Adsorption of atrazine and alachlor to aquifer material and soil

Atrazine [6-chloro-N-ethyl-N′-(1-methyl)-1,3,5 triazine-2,3-diamine] and alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl) acetamide] are agricultural herbicides used in large quantities and, as a consequence, are common contaminants in groundwater and surface water. The retention of these herbicides in soils and their degradation in aqueous environments is highly dependent upon their adsorption to solid surfaces. The adsorption of atrazine and alachlor was investigated on three typical Kansas and underlying aquifers known to be vulnerable to contamination. More alachlor was adsorbed to the soils and sediments than atrazine. The adsorption coefficients for atrazine were 2 to 5 times higher for soils than for aquifer sediments. For alachlor, the adsorption coefficients were 4 to 20 times higher for soil than for aquifer solids. Both linear and Freundlich isotherms represented the adsorption data well in all cases. The slope of the Freundlich isotherms, 1/n, was close to one, with the exception of alachlor adsorption onto the Topeka aquifer sediment (1/n = 0.67). The K _d values found in these studies were comparable to the lower range of those reported in the literature.