Generic Risk Assessment Methodology

Transcription

1 Generic Risk Assessment Methodology Introduction As of March 2010, the Environment Agency have published a number of new Soil Guideline Values (SGVs) and have modified their TOX reports for these contaminants. These are benzene, ethylbenzene, toluene, m-xylene, o-xylene, p-xylene, phenol, dioxins furans & dioxin-like PCBs, selenium, inorganic mercury, elemental mercury (metallic), methyl mercury, arsenic, cadmium and nickel. The previously published SGV reports released in 2002 no longer reflect the DEFRA updated approach and so the Environment Agency and DEFRA have withdrawn them. A revised version of the CLEA software (v1.06) and handbook can however be used by practitioners to generate their own Generic Assessment Criteria (GACs) that follow the updated approach. This document discusses the Mouchel derived GACs in more detail. The Environment Agency have additionally published two updated reports - "Human health toxicological assessment of contaminants in soil" (SR2) and "Updated technical background to the CLEA model" (SR3). DEFRA and the Environment Agency have withdrawn all the previous CLR 7-10 documents since these no longer fully reflect the revised approach. CLR7 contained information that is now addressed elsewhere or is covered by other guidance that is available; guidance on statistical analysis has been published by CL:AIRE and CIEH. The Environment Agency has also published a database of chemical information Compilation of Data for Priority Organic Pollutants for Derivation of Soil Guideline Values (SR7). This provides the chemical data (e.g. vapour pressure, solubility) for a number of organic substances that the Environment Agency consider priority contaminants. Chemical data for the metals however is likely to be included within new SGV reports when they are published. For these contaminants, and ones assessed by Mouchel but not considered priority contaminants, chemical data has been sourced from elsewhere. All contaminants require toxicity data (Health Criteria Values). These were previously published by the Environment Agency, however some of the derivations behind the HCVs has changed within SR2. As the Environment Agency issue a new substance specific TOX report they will withdraw the relevant existing report, however it can be used for deriving GACs until that point. It should be noted that the Environment Agency have stated that much of the existing information in these reports will not be affected by changes and that the TOX reports will continue to be a useful interim resource until the new reports are available. The LQM/CIEH Generic Assessment Criteria for Human Health Risk Assessment (2 nd edition) The Chartered Institute of Environmental Health (CIEH) along with LQM, have, as of August 2009, published GACs for 68 chemicals. Since these numbers have been subjected to a significant peer review, these GACs have been used in preference to Mouchel GACs where available. Mouchel of 12

2 The Soil Generic Assessment Criteria for Human Health Risk Assessment The Environmental Industries Commission (EIC), The Association of Geotechnical and Geoenvironmental Specialists (AGS) and Contaminated Land: Applications in Real Environments (CL:AIRE), have as of December 2009 published GACs for an additional 35 chemicals using the CLEA model (v1.06). Since these numbers have been subjected to a significant peer review, these GACs have been used in preference to Mouchel GACs where available. The CLEA model has been amended several times over the previous year. CLEA v1.04 was updated to v1.05 to correct the working of some of the background algorithms and improve the vapour uptake model. There is no significant difference in the working of v1.05 and v1.06; the only differences are cosmetic and that v1.06 has a new data protection password. SGV or GAC? An SGV (or GAC) represents an Intervention Value for chronic health risks above which, a potential significant risk to human health exists. This however, does not mean a risk actually exists at this time there may be site-specific conditions that prevent the risk. They therefore provide a value of soil contamination above which intervention should be undertaken to make sure that human health is protected; intervention may be further investigation or remediation. They are not statutory standards that must not be exceeded. Although an SGV is an authoritative, scientifically based value published by the Environment Agency, a GAC has no less science applied; it is however derived by a non- Environment Agency source. The produced screening values have been generated using generic assessment parameters and represent trigger values indicating to a risk assessor that above this concentration, soil concentrations may pose a possibility of significant harm (although further assessment and evaluation will usually be required). The screening values themselves do not represent the threshold at which there is a significant possibility of significant harm, nor do they automatically represent an unacceptable intake. This must be decided along with socio-political judgement, and the law entrusts decisions on this to the enforcing authorities. Generic Assessment Methodology The following standard land-uses have been retained: Residential with plant uptake Residential without plant uptake Commercial/Industrial Allotments Mouchel of 12

