Accelerated degradation of methyl iodide by agrochemicals

The fumigant methyl iodide (Mel, iodomethane) is considered a promising alternative to methyl bromide (MeBr) for soil-borne pest control in high-cash-value crops. However, the high vapor pressure of Mel results in emissions of a significant proportion of the applied mass into the ambient air, and this may lead to pollution of the environment. Integrating the application of certain agrochemicals with soil fumigation provides a novel approach to reduce excessive fumigant. emissions. This study investigated the potential for several agrochemicals that are commonly used in farming operations, including fertilizers and nitrification inhibitors, to transform Mel in aqueous solution. The pseudo-first-order hydrolysis half-life (t_1/2) of Mel was ∼ 108 d, while the transformation of Mel in aqueous solutions containing selected agrochemicals was more rapid, with t_1/2 < 100 d (t_1/2 < 0.5 d in some solutions containing nitrification inhibitors). The influence of these agrochemicals on the rate of Mel degradation in soil was also determined. Adsorption to soil apparently reduced the availability of some nitrification inhibitors in the soil aqueous phase and lowered the degradation rate in soil. In contrast, addition of the nitrification inhibitors thiourea and allylthiourea to soil significantly accelerated the degradation of Mel, possibly due to soil surface catalysis. The t_1/2 of Mel was <20 h in thiourea- and allylthiourea-amended soil, considerably less than that in unamended soil (t_1/2 > 300 h).