Acute and genetic toxicity of 1-nitropyrene and its fate after single oral doses to rats

The mammalian acute and genetic toxicity of 1-nitropyrene (NP) was studied because this and other nitroarenes are highly mutagenic toward bacteria and have been identified in emissions from combustion processes. A suspension of NP did not cause observable signs of acute toxicity and was not lethal when administered to mate and female rats at single oral doses as high as 5.0 g/kg. Histological examination of stomach, intestine, lung, heart, spleen, pancreas, adrenal, and kidney from rats euthanized at 4 and 14 d after treatment revealed no detectable differences from control rats. Urine and feces were collected for 4 d after treatment with 5.0 g/kg. About 70% of the dose was present in the feces as NP, and about 2% was present as the reduced metabolite 1-aminopyrene (AP). Sulfate and giucuronide conjugates of AP were present in small amounts f<1%) in the urine, showing that at least some of the dose was absorbed. Bone marrow cells from female rats given NP orally at 0.5, 1.5, and 5.0 g/kg showed a slight dose-related increase in the frequency of sister chromatid exchanges. Both NP and AP showed low mutagenicity in Chinese hamster ovary cells in vitro. Evidence of reductive metabolism of NP in rats raises concern about the potential exposure of humans to this compound. However, the weak in vivo and in vitro genetic toxicity of NP at high dose levels in mammalian systems suggests that the potential hazard may not be as high as predicted from bacteria! mutagenicity data.