3 SGVs are however only published for residential with plant uptake, commercial/industrial and allotments at a soil organic matter content of 6%. The above four land uses have been used within the GAC screening assessment. Public Open Space (POS) has additionally been derived. POS is not identified as a standard scenario, therefore to be conservative an allotment standard scenario was run with plant uptake switched off; this therefore assumed that the child visits the site regularly but does not live on a contamination plume 365 days a year as per the residential scenario. This value should only be used where this scenario is reasonably representative of the site use. All Generic Assessment Criteria were run as per the default values within CLEA v1.06 and SR3, As the soil organic matter content can have a large effect on the screening value, Mouchel have followed the approach of LQM/CIEH and EIC/AGS/CL:AIRE and produced GAC for soils of 6% SOM, 2.5% SOM and 1% SOM for each of the five land uses. Justification of parameters used in the derivation of Mouchel Screening Values Relevant guidance documents produced by the EA were used in the derivation of Mouchel GAC Screening Values, these included the recent publications: SR2, SR3, SR4, SR7 and TR1. SR3 provides the methodology and equations for the calculation of the new GACs. SR7 provides an information summary of the recommended chemical input parameters to be used when deriving screening values; its recommendations supersede the findings of P5-079/TR1. However it only provides data for a limited number of organic chemicals and contains no values for metals, dioxins, explosives, PCBs, and TPH bands. Where no EA published values exist for a particular contaminant, Generic Assessment Criteria (GAC) have been derived from toxicity or chemical properties from a variety of recognised sources. The primary sources of information were the values produced by LQM/CIEH and EIC/AGS/CL:AIRE. Remaining GACs have been derived using information gathered from the referenced sources in the EA and the LQM/CIEH and EIC/AGS/CL:AIRE publications. Metals: plant uptake CLEA v1.06 models plant uptake from six groups of plant (green leaf, root, tuber, herbaceous fruit, shrub fruit and tree fruit). The previous model (CLEA UK) only considered plant uptake from two groups, leafy and root. Until the SGV reports have been produced for the metals, there is limited guidance on how to model the plant uptake, and screening values are likely to be updated with the publication of each SGV report from the EA. Metals are modelled using the new method (the PRISM model) used in the CLEA v1.06 software. A soil to plant availability correction factor (δ) of 5 was used to model the plant uptake based on the relative availability of the metal in the soil solution, which is effected by soil chemistry. The value of 5 is based on a loam soil and may be higher in more organic soils. This value was obtained from The PRISM Foodchain Modelling Software: Parameter Values for the Soil/Plant Model (authored by M Thorne, R. Walke, P.Maul, published in March 2005) and partially republished in SR3. The PRISM model then requires a transference factor from the root to the edible vegetable parts of concern Mouchel of 12

