Methyl iodide, a fumigant under fire

Abstract

California just completed an assessment which indicates that the pesticide methyl iodide presents significant health risks to farm workers. The U.S. Environmental Protection Agency (EPA) approved the use of methyl iodide in 2008, after ignoring calls from leading scientists for an independent review. The pending registration of methyl iodide in California will have to wait for an external scientific review, which observers predict will have a significant impact on policy, this fall.Methyl iodide was developed to replace methyl bromide, a fumigant that is applied to soil to kill pests before crops such as strawberries, fruit vines, and nursery trees are planted.

Fumigant methyl iodide can methylate inorganic mercury species in natural waters

“…Here we report the results of a study on the methylation of mercury by CH 3 by CH 3 I. Further quantitative assessment suggests that CH 3 I-involved methylation of inorganic Hg could be an important source of CH 3 Hg þ in an environment where CH 3 I has been used in large amounts as a fumigant.…”

“…Anthropogenic input of CH 3 I to the environment has been rapidly increasing since the 1990s, after it was suggested as a replacement for the ozone-depleting fumigant methyl bromide (CH 3 Br). CH 3 I is preferred over CH 3 Br because it is similar to, or more effective than, CH 3 Br in controlling a wide variety of soil pests and weeds 2 , and it has less impact on the ozone layer owing to its rapid photodegradation in the troposphere 2 . The U.S. EPA approved the use of CH 3 I as a fumigant in 2008 (ref.…”

“…The potentially negative impact of using CH 3 I has not been adequately addressed 4 , despite its increasing use on farmland. Compared with CH 3 Br, CH 3 I degrades more slowly in soil, hence increasing its chance of being transported to an aquatic environment via runoff 5,6 .…”

“…Compared with CH 3 Br, CH 3 I degrades more slowly in soil, hence increasing its chance of being transported to an aquatic environment via runoff 5,6 . CH 3 I is known to have the capability of methylating several metals and metalloids, including Sn 2 þ , As 3 þ , Pb 2 þ and Hg 0 , following an oxidative addition mechanism [7][8][9][10] .…”

“…CH 3 I is known to have the capability of methylating several metals and metalloids, including Sn 2 þ , As 3 þ , Pb 2 þ and Hg 0 , following an oxidative addition mechanism [7][8][9][10] . Among these metals/metalloids, mercury deserves special attention because its methylation product, methylmercury (CH 3 Hg þ ), is among the most widespread of all highly toxic contaminants. Previous work has demonstrated that CH 3 I can be used as a methylation reagent for synthesizing CH 3 Hg þ from Hg 0 in a laboratory setting 10 .…”