Pesticide Removal In Natural Aquatic Systems

Pesticide occurrence in surface waters can be traced to several sources: agricultural runoff, industrial discharge, purposeful application, cleaning of contaminated equipment, and accidental spillage. Chlorinated hydrocarbons in aqueous solutions are readily adsorbed by clay materials. After adsorption, small fractions of some pesticides are gradually desorbed into the overlying water where the pesticide concentration is maintained at a dynamic equilibrium level. Drainage of clay-bearing waters from agricultural areas represents a continuous supply of pesticides to the aqueous solution. Desorption rates are not significantly affected by pH, temperature, salt and organic levels (Huang 1971).

The introduction of many new pesticides in recent years has created the need for reliable evaluation of the effects on the aquatic biota. The model ecosystem for these evaluations consists of glass aquaria arranged in a sloping soil-air-water interface (Metcalf, Sangha and Kapoor 1971). A food chain of plant and animal organisms, compatible with the environmental conditions simulated in the aquarium, is chosen for following radiolabeled DDT (labeled in the aryl rings with C14) and methoxychlor. Average data presented in Table 8.2.5 show a 13,000-fold increase in con-

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