Nitrite-induced volatile fecal mutagens: some preliminary studies.

Further studies are reported on the formation of volatile mutagens from normal human feces incubated with sodium nitrite at 37 degrees C. Volatile mutagens were detected using Ames' Salmonella typhimurium tester strain TA1535 on petrie plates inverted over samples in sealed containers. An optimal exposure period was shown to be approximately 24 hours. When plates inverted over samples were replaced periodically, mutagenicity during serial 24 hour or 48 hour periods could be measured. Mutagenicity was optimal during the second 24 hour period and the first 48 hour period with 0.6 M sodium nitrite, and in the first 24- and 48-hour period with 0.2 M sodium nitrite. Subsequent exposure periods showed decreasing mutagenicity with time. Because of the great differences in reactivity with nitrite in stools of healthy volunteers, the effect of mixing "high reacting" samples with "low reacting" samples were investigated. When "low reacting" samples were mixed with "high reacting" samples, a lower mutagenicity of the mixture was observed compared to a predicted "average" value. Autoclaving stool samples made very little difference in nitrite-induced mutagenicity and behavior in mixing experiments. Thus, fecal mutagens arise as a spontaneous chemical process involving nitrite ions and both dietary and flora factors may be important in their production or absence.