Human and Ecological Risk Assessment - Earthjustice

Section 2.0Problem Formulationof drinking water (although some households may drink bottled or treated water or may drinkwater outside the home, e.g., at work or at school).For ecological receptors, exposure assumptions were incorporated into the developmentof ecological benchmarks (see Appendix H), which were surface water and sedimentconcentrations corresponding to an HQ of 1.The time period for the exposure assessment was defined by the peak concentration in themedia of concern and the exposure duration. For human receptors, annual average mediaconcentrations were averaged over the randomly selected exposure duration around the peakconcentration for each run. To protect against chronic effects to ecological receptors, EPAconsidered the exposure duration over a significant portion of the receptor’s lifetime, and webelieve that one year is the appropriate period of time for that. To be protective, we used thehighest (peak) annual average concentration to estimate ecological exposure and risk.2.4.4 Risk EstimationRisk was estimated using several risk endpoints as particular measures of human healthrisk or ecological hazard. A risk endpoint is a specific type of risk estimate (e.g., an individual’sexcess cancer risk) that is used as the metric for a given risk category. The CCW risk assessmentevaluated cancer and noncancer endpoints for humans and noncancer endpoints for ecologicalreceptors. For human risk, the availability of toxicological benchmarks for cancer and noncancereffects determined which endpoints were evaluated for each constituent.EPA used two risk endpoints to characterize risk for the human receptors and a singlerisk endpoint, total HQ, to characterize risk for ecological receptors. These endpoints arediscussed in Section 3.9; in addition, uncertainty related to these endpoints is discussed inSections 4.4.2 (exposures to multiple constituents) and 4.4.3.4 (benchmark uncertainties).From the distribution of risks for each risk endpoint generated by the Monte Carloanalysis, the 50th and 90th percentile risks were selected and compared to a risk range of 1 in1,000,000 to 1 in 10,000 excess cancers and a hazard quotient greater than 1 for noncarcinogeniceffects. A hazard quotient greater than 1 was also used for the ecological risk criterion in the fullscalerisk assessment.April 2010–Draft EPA document. 2-16