantify impacts on health. This is achieved by

calculating the potential increase in hospital admissions or in mortality due to specific causes,

associated with increased air concentrations of specific toxic compounds. These calculations

are based on results of studies reported in the international scientific literature in which

statistical methods were used to compare changes in hospitalisation or mortality rates with

changes in air quality.

It is important to note that it is common to observe increases in mortality or hospitalisation rates

even when the available air concentrations do not exceed the environmental air quality

guidelines. Ambient air quality guidelines are used for management of air quality and are not

intended for risk quantification. Estimation of impacts of air pollutants on health may therefore

not be restricted to areas in which the guideline concentrations are exceeded, but should also

include areas in which concentrations are within limits. Current statistical methods use the

concept of relative risk ratios (RR) to derive the potential percentage increase in effects.

The potential number of additional deaths or hospital admissions brought on by an increase in

the concentration of a pollutant is calculated using the following approach of the World Health

Organization (WHO 2004):

1000/BPAFE ××= (4.1)

Where:

E Potential mortalities or morbidities per day or per year due to exposure to

the pollutant

AF The attributable fraction of mortalities or morbidities due to exposure to the

pollutant

B The population incidence of mortality or morbidity (e.g., deaths or

hospitalisation rates per 1 000 people)

P Size of the exposed population (number)

1RRAF −= (4.2)

Where:

RR The relative risk of mortality or morbidity due to exposure to the pollutant

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The relative risk of death (RR) is calculated as follows:

)( pdeathseRR

∆×∆= (4.3)

Where:

∆deaths Potential proportion change in mortality associated with a change in the

pollutant concentration of 1 µg/m3

∆p The modelled change in the mean pollutant concentration in µg/m3

Similar calculations can be made for morbidity cases.

In the above equation, the temporal denominator is determined by the averaging period of the

pollutant concentration used as a basis for calculation in the literature. Therefore, if the

averaging time of the pollutant was reported as daily (the daily mean concentration) in the

literature, the daily population incidence of the health effect must be estimated (per 1 000

people), and the modelled daily mean concentration used to calculate the potential number of

additional cases of the health effect. The result of the calculation will then reflect the potential

daily increase in that health effect incidence.

Toxicological parameters that were used in the risk assessment for the criteria pollutants PM10,

SO2 and NO2 are listed in Tables 4.1.1, 4.1.2 and 4.1.3, respectively.

Table 4.1.1: Summary of PM10 risk factors for health risk assessment. All risk

factors were derived from single-pollutant models.

Health effect Per cent increased risk per

10 µg/m3 PM10 increase

Reference

Short-term (based on a 24-hour mean PM10 concentrations)

Total non-accidental mortality 0.5 WHO 2005

Cardiovascular mortality 0.9 COMEAP 2006

Emergency department visits with cardiovascular disease, adults 65 and older

3 USEPA 2008

Hospital admissions with cardiovascular disease, adults 65 and older

0.75 USEPA 2008

Cardiac admissions 0.9 COMEAP 2006

Exacerbation of respiratory symptoms in children with asthma

5 USEPA 2008

Emergency department visits and hospital admissions in asthmatic children

2 USEPA 2008

Emergency department visits with COPD, adults 65 and older

3 USEPA 2008

Hospital admissions with COPD, adults 65 and older

1 USEPA 2008

Long-term (based on annual mean PM10 concentrations)

Respiratory symptoms (cough and wheeze)

32 USEPA 2008

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Table 4.1.2: Summary of SO2 risk factors for health risk assessment. All risk factors

were derived from single-pollutant models.


10 µg/m3 SO2 increase

Reference

Short-term (based on a 24-hour mean SO2 concentrations)


Respiratory mortality 0.5 APHEA 1, from Zmirou et al., 1998, cited by

USEPA 2004

Respiratory admissions 0.5 COMEAP 1998

Asthma admissions:

children 1- 14 years 1.3 Sunyer et al., 2003


Cardiovascular admissions 0.6 COMEAP 2006

Ischaemic heart disease

admissions 1.2 COMEAP 2006

Long-term (based on annual mean SO2 concentrations)

Nonaccidental mortality* 2 Pope et al., 2002

Cardiopulmonary mortality 1.16 Pope et al., 2002

Table 4.1.3: Summary of NO2 risk factors for health risk assessment. All risk factors

were derived from single-pollutant models.


