thiourea and 1-3-dichloro-1-propene

Soil fumigants are becoming an important source of volatile organic compounds (VOCs) in air, especially in some agricultural areas. 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. The agrochemical thiourea could rapidly transform volatile 1,3-D to nonvolatile products via an SN2 nucleophilic substitution reaction. A catalytic mechanism in thiourea-amended soil facilitated the conversion process. A packed soil column system was employed to investigate the emissions and distribution of 1,3-D and optimize the original fumigant emission-reduction strategy. Volatilization of 1,3-D from the soil surface was significantly reduced in columns amended with a thiourea RSB compared with that of 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 subsurface distribution of 1,3-D in the soil profile. Combined application of a thiourea RSB and plastic tarps had a synergetic effect in emission control and could eliminate the relatively high fumigant flux that occurs upon tarp disruption. Therefore, this reduced-risk practice was very effective in reducing atmospheric emissions of VOCs from soil treatment with halogenated fumigants.

Topics: Allyl Compounds; Catalysis; Hydrocarbons, Chlorinated; Soil; Thiourea

Halogenated fumigants have been used extensively in production agriculture to control soilborne pests. These types of pesticides are highly volatile and are prone to affect air quality and imperil public health. In the present 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 nonvolatile 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 on 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 studied comprehensively 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 surface. The present results clearly indicate that this chemical remediation technology has great potential to control the emissions of volatile halogenated organic contaminants and to mitigate atmospheric pollution.

Topics: Allyl Compounds; Chromatography, Gas; Gas Chromatography-Mass Spectrometry; Hydrocarbons, Chlorinated; Insecticides; Soil; Surface Properties; Thiourea