The objectives of this review are to summarize existing information on the occurrence of pesticides In groundwater and processes resulting in their detection; to identify existing technologies, and to describe missing information needed to make assessments arid predictions. Validated data on the occurrence of pesticides in groundwater are still limited. Pesticides can reach groundwater following normal agricultural usage and improper disposal and handling. Three frequently detected pesticides, aldlcarb, atrazine, and DBCP, are considered in detail, while other reported occurrences are summarized. r4obi1ity and transformation processes that determine the amount ot a pesticide actually reaching groundwater are described. Transformation processes include microbial metabolism and chemical reactions. While these processes are wel.1 researched for the root zone, less data are available on the subsoil and saturated zone. Other factors influencing the rate and amount of pesticide infiltration include the soil—subsoil—groundwater structure, depth of groundwater, macropore flow, and rainfall or water management practices. An attempt is made to quantify the pesticide properties and field conditions to predict their potential for leaching. Experimental and mathematical models are described and the importance of well designed field studies is emphasized.
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