Federal Contaminated Site Risk Assessment In Canada Part I: Guidence on Human Health Preliminary Quantitive Risk Assessment (PQRA)
2.5.6 Relative Absorption Factors and Exposure via Multiple Pathways
Few, if any, toxicological reference values (TRVs) exist specifically for the dermal exposure pathway. Therefore, dermal exposures will routinely be added to the oral dose, following adjustment for relative bioavailability or absorption, for subsequent comparison to the oral TRV.
For some contaminants of potential concern, separate TRVs are available for oral and inhalation exposures. In these cases, the exposures via these pathways should be determined separately for comparison to pathway-specific TRVs.
In cases where only an oral TRV is available, exposures by all routes (oral, dermal, inhalation) should be summed for comparison to the oral TRV.
For COPCs where multiple exposure pathways will be summed for comparison to a single TRV, it will be necessary to apply relative absorption factors (RAFs) in exposure calculations. Oral exposures should always be assumed to have a relative absorption of 100% (RAF = 1). Where inhalation exposures are being summed with oral exposures, the inhalation RAF will generally default to 1 unless there is good evidence that respiratory absorption is significantly less that 100%.
Where dermal exposures are being summed with oral exposures, the RAF values presented in Table 6 should be applied, unless more appropriate information has been identified and justified (with proper citations). For contaminants not listed in Table 6, other sources such as the Risk Assessment Information System (RAIS; http://risk.lsd.ornl.gov/rap_hp.shtml), Toxicological Profiles published by the Agency for Toxic Substances and Disease Registry (ATSDR; http://www.atsdr.cdc.gov/toxpro2.html), or other authoritative sources should be consulted. Where alternate data sources are consulted, they must be clearly cited and fully referenced.
For other forms of dermal exposures, such as those involving submersion in water, dermal absorption in units of ƒÊg/cm2-hour may be required. The source of such equations and assumptions, if required, should be clearly cited and fully referenced.
Table 6
Relative Dermal Absorption Factors (RAFDermal) Recommended for Preliminary Quantitative Risk Assessments
(after Ontario Ministry of Environment and Energy (OMEE), 1996b) |
| CHEMICAL |
AFDERMAL |
CHEMICAL |
AFDERMAL |
| ACENAPHTHENE |
0.2 |
DICHLOROETHYLENE, CIS-1,2- |
0.1 |
| ACENAPHTHYLENE |
0.18 |
DICHLOROETHYLENE, TRANS-1,2- |
0.1 |
| ACETONE |
0.1 |
DICHLOROPHENOL, 2,4- |
0.4 |
| ALDRIN |
0.25 |
DICHLOROPROPANE, 1,2- |
0.2 |
| ANTHRACENE |
0.29 |
DICHLOROPROPENE, 1,3- |
0.2 |
| ANTIMONY |
0.1 |
DIELDRIN |
0.25 |
| ARSENIC |
0.03 |
DIETHYL PHTHALATE |
0.02 |
| BARIUM |
0.1 |
DIMETHYL PHTHALATE |
0.07 |
| BENZENE |
0.08 |
DIMETHYLPHENOL, 2,4- |
0.26 |
| BENZO(A)ANTHRACENE |
0.2 |
DINITROPHENOL, 2,4- |
0.26 |
| BENZO(A)PYRENE |
0.2 |
DINITROTOLUENE, 2,4- |
0.13 |
| BENZO(B)FLUORANTHENE |
0.2 |
ENDOSULFAN |
0.2 |
| BENZO(G,H,I)PERYLENE |
0.18 |
ENDRIN |
0.25 |
| BENZO(K)FLUORANTHENE |
0.2 |
ETHYLBENZENE |
0.2 |
| BERYLLIUM |
0.03 |
ETHYLENE DIBROMIDE (DIBROMOETHANE, 1,2-) |
0.1 |
| BIPHENYL, 1,1- |
0.08 |
FLUORANTHENE |
0.2 |
| BIS(2-CHLOROETHYL)ETHER |
1 |
FLUORENE |
0.2 |
| BIS(2-CHLOROISOPROPYL)ETHER |
1 |
HEPTACHLOR |
0.2 |
| BIS(2-ETHYLHEXYL)PHTHALATE |
0.02 |
HEPTACHLOR EPOXIDE |
0.2 |
| BROMODICHLOROMETHANE |
0.1 |
HEXACHLOROBENZENE |
0.13 |
| BROMOFORM (TRIBROMOMETHANE) |
0.11 |
HEXACHLOROBUTADIENE |
0.2 |
| BROMOMETHANE |
0.1 |
