The Environmental Risk Assessment of Herbicide Glyphosate on Various Chinese Cultivated Soils

Glyphosate is the herbicide widely used in China. However, little is known on the processes governing the environmental fate of glyphosate in soils and its environmental risk for groundwater. Laboratory experiments were performed to evaluate the degradation, adsorption, and leaching behavior of glyphosate in three agricultural soils with high sand content and different soil organic carbon content. Glyphosate degraded very fast in soils, the half-lives of glyphosate for the three soils were between 3.3 d-6.9 d, and the main metabolite of glyphosate was amino methyl phosphonic acid (AMPA). The adsorption coefficient (K_F) values for the three soils were were 93.99 (loam), 89.31 (clay) and 61.05 (sand), which may mean that the organic matter is not the key for glyphosate adsorption on soil. Leaching tests, performed in manually packed soil glass-plate, indicated that glyphosate moved very slowly on the three types of soil thin layer, it mainly stayed at the zone of 0-2 cm. Thus, the leaching behavior of glyphosate coincided well with the results of the batch sorption and degradation experiments. All the data showed that glyphosate had a low potential threat to groundwater.