Leaching of Methyl Isothiocyanate in Plainfield Sand Chemigated with Metam‐Sodium

Soil column studies were undertaken to investigate the influence of soil water content and irrigation on leaching, distribution and persistence of methyl isothiocyanate (MITC) in a sandy soil chemigated with the soil fumigant metam-sodium. No leaching was obtained from columns at low water content (0.042 or 0.074 cm 3 cm -3 ). However, 8.4 (±2.8), 34.2 (±7.4) and 119.4 (±8.3) μg of MITC leached from columns at 0.105, 0.137 and 0.168 cm 3 cm -3 water content, respectively. Increased leaching resulted from sprinkler application of 25-mm of water to columns at 0.137 cm 3 cm -3 water content. Leaching of MITC constituted only a small fraction of the amount applied even in the worst case. Methyl isothiocyanate persisted in soil for 15 days at 2°C in varying amounts under the different water regimes. Relatively high amounts of MITC residues (8-12 mg kg -1 soil) were detected in the top 25-cm layer of all the soil columns. Degradation was the major pathway of dissipation for the chemical despite the soil water regime.