Mutagenic potential of binary mixtures of n1tro-polychlorinated dibenzo-p-dioxins and related compounds

The mutagenic potential of binary mixtures of nitro-polychlorinated dibenzo-p- dioxins and other environmentally related compounds was determined using Salmonella typhimurium strain TA98 in the standard plate incorporation assay. Samples tested included binary mixtures of 4-nitro-4’-chlorobiphenyl with G-nitro-4, 2’, 3’, 4’, 5’ - pentachlorobiphenyl, 4-nitrobenzo-p-dioxin with 4-nitro-2, 3, 8-trichlorodibenzo-p- dioxin, and benzo[a]pyrene with either nitropentachlorobiphenyl or nitrotrichlorodibenzo-p-dioxin. Inhibition was the primary interaction observed for the mixtures of polyhalogenated dioxins or biphenyls with the direct-acting mutagens nitrodibenzo-p-dioxin or nitrochlorobiphenyl. At the highest dose tested, nitrotrichlroodibenzo-p-dioxin or nitrochlorobiphenyl. At the highest dose tested, nitrotrichlorodibenzo-p-dioxin inhibited the bacterial mutagenicity of nitrodibenzo-p- dioxin by almost 50%, while pentachlorobiphenyl inhibited the mutagenicity of nitro- biphenyl by 34%. Conversely, synergism was the primary interaction observed for mixtures of halogenated aromatics with the promutagen benzo[a]pyrene. The addition of nitrotrichlorodioxin to benzo[a]pyrene enhanced the mutagenicity of the latter compound by as much as 70%, while the mutagenic potential of a mixture of ben- zo[a]pyrene and nitropentachlorobiphenyl was approximately 50% greater than the mutagenicity of benzo[a]pyrene alone. In summary, mixtures of nonmutagenic nitro- polyhalogenated biphenyls or dibenzo-p-dioxins appear to inhibit the mutagenicity of direct-acting mutagens, while these same compounds seem to enhance the mutagenic potential of the promutagen benzo[a]pyrene.