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Kinetics of Carbosulfan Degradation in the Aqueous Phase in the Presence of a Cosolvent

Institute of Terrestrial Ecology, Swiss Federal institute of Technology Zürich, Grabenstr. 3, CH-8952 Schlieren, Switzerland.

^* Corresponding author (furrer{at}ito.umnw.ethz.ch).

ABSTRACT

The degradation of the carbamate pesticide carbosulfan (2,3-dihydro-2,2-dimethyl-7-ben/ofuranyl [(dibutylamino)thio]methylcarbamate] was investigated in aqueous buffer solutions (pH 3.0–7.0) containing low (1%, v/v) and high (10–60%, v/v) concentrations of acetonitrile. The cleavage of the carbamyl N-S bond yields carbofuran (2,3-dihydro-2,2-dinicthyl-7-benzofuranol methylcarbamate). The rate of carbosulfan degradation depends on pH, the initial concentration of carbosulfan, acetonitrile concentration, shaking speed, ionic strength, and temperature. Carbosulfan was completely dissolved only in solutions with high acetonitrile concentrations. The concentration of acetonitrile needed for the complete dissolution of carbosulfan depended on the initial concentration of carbosulfan. In this case, the degradation is a pseudo-second-order reaction with respect to the concentration of carbosulfan and hydronium ion. The degradation reaction is promoted by the hydronium ion. In the case of low acetonitrile concentrations, where carbosulfan was not completely dissolved, the overall kinetics depend also on the slow dissolution process. The degradation of carbosulfan probably is not a pure hydrolysis reaction, but a protonation-intermolecular rearrangement reaction. The results indicate that the abiotic degradation of carbosulfan in natural waters is a very slow process when organic solvents and minerals are absent or present in only minor concentrations.

J. Wei, present address: Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.

Received for publication September 20, 1999.