Groundwater, Persistence, Pesticides, Adsportion, Mobility
Studies were conducted to determine the environmental persistence of the rice pesticides triclopyr, 2,4-D, benomyl and quinclorac. Triclopyr half-lives ranged from <7 d to >100 d depending on depth within the soil profile and clay content. Triclopyr persistence increased as depth within the profile increased and clay content increased. The benomyl metabolite MBC was present at greater than 50% of the initial amount after 9 months in the field. In simulated carryover field studies quinclorac exhibited the greatest potential for injury to subsequent rotational crops. Cotton and soybean growth was reduced when planted at four weeks after quinclorac application. The adsorption of triclopyr to three soils was measured by the batch equilibrium technique. Freundlich isotherms were linear and resulted in Kf values of 1.60, 1.41, and 2.75 for Crowley silt loam soil from depths of 0, 0.2, and 0.6 m, respectively, within soil profile. Soil thin-layer chromatography of triclopyr resulted in Rf values of 0.42, 0.69, and 0.40 for the Crowley silt loam soil from 0, 0.2, and 0.6 m depths. In controlled temperature and water potential degradation studies, triclopyr and 2,4-D degraded more rapidly at 3 0 C than at 15 C. The degradation rates of the two herbicides responded oppositely to water potential. 2,4-D degraded more rapidly under anaerobic conditions, whereas triclopyr degraded more rapidly under aerobic conditions.
Johnson, W. G.; Lavy, T. L.; Mattice, J. D.; Skulman, B. W.; Talbert, R. E.; and Smith, R. J.. 1991. Water Quality as Affected by Pesticides in Rice Production. Arkansas Water Resources Center, Fayetteville, AR. PUB156. 42