Relationship between mutagenicity and reactivity or biodegradability for nitroaromatic compounds.

Although many studies have reported that nitroaromatics such as 2,4,6-trinitrotoluene (TNT) have strong mutagenicity, the mechanism of mutagenic activity in these compounds has not yet been reported. We examined the mutagenicity versus reactivity and biodegradation by bacteria using TNT and its analogs (1,3,5-trinitrobenzene [TNB], 2,4,6-trinitroaniline [TNA], 2,4,6-trinitro-phenol [TNP], N,2,4,6-tetranitro-N-methyl-aniline [tetryl], 2,4-dinitrotoluene [24DNT], and 2,6-dinitrotoluene [26DNT]). Aromatic compounds harboring three nitro groups (except TNP) have high mutagenicity, judging from the results of the umu test using luminescent bacteria (Salmonella typhimurium strain TA1535/pTL210). Single-electron reduction potentials for these chemicals were -530, -555, -565, -575, -640, -674, and -764 mV for TNA, tetyl, TNT, TNB, 24DNT, 26DNT, and TNP, respectively, indicating that trinitro-aromatics (except TNP) were more reducible than other compounds. Pseudomonas sp. strain TM15, which was isolated from TNT-contaminated soils in the Yamada Green Zone, Kitakyushu City, Japan, could efficiently biotransform TNT, TNB, TNA, and tetryl; 24DNT, 26DNT, and TNP were less biodegradable. This strain converted all TNT analogs into reduction products; nitro groups were reduced to amino groups. We revealed that the mutagenicity of nitroaromatics correlate with reactivity and biodegradability. This finding may contribute to the elucidation of mutagenic expression of nitroaromatic compounds in organisms.