ARS | Publication request: TRANSFORMATION AND DETOXIFICATION OF HALOGENATED FUMIGANTS BY AMMONIUM THIOSULFATE

Submitted to: Journal of Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2000
Publication Date: July 22, 2000
Citation: Wang, Q., Gan, J., Papiernik, S.K., Yates, S.R. 2000. Transformation and detoxification of halogenated fumigants by ammonium thiosulfate. Journal of Environmental Science and Technology. 34(17):3717-3721.

Interpretive Summary: Soil fumigants are heavily used in the production of many food crops for controlling nematodes and other soil borne pests. Most of the currently used fumigants are highly volatile halogenated compounds. After injection into soil, fumigants tend to diffuse rapidly in soil and as a result, a significant fraction can enter the atmosphere or groundwater. Air and groundwater contamination by fumigants has toxicological significance due to their acute toxicity, probable carcinogenicity, or other adverse effects. In this study we investigated a novel approach to detoxify halogenated fumigants that include methyl bromide (MeBr), methyl iodide (MeI), propargyl bromide (PBr), chloropicrin (CP), and 1,3-D. Among these compounds, MeBr, CP and 1,3-D are currently registered halogenated fumigants, while MeI and PBr are being developed as alternatives to MeBr. The specific objectives of this study were to (1) determine the transformation rate of these fumigants by ATS, (2) to describe transformation mechanisms by evaluating reaction kinetics and activation energies, and (3) to demonstrate that the transformation products are less toxic than the parent fumigants.

Technical 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. 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 a benign chemical approach that may be used for mitigating environmental and health risks in fumigation.