10 µg/m3 increased

concentration in air Reference

Short-term exposure (mean of 24-hours, unless otherwise indicated)

0.28* Mean of Touloumi et al., 1997 and Samoli et al., 2006 Total nonaccidental mortality

0.56 Hoek, 2003 from HEI 2003


Respiratory admissions, all ages 0.5 COMEAP 1998, from Stedman et al., 1999


Long-term: Per cent increased risk per 10 µg/m3 annual NO2 increase

Total nonaccidental mortality 8.2 (CI: 2.3 - 15.2) Krewski et al. (2000)

Cardiopulmonary mortality 9.3 (CI: 1.3 - 19.5) Krewski et al. (2000)

5 Risks associated with exposure to airborne

manganese

5.1 Manganese toxicity

The major concern around environmental exposure to manganese relates to its neurotoxicity

(IRIS, 1993a; Mergler et al., 1999; ATSDR, 2000). Inhaled manganese compounds appear to

produce more toxic effects than exposure through ingestion. At comparable doses, it appears

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that more manganese reaches the brain following inhalation than from exposure through

ingestion. Chronic exposure is of interest and interpretations were thus made on annual

averaged ambient air concentrations of manganese.

Manganese is subject to many homeostatic controls, but overload or breakdown of these

mechanisms leads to increased delivery to the brain. Long-term occupational exposure to

manganese at relatively high levels in the manganese industry has been shown to lead to

progressive neurological dysfunction, which can produce a disabling syndrome known as

manganism (Mergler et al., 1999). The disease has been described as a slow deterioration,

which starts at weak neurological alterations, progressing to sub-clinical signs in individuals,

and finally develops into the serious condition of manganism. It was suggested that the

relationship between blood levels of manganese and neuro-dysfunction could be viewed on a

continuum, with early, subtle changes at low exposure levels, progressing into more severe

disorders at higher exposure levels. Results from eleven years of neurological health

surveillance at a manganese oxide and salt producing plant however showed no indications that

the sub-clinical effects suggested by Mergler et al. (1999) were pre-clinical, i.e., showing any

progress to clinical effects (Crump and Rousseau, 1999). The same cohort that formed the

basis for the earlier survey by Roels et al. (1987) was studied. In some cases the individuals

performed better in the psychomotor tests than they had eleven years before, despite the fact

that manganese blood levels had remained comparable. Interpretation of the data is however

difficult, because there is not a clear correlation between blood manganese level and exposure

(Lauwerys and Hoet, 1993). In view of the efficient homeostatic mechanisms controlling the

metabolism of manganese and its extremely short half-life in the blood system, blood levels

change very little with exposure. It is still uncertain what the minimum exposure level for the

onset of "subtle" neurological effects is, and whether these effects would indeed progress to

clinical detectable conditions. It should also be noted that the occupational exposure levels

associated with the observations were orders of magnitude higher than manganese levels in

environmental ambient air, even in areas in the vicinity of industrial sources of manganese.

5.2 Selection of an appropriate guideline concentration in air

USEPA (IRIS 1993a) derived a lowest-observed-adverse-effect level (LOAEL) for neurotoxic

effects of manganese from an occupational-lifetime integrated respirable dust concentration of

manganese dioxide (MnO2), based on the 8-hour time-weighted average (TWA) occupational

exposure multiplied by individual work histories in years (Roels et al., 1992; 1987). The

occupational LOAEL was then adjusted for non-occupational exposure and a safety factor of 1

000 was applied (a factor 10 to protect sensitive individuals, 10 for using a LOAEL instead of a

no-observed-adverse-effect level (NOAEL), and 10 to account for database limitations relating

to less-than-chronic periods of exposure in the occupational studies, and the lack of

reproductive and developmental toxicity data). Following this approach, the USEPA reference

concentration for airborne manganese based on neurotoxicity is 0.05 µg Mn/m3 (IRIS 1993a).

The World Health Organisation (WHO 2000) derived an air concentration guidance value for

manganese based on the same epidemiological data used by USEPA (Roels et al., 1992),

following the benchmark dose approach. After adjustment to continuous exposure, a safety

factor of 50 was applied (a factor 10 for interindividual variations in sensitivity, and a factor 5 for

potential developmental effects in children). At 0.15 µg Mn/m3, the WHO guidance value is

three times higher than the USEPA value.

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It is important to contextualise a reference concentration or guideline concentration, also

referred to as the acceptable concentration in air, all referring to the threshold concept. The

threshold hypothesis infers that a range of exposures from zero to some finite value can be

tolerated by an organism with essentially no chance of expression of the toxic effect.

