Methods for studying pesticides migration: analysis, comparison, and recommendations for use in assessing the risk of pesticides impact on groundwater

Abstract

Groundwater pollution with pesticides has affected every country on every continent. An important challenge for researchers and regulatorу bodies in all countries is to develop methods and tools for predicting the risks to groundwater that are associated with pesticide use. In this paper, the generally accepted methods for studying pesticides migration are reviewed and analyzed from the point of view of their applicability for assessing the risk of pesticides impact on groundwater. Using examples, it is shown that the available methods may be divided into two categories, direct and indirect ones. The indirect methods (mobility indices and field studies of pesticide migration) make it possible to compare the migration ability of a pesticide molecule and to determine the depth of penetration of the pesticide into the soil. The direct methods (modeling, lysimetric studies, and monitoring) provide for the determination of pesticide concentrations in groundwater or groundwater leachate, which makes such methods useful in assessing the risk of pesticide use. Thus, by comparing the measured pesticide concentrations in water with acceptable threshold values, it is possible to determine the risk level of a pesticide. Examples of calculating the mobility indices indicate that their estimates differ from each other. Disadvantages of migration field experiments are related to analytical problems and to the short duration of a study. Modeling the migration of pesticides is an effective tool that makes it possible to quickly determine pesticides concentration of in water runoff and to identify the pesticides that can pollute groundwater under specific soil and climatic conditions. Calculations show that for 40 pesticides out of 180 licensed for use in the Russian Federation, their predicted concentrations exceed 1 µg/l. The second method that allows to directly determine concentrations in leachate is lysimetric experiments. A long-term study of the migration of 4 pesticides showed that all toxicants migrate beyond the soil profile. A third useful tool is pesticides monitoring in groundwater. Further development and dissemination of this method for controlling pesticides in groundwater is an important task for the regulatory authorities and the scientific community of the Russian Federation in the near future.