Transformation and Detoxification of Halogenated Fumigants by Ammonium Thiosulfate

Abstract

Fumigants are commonly used at high rates (100-400 kg/ha) in warm regions to control soil-borne pests. Many fumigants, however, tend to move easily from the treated soil into the atmosphere or groundwater, resulting in air or groundwater pollution. We studied the transformation of the fumigants methyl bromide (MeBr), propargyl bromide (PBr), 1,3-dichloropropene (1,3-D), chloropicrin (CP), and methyl iodide (MeI) by fertilizer ammonium thiosulfate (ATS). All fumigants were rapidly dehalogenated by thiosulfate via nucleophilic substitution, and the rate of transformation followed the order MeBr≃MeI>PBr>1,3-D>CP. For all fumigants, the reaction followed second-order kinetics with activation energy of ∼73 kJ/mol, suggesting a similar rate-limiting step. In soil, amendment of ATS at 1.0 mmol/kg accelerated fumigant dissipation by 21-63 times for MeBr, MeI, and PBr and by 4.6-5.5 times for 1,3-D and CP. Preliminary toxicity assays using the luminescent bacterium Vibrio fisheri showed that ATS transformation largely eliminated the acute toxicity of fumigants to this organism. These results suggest that thiosulfate transformation of halogenated fumigants is likely a benign chemical approach that may be used for mitigating environmental and health risks in fumigation.