Monday, November 13, 2006

Degradation of Methyl iodide in Soil: Effects of Environmental Factors.

Mingxin Guo, Delaware State University, Delaware State University, 1200 N. DuPont Highway, Dover, DE 19901 and Suduan Gao, USDA-ARS, USDA-ARS SJVASC-Water Management Research, 9611 S Riverbend Ave., Parlier, CA 93648.

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.


Handout (.pdf format, 80.0 kb)