In December, the Department of Pesticide Regulation (DPR) approved the use of methyl iodide (also known as iodomethane) as a soil fumigant in California. But last week, following resignation of Mary-Ann Warmerdam from her position as Director of DPR, Governor Brown announced that the state could reconsider the controversial chemical’s approval.

At an Assembly hearing in February, members of the Health and Environmental Safety committees questioned whether the approval process was rushed, and whether it’s possible to reverse DPR’s decision.

The substance has been described by scientists as one of the most toxic in existence. It was originally approved with the intention of replacing methyl bromide, which is being phased out internationally to protect atmospheric ozone. Methyl iodide is listed under California Proposition 65 (passed in 1986) as a chemical known by the state to cause cancer or reproductive toxicity and is considered a potential occupational carcinogen by the National Institute for Occupational Safety and Health , the Occupational Safety and Health Administration and the Centers for Disease Control and Prevention. Presently, Washington and New York are the only states where methyl iodide is not approved for use.

The Environmental Protection Agency classifies it as “not likely to be carcinogenic to humans in the absence of altered thyroid hormone homeostatis” i.e. it is a human carcinogen but only at doses large enough to disrupt thyroid function (via excess iodide, similar to radioactive iodine). The EPA registered methyl iodide in 2007, but is presently conducting a public comment period on its use. Comments can be submitted through April 30th. More information on methyl iodide is available from the EPA website.



2 Comments so far

  1. Robert on April 5, 2011 7:15 am

    The process of registration was not rushed. For over 5 years, the US-EPA extensively studied methyl iodide, its hazard potential, and mitigations that would protect workers and the public. They called that review the most comprehensive and thorough every conducted on a pesticide by their agency. After the EPA registration, California took an additional three years of study before they registered it, answering every conceivable question, and imposed even stricter requirements than the federal agency. Again, its director said that their review was the most extensive and thorough ever conducted by DPR.

    The two most authoritative bodies responsible for scientific judgement on carcinogenicity say the state’s Prop 65 agency got it wrong. It used data that is now 32 years old to list methyl iodide. Later studies failed to show any human carcinogenic properties.

    And; finally, only one scientist, Dr. John Froines, an original member of the Chicago 8–yes that Chicago 8–says that methyl iodide is “one of the most toxic in existence.” Facts tell the truth–in a search of over 100 years of medical history and widespread use of the material in industrial processes and research laboratories, only 12 acute poisoning cases could be found.

  2. Andrea on April 9, 2011 7:18 am

    Robert, thank you for the additional information. Hopefully, the findings of the studies you mention will also be presented to the legislative committees as they review the matter, so they have all available data to help them better understand the issues.

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