4 (tuber/fruit/leaf/etc). The root-shoot correction factor, root-root store correction factor, roottuber correction factor, and the root-fruit correction factor (f int ) are not provided in the PRISM documentation. These vary according to whether the elements are transported via the xylem or phloem. For elements transported in the phloem (As, Cd, Ni and Se) it was noted in SR3 that for arsenic and cadmium that f int was assumed to be 0.5 for any internal plant compartment. Selenium, arsenic, cadmium and nickel have had an SGV report published and this contains the plant uptake parameters. Lead and other elements transported within the xylem will have f int values based on literature values and these will be published in the new SGV reports. Mercury (xylem transport) has had an SGV published that contains the relevant plant uptake parameters. Chromium, beryllium, copper, vanadium and zinc uptakes were calculated from measured and referenced correction factors reported in by CIEH/LQM. Plant uptake of antimony, barium and molybdenum was not modelled by EIC/AGS/CL:AIRE and GACs have only been derived for land uses which do not consider a plant uptake pathway. Mouchel have followed this latter approach for cobalt. Kow The soil to plant concentration factor for leafy vegetables is calculated using the Ryan et al equation for organic contaminants. SR3 states that where the log K ow of an organic chemical is reported to be outside the range of zero to four care should be taken when using this approach. All organic chemicals were modelled using the built-in CLEA algorithms, and no numeric concentration factors were used to produce any screening values for organic chemicals with a log K ow greater than four since no other model has been identified as suitable within SR3. This is the approach used by CIEH/LQM and EIC/AGS/CL:AIRE. The MDI background variable Screening values are derived such that the estimated Average Daily Exposure to a chemical, arising from its presence in soil at its screening value, when added to its background exposure (MDI), equals its TDI (i.e. ADE + MDI = TDI). For some chemicals, however, the MDI may already occupy a high proportion of the TDI or may even exceed it. SR2 states that it would therefore be impractical to propose SGVs on this basis without reserving a minimum proportion of the TDI for exposure from land. This is done through the implementation of the 50% rule (formerly the 20% rule). The updated guidance in SR2 (previously CLR 9) was applied to calculate the screening values for TPH and HCBD for which a background exposure is expected, but no Foods Standards Agency/Air Quality data could be found. The 50% rule is used to recalculate a MDI of a contaminant, so that a TDSI and screening value can be derived. It was calculated by following the same approach outlined by CIEH/LQM: MDI = 0.8 x TDI x bw The new guidance uses a 50% rule and so this formula was amended to: MDI = 0.5 x TDI x bw Mouchel of 12

5 TR1 states the updated body weights of the different age classes in the UK population. This reported a body weight for a 0-6yr old female at 13.3kg, which was used to calculate the MDI. Where the 0-6 yr old female is not the critical receptor (Commercial land use scenario), the algorithms within the CLEA model apply a correction factor to take account in the change in body weight. This is all done automatically and requires no extra data input. Where no UK MDI has been identified after the main UK literature sources have been searched, we have followed the guidance in the January 2009 update of SR3 in that If no data or information on background exposure is available, it should normally be assumed to be negligible and the MDI set to zero for all age groups. Saturation Limits The calculated GAC or SGV may exceed the soil saturation limit. Since the CLEA model does not account for oral or dermal exposure via direct contact with free phase, or inhalation exposure from vapours arising from free phase chemicals (LNAPL/DNAPL), it may under-estimate the risk to health at higher soil concentrations. The SGV/GAC should therefore be set at or equal to the lower of the aqueous or vapour saturation limits for the soil. Therefore although for some chemicals it is possible to calculate a value that exceeds the saturation limit, this is then capped at the saturation limit; thus the SGV for ethylbenzene for example at 2800mg/kg for a commercial land-use is set at vapour saturation rather than the modelled value (65,700mg/kg). However, for individual contaminants this could be over-ridden when the vapour inhalation pathway is not considered to be a critical pathway. For methyl mercury, a decision has been made by the Agency to ignore this rule as the vapour inhalation pathway is less than 10% of the total exposure. The same approach has been used by LQM/CIEH and EIC/AGS/CL:AIRE. Surrogates It is common practice to occasionally use a surrogate to screen a contaminant ie, using the benzene to screen trimethylbenzene. The toxicity of benzene is widely published, however much less data exists on the trimethylbenzenes which may be found in low concentrations within petrol. Surrogates should only be used where the surrogate chemical is similar to the chemical without screening values. Method for Deriving Chemical Database Parameters Literature Review Sources Physical Chemical Those chemicals with physical-chemical properties listed within the new Environment Agency publication SC050021/SR7 ( Compilation of Data for Priority Organic Pollutants for Derivation of Soil Guideline Values, 2008) have been used, and where not available the properties have been obtained from the previous Environment Agency publication P5-079 ( Review of the Fate & Transport of Selected Contaminants in the Soil Environment, 2003). Where these do not exist, a number of reference sources have been consulted, although the primary source where possible has been the CIEH/LQM and Mouchel of 12

