Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2006
Publication Date: 2/21/2006
Citation: Zheng, W., Yates, S.R., Papiernik, S.K., Wang, Q. 2006 Reducing 1,3-dichloropropene emissions from soil columns amended with thiourea. Environmental Science and Technology. 40(7):2402-2407.
Interpretive Summary: Soil fumigants have been used extensively to control plant pathogens in crop production. Atmospheric emissions are a major problem associated with fumigant use and many management practices have been developed to reduce emissions. Emissions increase the risk of stratospheric ozone depletion, bystander exposure, and may also contribute to the formation of near-surface (tropospheric) ozone. This has become a serious concern with the implementation of a new federal 8-hour ozone standard. Minimizing atmospheric emissions can reduce these adverse impacts from fumigating soil. Many methods have been developed to reduce emissions, but to date, no simple and cost-effective methodology is available. This research reports on the use of thiourea to create a reactive barrier at the soil surface. The hypothesis is that fumigant vapors that reach the reactive soil surface layer will be quickly degraded into non-volatile, non-toxic components. This would reduce the risk to public and environmental health from fumigant use. The surface amendment did not affect the fumigant distribution in the soil and significantly reduced volatilization. This methodology was found to be very effective in reducing the fumigant emissions and an effective strategy for minimizing atmospheric emissions of VOCs.
Technical Abstract: Soil fumigants are becoming an important source of volatile organic compounds (VOCs) in air, especially in some agricultural areas. The agrochemical, thiourea, can rapidly transform volatile halogenated fumigants to non-volatile products. In this study, we used thiourea to construct a reactive surface barrier (RSB) at the soil surface for reducing 1,3-dichloropropene (1,3-D) volatilization. Transformation of 1,3-D by thiourea was ascribed to an SN2 nucleophilic substitution reaction. A catalytic mechanism in thiourea-amended soil facilitated the conversion process. A packed soil column system was employed to evaluate the distribution and emissions of 1,3-D and optimize the original fumigant emission-reduction strategy. Volatilization from the surface of 1,3-D was significantly reduced in columns amended with a thiourea RSB compared with bare soil. Volatilization flux and cumulative emissions decreased with increasing thiourea application rate and increasing fumigation depth in packed soil columns. Surface amendment with the RSB did not affect the distribution of 1,3-D in the soil profile and is not expected to alter 1,3-D transport in soil. Combined application of a thiourea RSB and plastic tarps had a synergetic effect in emission control and could avoid large volatilization caused by tearing the films. Therefore, this reduced-risk practice was very effective in reducing the emission of 1,3-D and its volatile degradation products. These results clearly indicate that the thiourea RSB technique may be a feasible and effective strategy for minimizing atmospheric emissions of VOCs from soil treatment with halogenated fumigants.