Dechlorination of chloroacetanilide herbicides by plant growth regulator sodium bisulfite |
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Authors: | Haitao Bian Ping Liu |
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Affiliation: | a Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), Department of Environmental Science and Technology, Dalian University of Technology, Linggong Road 2, Dalian 116024, P.R. China b State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, P.R. China |
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Abstract: | Chloroacetanilide herbicides are frequently detected in groundwater and surface waters, and pose high risks to aquatic biota. In this study, sodium bisulfite (NaHSO3), a plant growth regulator used in China, was used to remove three chloroacetanilide herbicides including alachlor, acetochlor and S-metolachlor. These herbicides were rapidly dechlorinated by NaHSO3 in neutral conditions. The dechlorination was accelerated with increasing pH, temperature and NaHSO3 concentrations. Kinetic analysis and mass spectrum identification revealed that the reaction followed SN2 nucleophilic substitution, in which the chlorine was replaced by the reactive specie sulfite. Alachlor and its isomer acetochlor had similar reaction rates, whereas they were more readily transformed than S-metolachlor that had larger steric hindrance and weaker electrophilicity. The transformation products were chloroacetanilide ethane sulfonic acids (ESAs), which were also encountered as major metabolites of these herbicides in natural environment via common metabolic pathways and were less toxic to green algae compared to the parent herbicides. These results indicate that NaHSO3 can accelerate transformation of chloroacetanilide herbicides to the less toxic transformation products by nucleophilic substitution and dechlorination in aquatic environment. NaHSO3 can be potentially used for the removal of chloroacetanilide herbicides from wastewater effluent, spill sites and accidental discharge. |
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Keywords: | Chloroacetanilide herbicides Dechlorination Sodium bisulfite Ethane sulfonic acid (ESA) |
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