6 EIC/AGS/CL:AIRE GAC reports. For consistency the Reference List of SC050021/SR7 and the earlier Environment Agency P5-079 was reviewed and the main sources of data listed there were reviewed for this study. The following physical-chemical sources are listed below: CIEH/LQM, 2009 The LQM/CIEH Generic Assessment Criteria for Human Health Risk Assessment (2 nd Edition) EIC/AGS/CL:AIRE, 2009 The EIC/AGS/CL:AIRE Soil Generic Assessment Criteria for Human Health Risk Assessment. MacKay & Shui et al, 1991 Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals. Vols I-V, Lewis Publishers; RAIS. The Risk Assessment Information System Database. ( Oak Ridge National Laboratory, USA; CHEMFATE. SRC CHEMFATE Database, ( Syracuse Research Corporation; USEPA FATE Database. Office of Research & Development, Athens, GA, USA; OECD, OECD Integrated HPV Database. ( scripts/hpv/; NIST, NIST Chemistry Web book, NIST Standard Reference Database. IUPAC-NIST, IUPAC-NIST Solubility Database v1.0. NIST Standard Reference Database. Environment Agency SR7 notes that where a range of values were identified from a reference, an average was calculated (arithmetic mean), with the exception of Henry s Law constant, vapour pressure and water solubility where the geometric mean was used. This was used as the values typically ranged over an order of magnitude. Mouchel has followed this guidance. Chemical Data Derived from UK sources SR7: Benzene, Ethylbenzene, Toluene, Xylenes, Benzo(a)anthracene, Benzo(b)fluoranthene, Benzo(k)fluoranthene, Benzo(ghi)perylene, Dibenzo(ah)anthracene, Benzo(a)pyrene, Naphthalene, Fluoranthene, Pyrene, Chrysene, Indeno(123-cd)pyrene, Chlorobenzene, Chloroethene, 1,2 Dichloroethane, 1,1,2,2 Tetrachloroethane, 1,1,1,2 Tetrachloroethane, Tetrachloroethene, Tetrachloromethane, 1,1,1 Trichloroethane, Trichloroethene, Trichloromethane, Phenol, Pentachlorophenol, Hexachlorobutadiene. Mouchel of 12

7 2009/2010 SGV reports: Selenium, Mercury, Arsenic, Nickel, Cadmium, Phenol, BTEX, dioxins furans and dioxin like PCBs (EC7 PCBs have been based on congener 118, WHO 12 PCBs have been based on congener 126) CIEH/LQM: Cadmium, Chromium(III and VI), Beryllium, Boron, Copper, Vanadium, Zinc, USEPA 16 PAHs, Petroleum hydrocarbons (Environment Agency 16 fractions), Chloroalkanes and alkenes, Explosives, Pesticides, Chlorobenzenes, Phenol and Chlorophenols, Carbon disulphide and Hexachlorobutadiene. EIC/AGS/CL:AIRE: Antimony, Barium, Molybdenum, Bis 2 ethylhexyl phthalate, Diethyl phthalate, 2,4 Dinitrotoluene, cis 1,2 Dichloroethene, trans 1,2 Dichloroethene, Styrene, carbazole, Cresols. Mouchel Collated Physical Chemical Properties Physical and chemical properties for the mouchel derived GAC chemicals not listed in SR7, P5-079/TR1, a SGV report, or either of the CIEH/LQM or EIC/AGS/CL:AIRE GAC publications are detailed below: Table A: Properties of Dibenzofuran Value Units Reference CAS Henry s Law Constant atm.m 3.mol -1 Syracuse Henry s Law Constant atm.m 3.mol -1 Athens Henry s Law Constant cm 3.cm -3 RAIS Boiling point 553 K Mackay & Shui Air Diffusion Coefficient m 2 s -1 Athens Water Diffusion Coefficient m 2.s -1 Athens Vapour pressure 0.37 Pa Mackay & Shui Aqueous Solubility 4.95 mg.l -1 Mackay & Shui Aqueous Solubility 3.1 mg.l -1 Syracuse Log Koc 3.94 (-) Athens Log Kow 4.12 (-) Mackay & Shui Log Kow 4.12 (-) Syracuse Relative molecular mass g.mol -1 Mackay & Shui Dermal Absorption Fraction 0.01 (-) RAIS Mouchel of 12

