Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/3/2007
Publication Date: 9/15/2007
Citation: Zheng, W., Gan, J., Papiernik, S.K., Yates, S.R. 2007. Identification of Volatile/Semi-Volatile Products Derived from Chemical Remediation of cis-1,3-Dichloropropene by Thiosulfate. Environmental Science and Technology. 41(18):6454-6459.
Interpretive Summary: Volatile organic compounds (VOC), such as pesticides and fumigants can react in the atmosphere to produce ozone. Ozone is formed from the photochemical oxidation of nitrous oxides and VOCs and is causing increased regulation of agricultural VOC sources. It has been estimated that 10% of the total VOC in the San Joaquin and Sacramento Valleys is due to pesticide emissions. This has led the California Department of Pesticide Regulation (CDPR)to require a 20% reduction in pesticide-related VOC emissions from 1990 levels with possible future reductions of an additional 30% by 2010. Potential mandatory emission control strategies that could seriously affect producers include: a) no-spray days, b) required use of specific application methods/equipment, and c) less flexible, more costly reformulation of high VOC pesticides. Restrictive control strategies would place a significant financial burden on the agricultural community. Little information is available concerning the contribution of soil fumigation to secondary VOC emissions from fumigant degradation products. This research reports on experiments to determine if fumigant degradation in soil produces volatile and/or semi-volatile organic compounds.
Technical Abstract: The prevalent use of soil fumigants has resulted in air pollution in some agricultural regions. Our previous research showed that amendment of thiosulfate fertilizers at the soil surface may offer an effective and economical approach to reduce the emission of halogenated fumigants via a chemical remediation process. The transformation of cis-1,3-D by thiosulfate in aqueous solution and soil produces a nonvolatile Bunte ion (thiosulfate derivative of 1,3-D) as the primary reaction product. This study investigated the stability of this reaction product in different environmental media. Hydrolysis experiments demonstrated that the thiosulfate derivative was relatively stable in neutral and moderately acidic aqueous solutions. In contrast, the thiosulfate derivative was converted to a dialkyl disulfide via a base hydrolysis process in a pH 10 buffer solution. In a strongly acidic solution (2.0 M HCl), a mercaptan and a dialkyl disulfide compound were detected as two primary hydrolysis products. Transformation of cis-1,3-D in thiosulfate-amended soil to form the nonvolatile reaction product was abiotic mechanism. This initial reaction product would further undergo a series of biotic conversions in soil to yield several volatile or semi-volatile organic sulfur compounds. The formation and distribution of four volatile/semi-volatile products in the air and soil were detected in different soils treated with the thiosulfate derivative. This study indicated that the offensive odor occurring in soil treated with halogenated fumigants and thiosulfate fertilizers might arise from the generation and release of these and other volatile/semi-volatile organic sulfur products. The environmental fate and effects of such volatile/semi-volatile sulfur compounds should be considered in the application of sulfur-containing fertilizers in fumigated fields.