Human and Ecological Risk Assessment - Earthjustice

Appendix FHuman Exposure FactorsTable F-2. Summary of Human Exposure Factor Data Used in Modeling: ConstantsDescription Value Units SourceFraction contaminated: drinking water 1 Fraction EPA policyFraction contaminated: fish 1 Fraction EPA policyFraction of T3 fish consumed 0.36 Fraction U.S. EPA (1997b); Table 10-66Fraction of T4 fish consumed 0.64 Fraction U.S. EPA (1997b); Table 10-66Exposure frequency (adult, child) 350 d/yr EPA policyAveraging time for carcinogens (adult, child) 70 yr U.S. EPA (1989)The fraction contaminated for drinking water was assumed to be 1 (i.e., all drinking wateravailable for consumption at a site is potentially contaminated), with actual concentrationsdepending on fate and transport model results. Thus, households for which the drinking waterpathway was analyzed were assumed to get 100 percent of their drinking water fromgroundwater. Exposure frequency was set to 350 days per year in accordance with EPA policy,assuming that residents take an average of 2 weeks’ vacation time away from their homes eachyear.F.1.4 Variable ParametersF.1.4.1 Fish ConsumptionTable F-3 presents fish consumption data and distributions. Fish consumption data wereobtained from Table 10-64 of the EFH (U.S. EPA, 1997b). Data (in g/d) were available for adultfreshwater anglers in Maine. The Maine fish consumption study was one of four recommendedfreshwater angler studies in the EFH (U.S. EPA, 1997b). The other recommended fishconsumption studies (i.e., Michigan and New York) had large percentages of anglers who fishedfrom Great Lakes, which is not consistent with the modeling scenarios used in this risk analysis.The anglers in the Maine study fished from streams, rivers, and ponds; these data were moreconsistent with the CCW modeling scenarios. Although the Maine data have a lower mean thanthe Michigan data, the Maine data compared better with a national U.S. Department ofAgriculture (USDA) study. Also, the Maine study included percentile data, which werenecessary to develop a distribution.Percentile data were used to fit parametric models (gamma, lognormal, and Weibull), andmeasures of goodness of fit were used to select lognormal as the most appropriate model. Thefraction of fish intake that is locally caught was assumed to be 1 (in accordance with EPApolicy). The fraction of consumed T3 and T4 fish was 0.36 and 0.64, respectively (Table 10-66,U.S. EPA, 1997b).AgeCohortNTable F-3. Fish Consumption Data and DistributionDataMeanEFH Data (g/d)DataSD P50 P66 P75 P90 P95 DistributionDistributionPop-EstdMeanPop-EstdSDAll ages 1,053 6.4 2 4 5.8 13 26 Lognormal 6.48 19.9N = Number of samples; P50–P95 = Percentiles; Pop-Estd = Population-estimated; SD = Standard deviation.April 2010–Draft EPA document. F-5