8 Table B: Properties of Cyanide (free) and hydrogen cyanide Value Units Reference CAS Free CN Hydrogen cyanide Boiling point 298 K Athens (free) Boiling point 299 K Athens (HCN) Vapour Pressure 742 torr Athen (HCN) Log Kd 9.9 (-) RAIS Aqueous Solubility mg.l -1 Athens (HCN) Relative molecular mass g.mol -1 Athens (HCN) Relative molecular mass 27 g.mol -1 RAIS Dermal Absorption Fraction 0.01 (-) RAIS Method for Deriving Toxicity Database Parameters Literature Review Sources - Toxicity Data The main literature sources were the updated TOX reports produced by the Environment Agency, however these have only been published for the following contaminants; benzene, ethylbenzene, toluene, m-xylene, o-xylene, p-xylene, phenol, dioxins furans & dioxin-like PCBs, selenium, inorganic mercury, elemental mercury (metallic), methyl mercury, arsenic, cadmium and nickel. Updated toxicity data has not been published by the Environment Agency for the majority of priority contaminants. Therefore, to help plug this data gap CIEH/LQM and EIC/AGS/CL:AIRE have researched and published GACs for a large range of chemicals. Where no recent toxicity data has been produced by the Environment Agency the toxicity data has been sourced from within the CIEH/LQM and EIC/AGS/CL:AIRE GAC reports. The following literature sources have been reviewed following guidance in SR2: CIEH/LQM, 2009 The LQM/CIEH Generic Assessment Criteria for Human Health Risk Assessment (2 nd Edition) EIC/AGS/CL:AIRE, 2009 The EIC/AGS/CL:AIRE Soil Generic Assessment Criteria for Human Health Risk Assessment. RAIS. The Risk Assessment Information System Database. ( Oak Ridge National Laboratory, USA; IRIS. Integrated Risk Information System Database. ( USEPA; Mouchel of 12

9 SCORECARD. Charity based website/database that pulls in USEPA data and other sources: ( ); Agency for Toxic Substances & Disease Registry, Toxicological Profiles for: o Cresol 2006 WHO. International Programme on Chemical Safety. o EHC 168, Cresols, 1995 o EHC 140 Polychlorinated biphenyls & terphenyls WHO International Agency for Research on Cancer. IARC Monographs: o Vol. 18 Polychlorinated biphenyls & Polybrominated biphenyls, o Vol. 32 Carbazole, Toxicity Data Derived from UK sources TOX reports: Arsenic SC050021, Cadmium SC050021/TOX3, Mercury SC050021, Nickel SC050021/TOX8, Selenium SC050021, Cyanide TOX5, Benzene SC050021, Ethylbenzene SC050021, Toluene SC050021, Xylenes SC050021, Phenol SC050021/TOX9, Dioxins Furans & Dioxin-like PCBs SC050021/TOX12. CIEH/LQM 2 nd edition: Cadmium(III and VI), Chromium, Beryllium, Boron, Copper, Vanadium, Zinc, USEPA 16 PAHs, Petroleum hydrocarbons (Environment Agency 16 fractions), Chloroalkanes and alkenes, Explosives, Pesticides, Chlorobenzenes, Phenol and Chlorophenols, Carbon disulphide and Hexachlorobutadiene. EIC/AGS/CL:AIRE: Antimony, Barium, Molybdenum, Bis 2 ethylhexyl phthalate, Diethyl phthalate, 2,4 Dinitrotoluene, cis 1,2 Dichloroethene, trans 1,2 Dichloroethene, Styrene, Sourced Data: Cresols The EPA Carcinogenic classification is C Possible Human Carcinogen". There is limited evidence that it can cause cancer in animals in the absence of human data, but at present it is not conclusive. No data for cresol mixtures was given on RAIS, however there was some information for individual cresols. Limited information of cresol mixtures was found in other sources (scorecard), two screening values were therefore derived as cresols, using toxicity data from mixtures and o and m cresols which have similar properties and, the more toxic p- cresols. RAIS identified p-cresol as having an oral RfD 0.005mg/kg day -1 with a uncertainty factor of No inhalation dose was given, and the target organ is the CNS. The o- Mouchel of 12

