SORPTION OF ATRAZINE ON SOIL CLAY COMPONENTS

Distribution coefficients for sorption and desorption of atrazine were determined for all combinations of three chemical treatments and four particle size fractions prepared from a typical soil clay. Organic and inorganic components were 11 and 89% of the mass and contributed 68 and 32% of the affinity of the soil clay for atrazine, respectively. Organic matter associated with the coarse clay had substantially greater affinity for atrazine and exhibited greater sorption-desorption hysteresis than organic matter associated with the fine clay. Silicate minerals had a moderate affinity for atrazine and exhibited little sorption-desorption hysteresis. Free Fe compounds interacted with silicate minerals in the coarse and medium clay to reduce affinity of the silicate minerals for atrazine. The results suggest that atrazine is primarily retained on silicate clays by physical sorption but that both physical sorption and chemisorption contribute to retention of atrazine by soil organic matter.