Human and Ecological Risk Assessment - Earthjustice

Section 3.0Analysis3.1.2 Ecological BenchmarksThe ecological risk assessment addressed two routes of exposure for ecological receptors,direct contact with contaminated media and ingestion of contaminated food items. For eachconstituent for which ecological effect data were available, HQs were calculated using chemicalspecificmedia concentrations assumed to be protective of ecological receptors of concern. Tocalculate ecological HQs, these media concentrations (also known as chemical stressorconcentration limits [CSCLs]) were divided by the estimated media concentrations. The CSCLsare media-specific environmental quality criteria intended to represent a protective thresholdvalue for adverse effects to various ecological receptors in aquatic ecosystems (surface water andsediment). The CSCLs were developed to be protective of the assessment endpoints chosen forthis assessment. An HQ greater than 1 indicates that the predicted concentration exceeds theCSCL, and therefore, the potential for adverse ecological effects exists. In this regard, the use ofCSCLs to calculate an ecological HQ is analogous to the use of the reference concentration(RfC) for human health where the air concentration is compared to the health-basedconcentration (the RfC), and an HQ greater than 1 is considered to indicate the potential foradverse health effects.Table 3-2 shows the receptor types assessed for each exposure route (direct contact andingestion) in each environmental medium addressed by the full-scale CCW risk assessment.Table 3-2. Ecological Receptors Assessed by Exposure Routeand Medium (Surface Water or Sediment)Receptor TypeDirect Contact ExposureSurface Water(water column)Aquatic Community Sediment CommunityAmphibians Aquatic Plants and Algae Terrestrial PlantsIngestion ExposureMammals Birds Surface WaterSedimentEcological receptors that live in close contact with contaminated media are considered tobe potentially at risk. For the screening and full-scale analysis, these receptors are exposedthrough direct contact with contaminants in surface water and sediment. The benchmarks forreceptor communities (aquatic or sediment communities) are not truly community-levelconcentration limits in that they do not consider predator-prey interactions. Rather, they arebased on the theory that protection of 95 percent of the species in the community will provide asufficient level of protection for the community (see, for example, Stephan et al., 1985, foradditional detail). Appendix H summarizes the benchmark derivation methods for each receptorassessed for the direct contact route of exposure.April 2010–Draft EPA document. 3-6