ABSTRACT
298Groundwater contamination resulting from leaching of pesticides is a growing concern in major agricultural regions of the world. Leaching of soil applied herbicides can be affected by edaphic factors, climatic conditions, physical-chemical properties of the active ingredient and formulations, crop management practices, and herbicide application techniques. Principal methods of studying pesticide leaching include leaching columns, soil thin-layer chromatography, lysimeter, residue monitoring, and computer modeling. For leaching prevention, it is usually difficult to modify climatic conditions and soil related factors in a given agricultural region. Therefore, focuses should be on selecting proper herbicides, improving formulations, adapting appropriate crop management practices, and modifying application techniques. Leaching characteristics of many herbicides have been well documented. Studies about impacts of crop managements on leaching are often inclusive. Limited information is available on leaching minimization by improving formulations and using adjuvants. However, studies in this area have increased considerably over the last decade. Both naturally occurring and synthetic additives or adjuvants have been tested to reduce herbicide leaching. Active charcoal, pine kraft lignins, and starch granulation have been shown to decrease leaching of herbicides. Synthetic polymers and surfactants have also shown potential for reducing leaching. The additives in formulations or adjuvants may act not only as controlled release agents that release herbicide in small amounts over prolonged period but also function as agents to inhibit movement of herbicides in soil. Another approach to reduce herbicide leaching is enhancing herbicide efficacy thus decreasing herbicide input and amount of herbicide available for leaching. Additional measures such as use of postemergence herbicides, application timing in relation to rainfall, and improvement of application technology may also contribute toward minimized leaching.