HEXACHLOROCYCLOHEXANE, GAMMA (GAMMA-HCH) |
0.2 |
| CADMIUM |
0.14 |
HEXACHLOROETHANE |
1 |
| CARBON TETRACHLORIDE |
0.1 |
INDENO(1,2,3-CD)PYRENE |
0.2 |
| CHLORDANE |
0.05 |
LEAD |
0.006 |
| CHLOROANILINE, P- |
0.1 |
MERCURY |
0.05 |
| CHLOROBENZENE |
0.1 |
METHOXYCHLOR |
0.2 |
| CHLOROFORM |
0.1 |
METHYL ETHYL KETONE |
0.1 |
| CHLOROPHENOL, 2- |
0.26 |
METHYL ISOBUTYL KETONE |
0.1 |
| CHROMIUM(III) |
0.04 |
METHYL MERCURY |
0.2 |
| CHROMIUM(VI) |
0.09 |
METHYL TERT BUTYL ETHER |
0.1 |
| CHRYSENE |
0.2 |
METHYLENE CHLORIDE (DICHLORMETHANE) |
0.1 |
| COBALT |
0.1 |
METHYLNAPHTHALENE, 2- |
0.1 |
| COPPER |
0.1 |
MOLYBDENUM |
0.1 |
| CYANIDE |
0.3 |
NAPHTHALENE |
0.1 |
| DIBENZO(A,H)ANTHRACENE |
0.09 |
NICKEL |
0.35 |
| DIBROMOCHLOROMETHANE |
0.1 |
P,P'-DDD |
0.2 |
| DICHLOROBENZENE, 1,2- (O-DCB) |
0.1 |
P,P'-DDE |
0.2 |
| DICHLOROBENZENE, 1,3- (M-DCB) |
0.1 |
P,P'-DDT |
0.2 |
| DICHLOROBENZENE, 1,4- (P-DCB) |
0.1 |
PENTACHLOROPHENOL |
0.11 |
| DICHLOROBENZIDINE, 3,3'- |
0.54 |
PETROLEUM HYDROCARBONS (PHC; CCME F1 -F4) |
0.2 a |
| DICHLOROETHANE, 1,1- |
0.13 |
PHENANTHRENE |
0.18 |
| DICHLOROETHANE, 1,2- |
0.1 |
PHENOL |
0.26 |
| DICHLOROETHYLENE, 1,1- |
0.1 |
PYRENE |
0.2 |
| SELENIUM |
0.002 |
TRICHLOROETHANE, 1,1,2- |
1 |
| SILVER |
0.25 |
TRICHLOROETHYLENE |
0.1 |
| STYRENE |
0.2 |
TRICHLOROPHENOL 2,4,6- |
0.26 |
| TETRACHLOROETHYLENE |
0.1 |
TRICHLOROPHENOL, 2,4,5- |
0.26 |
| THALLIUM |
0.01 |
VANADIUM |
0.1 |
| TOLUENE |
0.12 |
VINYL CHLORIDE (CHLOROETHYLENE) |
0.16 |
| TRICHLOROBENZENE, 1,2,4- |
0.08 |
XYLENES (MIXED ISOMERS) |
0.12 |
| TRICHLOROETHANE, 1,1,1- |
0.1 |
ZINC |
0.02 |
a - see CCME, 2000
2.5.7 Carcinogens
For carcinogenic substances, only exposure in adult receptors need be determined, consistent with the methods employed by the CCME (1996) and Health Canada (1995) to derive soil quality guidelines for carcinogenic substances. The variability between adult exposure and lifelong average exposure is much smaller than the uncertainty inherent in the derivation of cancer slope factors. Therefore, the more complex lifelong average daily intake need not be determined for a preliminary quantitative risk assessment, unless preferred by the assessor.
When establishing health-based guidelines for soil quality, neither the CCME (1999) nor Health Canada (1995, for example) amortized shorter-than-lifetime exposures over average life expectancy. During the derivation of guidelines for industrial properties, for example, exposure was averaged to account for anticipated occupational exposures of 8 hours per day, 5 days per week, 48 weeks per year (CCME, 1996), but career-long exposure (say, 35 years) was not averaged over life expectancy. However, it is generally assumed that exposure to low doses or concentrations of a carcinogenic substance - i.e., relatively low environmental levels -- require a concurrent increase in exposure duration to initiate cancer. Also, cancer potency values (TD05,TC05, slope factor, unit risk) are typically derived on the assumption of lifelong exposure.
The validity and defensibility of exposure amortization for carcinogenic substances is under review by Health Canada. Until that review is complete, shorter-than-lifetime carcinogen exposures should be amortized over the average life expectancy (75 years) if the cancer risk is based on lifetime average daily exposure, or over 56 years (the duration of adulthood) if cancer risk is based on estimates in adults only. Recommended exposure durations for various land uses are presented in Table 4.
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