Wu Xiaomao

Adsorption, persistence and bioavailability of napropamide in soil

Soil adsorption is generally recognized as a key to controlling the fate and transports of a pesticide in environment, and it also affects the persistence and bioavailability of pesticide. The present study was conducted to investigate the adsorption, persistence and bioavailability of the herbicide napropamide in soils with different properties using high-performance liquid chromatography (HPLC). Soil adsorption of napropamide was determined using the batch equilibration technique described by a Freundlich isotherm equation with correlation coefficients (r)>0.99. Regression of adsorption coefficient (Kf) against selected soil indicates that organic matter (OM) content was the most influential factor governing adsorption of napropamide (P < 0.01) followed by clay content (P < 0.1). Napropamide had relatively longer persistence in soil, and its degradation in soil followed the first-order kinetics with the half-lives (t50) varying from 61.3 to 97.6 d, which appeared to decrease with soil OM content. The persistence of napropamide in sterilized soil was 2.09-3.65 times longer than that in the corresponding unsterilized soil, which indicated that microorganisms were the predominant contributors for the dissipation of napropamide in soil. Uptake and bioaccumulation of napropamide in soil by earthworm Eisenia foetida also mainly depended upon soil properties, especially the level of OM content (P < 0.05). The Kf values of napropamide were negatively correlated with t50 (r=-0.885, P < 0.05) and the bioaccumulation factor (r=-0.796, P < 0.05). The corresponding linear regression equation was t50=94.210-3.535 Kf and BAF=0.264-0.014 Kf, respectively. The results here revealed the potential of using the adsorption coefficient Kf as the model to evaluate the persistence and bioavailability of napropamide in soil.