Human and Ecological Risk Assessment - Earthjustice

Appendix ICalculation of Health-Based Numbers (HBNs) for CCW Constituent Screeninggroups) was selected. In all cases, the HBN calculations used central tendency exposure factors(e.g., body weight, exposure duration, exposure frequency, consumption rates).The equations used to calculate the HBNs are provided at the end of this appendix; TableI-2 lists the tables of equations by exposure pathway (Tables I-4 through I-8). Data used in theseequations to calculate the CCW HBNs can be found in the other appendices to this report, aswell as in Table I-9, which provides the age cohort–specific human exposure factors used in theHBN calculations.Table I-2. Key to Tables of Equations Used to Calculate HBNsEquation for Fish ConcentrationsI-4 Concentration in Fish at Different Trophic Levels (mg/kg)Equations for Human ExposureI-5 Daily Intake of Contaminant from Consumption of Fish (mg/kg BW/day)I-6 Daily Intake of Contaminant from Consumption of Drinking Water (mg/kg BW/day)Equations for Unit Risk Calculations and Health-based NumbersI-7 Cancer Risk and Hazard Quotient Due to Ingestion (unitless)I-8 Health-Based Concentration (mg/L)Groundwater HBNs were based on standard residential exposure assumptions fordrinking water consumption, using equations from (U.S. EPA, 1998a). The surface water HBNswere based on concentrations in fish estimated using an aquatic food chain model; thatmethodology is described in the rest of this section.The methodology used for estimating concentrations in fish was based on EPA’sMethodology for Assessing Health Risks Associated with Multiple Pathways of Exposure toCombustor Emissions (U.S. EPA, 1998a). An aquatic food chain model was used to estimate theconcentration of constituent that may accumulate in fish. It was assumed for this analysis thatfish are a food source for a recreational fisher. Trophic level three (T3) and four (T4) fish wereconsidered in this analysis. T3 fish are those that consume invertebrates and plankton. T4 fishare those that consume other fish. Most of the fish that humans eat are T4 fish (e.g., salmon,trout, walleye, bass) and medium to large T3 fish (e.g., carp, smelt, perch, catfish, sucker,bullhead, sauger). For metals other than mercury, the calculation of contaminants in fish wasbased on the total concentration of contaminants in the waterbody (i.e., dissolved and suspendedsolids). For mercury, the calculation of contaminants in fish was based on the dissolvedconcentration of methyl mercury in the waterbody.Fish tissue concentrations are dependent on a bioconcentration factor (BCF), which isused to estimate the amount of constituent being transferred from the waterbody into the fishtissue. Specifically, BCFs reflect the ratio between the tissue concentration in fish and theappropriate waterbody concentration. BCFs were developed for each constituent to reflectaccumulation in each trophic level considered. They were also developed to estimate theconcentration in the fish filet versus the total fish. Human receptors consume only the filetportion of the fish, which has a lower lipid content. Because some constituents tend toaccumulate in the fatty tissue, the concentration in the filet portion of the fish is sometimes lowerthan the concentration in the whole fish.April 2010–Draft EPA document. I-2