Dissipation of chlorpyrifos in pakchoi-vegetated soil in a greenhouse

The dissipation of chlorpyrifos in pakchoi-vegetated soil was investig ated in the summer and autumn in a greenhouse and field, respectively. The dissi pation of chlorpyrifos in pakchoi-grown soil was comparatively described by fitt ing the residue data to seven models (1st-order, 1.5th-order, 2nd-order, RF 1st- order, RF 1.5th-order, RF 2nd-order, and bi-exponential or two-compartment model s). Statistical analysis was performed using the SPSS 11.5 statistical package. The bi-exponential model was selected as the optimal model according to the coef ficient of determination r2. The dissipation half-lives (DT50) of chlorpyrifos i n pakchoi-vegetated soil at the recommended dose in the summer and autumn, calcu lated by the bi-exponential model, were 0.6 and 1.2 d in a greenhouse, 0.4 and 1 .0 d in a field, respectively; the corresponding values at double dose were 1.2 and 2.1 d in a greenhouse, 0.5 and 1.3 d in a field, respectively. The kinetic d ata indicate the dissipation of chlorpyrifos in pakchoi-grown soil in a greenhou se is slower than that in a field, and dissipates slower in the autumn than in t he summer.