Human and Ecological Risk Assessment - Earthjustice

Section 3.0Analysis• Appendix K, Screening Analysis Results, provides the results of the screening analysisfor human and ecological receptors.• Appendix L, Time of Travel to Receptor Well, provides figures showing, for selectedCCW constituents, cumulative percentiles of the time it took for the peak concentrationto reach a receptor well for each source type.3.1 Toxicity AssessmentThe assessment of human risks from disposal of a waste stream like CCW begins byassessing, for constituents in the waste, the ability of each chemical to cause an adverse humanhealth effect, which depends on the toxicity of the chemical, the chemical’s route of exposure toan individual (ingestion, inhalation, or direct contact), the duration of exposure, and the dosereceived (the amount that a human ingests or inhales). Similar principles apply to ecologicalreceptors, although exposure duration is much shorter than for human receptors because humansgenerally live longer than ecological receptors. For a risk assessment, the toxicity of aconstituent is defined by a human health or ecological benchmark for each route of exposure. Abenchmark is a quantitative value used to predict a chemical’s possible toxicity and ability toinduce an adverse effect at certain levels of exposure. Because different chemicals causedifferent health effects at different doses, benchmarks are chemical-specific.Appropriate human health and ecological benchmarks for the constituents of potentialconcern in CCW wastes were collected for use in the screening assessment and in the full-scalerisk assessment. Although these assessments were conducted in 2002 and 2003, the benchmarksand risks presented in this 2009 report were updated to reflect current toxicity data. 4 The datasources and collection methodology for these benchmarks are described briefly in Sections 3.1.1(human health benchmarks) and 3.1.2 (ecological benchmarks), and in more detail in AppendixG (human health benchmarks) and Appendix H (ecological benchmarks).3.1.1 Human Health BenchmarksHuman health benchmarks for chronic oral exposures were needed for the full-scaleanalysis. These health benchmarks were derived from toxicity data based on animal studies orhuman epidemiological studies. Each benchmark represents a dose-response estimate that relatesthe likelihood and severity of adverse health effects to exposure and dose. This section presentsthe noncancer and cancer benchmarks used to evaluate human health effects that may result fromexposure to the constituents modeled.Chronic human health benchmarks were used to evaluate potential noncancer and cancerrisks. These include reference doses (RfDs) to evaluate noncancer risk from oral exposures andoral cancer slope factors (CSFs) to evaluate cancer risk from oral exposures. The benchmarks arechemical-specific and do not vary between age groups.4 Because the risk calculations are linear and occur at the end of the analysis, all screening and full-scale results canbe simply scaled to accommodate any changes in human health and ecological benchmarks.April 2010–Draft EPA document. 3-3