Furthermore, the threshold focuses on the most sensitive members of the population, thus

aimed at the protection of all members of the population.

Generally, the threshold is viewed as an "acceptable" exposure concentration, and, by inference,

any concentration greater than the threshold is regarded as "unacceptable." This strict

demarcation between what is "acceptable" and what is "unacceptable" is contrary to the views

of most toxicologists, who typically interpret the reference or guideline concentration as “a

relatively crude estimate of a level of chronic exposure that is not likely to result in adverse

effects to humans”. This reasoning follows from the USEPA description for use of reference

doses in risk assessment (IRIS 1993b). Similar reasoning applies to the assessment of

concentrations in air and exposure through inhalation. The threshold is “generally viewed by

risk assessors as a ‘soft’ estimate, whose bounds of uncertainty can span an order of

magnitude”. That is, within reasonable limits, where exposures at concentrations in air are

somewhat higher than the reference or guideline concentration, exposure may be associated

with increased probability of adverse effects, but that probability is not a certainty. Similarly,

while the reference concentration or guideline is considered to be a level at which the probability

of adverse effects is low, the absence of all risk to all people cannot be assured at this level.

This "softness" of the threshold argues for careful case-by-case consideration of the

toxicological implications of individual scenarios, to ensure that the reference concentrations or

guidelines are not given a degree of significance that is scientifically unwarranted. In the

assessment of exposure to airborne manganese, this awareness is important, as will be shown

in the following paragraphs.

The USEPA and WHO guidelines are the most prominent to consider in manganese health risk

assessments, because these agencies are considered reputable and their data have been peer

reviewed. It appears that the USEPA reference concentration (RfC) of 0.05 µg Mn/m3 is

considered by several reviewers to be overly conservative. Even from within USEPA, using

different methods of interpretation of the same data, it has been suggested that the best

estimates for a RfC for manganese fall in the range 0.09 to 0.2 µg Mn/m3 (Davis et al., 1998).

Even the lowest value in this range is higher than the official RfC (IRIS, 1993a).

Various other authors have published guideline concentrations for manganese in air, either as

independent interpretations of published data, or as critical reviews of the USEPA and WHO

documents. A review by scientists in the National Institute of Public Health and the

Environment (RIVM) in Bilthoven, The Netherlands, is particularly important to note. In

response to a request from the WHO European Centre for Environment and Health, approaches

for deriving an ambient air guideline concentration for manganese were reviewed (Slob,

Janssen and Pieters, 1996). It was concluded that a benchmark dose of 26 µg/m3, as derived

from the study by Roels et al. (1992), was a better basis for calculating a guideline

concentration than the LOAEL of 50 µg/m3 from the same study, as used by USEPA in deriving

a reference concentration. An uncertainty factor of 10 for using a LOAEL instead of a NOAEL

was considered unnecessary, because the benchmark dose can be treated as a NOAEL. The

application of additional uncertainty factors is warranted only when there are clear indications

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that endpoints other than neurotoxicity may be more sensitive to exposure. In the case of

manganese, according to the authors (Slob, Janssen and Pieters, 1996), there was no well-

established evidence of developmental and reproductive effects in humans. Limitations in

chronic exposure information were considered insufficient to show the need for additional

uncertainty factors. The reviewers found the USEPA uncertainty factor of 1 000 excessive, and

concluded that the previous WHO guidance value of 1 µg Mn/m3 (WHO 1987) would be

adequately protective for the toxicological endpoints of concern.

Crump et al. (1994) suggested that a reference concentration of 3 µg Mn/m3 is scientifically

defensible, based on the same data that were used by USEPA for setting the reference

concentration of 0.05 µg Mn/m3.

The WHO guidance value is three times higher than the USEPA reference concentration, but

RIVM has provided credible support for a guidance value 20 times higher than the USEPA

reference concentration. Available information indicates that it is unlikely that any neurological

effects would be observed following chronic exposure to concentrations up to 1 µg Mn/m3 and

considering the interpretations of Crump et al. (1994), even concentrations up to 3 µg Mn/m3 are

not expected to be linked to any observations of neurological effects upon chronic exposure.

INFOTOX thus applied the range of guideline concentrations between 1 and 3 µg/m3 as

reasonable criteria to assess the potential for development of neurological effects upon chronic

inhalation of airborne manganese.

