Hydrolytic and photoinduced degradation of tribenuron methyl studied by HPLC-DAD-MS/MS

Abstract

The©paper©studies,©with©the©help©of©HPLC-DAD-MS/MS©technique,©the©hydrolytic©and photoinduced©degradation©processes©that©take©place©in©aqueous©solutions©of©tribenuron methyl,© both© when© preserved© in© the© dark© and© when© undergoing© solar© box© irradiation© under conditions© that© simulate© sun© light.© The© results© indicate© that© the© degradation© products© formed by© hydrolysis© alone© and© by© photoirradiation© are© the© same,© but© kinetics© of© the© hydrolysis reaction©is©much©slower.©The©degradation©products©are©identified©as©2-methoxy-4-methylamino-6-methyl-1,3,5-triazine© (P1),© methyl© 2-aminosulfonylbenzoate© (P2),© and© saccharin© (P3)© and© quantified.© Ecotoxicological© biotests© performed© on© 0.1© g L Ϫ1 photoirradiated solutions of the herbicide give a border line toxicity situation comparable to that of the precursor and indicate that the herbicide is characterized by low persistence in the environment, as required. Its degradation, however, does not lead to mineralization but to the formation of products of comparable toxicity. To evaluate the matrix effects, the photodegradation of the herbicide is also studied in the presence of rice paddy waters: the process is slower than in ultrapure water but leads to the same products. Experiments performed for comparison by irradiating ultrapure water solutions with UV lamp (254 nm) show that the degradation process is not only faster with respect to sunlight, but gives a different pathway, without in anyway leading to mineralization. T he more recent herbicide formulations are designed to offer advantages of the highest selectivity together with the lowest persistence in the environment: sulfonylurea herbicides meet these requirements. But, unfortunately, lower persistence in the environment does not necessarily correspond to lower toxicity, since many herbicides undergo natural degradation reactions in the environment that do not lead to mineralization but to the formation of new species potentially more toxic and stable than the precursors [1][2][3][4][5]. The evaluation of the degradation pathway and the structures and toxicity of the degradation products is therefore of paramount importance.The natural degradation of sulfonylurea herbicides takes place through aqueous hydrolysis reactions [6 -8], microbial processes (mainly occurring in soils) [9 -11], or photodegradation reactions [1-3, 5, 12-14]. These processes in surface waters and in soil are concomitant [7,15,16].HPLC-DAD-MS/MS methods are employed here to investigate and compare the hydrolytic and photoinduced degradation pathways of aqueous solutions of tribenuron methyl (methyl [2-4-methoxy-6-methyl-1,3,5-triazin-2-yl(methyl)carbamoyl sulfamoyl]benzoate) (Scheme 1), largely used against broad-leaved weeds in crops of cereals and in particular of rice.TiO 2 assisted photodegradation often leads to complete mineralization and can be used to dissipate pollutants in remediation strategy [17][18][19][20]. We are interested here to study the natural photodegradation of tribenuron methyl in...

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