Products and Kinetics of Cloransulam-methyl Aerobic Soil Metabolism

Academic Article

Abstract

  • Cloransulam-methyl aerobic soil metabolism was investigated to ascertain rates and products of environmental dissipation. Cecil loamy sand and Hanford loam fortified with 66 ng of [14C]-cloransulam-methyl g-1 of soil were incubated in the dark at 25 °C and 100 kPa of moisture potential under positive O2 pressure for up to 357 days. Cloransulam-methyl exhibited a biphasic pattern of degradation. Aerobic soil half-lives were 9 and 13 days, respectively, on Cecil and Hanford soils for data fit to a two-compartment model and 16 and 21 days, respectively, for data fit to a first-order initial rate model. Degradation rates decreased ≈ 10-fold when soils were incubated at 5 °C or when sterilized by γ-irradiation. Evolved 14CO2 accounted for up to 10% of applied 14C. Metabolites (cloransulam, 5-hydroxycloransulam-methyl, and 5-hydroxycloransulam) occurred in acetone/acetic acid extracts at maximum concentrations of 25, 9, and 8 ng g-1, respectively, and were significantly less phytotoxic than the parent molecule. Bound residues accumulated up to 76% of applied 14C. Degradation rate and sorptivity were further investigated on 16 soils fortified with 189 ng g-1 of [14C] cloransulam-methyl and incubated for up to 55 days. Apparent first-order half-lives ranged from 13 to 28 days (mean ± SE = 18 ± 4 days). Apparent Kd values, produced using a two-step extraction, ranged from 0.19 to 4.89 L kg-1 for cloransulam-methyl. Cloransulam-methyl metabolites, when present, tended to exhibit lower Kd values than the parent molecule. Apparent Kd increased with time.
  • Authors

    Digital Object Identifier (doi)

    Author List

  • Wolt JD; Smith JK; Sims JK; Duebelbeis DO
  • Start Page

  • 324
  • End Page

  • 332
  • Volume

  • 44
  • Issue

  • 1