5.3 Risk quantification methodology

The potential risk associated with exposure to manganese as a noncarcinogen in air is

expressed through a hazard quotient (HQ), which is the air concentration divided by the

reference concentration or tolerable concentration in air. The HQ is therefore a comparison of

an estimated chemical exposure with a reference exposure concentration below which adverse

health effects are unlikely to occur. The value is used to evaluate the potential for noncancer

health effects, such as organ damage, from chemical exposures. Where an HQ exceeds 1,

health effects may occur and the situation requires further investigation. The calculation is

presented in Equation 5.1.

TCAorRfCCHQ air= (5.1)

Where:

HQ Hazard quotient

Cair Concentration of manganese in air (mg/m3)

RfC or TCA Reference concentration or tolerable concentration of manganese in air

(mg/m3)

The RfC for manganese was selected according to the options outlined in Section 5.2.

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6 Methodology for quantification of exposure

USEPA provided general guidance on how to characterise exposures and risks when

conducting risk assessments (USEPA 1998), following the concepts of CTE and RME. CTE

and RME refer to central tendency exposure and reasonable maximum exposure, respectively.

CTE represents the most likely exposure scenario under which conditions the majority of

individuals would be subjected. The RME is the maximum exposure that is reasonably

expected to occur in the scenario under investigation. Under this approach, some intake

variables (e.g., exposure frequency, duration of exposure and intake rate) may not be at their

individual maximum values, but when in combination with other variables, will result in estimates

of the RME (USEPA 1989). USEPA guidance recommends estimating the high-end exposure

by "...identifying the most sensitive parameters and using maximum or near-maximum values

for one or a few of these variables, leaving others at their mean values…” (USEPA 1992). The

recommendation is based on the fact that maximising all variables would result in an estimate

that is above the range of actual values observed in the population.

In stead of basing exposure quantification on the maximum concentrations of substances

measured or predicted in an environmental setting, INFOTOX evaluates concentration isopleths

of the contaminants to estimate concentrations that would correspond with CTE and RME.

Exposures are thus measured in ranges and the best estimates of CTE and RME are made by

interpolating between the concentration isopleths. It must be taken into account that residents

of an area under assessment have activity patterns that lead to averaged exposures in an area

rather than point exposures for the entire averaging period at a single concentration.

7 Quantitative human health risk assessment for

criteria pollutants

7.1 Particulate matter (PM10)

Table 7.1.1 lists the highest PM10 concentrations associated with the M14 operations for

Scenario 1, which represents the current scenario without implementation of the Metalloys

Emissions Reduction Strategy (Kornelius and Krause, 2010).

Figures 7.1.1 and 7.1.2 show PM10 concentration isopleths for highest daily and annual

averaged concentrations for Scenario 1, respectively.

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Table 7.1.1: Highest daily and annual averaged ambient air concentrations of PM10

at residential locations in the study area (M14 Operations, Scenario 1)


Highest daily PM10 Annual averaged PM10 Receptor area

µg/m3

Acorn Park 3.31 0.91

Aerovaal 6.81 0.96

Dadaville 2.96 0.27

Debonair Park 1.05 0.13

Falcon Ridge 3.03 0.39

Henley on Klip 3.93 0.50

Meyerton 11.8 2.72

Meyerton Park 38.9 10.1

Redan 3.92 1.37

Roshnee 3.69 0.43

Rothdene 12.8 6.91

Rust te Vaal 5.65 0.76

Sobekeng 1.31 0.08

Sonland Park 1.97 0.34

Three Rivers 3.26 1.16

Kornelius and Krause (2010) predicted the highest daily PM10 concentration in Meyerton Park

(38.9 µg/m3). This location is between the green and orange concentration isopleths in

Figure 7.1.1 (25 µg/m3 and 50 µg/m3, respectively), which represents a very small area just

across the Metalloys fence line and is not representative of exposures in the greater Meyerton

Park residential area.

Following the approach of selecting areas of CTE and RME for the highest daily PM10

predictions as presented in Section 6, it is reasonable to estimate CTE values at 15 µg/m3 and

RME at 25 µg/m3 for Scenario 1. Other residential areas in the vicinity of the Metalloys

operations will experience lower PM10 levels, as shown in Figure 7.1.1.

Annual averaged PM10 concentrations were estimated as 1 µg/m3 for CTE and 2.5 µg/m3 for

RME in the Meyerton Park residential area. Other residential areas in the vicinity of the

Metalloys operations will experience lower PM10 levels, as shown in Figure 7.1.2.

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Furnace (Scenario 1) (Kornelius and Krause, 2010).

Figure 7.1.2: Annual averaged PM10 concentrations associated with the proposed

M14 Furnace (Scenario 1) (Kornelius and Krause, 2010).

