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Why U.S. EPA Should Reconsider its Methyl Iodide Decision

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In October, 2008 US EPA approved the registration of methyl iodide without time limitations. See C&EN article of October 27, 2008.

On July 7, 2008, Florida approved a conditional methyl iodide registration. On January 14, 2009, New York sent a letter to Arysta LifeScience accepting withdrawal of the corporation's applications to register methyl iodide products. New York cited concern "for significant worker exposure potential" and "for exposure to bystanders and nearby residents from both routine applications and mishaps associated with the application of these products."

According to the Florida Department of Agriculture and Consumer Services (FDACS), labels for methyl iodide in Florida require "additional safety measures and enhance clarity and enforceability" beyond the federal labels. The Farmworker Association of Florida was actively engaged with US EPA and FDACS during the registration process and won additional protections, including groundwater and air monitoring studies and poisoning incident reporting. Partial protection of groundwater contamination is to be achieved by prohibiting application during rain. The labels also mandate documentation of evacuation of occupied dwellings in methyl iodide buffer zones. Like the new federal labels for chloropicrin, methyl bromide, and methyl isothiocyanate, field reentry intervals are extended to five days and tarp cutters and removers are included in the definition of applicators and other handlers so they will receive better training and protection.

The California Department of Pesticide Regulation (DPR) has assembled a Scientific Review Panel to evaluate methyl iodide.  DPR will take a decision on the registration of methyl iodide for agricultural use in California in the first quarter of 2009.

Introduction

The U.S. Environmental Protection Agency (EPA) registered methyl iodide (also called iodomethane) on October 5th, 2007. The State of California entered methyl iodide into its evaluation process on August 22nd, 2007. The registration of methyl iodide (also known as iodomethane) as a new chemical is touted as a replacement for methyl bromide for soil fumigant applications. EPA registered methyl iodide despite a concerted effort resulting in a September 25, 2007 letter from dozens of distinguished chemists saying that it is “astonishing” that the EPA is considering “broadcast releases of one of the more toxic chemicals used in manufacturing into the environment.” Although EPA announced it would “address recent questions prompted by the pending registration of iodomethane,” it went ahead with the registration a few days later. EPA took the unusual step of registering methyl iodide for only one year. There were hopes for a reversal of the decision, however a year later in October, 2008 EPA extended the conditional registration of methyl iodide without time limits.

Fumigant pesticides are volatile, drift-prone chemicals injected into the soil at application rates of 50-400 pounds per acre. The maximum application rate for methyl iodide is 175 pounds per acre. Chemically related to methyl bromide—a fumigant scheduled for phaseout under the Montreal Protocol because of its ozone-depleting potential—methyl iodide is much more reactive than methyl bromide, reacting with air and water before it can be transported to the stratospheric ozone layer.[1]For this reason, methyl iodide is not an ozone-depleting chemical; nevertheless, there are a number of reasons why EPA should have refused the registration of this chemical.

Help Stop Methyl Iodide Registration in California

Right now the California Department of Pesticide Regulation is considering the registration of methyl iodide in the state of California, despite the fact that is "known to the state of California to cause cancer" and it is listed under proposition 65.

If methyl iodide is registered in California and becomes a popular replacement for the other fumigants, millions of pounds of it will be released each year into the environment, especially in strawberry-growing areas where methyl bromide is currently popular. Methyl bromide is being phased out due to its serious environmental problems, and farmers that use it are eagerly awaiting methyl iodide as a replacement.

The best way to stop methyl iodide from being used in California especially in strawberry-growing areas, is to stop it from being registered in California. This is going to take a lot of pressure on the Department of Pesticide Regulation because they are getting a lot of requests from growers to register it, despite its hazards.

Arysta LifeScience is the registrant for the chemical. A preliminary risk assessment was released in January 2006, with a public comment period that closed on February 21, 2006. PANNA submitted both general and technical comment letters to EPA on this pesticide. You can download these letters here:

In addition, over 12,500 individuals weighed in to tell EPA that they did not want this toxic chemical used in their communities and workplaces.

On April 19, 2006, the US EPA announced that it was denying registration for methyl iodide in 2006, and that the chemical might be reconsidered in 2007.

On September 28, 2007, US EPA announced that it had “conducted a thorough scientific evaluation of the soil fumigant iodomethane.” But—apparently in response to the aforementioned September 25 letter from dozens of distinguished scientists to EPA Administrator Stephen Johnson, asking that registration be delayed while an independent panel of scientists assessed the evidence—the Agency briefly delayed registration.

Recent News on Methyl Iodide Registration:

Public Health Will Be Endangered if Methyl Iodide Is Used

Enough is known about this chemical to predict that its use for soil fumigation will result in unhealthful human exposures. A history of mass poisonings involving other fumigants is part of the basis forth is prediction.

For a recent example, consider the 121 people who were poisoned in Nevada on September 26, 2007, even as EPA was days away from its decision on methyl iodide. EPA's proposed buffer zones for iodomethane are at most 500 feet. The farmworkers who were poisoned were in a field half a mile from the one being fumigated. One can readily see from this incident that EPA's maximum 500-foot buffer zones are a fraction of the size that would be required to prevent recurrences of poisonings. Unfortunately, "feasibility" dictates the buffer zone sizes as much as health protection.

