Chlorine has been widely employed for the disinfection of drinking water. Additionally, it has thecapacity to oxidize many organic compounds in water. Isoxaflutole (Balance; IXF) belongs to a newclass of isoxazole herbicides. Isoxaflutole has a very short soil half-life and rapidly degrades to astable and phytotoxic metabolite, diketonitrile (DKN). Further degradation of DKN produces anonbiologically active benzoic acid (BA) metabolite. In experiments using high-performance liquidchromatography-UV spectroscopy (HPLC-UV) and HPLC tandem mass spectrometry (HPLC-MS/MS), DKN was found to rapidly react with hypochlorite in tap water, yielding the BA metabolite as themajor end product. One milligram per liter (19
M) of hypochlorite residue in tap water was able tocompletely oxidize up to 1600
g/L (4.45
mol/L) of DKN. In tap water, the disappearance of IXFwas much more rapid than in DI water. As soon as the IXF is hydrolyzed to DKN, the DKN quicklyreacts with the OCl
- to form nonphytotoxic BA. As a result, the herbicide solutions prepared with tapwater at 500
g/L will no longer possess any herbicidal activity after 48 h of storage. However, inagronomic settings, highly concentrated
tank solutions (600-800 mg/L) may be prepared with tapwater since the conversion of IXF to BA would represent <5% of the herbicide; therefore, any impacton the herbicide efficacy would be negligible. Results of this study show that current chlorinationdisinfection protocols in municipal water systems would completely eliminate the phytotoxic form ofthis new herbicide, DKN, from drinking water supplies; yet,
farmers can use chlorinated tap waterwithout significant loss of efficacy.Keywords: Isoxaflutole; hypochlorite, disinfection, herbicide; metabolites; chromatography; diketonitrile; benzoic acid metabolite, HPLC-MS/MS; HPLC-UV