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Table 7.1.2 lists the highest daily and annual averaged PM10 concentrations for Scenario 2,

which represents the scenario after implementation of the Metalloys Emissions Reduction

Strategy (Kornelius and Krause, 2010).

Table 7.1.2: Highest daily and annual averaged ambient air concentrations of PM10

at residential locations in the study area (Scenario 2) (Kornelius and

Krause, 2010).

Highest daily PM10 Annual averaged PM10 Receptor area

µg/m3


Aerovaal 4.43 0.65

Dadaville 2.30 0.18




Meyerton 11.6 1.60


Redan 2.57 0.81

Roshnee 3.62 0.31

Rothdene 8.31 3.83


Sobekeng 1.25 0.06



Figures 7.1.3 and 7.1.4 show PM10 concentration isopleths for highest daily and annual

averaged exposure scenarios for Scenario 2, respectively. The highest concentrations are

marginally lower and the locations of these highest points are closer to the Metalloys Site. The

resolution of the isopleths close to the site did not allow for adjustment of the CTE and RME

values and the estimates for Scenario 1 were applied in the risk assessment (15 µg/m3 for CTE

and 25 µg/m3 for RME). It is however acknowledged that exposures under Scenario 2 would be

slightly lower than under Scenario 1.

Annual averaged PM10 concentrations for Scenario 2 were estimated as 1 µg/m3 for CTE and

2.5 µg/m3 for RME. Similar to the daily maxima, the resolution of the isopleths close to the site

did not allow for adjustment of the CTE and RME values and the estimates for Scenario 1 were

applied in the risk assessment. It is however acknowledged that annual averaged exposures

under Scenario 2 would be slightly lower than under Scenario 1.

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Furnace (Scenario 2) (Kornelius and Krause, 2010).

Figure 7.1.4: Annual averaged PM10 concentrations associated with the proposed

M14 Furnace (Scenario 2) (Kornelius and Krause, 2010).

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Following the calculations described in Section 4, the attributable fraction of cases due to PM10

levels associated with the proposed M14 Furnace was calculated. The calculations were based

on estimated PM10 concentrations for Scenario 1 (without the Metalloys Emissions Reduction

Strategy). Attributable fractions for CTE and RME will be lower for Scenario 2 but, as pointed

out above, the resolution of the concentration isopleths did not allow accurate determination of

concentrations.

Table 7.1.3: Attributable fraction of cases due to exposure to PM10.

Health effect

Short-term (based on a 24-hour mean PM10 concentrations) CTE RME

Total non-accidental mortality 0.008 0.012

Cardiovascular mortality 0.014 0.023

Emergency department visits with cardiovascular disease, adults 65 and older 0.046 0.078

Hospital admissions with cardiovascular disease, adults 65 and older 0.011 0.019

Cardiac admissions 0.014 0.023

Exacerbation of respiratory symptoms in children with asthma 0.078 0.133

Emergency department visits and hospital admissions in asthmatic children 0.030 0.051

Emergency department visits with COPD, adults 65 and older 0.046 0.078

Hospital admissions with COPD, adults 65 and older 0.015 0.025

Long-term (based on annual mean PM10 concentrations)

Respiratory symptoms (cough and wheeze) 0.033 0.083

Some examples should serve to clarify the significance of the numbers in Table 7.1.3, as

follows:

For example, the CTE for total non-accidental mortality is associated with an AF of 0.008, i.e.,

0.8 per cent of total non-accidental mortalities after commissioning of the proposed M14

Furnace would be due to PM10 emitted from the M14 Furnace. Similarly, exacerbation of

respiratory symptoms in asthmatic children may be associated with the M14 Furnace emissions

at a level of 7.8 per cent for CTE, or at 13.3 per cent for the small area classified for RME. The

other health effects data have similar significance. It is however difficult to interpret the data

without baseline data on mortality and morbidity in the study area.

Considering the relatively small residential area of concern and limited population size in which

the CTE and RME have been determined, it is expected that the additional number of cases

based on excess mortality and morbidity relating to the causes listed in Table 7.1.3 would be so

low that it is unlikely that it will be measurable.

7.2 Sulphur dioxide

Table 7.2.1 presents the highest daily and annual averaged concentrations of SO2 across

residential locations in the study area.

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Table 7.2.1: Highest daily and annual averaged ambient air concentrations of sulphur

dioxide at residential locations in the study area (Kornelius and Krause,

2010).

