Organic matter degradation, effects diffusion

Due to its gaseous nature it may have an effect on the stratospheric ozone layer [281, 402, 404]. After injection into soil for fumigation, methyl bromide rapidly diffuses through the soil pore space to the soil surface and then into the atmosphere [159,162,163,405,406]. Since a plastic sheet typically covers the soil surface, the rate of emission into the atmosphere depends upon the thickness and density of the plastic, if other conditions are the same [159, 406]. Other routes of disappearance from soil include chemical hydrolysis, methylation to soil organic matter through free radical reactions, and microbial degradation [ 136,159,405,407]. Several reports appeared on the study of the microbial transformations of methyl bromide, summarized as follows ... 

A majority of the extracellular enzymes released by the microbes are bound to the solid surface (such as particulate detrital matter or soil organic matter in clays), but a small fraction remains in the soil pore water (Eigure 5.17). Those free in soil pore water are most susceptible to microbial degradation and chemical alteration. Surface-bound enzymes may not be as effective as free enzymes because of a slow rate of substrate diffusion to the sites where enzymes are present. 

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