Soil Vapor Extraction Reduces Gas-Phase MITC and Subsequent Phytotoxicity After Dazomet Fumigation

Dazomet (DZ) is widely used for soil fumigation, but its active product methyl isothiocyanate (MITC) may persist after treatment and cause phytotoxicity to subsequent crops. This study evaluated a portable activated-carbon-coupled soil vapor extraction (SVE) system for post-fumigation management of residual MITC. An L9 (33) orthogonal experiment was used to optimize MITC recovery from activated carbon, and field experiments were conducted at two agricultural sites in Beijing. At each site, three SVE plots and three concurrently fumigated no-SVE control plots were established. Ethyl acetate extraction at an activated-carbon-to-solvent ratio of 1:1 with 120 min oscillation provided recoveries of 84.5–98.6%. During SVE operation, changes in gas-phase and soil-phase MITC concentrations were observed within the treated plots, and MITC was recovered from the activated-carbon cartridges. After 7 days of laboratory aeration, SVE-treated soils supported complete cucumber germination and improved seedling growth relative to fumigated no-SVE controls, indicating reduced residual phytotoxicity under the tested bioassay conditions. Soil-phase MITC increased during the same interval, suggesting redistribution of MITC between phases and possibly reflecting continued DZ transformation.