Highest daily Annual averaged Receptor area

µg/m3


Aerovaal 1.34 0.10

Dadaville 1.11 0.09




Meyerton 3.55 0.50


Redan 2.33 0.31

Roshnee 1.10 0.08

Rothdene 7.26 0.56


Sobekeng 1.01 0.06



Kornelius and Krause (2010) predicted the highest daily SO2 concentration in Meyerton Park

(13.6 µg/m3). This location is inside the orange concentration isopleths in Figure 7.2.1

(> 10 µg/m3), which represents a very small area just across the Metalloys fence line and is not

representative of exposures in the greater Meyerton Park residential area.

Following the approach of selecting areas of CTE and RME as presented in Section 6, it is

reasonable to estimate air concentrations for the Meyerton Park residential area at

approximately 5 µg/m3 for CTE and for RME not exceeding 10 µg/m3. Other residential areas in

the vicinity of the Metalloys operations will experience even lower SO2 levels, as shown in

Figure 7.2.1.

Following the calculations described in Section 4, the attributable fraction of cases due to the

highest RME daily SO2 levels associated with the proposed M14 Furnace was calculated.

These data are listed in Table 7.2.2. CTE levels were too low to be linked to measurable

adverse health effects. Considering the relatively small residential area in which the RME has

been determined, it is expected that the number of cases based on excess mortality and

morbidity relating to the modelled increased SO2 concentrations would not be measurable at

any level of confidence.

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Table 7.2.2: Attributable fraction of cases due to exposure to sulphur dioxide.

Health effect RME

Short-term (based on a 24-hour mean SO2 concentrations)

Cardiovascular mortality 0.8

Respiratory mortality 0.5

Respiratory admissions 0.5

Asthma admissions: children 1 - 14 years 1.3

Cardiac admissions 2.4

Cardiovascular admissions 0.6

Ischaemic heart disease admissions 1.2

Annual averaged SO2 concentrations in Meyerton Park were estimated as 0.5 µg/m3 CTE and

1.5 µg/m3 for RME. These concentrations were so low that it would not be possible to find

increases in total non-accidental mortality and cardiopulmonary mortality on a statistical basis

that may be associated with chronic exposure to SO2 emissions from the M14 Furnace.

Figure 7.2.1: Highest daily SO2 concentrations associated with the proposed M14

Furnace (Kornelius and Krause, 2010).

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Figure 7.2.2: Annual averaged SO2 concentrations associated with the proposed M14


7.3 Nitrogen dioxide

Table 7.3.1 presents the highest daily and annual averaged concentrations of NO2 that may be

associated with operation of the proposed M14 Furnace across residential locations in the study

area.

Kornelius and Krause (2010) predicted the highest daily NO2 concentration in Meyerton Park

(3.34 µg/m3). This location is approximately on the purple concentration isopleths in

Figure 7.3.1, which represents a very small area just across the Metalloys fence line and is not

representative of exposures in the greater Meyerton Park residential area.

Following the approach of selecting areas of CTE and RME for the highest daily concentrations

in the Meyerton Park residential areas as presented in Section 6, it is reasonable to estimate

CTE values at approximately 1 µg/m3 and RME at approximately 2 µg/m3 Other residential

areas in the vicinity of the Metalloys operations will experience even lower NO2 levels, as shown

in Figure 7.3.1.

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Table 7.3.1: Highest daily and annual averaged ambient air concentrations of

nitrogen dioxide (Kornelius and Krause, 2010).

Highest daily Annual averaged Receptor area

µg/m3


Aerovaal 0.23 0.02

Dadaville 0.19 0.02




Meyerton 0.62 0.09


Redan 0.41 0.05

Roshnee 0.19 0.01

Rothdene 1.27 0.10


Sobekeng 0.18 0.01



Figure 7.3.1: Highest daily NO2 concentrations associated with the proposed M14


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Figure 7.3.2: Annual averaged NO2 concentrations associated with the proposed M14


Considering the small daily maximum increases in NO2 in Meyerton Park that can be ascribed

to the operation of the proposed M14 Furnace, it was not meaningful to calculate potential

increases in total non-accidental mortality and cardiovascular mortality. Also, it was not

meaningful to estimate increases in hospital admissions for respiratory and cardiac conditions.

It will not be possible to observe these conditions on any meaningful statistical basis at these

low NO2 concentrations experienced by a relatively small number of receptors.

