The fate and mobility of chlorsulfuron was determined in several Γeld studies with 14C-labeled chlorsulfuron. A study comparing fall with spring applications (D100 g AI ha~1) to in-situ soil columns (35 cm depth) in neutral to alkaline soils (pH 6Γ9Γ8Γ2, OM 1Γ0Γ5Γ3) located in CO, ID and ND demonstrated that fall treatments did not persist longer into the following year than spring treatments. Mobility into the soil proΓle appeared to be initially faster following fall applications at the ID and ND sites, but di β erences between application seasons appeared to moderate with time. A Γeld-soil metabolism study conducted at Madera, CA on a sandy loam soil (pH 6Γ3Γ6Γ9 and 0Γ3Γ 0Γ4% OM with depth) with chlorsulfuron (D158 g AI ha~1) demonstrated rapid dissipation of chlorsulfuron (pseudo-Γrst-order half-life 18 days). No intact chlorsulfuron was found after the 120-day sampling. Major metabolites observed in this study were chlorobenzenesulfonamide (2-chlorobenzenesulfonamide) and triazine amine (4-methoxy-6methyl-1,3,5-triazin-2-amine), products of bridge cleavage, and O-desmethylchlorsulfuron
No intact chlorsulfuron was detected below the 0Γ15 cm layer at any sampling (maximum depth 60Γ 90 cm), but chlorobenzenesulfonamide and ring-opened carbamoyl guanidine (1-(2chlorophenylsulfonyl)-3-(ureido-imino)urea) were found at the 15Γ30 cm depth. In a similar study conducted on a silt loam soil in Moscow, ID (pH 6Γ1Γ6Γ9 and 2Γ2Γ1Γ0% OM with depth), overall dissipation was much slower than at Madera, CA due to the cooler climate (average soil temperature 8Γ6Β‘ versus 20Γ0Β‘). The initial rate of chlorsulfuron dissipation was similar (pseudo-Γrst-order half-life 18 days), but dissipation exhibited a distinctly slower second stage (half-life 109 days) not exhibited at Madera, CA. By the 370-day sampling no intact chlorsulfuron was detected. The chlorobenzenesulfonamide and triazine amine were the major metabolites found in this study, accounting for approximately 38 and 30%, respectively, of the initial chlorsulfuron at the last sampling (571 days). Other metabolites were found in lesser amounts, including Odesmethylchlorsulfuron, ring-opened carbamoyl guanidine, hydroxy triazine amine (4amino-6-methyl-1,3,5-triazine-2-ol), triazine urea ((4-methoxy-6-methyl-1,3,5-triazin-2-yl) urea), an undi β erentiated bound fraction and an unidentiΓed group of polar components. The presence of triazine urea indicates that soil-surface photolysis (or indirect photolysis) may have been operative. In the study in Moscow, ID, no intact chlorsulfuron was found below the 0Γ15 cm layer at any sampling (maximum depth 75 cm). Movement of total radioactive components was restricted to a maximum depth of 60 cm at Madera, CA and 50 cm at Moscow, ID. The overall water balance over the duration of both studies was negative, helping to explain the observed lack of leaching. The PRZM3 model was used to predict the distribution proΓle of chlorsulfuron at the Moscow, ID site for which the base case overpredicted leaching (down to 20Γ30 cm) and predicted the depletion of the surface layer, which did not occur. The prediction was improved by arbitrarily doubling the K oc value and using a slightly higher than measured soil bulk density.
1998 SCI (