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.