Environmental Behavior Of Microencasulated Chlorpyrifos In Soil And Its Effects On Soil Microbial Communities

Chlorpyrifos is a broad-spectrum organophosphorous insecticide widely used to control agricultural pests. Microcapsule (MC) has supposed to be a substitute for the conventional formulations of chlorpyrifos, such as emulsifiable concentration (EC). For the evaluation on the environmental safety of chlorpyrifos-MC, its environmental behaviors in soils and effects on soil microbial communities were studied in this dissertation. The risk that the chlorpyrifos-degradation ability of soil was enhanced by application of MC formulation was also investigated. The results were summarized as follows:1. Environmental behaviors of chlorpyrifos-MC in soilThe chlorpyrifos residues in MC-treated soils decreased slowly before60d, and the residual periods with the fortification levels of5and20mg/kg reached120d. The out-capsule residues of chlorpyrifos in MC-treated soil could be stabilized in the period ranging from15to60d. The chlorpyrifos residues decreased via a first-order model in EC-treated soils, and half-lives of chlorpyrifos with the fortification levels of5and20mg/kg were6.19and5.92days, respectively.The adsorption isotherms of chlorpyrifos-MC and chlorpyrifos-EC on soil could be described well with the Freundlich equation. The constants Kf values for MC on soil and sand were355.505and225.198, and for EC were359.065and94.117, respectively. The amounts of chlorpyrifos under EC formulation that desorbed from soil in four desorption steps were decreased sequentially, while those under MC were not stable. The vertical mobility of two formulations of chlorpyrifos in sand column were obvious. It was leachable of chlorpyrifos-EC in soil column, however, the vertical mobility of chlorpyrifos-MC could not be observed under the same leaching condition.2. Effects of chlorpyrifos-MC on soil microbial communitiesSoil bacterial community structures in the MC-treatments with5or20mg/kg chlorpyrifos were not changed throughout the whole experimental period, while the structures were significantly changed in EC-treatments with two concentrations of chlorpyrifos before120d. And a period of over240d was needed for the EC-treated soil to recover bacterial community to the level of the control.Fungal community structures were significantly changed in soils treated with two formulations of chlorpyrifos. Soil fungal community structure in the MC-treatment with5mg/kg (or20mg/kg) chlorpyrifos could recover to the level of the control after15d (or90d), while the structure in the EC-treatment with5mg/kg (or20mg/kg) chlorpyrifos recovered after30d (or90d).3. Effects of chlorpyrifos-MC on soil respiration and enzymes activityChlorpyrifos-MC and chlorpyrifos-EC had different effects on soil respiration and enzymes activities. The soil respiration and urease, catalase, acid phosphatase, and alkaline phosphatase activities could be enhanced by5mg/kg chlorpyrifos in MC-treatment, and the effective period to the catalase, the acid/alkaline phosphatase could be up to120d. Though the respiration, the activities of catalase and phosphatases could be enhanced by20mg/kg chlorpyrifos in MC-treatment, the activities of urease and sucrase were inhibited. The soil respiration and the activities of enzymes mentioned above were inhibited by chlorpyrifos-EC, and the inhibition efficiency increased with the increase of the chlorpyrifos concentration. However, the temporary-affected respiration and enzymes activities in EC-treatments could recover to the control level after30d.4. Chlorpyrifos-degradation ability of soil microorganisms induced by chlorpyrifos-MCA total of25chlorpyrifos-degradation strains were isolated from the soils in treatments of chlorpyrifos-MC (4bacteria and12fungi) and chlorpyrifos-EC (2bacteria and7fungi). All degradation strains were grouped into16different types based on the enterobacterial repetitive intergenic consensus PCR (ERIC-PCR) pattern similarities. Strains isolated from MC-and EC-treated soils belonged to14and8ERIC-types, respectively. Six strains that were isolated from MC-and EC-treated soils belonged to similar ERIV-types. All ERIC-type strains were similar to nine known species according to the BLAST analysis at the NCBI website. Strains Alternaria tenuissima, Enterobacter cloacae, and Bacillus thuringiensis were firstly revealed to have a chlorpyrifos-degradation ability.The half-lives of chlorpyrifos in two soils, which had been treated with chlorpyrifos-MC and chlorpyrifos-EC (20mg/kg) for240day respectively, were5.3and5.9d. The former differed significantly from control (P<0.05), and there was no difference between the latter and control (P>0.05).