Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2006
Publication Date: 2/7/2007
Citation: Zhang, Y., Wang, D. 2007. Emission, Distribution And Leaching Of Methyl Isothiocyanate And Chloropicrin Under Different Surface Containments. Chemosphere 68 (2007) 445-454. Interpretive Summary: Fumigants, in nature, are volatile. In addition to degradation, atmospheric emission often accounts for one of the main losses after application in field soils. The rate of emission depends on vapor pressure, transport rate from injection zone to soil surface, and surface containments that would reduce emission losses into the atmosphere. The study showed that the HDPE film was not effective in containing these two fumigants in the soil. Surface application of a small amount of water before tarp cover had little or no effect on reducing the emission. Daily application of large amount of water at a slow rate virtually eliminated MITC and CP emission losses because a nearly saturated condition was created for the surface soils by forming a ‘‘true’’ water seal. A limitation with the daily irrigation surface containment was the potential for small leaching losses to deeper depths. This could be a concern in areas where soils are very sandy and the groundwater level is close to the soil surface.
Technical Abstract: The environmental fate of fumigants methyl isothiocyanate (MITC) and chloropicrin (CP) is of great concern for potential air and groundwater contamination while retaining sufficient concentrations for pest control efficacy. The emission, gas phase distribution, leaching, and persistence of MITC and CP were examined in repacked columns filled with sandy soils under three surface conditions: tarp without irrigation, tarp with limited irrigation, and 5-d irrigation without tarp cover. For MITC, cumulative emission constituted 62%, 36%, and 0.3% of the amount applied under tarp without irrigation, tarp with limited irrigation, and 5-d irrigation without tarp surface conditions, respectively. The corresponding cumulative emission losses were 45%, 30%, and 5.4% for CP. During the first 24 h after injection, soil air concentrations of the two fumigants were much higher in the 15–25 cm depth range than other depths in the soil profile. Small amounts of leaching occurred for both fumigants, indicating potential for groundwater contamination should heavy rain fall or irrigation occurs immediately after soil fumigation. Very small amounts of residual MITC and CP (<2%) were found in the soil 24 days after the experiment. The study clearly showed that atmospheric emission and degradation were the two primary pathways of MITC and CP dissipation during soil fumigation. Emission could be effectively reduced with 5-d irrigation if small leaching is acceptable or be prevented.