Last week (December 1, 2010), the California Department of Pesticide Regulation (CDPR) registered the soil fumigant Midas for use in the state following months (years) of controversy and protests. I’ve been meaning to talk a bit about soil fumigation in this blog and I’ll try to address the general issues in a future post. For today, I’ll focus on methyl iodide since it is a "hot topic".
Midas, marketed in the US by Arysta LifeScience, is a combination of methyl iodide (aka iodomethane) and chloropicrin and has been proposed as one viable alternative to methyl bromide. Midas received a federal registration in 2007 and has been available in 47 states for several years; however, the primary market so far has been high-value fruit and vegetable crops in Florida and other southeastern states. California, New York, and Washington generally have additional regulatory steps in the registration of new pesticides and often register products several years after US EPA approval. As I understand it, Arysta is not currently pursuing registrations of Midas in New York and Washington due to the cost of registration versus the limited market for soil fumigants but the California specialty crop market is obviously the ripest remaining fruit.
There have been many newspaper articles and blog posts about the dangers of methyl iodide. Many are clearly very agenda-driven and/or simply regurgitation of other clearly biased reports like this one from the Sacramento Bee http://www.sacbee.com/2010/12/04/3231811/inexplicably-state-approves-new.html?storylink=lingospot_related_articles . This particular writer shows a fundamental lack of understanding of soil fumigation by suggesting that one extra weeding operation per year in strawberry fields would eliminate the need for a fumigant. While weed control is one of the targets of soil fumigants, the primary soil pests in California strawberry are soil diseases (like Verticilium dahlia) that can cause catastrophic crop failure. Other crops like orchards, vineyards, and nurseries face other soil diseases and plant parasitic nematodes (tiny roundworms) that feed on crop roots.
I think a better place to start reading is this article in The Californian which presents a point-counterpoint by Jim Sims (UC Riverside) and Susan Kegley (Pesticide Action Network) http://www.thecalifornian.com/article/20101204/OPINION02/12040332/Point-counterpoint-use-of-methyl-iodide . Another reasonably well written article about Midas in strawberries can be found in the same issue of The Californian http://www.thecalifornian.com/article/20101204/NEWS01/12040314/New-pesticide-new-dilemma .
I don’t have the expertise to comment about the acute or chronic toxicity of methyl iodide directly. However, I would make two primary points about toxicity that should be remembered by critical readers and consumers and one point about how and where methyl iodide is likely to be used in California.
First, methyl iodide is indeed a toxic compound. News flash: It’s supposed to be. Fumigants, whether for killing pests in the soil, killing pests in products for import/export, or for killing termites and other pests in your (vacated) house are designed to move in the gas phase and penetrate into corners and crevasses and kill pathogens, insects (eggs, larvae, adults), weeds, rodents, etc. This is true for methyl iodide, methyl bromide, chloropicrin, 1,3-dichloropropene, or pretty much any gaseous fumigant – that’s how and why they work. No fumigant is without danger to humans
Second, a lot of critics of methyl iodide (and many other pesticides) point to the carcinogenicity of the compound. In the point-counterpoint article I linked above, Jim Sims quoted Lois Gold and Bruce Ames of UC Berkeley who remind us that "high-dose effects in rodent cancer tests….are not relevant to low-dose human exposure". This basically means that if you feed or inject a lab animal with high amounts of a compound and it gets a tumor, it does not directly follow that low exposure in humans will also cause cancer.
This made me think of the nearly ubiquitous warnings about the presence of "compounds known by the state of California to cause cancer" so I took a look at the Prop 65 list of "Chemicals known to the state to cause cancer or reproductive toxicity (November 12, 2010)". http://oehha.ca.gov/prop65/prop65_list/files/P65list11122010.pdf . There are a lot of "chemical" names on that list but a quick run through also revealed several other carcinogens that we seem to be willing to risk including: aspirin, alcohol, carbon monoxide, diesel engine exhaust, unleaded gasoline, oral contraceptives, testosterone, estrogen, tobacco smoke, nicotine, wood dust, black carbon dust, etc. I’m sure if I looked at the labels of various products under my sink or in my garage, I would recognize many more carcinogens on this list. My point is not that methyl iodide or any other fumigant is great for the world. The point is that we take risks daily and that some tools we use in agriculture and in our non-agricultural lives have dangers.
Methyl iodide is not likely to be all that widely used in California, at least not compared to many other pesticides. Soil fumigants are used before the crop is planted – they are not used on the crop itself as they would kill the plants (see my broad-spectrum toxin point above). Fumigants are quite expensive to the growers, thus, they will be only used in high-value crops that see sufficient benefit to the costs – not in very many crops in the state. The previous standby, methyl bromide, has become too expensive for many crops and methyl iodide (and specialized plastic films) are likely to be at least as expensive as methyl bromide. Because of safety concerns (and public scrutiny) DPR will require large buffer zones (unfumigated areas) around fields which will further limit amount of treated acreage. Between the potential crop acreage, estimated cost of the fumigant and tarps, and regulatory restrictions , I don’t think we will see all that many acres treated with the product. For example, according to Arysta, after three years, only about 16,000 acres has been treated with Midas in the other 47 states http://www.arystalifescience.us/usa/media/California_Registers_Midas.pdf .
I am an advocate for agriculture – as a lifestyle, vocation, industry, and national security interest. I would much rather our agricultural industries remain in the state rather than move to other countries (where pesticide rules and farm worker rights may not be as restrictive…) and have valuable farmland turned into more subdivisions and strip malls. I am absolutely in favor of finding and implementing integrated pest management strategies for fumigation-dependant industries. Likewise, I support organic agriculture and its ever growing market niche. However, to maintain current levels of productivity in the short term, several California industries still need soil fumigants. Methyl iodide may help bridge the gap until more feasible and economically viable alternatives are available.
The Midas story will be interesting to watch over the next few months, I’m sure.
Edit 12-14-10 to add a link to another Sacramento Bee opinion article. This one is a response from Mary-Ann Warmerdam, the director of the California Department of Pesticide Regulation.
http://www.sacbee.com/2010/12/11/3249709/states-methyl-iodide-analysis.html?storylink=lingospot_related_articles
Brad
Disclaimer: I have conducted soil fumigant research (including on methyl iodide) while employed by UC Davis and in a previous position with the USDA-ARS. Our work has been funded by grants from the US government, California commodity commissions, and the pesticide industry. In the early and mid-2000's, some of this work was supported by Arysta LifeScience.