Microencapsulated chlorpyrifos: Degradation in soil and influence on soil microbial community structures

Abstract

Degradation kinetics of microencapsulated chlorpyrifos (CPF-MC) in soil and its influence on soil microbial community structures were investigated by comparing with emulsifiable concentration of chlorpyrifos (CPF-EC) in laboratory. The residual periods of CPF-MC with fortification levels of 5 and 20mg/kg reached 120days in soil, both of the degradation curves did not fit the first-order model, and out-capsule residues of chlorpyrifos in soil were maintained at 1.76 (±0.33) and 5.92 (±1.20) mg/kg in the period between 15 and 60days, respectively. The degradation kinetics of CPF-EC fit the first-order model, and the residual periods of 5 and 20mg/kg treatments were 60days. Bacterial community structures in soil treated with two concentrations of CPF-MC showed similarity to those of the control during the test period, as seen in the band number and relative intensities of the individual band on DGGE gels (p>0.05). Fungal community structures were slightly affected in the 5mg/kg treatments and returned to the control levels after 30days, but initially differed significantly from control in the 20mg/kg treatments (p<0.05) and did not recover to control levels until 90days later. The CPF-EC significantly altered microbial community structures (p<0.05) and effects did not disappear until 240days later. The results indicated that the microcapsule technology prolonged the residue periods of chlorpyrifos in soil whereas it decreased its side-effects on soil microbes as compared with the emulsifiable concentration formulation.