Organoclays as Soil Amendments to Increase the Efficacy and Reduce the Environmental Impact of the Herbicide Fluometuron in Agricultural Soils

The use of pesticides in agriculture has become a source of pollution of soil and water in the last decades. Extensive pesticide transport losses due to leaching and runoff produce nonpoint source contamination of soils and water. One of the soil processes that reduce pesticide transport losses is adsorption by soil particles; therefore, enhancement of pesticide retention by soil can be used as a strategy to attenuate the environmental impact of pesticides. In this work, organoclays were prepared by treating Wyoming montmorillonite (SWy-2) and Arizona montmorillonite (SAz-1) with different organic cations and were assayed as soil amendments to enhance the retention and reduce the leaching losses of the herbicide fluometuron [N,N-dimethyl-N-[3-(trifluoromethyl)phenyl]urea] in soils. Two agricultural soils from Southern Spain were selected for being high-risk scenarios of ground and surface water contamination. First, a batch adsorption study was conducted to identify organoclays with high affinity for fluometuron. Among the different organoclays assayed, spermine-treated Wyoming montmorillonite (SW-SPERM) displayed high and reversible adsorption of fluometuron and was selected as an amendment for subsequent persistence, leaching, and herbicidal activity experiments of fluometuron with unamended and amended soils. Amendment of the soils with SW-SPERM at rates of 1%, 2%, and 5% greatly enhanced fluometuron retention by the soils and retarded fluometuron leaching through soil columns. Incubation experiments revealed that the persistence of the herbicide in the amended soils was similar to that in unamended soils and that most of the herbicide was ultimately available for degradation. Bioassays demonstrated that the reduced leaching losses of fluometuron in soils amended with SW-SPERM may result in increased herbicide efficacy if heavy rainfall events occur shortly after herbicide application.