Annual averaged NO2 concentrations were estimated as approximately 0.2 µg/m3 for CTE and

approximately 0.3 µg/m3 for RME. These concentrations are too low to expect any measurable

manifestation of increased mortality due to chronic exposure to NO2 in the small community.

8 Quantitative human health risk assessment for

manganese

Table 8.1 presents the annual averaged concentrations of manganese that are relevant in the

assessment of potential health effects of the proposed M14 Furnace across residential locations

in the study area. The highest concentrations were predicted in Meyerton Park.

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Table 8.1: Highest annual averaged ambient air concentrations of manganese at

residential locations in the study area (Kornelius and Krause, 2010).

Existing M14 Existing + M14

Scenario 1 Scenario 2 Scenario 1 Scenario 2 Scenario 1 Scenario 2 Receptor area

µg/m3

Acorn Park 0.30 0.17 0.10 0.07 0.40 0.24

Aerovaal 0.28 0.17 0.10 0.07 0.37 0.24

Dadaville 0.10 0.06 0.04 0.03 0.14 0.10

Debonair Park 0.04 0.03 0.01 0.01 0.05 0.03

Falcon Ridge 0.12 0.07 0.05 0.04 0.17 0.10

Henley on Klip 0.17 0.10 0.06 0.05 0.23 0.15

Meyerton 0.97 0.51 0.39 0.30 1.36 0.82

Meyerton Park 4.05 2.38 2.04 1.96 6.09 4.34

Redan 0.46 0.26 0.14 0.10 0.59 0.35

Roshnee 0.13 0.08 0.04 0.04 0.17 0.12

Rothdene 2.30 1.14 0.68 0.36 2.98 1.50

Rust te Vaal 0.24 0.14 0.08 0.07 0.32 0.21

Sobekeng 0.03 0.02 0.01 0.01 0.05 0.03

Sonland Park 0.10 0.06 0.04 0.03 0.14 0.09

Three Rivers 0.41 0.23 0.12 0.10 0.53 0.32

The manganese concentrations of interest are those associated with current operations, the

incremental modelled addition of concentrations due to the M14 Furnace, and the cumulative

concentrations. Modelling was conducted for Scenarios 2, to represent the situation after

implementation of the Metalloys Emissions Reduction Strategy (MERS) (Kornelius and Krause,

2010).

Following the approach of selecting areas of CTE and RME in the Meyerton Park residential

areas as presented in Section 6, it is reasonable to estimate CTE and RME values as

summarised in Table 8.2. These values refer to Figures 8.1 to 8.3. Other residential areas in

the vicinity of the Metalloys operations, as shown in the concentration isopleths, will experience

lower manganese levels than those listed in Table 8.2, typically ranging between 0.05 and 0.5

µg/m3, with a maximum of 1 µg/m3.

Table 8.2: Estimates of the highest annual averaged manganese concentrations at

residential locations in the study area for CTE and RME levels.

Existing with MERS M14 Existing with MERS + M14 Exposure estimate

µg/m3

CTE 0.8 0.8 1.0

RME 2.0 1.0 2.5

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Figure 8.1: Baseline annual averaged manganese concentrations after

implementation of the Metalloys Emissions Reduction Strategy


Figure 8.2: Annual averaged manganese concentrations associated only with the

proposed M14 Furnace (Kornelius and Krause, 2010).

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Figure 8.3: Annual averaged manganese concentrations cumulative for baseline and

the proposed M14 Furnace (Kornelius and Krause, 2010).

The largest part of the study area would be exposed to annual averaged ambient air

concentrations of manganese less than 1 µg/m3, based on cumulative concentrations including

baseline emissions from current Metalloys operations and the proposed M14 Furnace. The

discussion assumes implementation of the Metalloys Emissions Reduction Strategy.

The entire body of toxicological and epidemiological information as summarised in Section 5

was taken into account in Section 9.2 in the interpretation of exposure to airborne manganese.

9 Conclusions

9.1 Criteria pollutants

This INFOTOX human health risk assessment interpreted modelled air concentrations of the

criteria pollutants [particulate matter (PM10), sulphur dioxide (SO2), and nitrogen oxides

(represented by NO2)] at receptor locations in the study area, based on data that were produced

by Kornelius and Krause (2010). Exposure concentrations were interpreted in terms of mortality

or hospitalisation rates for respiratory or cardiovascular causes as a measure of pollution-

associated illness, which is an approach that is mostly applied in epidemiological studies.

Central tendency exposure (CTE) and reasonable maximum exposure (RME) estimates were

obtained from concentration isopleths of the criteria pollutants that were superimposed on a

map of the study area. Residential areas were indicated on the map and it was possible to

estimate airborne concentrations of contaminants at selected locations in the study area.

