Stochastic environmental risk analysis: an integrated methodology for predicting cancer risk from contaminated groundwater

Stochastic environmental risk assessment considers the effects of numerous biological, chemical, physical, behavioral and physiological processes that involve elements of uncertainty and variability. A methodology for predict ing health risks to individuals from contaminated groundwater is presented that incorporates the elements of uncertainty and variability in geological heterogeneity, physiological exposure parameters, and in cancer potency. A n idealized groundwater basin is used to perform a parametric sensitivity s tudy to assess the relative impact of (a) geologic uncertainty, (b) behavio ral and physiological variability in human exposure and (c) uncertainty in cancer potency on the prediction of increased cancer risk to individuals in a population exposed to contaminants in household water supplied from grou ndwater. A two-dimensional distribution (or surface) of human health risk w as generated as a result of the simulations. Cuts in this surface (fractile s of variability and percentiles of uncertainty) are then used as a measure of relative importance of various model components on total uncertainty an d variability. A case study for perchloroethylene or PCE, shows that uncert ainty and variability in hydraulic conductivity play an important role in p redicting human health risk that is on the same order of influence as uncer tainty of cancer potency.