Skip to main content
ARS Home » Research » Publications at this Location » Publication #61457
Title: PRODUCTS AND KINETICS OF CLORANSULAM-METHYL AEROBIC SOIL METABOLISM

Author
item WOLT, JEFFREY - DOWELANCO
item SMITH, JOELENE - DOWELANCO
item SIMS, GERALD
item DUEBELBEIS, DENNIS - DOWELANCO

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cloransulam-methyl is a new sulfonamide herbicide used to control broadleaf weeds in soybean. Proposed application methods include both soil and foliar treatments. Very low rates are proposed. Our study examines the fate of the compound (degradation rate and identity of degradation products) in soil. This is the first and only such study available for this compound at this time. The results of the study suggest that the time for half of this herbicide to dissipate ranged from 9 to 28 days in 18 different soils. Although three degradation products were identified, most of the cloransulam-methyl became strongly bound to soil organic matter. The results of this study will be used to evaluate this experimental compound for registration, and will help determine how it is used by growers. Basic information about the interactions between sulfonamide herbicides and soils are revealed, and a new procudure for characterizing bound (to organic matter) herbicides is introduced.

Technical Abstract: Cloransulam-methyl [CAS 147150-35-4] aerobic soil metabolism was investigated to ascertain rates and products of environmental dissipation. Cecil loamy sand and Hanford loam fortified with 66 ng cloransulam-methyl per g soil (14C-labeled in either the 7, 9-position of the pyrimidine ring of uniformly labeled in the phenyl ring) were incubated in the dark at 25 degrees C and 100-kPa moisture potential under positive 02 pressure. Cloransulam-methyl exhibited a biphasic pattern of degradation over the 357-day time course of the study. Average aerobic soil half-lives were 9 and 13 days, respectively, on Cecil and Hanford soils when data were fit to a nonlinear two-compartment model. Rates of cloransulam-methyl degradation decreased about 10-fold when soils were incubated at 5 degrees C or when sterilized by gamma-irradiation. Mineralization accounted for up to 10% of applied 14C by 357 days after treatment (DAT). Extractable metabolites (cloransulam, 5-hydroxycloransulam-methyl, and 5-hydroxycloransulam) occurred at maximum concentrations of 25, 9, and 8 ng g-1, respectively, and were significantly less phytotoxic than the parent molecule. Bound residue accounted for 76% of applied 14C on Cecil loamy sand at 367 DAT. The pool of bound residues was reduced to < 8% of applied 14C by sequential extraction with acetone/1 M HC1, citrate-dithionate, and 1 M NaOH. Additionally, degradation rate and sorptivity were investigated on sixteen soils fortified with cloransulam-methyl (189 ng g-1) and incubated in the dark for up to 55 days at 25 degrees C and 100-kPa moisture potential under positive 02 pressure. Apparent first-order half-lives ranged from 13 to 28 days.