LEACHING OF METHYL ISOTHIOCYANATE IN PLAINFIELD SAND CHEMIGATED WITH METAM-SODIUM

Soil column studies were undertaken to investigate the influence of so il water content and irrigation on leaching, distribution and persiste nce of methyl isothiocyanate (MITC) in a sandy soil chemigated with th e 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) mu g of MITC leached from columns a t 0.105, 0.137 and 0.168 cm(3) cm(-3) water content, respectively. Inc reased leaching resulted from sprinkler application of 25-mm of water to columns at 0.137 cm(3) cm(-3) water content. Leaching of MITC const ituted only a small fraction of the amount applied even in the worst c ase. Methyl isothiocyanate persisted in soil for 15 days at 2 degrees C in varying amounts under the different water regimes. Relatively hig h 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 pat hway of dissipation for the chemical despite the soil water regime.