Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2005
Publication Date: 8/1/2005
Citation: Zheng, W., Papiernik, S.K., Guo, M., Dungan, R.S., Yates, S.R. 2005. Construction of a reactive surface barrier to reduce fumigant 1,3-dichloropropene emissions. Environmental Toxicology and Chemistry. 24(8):1867-1874. Interpretive Summary: Soil fumigants are highly volatile pesticides that are widely used to control soilborne pests prior to planting a variety of economically-important crops. The fumigant 1,3-D is a highly volatile halogenated fumigant widely used in the U.S. as an alternative to methyl bromide. Since 1,3-D is classified as a probable human carcinogen, human exposure to the fumigant via inhalation or ingestion is a toxicological threat. Therefore, it is important to minimize atmospheric emissions of 1,3-D to protect air quality and human health. Recently, a chemical remediation technology, "reactive surface barrier" (RSB), has been proposed as a means of impeding fumigant emission from the soil surface. In this approach, a thin-layer RSB is constructed by applying reactive agrochemicals to the soil surface, so that fumigant vapors are intercepted and rapidly degraded at the soil-air interface, thereby significantly reducing atmospheric emissions. The feasibility of the method largely depends on the reactivity of the fumigant and the RSB agrochemicals in soil as well as the mobility, persistence, and toxicity of the transformation products. This research characterized the rapid transformation of 1,3-D by thiourea and allylthiourea to provide information for the construction of a RSB with these agrochemicals. The results of a field trial indicated that a thiourea RSB reduced cumulative 1,3-D emissions by more than 80% relative to that in bare soil. The present results clearly indicate that this chemical remediation technology has great potential to control the emissions of volatile halogenated organic contaminants and mitigate atmospheric pollution, and provide important information for the further optimization of this technology for field application. If successful, this technology will provide additional tools for producers to comply with increasingly stringent regulations to protect human and environmental health.
Technical Abstract: Halogenated fumigants have been used extensively in production agriculture to control soil-borne pests. These types of pesticides are highly volatile and are prone to affect air quality and imperil public health. In this study, a chemical tarp approach, termed a reactive surface barrier (RSB), was developed to reduce the emission of fumigant 1,3-dichloropropene (1,3-D) from the soil surface. The agrochemicals thiourea and allylthiourea were tested as active reagents for the construction of a RSB, where these soil amendments react with 1,3-D to form non-volatile isothiuronium ions at the soil surface, and thereby impede fumigant emission into the atmosphere. The feasibility of the method largely depends on the reactivity of 1,3-D and the RSB agrochemicals in soil as well as the mobility, persistence, and toxicity of the transformation products. Therefore, the reaction kinetics and transformation mechanism of 1,3-D by thiourea and allylthiourea were comprehensively studied in aqueous solution and soil. A catalytic process occurring at the surface of soil colloids facilitated the reaction between 1,3-D and thiourea in amended soils. The rate of 1,3-D transformation in thiourea-amended soil increased with decreasing soil moisture or increasing thiourea amendment level. In a field trial, a thiourea RSB reduced cumulative 1,3-D emissions by more than 80% relative to that in bare soil. The present results clearly indicate that this chemical remediation technology has great potential to control the emissions of volatile halogenated organic contaminants and mitigate atmospheric pollution.