Real-world incidents are corroborated by EPA's detailed models which show that the buffer zones they have settled on are inadequate a few percent of the time for those who are unfortunate enough to be in the downwind direction. The game of roulette depends principally on the weather on the day of the fumigation. Light winds and clear skies near sunset lead to "inversions" which keep fumigants escaping from the ground from dispersing. Under these conditions, the models show and real-world incidents confirm that unhealthy concentrations of fumigant gas build up over thefield and then slowly drift into neighboring communities.

Unless EPA's decision to approve methyliodide as a soil fumigant is reversed, farmworkers, rural communities,and new suburbanites whose properties face or abut fields will be at risk, particularly those in States with high fumigant use—California,Washington and Florida. Public health protection should be the primary consideration for pesticide registration, and EPA should use the 1-year registration as an opportunity to reverse its decision on methyl iodide.

Methyl Iodide is Chemically Reactive

Chemists use special techniques to protect themselves while handling even small quantities of methyl iodide in the laboratory. Source: PANNA Archives

Methyl iodide is widely used in chemical synthesis because of its extraordinary ability to react with electron-rich molecules. Specifically, it reacts readily with biomolecules like DNA, the genetic material in cells, in a process that alters the structure of DNA, causing mutations. Synthetic chemists treat this chemical with great respect, handling it only in a hood under an inert atmosphere and using specially sealed bottles and syringes for transfer to ensure that none of this highly toxic chemical escapes. The proposed release of massive amounts of this chemical into the environment is contrary to safe chemical management practices.

Methyl Iodide Will Contaminate Air and Water

Because methyl iodide is highly volatile, it is as drift-prone as other fumigants.[2] As a result, bystander inhalation exposure will be high if this chemical is applied as a soil fumigant. Methyl iodide is also a volatile organic compound (VOC) that will contribute to ground-level ozone, which is known to exacerbate asthma and other respiratory diseases.

Soil fumigation with methyl iodide poses a risk of groundwater contamination as well. A study of methyl iodide-treated soils demonstrated that cumulative volatilization losses from sandy loam soils ranged from 94% of the amount applied in non-tarped soils to 75% in soils covered with high-barrier tarps. [3] Tarping increased downward movement of the pesticide into the soil, which increased leaching into groundwater. The half-life of methyl iodide in soil depends on soil type, from 42 to 63 days for sandy loam soils and 9 to 13 days in soils rich in organic matter. [4]

Methyl Iodide is Acutely Toxic

Methyl iodide affects the nervous system, the lungs, liver, and kidneys. Symptoms of acute poisoning from inhalation include dizziness, sleepiness, nausea, diarrhea, slurred speech, lack of coordination, and muscle convulsions. [5] Methyl iodide is six times more acutely toxic than methyl bromide, and about twice as toxic as 1,3-dichloropropene (Telone).[6] To date, neither U.S. EPA nor California’s Department of Pesticide Regulation have set an acceptable level of human exposure for this chemical, but the National Institute of Occupational Safety and Health has set an eight to ten-hour worker (adult male) exposure limit of 10 mg/m3 based on the chemical's acute toxicity. [6] "Acceptable" exposures for children developed through risk assessment are typically 10-1,000 times lower than those for healthy adult males. EPA has listed methyl iodide as a Hazardous Air Pollutant generally known or suspected to cause serious health problems.

Methyl Iodide is a Carcinogen

The chemical reactivity of methyl iodide mentioned above has biological consequences. Vapors of methyl iodide induce DNA damage and are “mutagenic to bacteria in the presence or absence of an exogenous metabolic system” (the Ames test). [7] Methyl iodide is also commonly used to create mutant mammalian cell lines in the laboratory. [8]Radioactive labeling studies in rats demonstrate DNA damage to the lungs and digestive tract specifically caused by methyl iodide. [9]Because of this chemical reactivity, the National Institute of Occupational Safety and Health (NIOSH) recommended that methyl iodide be considered as a potential occupational carcinogen, [10] and the state of California lists it as a chemical "known to the State of California to cause cancer." [11]

The International Agency for Research on Cancer (IARC) indicates that: "No epidemiological data relevant to the carcinogenicity of methyl iodide were available. There is limited evidence in experimental animals for the carcinogenicity of methyl iodide." Because of this lack of data, IARC lists this chemical as "unclassifiable" as to its carcinogenicity. [12] While there are no recent cancer studies in the primary literature, the older animal studies cited and described by IARC indicate that cancers resulted from exposure to this chemical in all experiments at most dose levels tested, and in some instances from only a single moderate exposure.[13]

