Sorption and Leaching Potential of Acidic Herbicides in Brazilian Soils

Abstract Leaching of acidic herbicides (2,4-D, flumetsulam, and sulfentrazone) in soils was estimated by comparing the original and modified AF (Attenuation Factor) models for multi-layered soils (AFi). The original AFi model was modified to include the concept of pH-dependence for K d (sorption coefficient) based on pesticide dissociation and changes in the accessibility of soil organic functional groups able to interact with the pesticide. The original and modified models, considering soil and herbicide properties, were applied to assess the leaching potential of selected herbicides in three Brazilian soils. The pH-dependent K d values estimated for all three herbicides were observed to be always higher than pH-independent K d values calculated using average K oc data, and therefore the original AFi model overestimated the overall leaching potential for the soils studied.