Because of the importance of soil in biologically reducing the quantity and retarding the rate of pollutant movement into groundwater, this laboratory study was initiated to evaluate the adsorption, mobility, and degradation of large concentrations of the pesticide atrazine, methyl parathion, terbacil, trifluralin, and 2, 4-D in soils representing four major soil orders in the United States. Solution concentrations ranged from zero to the aqueous solubility limit for each pesticide. The mobility of each pesticide increased as its concentration in the soil solution phase increased. These results were in agreement with the adsorption isotherm data. Pesticide degradation rates and soil microbial populations generally declined as the pesticide concentration in soil increased; however, some soils were able to degrade a pesticide at all concentrations studied, while others remained essentially sterile throughout the incubation period (60 to 80 days). As shown by measurements of 14CO2 evolution, total CO2 evolution was not always a good indication of pesticide degradation. Several pesticide metabolites were formed and identified. Bound residues of trifluralin and atrazine at the end of the incubation period appeared to be related to types of metabolites formed. The observed increase in pesticide mobility for large pesticide concentrations in the soil invalidates, in many cases, the usefulness of the existing low concentration data base for designing pesticide waste disposal sites.

Prepared for U.S. Environmental Protection Agency, Office of Research and Development, Municipal Environmental Research Laboratory, Cincinnati, Ohio, submitted by the University of Florida, Gainesville, under grant no. R-803849. Includes bibliographical references (pages 103-112).