| Pesticides are of great environmental concern due to their widespread use in the (?)ast several decades and their potential toxic effects. Clomazone is a new herbicide, the environment fate of clomazone and the ecotoxicological effects of clomazone were studied in this paper. Some biomarkers of earthworm were also chosen in the study.The hydrolysis and photolysis of clomazone in aqueous solutions and natural water were assessed under natural and controlled conditions in this work. Hydrolysis experimental results showed that no noticeable hydrolysis occurred in aqueous buffer solutions (25±2℃, pH4.5±0.1, pH7.4±0.1, pH9.0±0.1;50±2℃, pH4.5±0.1, pH7.4±0.1) or in natural water up to90d, and the half-life of clomazone in pH9.0±0.1buffer solutions at50±2℃was50.23d. The rate of photodecomposition of clomazone in aqueous solutions followed first-order kinetics both in UV radiation and natural sunlight. The degradation rates were faster under UV light than sunlight, with the half-lives of51.35-58.75min and86.65-135.92d, respectively. Furthermore, it was found that the degradation of clomazone would be enhanced by the addition of the photosensitizers such as H2O2and riboflavin in natural sunlight. Under UV light, four major photoproducts, which identified as2-Chlorobenzamide, N-hydroxy-(2-benzyl)-2-methylpropan-amide,2-[2-phenol]-4,4-dimethyl-3-isoxazolid inone and2-[(4,6-dihydroxyl-2-chlorine phenol)]-4,4-dimethyl-3-isoxazolidinone. were detected by HPLC-MS.Contact filter paper test and artificial soil test (OECD) were used in this paper to study the acute toxic tests of clomazone on earthworm. Results showed that the LC50of clomazone on earthworms was respectively5.625μg·cm-2(48h)by contact filter paper test, as well as174.924mg·kg-1(7d) and123.437mg·kg-1(14d) by artificial soil test.Boss soil test was used to study the effect of clomazone on earthworm growth, survival, production. Results showed that the lower clomazone concentration(5mg·kg-1, p<0.01) could significantly inhibited the reproduction of earthworm. The significant dose-response relation were found among clomazone concentration and inhibition rate of earthworm growth and reproduction, and the reproduction was more sensitive.Effects of clomazone at different concentration on activity of antioxidative enzymes were studied with an artificial soil test after14days of exposure. During the exposure period, the SOD activity had an initial significant increase (p<0.05) and followed by a gradual decrease. When the earthworms were exposed to10mg kg-1and20mg·kg-1of clomazone, the activity of SOD increased significantly with induced rate of19.56%and13.03%, respectively. The activity of CAT had no significant change at the low concentrations (10mg·kg-1,20mg·kg-1), and was induced at the higher concentrations (40,80mg·kg-1) with induced rate of43.42%and68.08%, respectively. The content of T-AOC was inhibited first but induced, then recovering to the level of control gradually. The content of T-AOC exposed to the concentration of20mg·kg-1decreased significantly with inhibition rate of44.54%. The activity of GSH-Px was inhibited significantly during the period of exposure.Comet assay was used to test the genotoxicity changes of clomazone on earthworm coelomocytes. The results showed that clomazone could induce DNA damage of earthworm coelomocytes at different exposure concentration. The significant dose-effect relationships were found among clomazone concentration and tail DNA percent, OTM as well as tail length (p<0.01). The activity of antioxidative enzymes and DNA damage could be as biomarkers to indicate the direct toxic effect of clomazone on soil animals.The results indicated that photoreaction was an important dissipation pathway of clomazone in natural environment. Clomazone had direct toxic effects on earthworm. The reproduction and DNA damage of clomazone on earthworm will be used as sensitive biomarkers. |
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