Developing Health-Based Cleanup Goals for Tetrachloroethene and Its Biotransformation Products in the Presence of Petroleum Hydrocarbons. Xuannga Mahini, Michelle Medeiros, and Rachel Konishi, Ogden Environmental and Energy Services, 680 Iwilei Road, Suite 660, Honolulu, HI 96817
The contamination of environmental media with both chlorinated aliphatic solvents and petroleum hydrocarbons is widespread at several hazardous waste sites. Results of different investigations have shown that the reductive biotransformation of chlorinated aliphatics with a high degree of chlorine substitution (e.g. tetrachloroethylene or PCE) occurs in an anaerobic environment. It has also been shown that microbially catalyzed transformation reactions are facilitated by coupling the oxidation of petroleum hydrocarbons with the reduction of chlorinated aliphatics. The sequential dechlorination products are trichloroethylene (TCE), dichloroethylene isomers (DCE), and vinyl chloride (VC), which is a human carcinogen. Derivation of health-based cleanup goals (HBG) for chlorinated aliphatics and petroleum hydrocarbons at these sites poses an enormous challenge because chemical-specific HBGs for the parent and intermediate dechlorination compounds (based on an acceptable risk level of concern) may not be protective of human health if they can be biotransformed to the more toxic VC in the environment. Thus, at a military laundry facility in Hawaii, chemical-specific biotransformation rates for chlorinated aliphatics were used, coupled with empirical data in different environmental media, in the calculation of health protective HBGs for both chlorinated aliphatics and petroleum hydrocarbons. HBGs for these contaminants in the soil were set at levels that would be protective of human health via direct contact to the soil, inhalation of emanating organic vapor, and potential domestic use of the underlying ground water.