Methyl iodide?

[Miles]

A rather alarming piece concerning the use of methyl iodide as a pesticide on strawberries recently came to my attention. My first reaction was to think, "How terrible! I eat 'conventional' (not 'organic') strawberries: am I going to be ingesting this carcinogen?" But then it occurred to me that such alarms often get raised on an unsound basis. So I figured that, before I accept the claims made in this piece, I might seek comment from those who know something about the chemical in question. Here is an extract from the piece in question (from Credo Action). Does anyone know anything bearing on the reliability of its claims?

 

Tell the E.P.A.: No more methyl iodide

 

Methyl iodide is a nasty chemical. It is a known neurotoxin and endocrine disruptor, and scientists in labs handle only small amounts using special protective equipment because it is so toxic. But do you know where else it is used? As a pesticide on strawberries and other food crops. [. . .]

 

Methyl iodide has been subject to ongoing controversy in its approval process. The U.S. EPA approved methyl iodide for agricultural use in 2007, amid criticism from more than 50 prominent scientists1 that the process was hidden from public view and the research focus was too limited. In California, evidence has come to light that the DPR ignored advice from its own scientists. The head of that agency has since resigned -- to work for the chemical company Clorox.

 

There is little to debate about methyl iodide's toxicity. It is a known neurotoxin, disrupts thyroid function, damages developing fetuses, and has caused lung tumors in laboratory animals. Fumigating fields with the gas -- even with the strictest regulations -- would no doubt still result in unacceptable exposures to farmworkers and surrounding populations.

 

Edited to add: I also found an article under the headline "Warning about strawberry field chemical ignored, scientists say" (June 7, 2010) at a Web publication called California Watch. It substantiates the claims made in the Credo Action piece. Extract:

 

 

Conventional strawberry growers have spent a decade looking for a viable alternative and have turned up only one: methyl iodide. Under the new regulation, farmers would use the chemical as a fumigant to sterilize the soil before the plants go in.

 

Lab tests involving rats and rabbits show methyl iodide can cause thyroid cancer and miscarriages. But scientists say methyl iodide is also a neurotoxin. Although this research is less well-developed, case studies of people who were accidentally exposed to methyl iodide show "chronic, irreversible brain damage," according to John Froines, a chemist at UCLA who chaired the independent review panel.

 

Amid this evidence, scientists at the DPR recommended a maximum exposure of .8 parts per billion for farmworkers. State regulators are proposing 96 parts per billion, over an eight-hour day.

 

Scientists on the review panel said methyl iodide hasn't been sufficiently studied to justify the larger amount. They're concerned about damage the fumigant could inflict on developing brains in infants and children, including subtle changes to IQ, or behavioral changes that might take years to detect.

Because of these concerns, the scientists added an extra "uncertainty factor" to their calculations, which lowered recommended exposure levels by a factor of ten.

 

The DPR's scientists say they were left guessing as to how their supervisors had made the jump to the larger amount, according to e-mails obtained by KQED'S "Quest." In the e-mails, staff scientists said the uncertainty factor appears to have been removed.

Edited April 26, 2011 by Miles

[mississippichem]

The toxicity claims are true. Iodomethane is quite toxic. But read this, evidently the risk of ingesting iodomethane from produce is low:

 

The rate of abiotic hydrolysis is slow at temperatures relevant to agricultural conditions,

with a half-life of 113 days at 25 ˚C and pH = 7. The photolysis rate of iodomethane

dissolved in water is faster (13.1 day half-life). Iodomethane displays low sorption to

soil. Coupled with its high vapor pressure, iodomethane is therefore mobile in soil/water

systems. It is quickly metabolized by soil microorganisms under aerobic conditions with

an aerobic soil metabolism half-life of 2 hours. Under anaerobic conditions, the

degradation rate is slower with an anaerobic soil metabolism half-life of 41.8 hours. An

iodomethane terrestrial field soil dissipation study and concurrent volatilization study

were conducted using tarped bare ground sites in a commercial strawberry production

area of Watsonville, CA and a commercial strawberry/tomato production area of Dover,

FL. Based on residues in a 0 to 24 inch soil sample core, the field dissipation half-life

was 5.0 days. The highest levels of iodomethane in air occurred immediately after

application, ranging from 0.01 to 0.065 ppm.

 

California Environmental Protection Agency, August 2009.

 

Read the full paper at: www.cdpr.ca.gov/docs/risk/mei/mei_vol3_ef.pdf

 

I'm no toxicologist, but I doubt you have much to worry about. Don't be suckered in by the "Organic Food" mongers.

Edited April 26, 2011 by mississippichem

[Horza2002]

While yes, iodode methane is very very nasty...its is toxic and carcinogen. The MSDS is in the link below:

 

http://msds.chem.ox.ac.uk/IO/iodomethane.html

 

However, as mississipichem has said, it is not a stable molecule. In the C-I bonds are very weak and so are undergo photolysis very easily. Not only that, but iodomethane is a good electrophile..so much so that it will react with water reasonably quickly to give hydrogen iodide and methanol.

 

So overal, no I wouldn't be worried at all.