"Groups of BD rats (substrain and sex unspecified), about 100 days old, received weekly subcutaneous injections of 10 (16 animals) or 20 mg/kg body weight (eight animals) methyl iodide (purity unspecified) in arachis oil for about one year (total dose, 500 or 900 mg/kg body weight), or a single subcutaneous injection of 50 mg/kg body weight (14 animals), and were observed for life. Four and two animals in the first two groups, respectively (25%), died of pneumonia. Subcutaneous sarcomas occurred in 9/12 rats injected with 10 mg/kg body weight, in 6/6 rats injected with 20 mg/kg body weight and in 4/14 rats given a single injection of 50 mg/kg body weight. No subcutaneous tumor was reported to have occurred in control rats ... injected with arachis oil alone. Local tumors occurred more than one year after the first injection; histologically, these were fibrosarcomas and spindle-cell and round-cell sarcomas. In most cases ... pulmonary and lymph-node metastases were observed."
[IARC. Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man. Geneva: World Health Organization, International Agency for Research on Cancer, 1972-PRESENT. (Multivolume work).V41 218 (1986)]

Click here to download a summary of the animal studies that have been done to date.

In its recent risk assessment [14] EPA found that methyl iodide caused thyroid tumors, but invoked a previously unheard of cancer ranking -- "Not likely to be carcinogenic to humans at doses that do not alter rat thyroid hormone homeostasis." Download the EPA Cancer Assessment. It is worth noting that the Cancer Assessment Review Committee used only a single study to come to this conclusion -- a study in which 62-66% of the rats in both the control group and the high dose group died during the experiment and only 52-54% of the rats in the other dose groups survived (see p. 11 in the Cancer Assessment), bringing into question the scientific validity of the study. Of particular concern is that the registrant, Arysta LifeSciences, determined the number of tumors caused by methyl iodide only for animals that survived beyond the first year of the study. (See page 7 in the Cancer Assessment, footnote to table 1). In addition to the thyroid tumors observed in the survivors of the study, large and significant changes were observed in thyroid hormone levels, which are intimately tied to metabolic disorders and immune function. EPA did not evaluate the possible health outcomes of these changes. Other toxic effects noted by EPA include respiratory tract and salivary gland lesions, neurological toxicity, reduced body weight, and developmental toxicity (manifested as fetal losses and decreased live births). Download the EPA Health Effects Assessment.

Methyl Iodide Interferes with Metabolic Processes

Several studies indicate that at intermediate doses, methyl iodide interferes with both lipid and glucose metabolism. Injection of male rabbits with 57 mg/kg of MeI for 2 days resulted in a five-fold increase in plasma triglyceride levels, with a significant increase in the very low density lipoprotein (the "bad cholesterol") and accumulation of fatty deposits in the liver. [15]

Another study showed that when methyl iodide was injected into rabbits, basal levels of insulin and glucagons increased, and plasma glucose levels responded abnormally to insulin and glucose injections, indicating disturbances in the regulation of carbohydrate metabolism. [16]

Resources

  1. S.R. Yates, Methyl Iodide as a Replacement for Methyl Bromide: Environmental Implications, Agricultural Research Service, U.S. Department of Agriculture, October 15, 1996.
  2. The vapor pressure of methyl iodide is 400 mm Hg, compared to 1,800 mm Hg for methyl bromide, 18 mm Hg for MITC and 29 mm Hg for 1,3-dichloropropene (Telone).
  3. J. Gan, et al., J. Env. Qual. 1997, 26: 1107–15, as cited in the Hazardous Substances Data Bank, National Library of Medicine.
  4. J. Gan and S.R. Yates, J. Agr. Food Chem., 1996, 44: 4001–8, as cited in the Hazardous Substances Data Bank, National Library of Medicine.
  5. Methyl Iodide Product Information, Iodine.com.
  6. a) Documentation of the Threshold Limit Values and Biological Exposure Indices, American Conference of Governmental Industrial Hygienists, Inc., 6th ed. Volumes I, II, III. Cincinnati, OH: ACGIH, 1991, p. 1013.
    b) Methyl Iodide, Chemical Health and Safety Data, U.S. National Toxicology Program.
  7. Methyl Iodide (Iodomethane), Air Toxics Website, U.S. EPA.
  8. M.M. Moore, D. Clive, Environ. Mutagen., 1982, 4: 499-519.
  9. Carbon-14 labeling studies indicate that methyl iodide methylates DNA, with DNA adducts detected in the stomach, forestomach, liver and lung of male and female rats exposed to [14C]-methyl iodide orally or by inhalation. IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man, Geneva: World Health Organization, International Agency for Research on Cancer, 1999, 71: 506.
  10. Monohalomethanes: Methyl Chloride, Methyl Bromide, Methyl Iodide, National Institute for Occupational Safety and Health, September 27, 1984, page 22.
  11. California Proposition 65 list, California Office of Environmental Health Hazard Assessment.
  12. IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man, Geneva: World Health Organization, International Agency for Research on Cancer, 1986, 41: 222.
  13. IARC monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man, Volume 15 (1977), 41 (1986) and 71 (1999).
  14. Iodomethane Preliminary Risk Assessment, US EPA, Docket ID #EPA-HQ-OPP-2005-0252, Go to Docket.
  15. H. Matsui, et al., Sangyo Igaku, 1982, 24: 85-89.
  16. H. Matsui, et al., Hormone Metab. Res. 1982, 14: 676-67.

See the complete list ofresources about pesticide drift.

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