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Meyerton Park, which is directly adjacent to the Metalloys Site, was identified as the residential

area that receives the highest concentrations of pollutants from sources on the Metalloys Site.

All other residential locations are under concentration isopleths at much lower levels. INFOTOX

applied the methodology outlined in Section 4 and calculated the potential fractional increase in

the incidences of mortality and morbidity associated with increased concentrations of PM10 and

SO2-. In the absence of baseline data on mortality and emergency room visits or hospitalisation

rates for specific health effects, it is not possible to relate the fractional increases to actual

numbers of cases. Considering the relatively small residential area in which the CTE and RME

have been determined, it is expected that the number of cases based on excess mortality and

morbidity relating to the modelled increase in PM10 and SO2 concentrations would be small, if

not insignificant. It is not possible to make a more conclusive statement on the available

information.

Predicted increases in NO2 that could be ascribed to the operation of the proposed M14

Furnace were so small that it is not meaningful to calculate potential associated increases in

mortality or morbidity.

9.2 Airborne manganese

The manganese concentrations of interest in the study area are those associated with current

operations, the incremental modelled addition of concentrations due to the M14 Furnace, and

the cumulative concentrations.

As with PM10, the Meyerton Park residential area was identified as the area that would be

subjected to the highest airborne manganese concentrations. The estimated concentrations

exceeded the conventional USEPA and WHO guideline concentrations and the significance

thereof had to be interpreted in terms of potential health effects in the population. Predicted

exposures to manganese in all other residential areas were shown to be lower and are thus of

lesser concern.

Considering the whole body of toxicological and epidemiological information on manganese as

summarised in Section 5, it is concluded that it is unlikely that the estimated CTE and RME

exposures in Meyerton Park would lead to measurable adverse health effects on chronic

exposure under the concentrations that Kornelius and Krause (2010) predicted in their

dispersion estimates. This is based on reviews of manganese epidemiological information by

scientists in the National Institute of Public Health and the Environment (RIVM) in Bilthoven,

The Netherlands (Slob, Janssen and Pieters, 1996) and Crump et al. (1994). There is no

convincing new evidence on manganese risks associated with inhalation exposures that may

dispute these interpretations.

The annual averaged manganese concentrations for all scenarios in Table 8.2 are within the

reference concentration range of 1 to 3 µg/m3. Hazard quotients would typically be ≤ 1 at such

exposure concentrations.

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10 Uncertainty review

The human health risk assessment for criteria pollutants followed standard international practice,

based on methodologies applied in epidemiological studies. The interpretation of exposure

concentrations in terms of mortality or hospitalisation rates for respiratory or cardiovascular

causes as a measure of pollution-associated illness is thus presented with confidence.

However, the absence of information on population numbers and baseline health data places a

limitation on a definitive statement about the incidence of health effects due to PM10 and SO2 in

Meyerton Park.

It was not easy to quantify the reduction in ambient air concentrations of PM10 in Meyerton

Park due to the Metalloys Emissions Reduction Strategy from the Airshed report (Kornelius and

Krause, 2010). Considering the inherent uncertainties associated with dispersion modelling, the

approach of applying the concepts of CTE and RME provided data that were in better context

with potential health effects than single-point exposure data.

The conclusion that it is unlikely that the estimated CTE and RME exposures to manganese in

Meyerton Park would lead to measurable adverse health effects on chronic exposure under the

concentrations of exposure in Meyerton Park is based on credible interpretation of

epidemiological data and is presented with confidence. Exposure to manganese at other

residential locations in the study area is predicted to be lower than in Meyerton Park and

associated health risks would thus also be lower.

Airshed (Kornelius and Krause, 2010) recommended that the M14 Furnace be commissioned after implementation of the Metalloys Emissions Reduction Strategy to minimise potential cumulative air quality impacts. This probably relates to regulatory compliance with ambient air quality standards, but direct association with health effects cannot be made.

11 Recommendations

Meyerton Park has been identified as the residential area with the highest potential for adverse

health effects due to PM10 emissions from the Metalloys works. A more definitive statement on

health risks could be made if population numbers and estimates of age distribution for the area

were known. Furthermore, it will be helpful if concentration isopleths across Meyerton Park

were presented with a higher resolution. However, such additional information would not

change the overall conclusion that risks associated with emissions from the proposed M14

Furnace would be small, if not insignificant.

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