Mutagenic interactions of model chemical mixtures

Although current methodology for human health risk assessment assumes additive interactions among the contaminants of a complex mixture, chemical interactions may occur which produce synergistic or antagonistic effects. In this study, the mutagenic response of three model compounds, benzo(a)pyrene (B(a)P), pentachlorophenol (PCP) and 2,4,6-trinitrotoluene (TNT), were tested individually and in binary and tertiary solutions, using the Salmonella/microsome assay with each of three bacterial tester strains (TA97a, TA98, and TA100). For all strains, B(a)P was mutagenic with metabolic activation (Arochlor 1254-induced Sprague-Dawley rat liver S9 fraction), TNT was mutagenic without metabolic activation, and pentachlorophenol was inactive both with and without metabolic activation. In binary and tertiary solutions, pentachlorophenol had no effect on the mutagenicity of B(a)P or TNT, independent of metabolic activation. For strain TA97a, the mutagenicity of B(a)P with metabolic activation was slightly decreased in the presence of TNT; the mutagenicity of TNT without metabolic activation was slightly decreased in the presence of B(a)P and PCP; and the mutagenicity of the tertiary solution (496 revertants/10 ug) with metabolic activation was lower than the mutagenicity of B(a)P alone (729 revertants/10 ug). The mutagenicity of B(a)P in strain TA98 with activation was inhibited by the addition of TNT. Studies conducted using several concentrations of TNT or B(a)P indicate that the inhibition of B(a)P mutagenicity was increased as the concentration of TNT increased. Assays performed using four concentrations of S9 indicated the inhibition of B(a)P mutagenicity was relatively unaffected by the level of S9. The data suggest that an interaction in the presence of TNT limits the concentration of B(a)P that is capable of reaching or binding with bacterial DNA. (C) 1998 Elsevier Science Ltd. All rights reserved.