Impacts Of Chlorothalonil On Degradation Behavior Of Chlorpyrifos, Butachlor

Pesticides are purposefully introduced into agricultural systems for the protection of crops against harmful organism. A series of side effects on environmental quality, safety of agricultural products, and human health caused by pesticide residues has been reported. There is an increasing concerns on risk assessment of pesticide residues, and a great deal of studies have been conducted to examine the fate of pesticides in the environment. However, little information is available to describe fate of multiple pesticides co-existed in the environment.In this study, chlorpyrifos, chlorothalonil and butachlor were choosed as models of insecticide, fungicide and herbicide to examine their degradation behaviors alone and in combination.The data obtained in this study indicated that the degradation curves of chlorpyrifos, chlorothalonil and butachlor in soil were fitted to the first-order equation. The degradation rate constants of chlorpyrifos, chlorothalonil and butachlor at low concentration were 0.0330, 0.2092 and 0.1013, respectively. The corresponding half-lives for chlorpyrifos, chlorothalonil and butachlor were calculated to be 21.0d, 3.3d and 6.8d, respectively. The half-lives of chlorpyrifos, chlorothalonil and butachlor at higher concentration were 26.2d, 3.5d, 7.2d, respectively. The degradation rate of chlorpyrifos at low concentration was significantly (P<0.05) faster than that at higher concentration in soil, whereas no significant difference for chlorothalonil and butachlor degradation was observed between low and higher concentrations.The degradation rate constants of chlorpyrifos combined chlorothalonil at low and high levels were measured to be 0.0264, 0.0246 with half-lives of 26.3d, 28.2d, respectively. Compared to those for chlorpyrifos alone existed in soil, the degradation of chlorpyrifos was slightly inhibited by the addition of chlorothalonil at high concentration. A similar effect of chlorothalonil on butachlor degradation was observed. The degradation rate constants of butachlor combined with chlorothalonil atlow and high levels were determined to be 0.0846, 0.0563, and their half-lives were 8.2d, 12.3d. The date indicated that degradation of butachlor in soil was indistinctively inhibited by the existing of chlorothalonil at low concentration, and was significantly inhibited by the existing of chlorothalonil at high concentration. It has been reported that soil microorganisms are inhibited by the addition of chlorothalonil. It is likely that the inhibitory effect of chlorothalonil on soil microorganisms caused the decreased degradation of chlorpyrifos and butachlor.The results suggested that the degradation behaviours of multiple pesticides co-existing in soil differ from those of single in soil. The difference depends on the amount and species of the pesticide existing together.