Development of toxicity criteria for petroleum hydrocarbon fractions in the Petroleum Hydrocarbon Criteria Working Group approach for risk-based management of total petroleum hydrocarbons in soil.

The Total Petroleum Hydrocarbon Criteria Working Croup (TPHCWG) was formed in 1993 based on the observation that widely different clean-up requirements were being used by states at sites that were contaminated with hydrocarbon materials such as fuels, lubricating oils, and crude oils. These requirements were usually presented as concentration of total petroleum hydrocarbon (TPH), and ranged from 10 to over 10,000 mg TPH/kg soil. Members of this multi-disciplinary group, consisting of representatives from industry, government and academia, jointly recognized that the numerical standard was not based on a scientific assessment of human health risk and established the following goal for the effort: To develop scientifically defensible information for establishing soil cleanup levels that are protective of human health at hydrocarbon contaminated sites. The approach developed by the TPHCWG for TPH hazard assessment consisted of dividing the petroleum hydrocarbon material into multichemical-containing fractions with similar fate and transport characteristics. These fractions were then assigned fate and transport properties (volatilization factor, soil leaching factor, etc.) and toxicity values (RfDs/RfCs) representative of the fraction. The actual site specific hazard assessment and derivation of cleanup levels is accomplished by analyzing sites to determine which fraction(s) is present and applying the appropriate fate, transport and toxicity factors. The method used by this group to determine TPH Faction specific toxicity criteria is a surrogate approach intended to supplement the indicator approach. Indicators are single, carcinogenic hydrocarbon compounds which are evaluated/regulated individually at either the federal or state level. The TPHCWG surrogate approach utilized all appropriate fraction specific toxicity data (single compound and mixture/product), minus the carcinogenic indicator compounds, to derive the fraction specific RfDs and RfCs. This hazard assessment method for petroleum contaminated sites would be utilized where indicator compounds are not present or are below/remediated to regulatory action levels. Derivation of the RfD/RfC values for the n-hexane containing aliphatic C5-C8 fraction is examined in detail to illustrate the underlying assumptions and use of existing data employed by the TPHCWG to develop fraction specific toxicity criteria. Toxicity RfDs/RfCs for all of the model fate and transport based fractions are also presented.