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United States Department of Agriculture

Agricultural Research Service

Title: Dehalogenation of Halogenated Fumigants by Polysulfide Salts

Authors
item Bondarenko, Svetlana - UNIVERSITY OF CALIFORNIA
item Gan, Jianying - UNIVERSITY OF CALIFORNIA
item Zheng, Wei - UNIVERSITY OF CALIFORNIA
item Yates, Scott

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 7, 2006
Publication Date: July 4, 2006
Citation: Bondarenko, S., Gan, J., Zheng, W., Yates, S.R. 2006. Dehalogenation of halogenated fumigants by polysulfide salts. Journal of Agricultural and Food Chemistry. 54(15):5503-5508

Interpretive Summary: Fumigants are among the most widely used pesticides in agriculture. Because they are highly mobile and toxic, contamination of air and groundwater is of great environmental concern. Experiments were conducted to investigate the degradation (i.e., dehalogenation) of several fumigants with polysulfide compounds. The reactions of polysulfides and several fumigants were extremely rapid. When the initial fumigant and polysulfide concentrations were the same (1:1), the observed times to degrade one half of the fumigants were 24.2, 25.2, and 63.6 h, for methyl iodide, cis-1,3-dichloropropene, and trans-1,3-dichloropropene, respectively. When the initial polysulfide concentration was 5-times greater than the fumigant, the corresponding degradation times values were only 3.2, 1.5, and 5.2 h. Chloropicrin was found to be much more reactive than other fumigants for similar conditions. In a 1:1 solution, more than 90% of the chloropicrin disappeared in 1 hour. These reactions also occurred at a higher rate in a nitrogen atmosphere than in air. This suggests that the reaction occurs through nucleophilic substitution for MeI and 1,3-D, but likely reductive dehalogenation for CP. Given the high reactivity of polysulfide toward halogenated fumigants, this reaction may be used as a pollutant-treatment strategy, such as with disposal of fumigant wastes, treatment of fumigant-containing wastewater, and cleanup of fumigant residues in environmental media.

Technical Abstract: Halogenated fumigants are among the most heavily used pesticides in agriculture. Because of their high mobility and toxicological characteristics, the contamination of air or groundwater by these compounds has been a great environmental concern. In this study, we investigated the dehalogenation reaction of several halogenated fumigants with polysulfides. The reactions of polysulfides and methyl iodide (MeI), 1,3-dichloropropene (1,3-D), and chloropicrin (CP) were extremely rapid. When the initial fumigant and polysulfide concentrations were both 0.2 mM, the observed half-lives (T1/2) of MeI, cis-1,3-D, and trans-1,3-D were 24.2, 25.2, and 63.6 h, respectively. When the initial polysulfide concentration was 1.0 mM, the corresponding T1/2 values were only 3.2, 1.5, and 5.2 h. Under similar conditions, CP was much more reactive than other halogenated fumigants toward polysulfides. In a polysulfide solution (0.2 mM), more than 90% of the spiked CP disappeared in 1 h. These reactions occurred at a higher rate in a nitrogen atmosphere than in air. Analysis of reaction kinetics and initial products suggest that the reaction is SN2 nucleophilic substitution for MeI and 1,3-D, but likely reductive dehalogenation for CP. Given the high reactivity of polysulfide toward halogenated fumigants, this reaction may be used as a pollutant-treated strategy, such as disposal of fumigant wastes, treatment of fumigant-containing wastewater, and cleanup of fumigant residues in environmental media.

Last Modified: 10/21/2014
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