Fenitrothion [O, O-dimethyl O-(3-methyl-4-nitrophenyl)phosphorothioate], a typical organophosphorus pesticide, is widely used as an insecticide in Japan. In this study, 3-methyl-4-nitrophenol (3M4NP), which is a typical hydrolysate of fenitrothion, was focused as a possible mutagen precursor because it is reported as a common contaminant in raw water for water works, and is capable of forming mutagens when it is chlorinated in water works. In order to examine molecular formulae of mutagens produced from 3M4NP, a chlorinated 3M4NP sample was analyzed with a high-resolution LC/MS. Several peaks were found in a base peak chromatogram. A peak of m/z 215.971 was focused to be analyzed, suggesting a formation of C 7 H 4 O 5 NCl (mass error = 0.397 mmu or 1.837 ppm). To examine the chemical structure of the found substance, MS 2 experiments were conducted with a collision induced disassociation technique. Four product ions: m/z 198.9679, 187.9757, 170.9731 and 136.0043 which can be attributed to losses of OH, CO, COOH and Cl functional groups were observed. From these fragment ions and the structure of 3M4NP, the substance was extrapolated to be chloro-5-hydroxy-2-nitrobenzoic acid (C5H2NB). The mutagen formation potential (MFP) of 5-hydroxy-2-nitrobenzoic acid, which is considered to be a precursor of C5H2NB, was tested and the MFP of 3,400 net rev./µmol was observed.

The contribution of selected pesticides to the mutagen formation potential (MFP) of river waters was studied. The concentrations of the pesticides in river water samples were determined by means of a quadrupole GC-MS. Twelve out of 39 pesticides measured were detected in the water samples collected from Kotsuki River. Ames mutagenicity assays (preincubation method) using Salmonella typhimurium TA100 without metabolic activation by S9 mix (TA100-S9) were performed to measure the MFP. From all the samples collected, significant MFPs were detected. The maximum contribution of the pesticides to the MFP of the river water samples was 0.11%, indicating that the effect of the pesticides found in this study on the MFP of the river water samples is insignificant. The contribution of pesticide degradation products to the MFP of river waters should be investigated in order to see whether pesticide degradation products affect the MFP of river waters.

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