Chlorothalonil, Endosulfan Degradation Dynamics In The Soil And On Soil Microbial Community Diversity,

Pesticides are used all over the world to protect plants by controlling or destroying weeds, insects, fungi and other pests. As most of them end up in the soil either during or after use, their fate in this medium were studied. Microbial degradation is the primary route for loss, and is therefore the key process affecting the dynamics of pesticide residues in soil. Both the accumulation of pesticides in the soil and their dispersion in the environment depend chiefly on the characteristics and overall functioning of the ecosystem and the characteristics of the pesticide itself. Laboratory methodologies have been used widely to assess effects of pesticides on key species of soil organisms or particular soil processes. In this study, the degradation of two commonly used pesticides (chlorothalonil and endosulfan) in soil and their influences on soil microbial diversity were investigated. The results were summarized as follows.chlorothalonil in soil was degraded rapidly and its half-lives at concentrations of 1.5, 3.0, and 6.0mg/kg were measured to be 5.1, 4.9, and 4.4 d, respectively. The soil microbial population was significantly inhibited at 3 d after chlorothalonil (3.0 and 6.0 mg/kg) treatments, and Simpson and McIntosh indices were much lower than those of the control, and afterwards the inhibitory effect was decreased gradually. Soil microbial diversity was recovered to the level of the control at 21 d. No significant inhibition on Shannon index was observed throughout the experiments, indicating that chlorothalonil application would not affect the richness of soil microbial species.The degradation of endosulfan in soil was slow and its half-lives at levels of 3.0, 6.0 and 12.0 mg/kg were measured to be 21.9, 32.2 and 33.5 d, respectively. The soil microbial population was significantly inhibited at 16 d after endosulfan treatments, and Simpson and McIntosh indices were much lower than those of the control. Soil microbial diversity was recovered to the level of the control at 64 d. Throughout the experiments, no significant inhibition on Shannon index was observed, indicating that endosulfan application would not affect the richness of soil microbial species.The degradation of endosulfan and chlorothalonil in soil was inhibited by one another. The half-lives of chlorothalonil (3.0 mg/kg), in combination with endosulfan at concentrations of 3.0, 6.0, and 12.0 mg/kg, were measured to be 7.0 d, 7.9 d, and 8.9 d, respectively. Compared with the controls (5.8 d), the half-lives were prolonged 1.2 d, 2.1 d and 3.1 d, respectively. The results showed that the degradation of chlorothalonil was inhibited significantly by endosulfan, and the inhibitory effect was increased with the concentration of endosulfan. Similarly, the half-lives of endosulfan, in combination with chlorothalonil (3.0 and 6.0 mg/kg), were measured to be 44.4 d and 56.8 d, respectively. Compared with the control (31.8 d), the half-lives were prolonged 12.6 d, 25.0 d, respectively. The results showed that the degradation of endosulfan (6.0mg/kg) was inhibited significantly by chlorothalonil (3.0 and 6.0 mg/kg), and the inhibitory effect was increased with the concentration of chlorothalonil.