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INITIAL RELEASE DDJC Tracy APPENDIX C: Estimated Exposures and Health Effects Estimates of Human Exposure Doses and Determination of Health Effects Deriving Exposures Doses ATSDR estimated the human exposure doses for the following pathways) ingestion of private well water; 2) incidental ingestion of Day Care Center's play yard surface soil by children; and 3) ingestion of fish from the stormwater lagoon. Deriving exposure doses requires evaluating the concentrations of the contaminants to which people may have been exposed and the frequency and duration of those exposures. Health effects are also related to individual characteristics—such as age, gender, and nutritional status—that influence how a chemical might be absorbed, metabolized, and eliminated by the body. Together, these factors help influence the individual's physiological response to chemical contaminant exposure and potential noncarcinogenic and carcinogenic health outcomes. In the absence of site-specific exposure information, ATSDR applied several conservative exposure assumptions to define sit-specific exposure as accurately as possible for residents near the DDJC Tracy site. Evaluating Potential Health Hazards The estimated exposure doses are used to evaluate potential noncancer and cancer effects associated with chemicals of concern. When evaluating noncancer effects, ATSDR uses standard health guidelines, including ATSDR's Minimal Risk Levels (MItLs) and EPA's Reference Doses (RfDs), to determine whether adverse effects will occur. The chronic MRLs and RfDs are estimates of daily human exposures to a substance that are unlikely to result in adverse noncancer effects over a specified duration. ATSDR compared estimated exposure doses associated with DDJC Tracy exposure scenarios to conservative health guidelines such as chronic MRLs or RfDs for each contaminant of concern, if available. If the exposure dose is greater than the MRI, or RfD, then a possibility exists that noncancer effects could occur. In general, MRLs and RfDs are based on levels of exposure reported in animal or human studies and consider the most sensitive outcome observed for oral or inhalation exposures. MRLs and RfDs are derived from the level at which no effects were observed in the study (i.e., the "no- observed-adverse-effects level" [NOAEL]) or the lowest level at which effects-are observed (i.e., the"lowest-observed-adverse-effects level" [IAAEL]). To derive the MILL, uncertainty(safety) factors are applied to the NOAELs or LOAELs to account for variation in the human population and the uncertainty involved in extrapolating from animal studies to reflect human exposures. C-1