Human and Ecological Risk Assessment - Earthjustice

Section 4.0Risk CharacterizationThe third category of constituents is those that were not screened out, and were analyzedusing risk attenuation factors (chromium, fluoride, manganese, nickel, and vanadium). Becauseall that is known is that these constituents have the potential to pose a risk to human health, theycannot currently be compared to the damage case results.The final category of constituents is those that were not evaluated at either the screeningor modeling stages because no health-based values were available for comparison. These fourconstituents (chlorine, iron, lithium, and sulfate) appeared in damage cases because ofexceedences of aesthetic or state levels, not because of a known risk to human health.Table 4-20 compares the results from the 2007 draft risk assessment with the damagecases reported in U.S. EPA (2007) for the fish consumption pathway. The only fish consumptionadvisories documented in CCW damage cases are for selenium. This is consistent with the riskassessment for selenium. The two constituents that do not pose a risk in the risk assessment(cadmium and thallium) were also not part of any fish consumption advisories in the damagecases. The one inconsistency is arsenic, for which the risk assessment shows a cancer risk of 1 in50,000, slightly exceeding an excess cancer risk of 1 in 100,000. However, no arsenic fishconsumption advisories exist at proven damage case sites. This inconsistency could indicate that(1) the risk assessment was conservative with respect to arsenic, (2) not enough time has passedto see arsenic appear in fish advisories at these sites, or (3) the arsenic exceedences have notbeen detected in random fish tissue samples thus far.Table 4-20. Modeled 90th and 50th Percentile Risk Results vs.Reported Fish Consumption ExceedencesDamage Cases b Consistent Results as of 2007 cConstituent 90th %ile 50th %ile2007 Risk Assessment aArsenic – – NoCadmium – – – YesSelenium – YesThallium – – – Yesa = Constituent underwent full probabilistic modeling and was shown to pose a risk to human health inthe landfill scenario, the surface impoundment scenario, or both.– = Constituent underwent full probabilistic modeling and was not shown to pose a risk to human healthb = At least one proven damage case showed a fish consumption advisory for this constituent.– = No proven damage cases have yet shown a fish consumption advisory for this constituent.cYes = Results of risk assessment and damage cases either both indicated a risk to human health or bothindicated no risk to human health.No = The risk assessment indicated risks where none have yet been found in a proven damage case.April 2010–Draft EPA document. 4-25