PH06 Agrochemicals, Pesticides, Pharmaceuticals
Exhibit Hall
8:00 AM - Thursday
(PH064) Enhanced degradation of chloroacetanilide herbicides by polysulfide salts.
Bondarenko, S1, Gan, Jay1, 1 University of California, Riverside, CA, USA
ABSTRACT- Chloroacetanilide herbicides are widely used to control weeds in corn, soybean, and other row crops across the United States. Monitoring studies have shown widespread presence of chloroacetanilide herbicides in the hydrological systems including both surface streams and groundwater resources. In this study, we investigated the enhanced degradation of chloroacetanilide herbicides alachlor, propachlor, acetochlor, and metolachlor by polysulfide salts in water and soil. In the solution phase, amendment of sodium tetrasulfide drastically enhanced the disappearance of all chloroacetanilide herbicides, and the rate of enhancement followed an order propachlor > alachlor > acetochlor > metolachlor. When the initial herbicide and polysulfide concentrations were both at 0.2 mM, the observed half-life (T1/2) values of propachlor, alachlor, acetochlor, and metolachlor were 108, 387, 439, and 633 h, respectively. When the initial concentration of sodium tetrasulfide was increased to 1.0 mM, the corresponding T1/2 further decreased to only 0.6, 2.3, 2.6, and 14.1 h. The reaction was also found to proceed at a higher rate under a nitrogen atmosphere. Significantly enhanced transformation was also found in soil that was pre-treated with polysulfides. Analysis of the reaction kinetics and initial products suggest that the reaction was SN2 nucleophilic substitution in which the chlorine on the herbicide molecule was displaced by a sulfur dianions. Given the great efficiency and the wide availability of polysulfide salts, it is highly likely that this reaction may be used for decontaminating residues of chloroacetanilide herbicides in environmental media.
Key words: polysulfide, chloroacetanilide herbicide, soil, water