Abstract
Triazine-2-14C metsulfuron–methyl is a selective, systemic sulfonylurea herbicide. Degradation studies in soils are essential for the evaluation of the persistence of pesticides and their breakdown products. The purpose of the present study was to investigate the degradation of triazine-2-14C metsulfuron–methyl in soil under laboratory conditions. A High Performance Liquid Chromatograph (HPLC) equipped with an UV detector and an on-line radio-chemical detector, plus a Supelco Discovery column (250 x 4.6 mm, 5 μm), and PRP–1 column (305 x 7.0 mm, 10 μm) was used for the HPLC analysis. The radioactivity was determined by a Liquid Scintillation Counter (LSC) in scintillation fluid. The soil used was both sterilized and non-sterilized in order to observe the involvement of soil microbes. The estimated DT50 and DT90 values of metsulfuron-methyl in a non-sterile system were observed to be 13 and 44 days, whereas in sterilized soil, the DT50 and DT90 were 31 and 70 days, respectively. The principal degradation product after 60 days was CO2. The higher cumulative amount of 14CO2 in 14C- triazine in the non-sterilized soil compared to that in the sterile system suggests that biological degradation by soil micro-organisms significantly contributes to the dissipation of the compound. The major routes of degradation were O-demethylation, sulfonylurea bridge cleavage and the triazine “ring-opened.”
Highlights
The environmental fate of pesticides in the soil is viewed with great concern today, due to the potential effects on surface and ground water quality
The different rates of mineralization indicate that the phenyl moiety is more susceptible to microbial attack than the triazine moiety on the molecule [18,19]
The dissipation of metsulfuron-methyl in the soil involves both chemical and microbial processes, and this is true for other sulfonylurea herbicides as well
Summary
The environmental fate of pesticides in the soil is viewed with great concern today, due to the potential effects on surface and ground water quality. The rate of mobility and degradation in the soil are the most important processes that determine the fate of pesticides in soils. Degradation studies in soils are essential for the evaluation of the persistence of pesticides and their breakdown products. Data on the rate of degradation are extremely important as they permit prediction of the levels likely to remain in soil and assessment of potential risk associated with exposure. Microbial degradation of pesticides should be studied under field conditions but this is often dogged by problems due to the interplay of several factors of spatial and temporal variability. Laboratory degradation studies have the merit of being carried out under controlled conditions which allow for the measurement of PLOS ONE | DOI:10.1371/journal.pone.0138170 October 5, 2015
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