Using the EPC approach to develop health-based soil and water screening concentrations for environmental chemicals

Reference doses (RfDs) and reference concentrations (RfCs) developed by the United States Environmental Protection Agency (USEPA) are typically used to assess the risk of potential adverse human health effects from exposure to environmental chemicals. For a large number of chemicals, however, USEPA RfDs or RfCs have not yet been determined. Thus, for risk assessments that involve a large number of chemicals, there may not be USEPA- or state-derived toxicity constants for all chemicals present at a particular site. A potential solution to this problem is to use estimated permissible concentrations (EPCs) to develop acceptable daily dosages from occupational exposure limits. The EPC is defined as the concentration of a chemical which, under continuous exposure conditions, is expected to be devoid of all acute and chronic toxicities. EPC values are based on allowable occupational exposure limits such as threshold limit values (TLVs), which are workplace exposure guidelines suggested by the American Conference of Governmental Industrial Hygienists. In the present analysis, the EPC method was used to develop interim toxicity constants for more than 30 chemicals which possess TLVs and which appear in the Appendix VIII Hazardous Constituents list, but for which the USEPA has not yet assigned a current RfD or RfC. Appendix VIII chemicals are commonly found at hazardous waste and other sites. Consequently, the development of toxicity constants for the more than 30 chemicals on this list would prove to be most useful for risk assessment purposes. These toxicity constants were then used, together with standard exposure assumptions, to develop acceptable human health-based soil and water concentrations for these chemicals. The use of these values as interim guidance would therefore allow individuals responsible for assessing human health effects posed by environmental contamination to address all site chemicals without performing extensive, chemical-specific toxicological analyses.