Effects of adsorption on degradation and bioavailability of metolachlor in soil
The ability of soil to adsorb metolachlor strongly influences its environmental fate, but little information is available on the correlation of its soil adsorption with degradation and bioavailability. The present study was conducted to characterize adsorption, degradation and bioavailability of metolachlor in five soils with different properties, and to investigate the effect of soil adsorption on degradation and bioavailability. Metolachlor was weakly adsorbed to the tested soils with adsorption coefficients ranging from 0.36 to1.18 μg1-n mLn g-1, suggesting its potential to move downward with percolating water. Adsorption followed a Freundlich isotherm and was positively correlated with soil organic matter (OM) content (p < 0.01). Degradation of metolachlor in soils obeyed the first-order kinetics, yielding the half-life varying from 37.9 to 49.5 days, which was significantly influenced by soil OM content (p < 0.01). The prolonged half-life by sterilization indicated that biodegradation was the dominant pathway for metolachlor degradation in soils. Uptake and bioaccumulation of metolachlor in soils by Eisenia foetida was also mainly controlled by soil properties, especially OM. Adsorption coefficients were negatively related to half-lives (p < 0.01) and bioaccumulation factors (p < 0.05), indicating that adsorption coefficients might be useful for predicting degradation and bioavailability of metolachlor in soils.