Human and Ecological Risk Assessment - Earthjustice

Section 3.0Analysischild was aged from 1 year to 25 years, spending 5 years in cohort 1, 6 years in cohort 2, 8 yearsin cohort 3, and 6 years in cohort 4, for a total of 25 years).3.8.2 Exposure FactorsThe exposure factors used in the risk assessment are listed in Table 3-13, along with theirdata sources and variable type (i.e., whether they were represented as a distribution or a fixedvalue in the Monte Carlo analysis). These exposure factors were used to calculate the dose of achemical based on contact with contaminated media or food, the duration of that contact, and thebody weight of the exposed individuals.Table 3-13. Human Exposure Factor Input Parameters and Data SourcesParameter Variable Type Data SourceBody weight (adult, child) Distribution U.S. EPA (1997c)Ingestion rate: fish (adult, child) Distribution U.S. EPA (1997d)Ingestion rate: drinking water (adult, child) Distribution U.S. EPA (1997c)Exposure duration (adult, child) Distribution U.S. EPA (1997e)Exposure frequency (adult, child) Fixed (constant) U.S. EPA policyFraction contaminated: drinking water Fixed (constant) U.S. EPA policyFraction contaminated: fish Fixed (constant) U.S. EPA policyFraction of TL3 fish consumed Fixed (constant) U.S. EPA (1997d)Fraction of TL4 fish consumed Fixed (constant) U.S. EPA (1997d)Human lifetime (used in carcinogenic risk calculation) Fixed (constant) U.S. EPA policyThe primary data source of human exposure model inputs used in this risk assessmentwas EPA’s Exposure Factors Handbook (EFH; U.S. EPA, 1997c-e). The EFH summarizes dataon human behaviors and characteristics related to human exposure from relevant key studies andprovides recommendations and associated confidence estimates on the values of exposurefactors. These data were carefully reviewed and evaluated for quality before being included inthe EFH. EPA’s evaluation criteria included peer review, reproducibility, pertinence to theUnited States, currency, adequacy of the data collection period, validity of the approach,representativeness of the population, characterization of variability, lack of bias in study design,and measurement error (U.S. EPA, 1997c-e). For exposure factors that were varied in the MonteCarlo analysis, probability distribution functions were developed from the values in the EFH.The data sources and assumptions for intake and other human exposure factors used inthis analysis are described below. Appendix F presents the exposure factors used and describesthe rationale and data used to select the form of the distributions (e.g., normal, lognormal,gamma, Weibull) for those exposure factors that were varied in the probabilistic analysis. Datafor three child cohorts (ages 1–5, 6–11, and 12–19 years) and adults were used. However, asmost infants are breastfed and therefore are not exposed to fish or water, they were excludedfrom the risk assessment (i.e., modeling start age for a child is 1 year).• Body Weight. Distributions of body weight were developed for adult and child receptorsbased on data from the EFH.April 2010–Draft EPA document. 3-42