Methyl iodide (MeI) is a promising alternative to the phased-out fumigant
methyl bromide, and its environmental fate following soil fumigation is of
great concern. Experiments were conducted to investigate the effect of various environmental factors on the degradation
rate of MeI in soil. The chemical MeI
was spiked into moist soils and incubated under different conditions for
pre-determined times. Remaining MeI was extracted and
measured. The degradation rate of MeI in soils was evaluated based on its residual
amount. In soil, MeI degraded following pseudo
first-order kinetics. At 20șC MeI had a half life of 32 d in a sandy loam soil
with 10% moisture content. It degraded more
rapidly as temperature increased, exhibiting a half life of 23 d at 30 șC.
Soil moisture content in a range of 5%-15% did not influence its
degradation. When the soil was amended
with 10% of steer manure, the half life of MeI at
20șC was shortened to 4 d. In both non-amended and manure-amended soils, removal
of organic matter via combustion greatly increased, while sterilization by
autoclave only slightly increased the half life of MeI,
indicating predominance of chemical reactions in MeI
degradation. Soil texture and mineralogy
did not affect the degradation rate of MeI, as revealed
by the fact that MeI degraded at the same rate in
organic matter-removed, different textured soils (sand, sandy loam, and clay
loam). The results suggest that to accelerate MeI
degradation, temperature and organic amendment should be considered.