|Lerch, Robert - Bob|
Submitted to: Symposium on the Fate and Chemistry of Modern Pesticides Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 6/1/2004
Publication Date: 8/16/2004
Citation: Lin, C., Lerch, R.N., Garrett, H.E., George, M.F. 2004. Degradation of isoxaflutole (balance) by hypochlorite in tap water. In: Proceedings of the Symposium on the Fate and Chemistry of Modern Pesticides, August 16-19, 2004, Vail, CO. p. 34. Interpretive Summary:
Technical Abstract: Chlorine has been widely employed for the disinfection of drinking water. Additionally, it has the capacity to oxidize many organic compounds in water. Isoxaflutole (Balance; IXF) belongs to the new class of isoxazole herbicides. Isoxaflutole has a very short soil half-life and rapidly degrades to a stable and phytotoxic metabolite, diketonitrile (DKN). Further degradation of DKN produces a nonbiologically active benzoic acid (BA) metabolite. In experiments using high performance liquid chromatography-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 benzoic acid metabolite as the major end product. One mg/L of hypochlorite residue in tap water was able to completely oxidize up to 1600 ug/L (4.45 umole/L) of DKN. In tap water, the disappearance of IXF became much more rapid than in DI water. As soon as the IXF was hydrolyzed to DKN, the DKN quickly reacts with the OCl- to form BA. As a result, the herbicide solutions prepared with tap water at 500 ug/L will no longer possess any herbicidal activity after 48 hours of storage. However, in agronomic settings, highly concentrated tank solutions (600 to 800 mg/L) may be prepared with tap water since the conversion of IXF to BA would represent < 5% of the herbicide, and therefore, any impact on the herbicide efficacy would be negligible. Results of this study show that chlorine disinfection completely eliminates the phytotoxic form of this new herbicide, DKN, from drinking water supplies, yet farmers can use chlorinated tap water without significant loss of efficacy.