Behavior of Pesticides in Soils

Abstract

The behavior of pesticides in soils has been the subject of research long before pollution became a byword. In recognition that soil is the ultimate sink for most widely used pesticides, and given the impetus of recent public awareness of the quality of our environment, the past decades have marked much progress in the understanding of the fate and behavior of pesticides in soils. A strong case for the continued use or precipitate abandonment of agricultural pesticides is inappropriate. It is reasonable, however, to note the vitally important role pesticides have assumed in increasing the quantity and quality of foodstuffs, timber, and ornamental plants; in improving animal health; and in combating certain diseases transmitted to man. This chapter reviews the behavior of pesticides in soils from the standpoint of processes affecting pesticides (physicochemical and metabolic), the effect of pesticides on the soil microbiota, and the implications of these processes on persistence, bioactivity, and plant uptake. Adsorption, the most influential process affecting pesticides in soils, depends on both soil and pesticide properties. Other significant soil factors include total surface area, water content, temperature, and pH. Pesticide properties that are relevant include overall chemical character and configuration, dissociation constant, water solubility, charge distribution, and molecular size. Movement of the pesticides occurs by leaching, volatilization, or runoff. The importance of photodecomposition as a process degrading pesticides in soils is uncertain. Generally, photolysis occurs more readily for compounds in solution, with soil inhibiting the reaction.