10 cresol had a chronic oral RfD of 0.05 mg/kg day -1 and m-cresol a chronic oral RfD also of 0.05mg/kg day -1. No data was available regarding an Inhalation RfD. Scorecard listed an inhalation reference concentration (Chronic reference exposure level CREL) of 4µg/m 3 for p-cresols ( mg/kg bw day -1 ) and 600 µg/m 3 (0.171mg/kg bw day -1 ) for mixed cresols. These figures were reported by California EPA, Office of Environmental Health Hazard Assessment. The EIC/AGS/CL:AIRE GACs are based on a paper released in 2008 which gives a TDIoral of 100 µg/kg BW/day. The GACs produced by EIC/AGS/CL:AIRE GACs only include an oral TDI and compare inhalation exposure against an oral HCV. Cresols are highly volatile and the lungs have been identified as target organs. Therefore we used an inhalation TDI (sourced from the Californian EPA) as we believe that this is an important pathway that should be modelled against its own TDI. We were concerned that by using the EIC/AGS/CL:AIRE GACs which are based solely on a HCV for oral exposure we may be underestimating the potential risks. To incorporate the EIC/AGS/CL:AIRE study and more recent 2008 investigation data we have produced our GAC by applying the inhalation TDI from the Californian EPA to the EIC/AGS/CL:AIRE data. We still believe the literature indicates that p-cresol is more toxic and so we have produced one screening value for p-cresols and one for total cresols. These revised values use the HCVs below; Cresols oral TDI = 100ug/kg BW/day Inhal TDI 171 ug/kg BW/day p-cresols oral TDI = 100 ug/kg BW/day Inhal TDI 1.14 ug/kg BW/day Carbazole There was little data on Carbazole. The EIC/AGS/CL:AIRE commented that insufficient data was available to agree HCV and thus GAC were not derived. However, RAIS provided a slope factor for oral exposure of 0.02mg/kg day, and a dermal slope factor of 0.029mg/kg day. Based on a risk level of 1 in 100,000 (1E-05), an ID o of mg/kg day has been calculated. ATSDR classify Carbazole as classification 3, not enough information to classify as a carcinogen. We have assumed this is a non-threshold substance based on RAIS. Dibenzofuran This is classified as not a human carcinogen by the US. The USEPA IRIS database classes this as D (non-carcinogen). RAIS provides a Reference Dose (TDI o ) of 0.002mg/kg day for oral exposure and mg/kg day for dermal exposure. TOX12 only looks at the Polychlorinated dibenzofurans, so has not been used for this assessment. No MDI information could be found, although it has been assumed to be a threshold substance. Mouchel of 12

