Enzyme immunoassay determination of atrazine degradation in soil: Moisture,sterilization, and storage effects

Enzyme immunoassay (EIA) microtiter plate analysis was used to quantify atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5 triazine), fortified at 0, 50, and 500 or 549 ng/g, to Baxter and Maury silt loam soil sampled in 1965 and 1991. In the first experiment, aged soils (sampled in 1965 and stored air‐dried) were fortified with atrazine and then incubated in the dark at 0, 75, 150, 225 and 300 g/kg moisture for 15, 80, 154, and 289 d. In a second experiment, fresh soils were fortified with atrazine and incubated in the dark at 0, 150, and 300 g/kg moisture for 9, 15, 35, 55, 83, and 145 d. One half of the treatments in the second experiment were sterilized with 497 ng/g HgCl₂. Twenty milliliters of acetonitrile: water (9: 1) was used to extract 4 or 5 g of soil by vortex mixing at each sampling date. The soil extract was diluted, 80 μl incubated with antibody‐coated wells, and color development read using a microtiter plate reader. Recovery of atrazine from soil was 98% 5 d after fortification. Pesticide recoveries and first‐order degradation rates were dependent on the freshness and moisture content of the soil sample. Pesticide degradation was slower and recoveries higher in soil that had been air dried and stored since 1965, prior to fortification. More atrazine was extracted from soil maintained at 0 g/kg moisture than from soil maintained at 300 g/kg moisture over time.