Derivation of risk management criteria for chemicals of unknown toxic potency at contaminated sites

Environmental investigations of former industrial sites often detect the pr esence of chemicals for which no soil criteria exist and for which regulato ry agencies have not derived estimates of toxic potency. This poses a consi derable problem for making informed risk management decisions involving sit es where such chemicals are present. As a result, a methodology has been de veloped for making risk-based decisions for chemicals of unknown toxic pote ncy in soil at contaminated sites. The method is based on principles and pr ocedures used by the US Food and Drug Administration (USFDA), the US Enviro nmental Protection Agency (USEPA) and the Canadian Council of Ministers of the Environment (CCME). After analyzing the data on hundreds of carcinogeni c and non-carcinogenic substances, the USFDA and other leading researchers have concluded that, if no toxicological data is available on a chemical, e xposures less than 1.5 mu g/person/day (i.e., 0.02 mu g/kg body weight/day) are unlikely to result in appreciable health risks even if the substance w as later found to be a carcinogen. To develop maximum soil concentrations t hat will be protective of human health (i.e., Risk Management Criteria or R MC), the above exposure limit of 0.02 mu g/kg body weight/day has been assu med to be protective of risks from exposure to chemicals lacking toxicologi cal data. Using a stochastic risk assessment model for estimating exposures to chemicals from contaminated sites, our analyses indicate that a soil co ncentration of 2 mu g/g would be protective of human health for land uses t hat include residential, commercial, and industrial development provided no major indirect pathways exist at the site. If indirect pathways exists (e. g., vapor infiltration of soil gases, uptake of chemicals into garden produ ce, etc.), alternate RMC could be developed, that include such indirect pat hways, using the methodology provided in this paper Used by experienced ris k assessors, the approach is a scientifically defensible screening method t hat will preclude many chemicals from unnecessary evaluation, while allowin g risk assessors to focus efforts on chemicals of greater concern and make informed risk management decisions.