11 Polychlorinated Biphenyls EC7 The EC 7 PCBs represent a group of PCBs that are more commonly encountered than the WHO 12. The EC7 have been found to accumulate in human milk and animal tissue and so may be considered more of a risk, although the WHO 12 contains the most toxic PCBs. PCB 118 is the only dioxin like PCB out of the EC 7, therefore the screening value has been derived based upon the World Health Organisation Toxic Equivalency Factor (WHO TEF) of which is referenced in the Agency SGV. This has been applied to the HCV for 2,3,7,8-TCDD to derive a PCB screening value for the EC7 PCBs. The Dioxins SGV report (SC050021) looks at the dioxin-like PCBs. TEFs for dioxin-like PCBs range from 0.1 to when compared to the most toxic dioxin (2,3,7,8-TCDD). TOX12 (old approach) which has an TDI o µgkg -1 / BW day -1 and an oral MDI of µg day -1 for 2,3,7,8-TCDD. Since the updated Dioxins SGV report provides a TEF of (WHO, 2005) for the dioxin-like PCB 118, we have applied this TEF to the HCV for 2,3,7,8-TCDD to calculate risk from the PCBs that make up the EC 7. Based on the TEF of , this produces a TDI of 66ng/kg bw day -1 (or µg/kg bw day). RIVM produced a TDI of 10ng/kg bw day -1 to produce a conservative assessment we have used the RIVM value to derive our EC 7 GAC. RIVM also produced a MDI of 0.1 µg day -1, this has been applied instead of the MDI stated in the SGV as it more accurately represents the higher exposure to the EC 7 PCBs compared to the WHO 12 PCBs. It should be noted that the EC7 PCBs screening value is applicable only to the EC 7 PCBs, of which congener 118 is the most dioxin like and is a commonly measured congener. The RAIS database assumes carcinogenicity and therefore includes slope factors. Due to the varying properties (dioxin-like, non dioxin-like) it provides a range of slope factors; oral slope factors range from 2 to 0.07mg/kg day, and inhalation slope factors from 2 to 0.35mg/kg day. Although all other sources indicate that PCBs are a non-threshold substance, the updated SGV report identifies PCBs as threshold only. Polychlorinated Biphenyls WHO12 The WHO 12 PCBs represent the most toxic group of PCBs. Although the EC 7 PCBs are more commonly encountered they are not generally as toxic as the WHO 12. PCB 126 is the most toxic PCB out of the WHO 12, therefore the screening value has been derived based upon the World Health Organisation Toxic Equivalency Factor (WHO TEF) of 0.1. This has been applied to the HCV for 2,3,7,8-TCDD to derive a PCB screening value for the EC7 PCBs. The Dioxins SGV report (SC050021) looks at the dioxin-like PCBs. TEFs for dioxin-like PCBs range from 0.1 to when compared to the most toxic dioxin (2,3,7,8-TCDD). TOX12 (old approach) identifies an TDI o µgkg -1 / BW day -1 and an oral MDI of µg day -1 for 2,3,7,8-TCDD. Since the updated Dioxins SGV report provides a TEF of 0.1 (WHO, 2005) for the dioxinlike PCB 126, we have applied this TEF to the HCV for 2,3,7,8-TCDD to calculate risk from the PCBs that make up the WHO12. Based on the TEF of 0.1, this produces a TDI of Mouchel of 12

12 µg/kg bw day). It should be noted that the WHO12 PCBs HCV is applicable only to the WHO 12 PCBs, of which congener 126 is the most toxic and is a commonly measured congener. The RAIS database assumes carcinogenicity and therefore includes slope factors. Due to the varying properties (dioxin-like, non dioxin-like) it provides a range of slope factors; oral slope factors range from 2 to 0.07mg/kg day, and inhalation slope factors from 2 to 0.35mg/kg day. Although all other sources indicate that PCBs are a non-threshold substance, TOX12 identifies PCBs as threshold only. Cyanide In the absence of any updated guidance from the Environment Agency the TOX 5 Cyanide report produced under the old approach has been used to source the health criteria values for the Mouchel derived GAC. This report does not consider the carcinogenicity of cyanide and assesses the risks based upon a tolerable daily intake. The following values were reported in TOX 5. TDI o 12 µgkg -1 / BW day -1, TDI i 0.9 µgkg -1 / BW day -1. Background values were an MDI oral of 300µg/day and MDI inhal of 0.06µg/day. Mouchel of 12