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A Closer Look: Pesticides in strawberry fields

Scientists say methyl bromide threatens the ozone layer, and its alternative, methyl iodide, is a threat to workers and their families.

June 28, 2010|By Jill U Adams, Special to the Los Angeles Times
  • The Environmental Working Group, an advocacy group, ranks strawberries as one of the three worst fruits and vegetables with regard to pesticide exposure. (Peaches and celery are the other two.)
The Environmental Working Group, an advocacy group, ranks strawberries… (Stephen Osman / Los Angeles…)

California strawberry farmers may soon have a new pesticide to use on their fields. The state's Department of Pesticide Regulation is recommending approving use of the soil fumigant methyl iodide.

However, scientists say that methyl iodide is very toxic and can cause cancer, brain damage and miscarriages. An independent panel of scientists, invited to review the health


FOR THE RECORD:
Pesticide: An article in Monday's Health section on the debate over a pesticide that may be approved for use on strawberry crops said that molecular biologist Edward Loechler works at Brandeis University. He is at Boston University. —

risk data and safe exposure levels recommended for farmworkers and nearby communities, were shocked that the state is still moving toward approval and at higher levels of exposure than what the department's scientists proposed.

Methyl iodide received approval from the U.S. Environmental Protection Agency in 2007, accompanied by a similar uproar. Fifty-four eminent academic scientists and physicians wrote a letter to the agency, urging them to prevent the chemical's use.

In California, new pesticides must undergo an additional layer of review. As part of that review, risk assessment scientists within the Department of Pesticide Regulation settled on 0.8 parts per billion as an acceptable exposure level of methyl iodide. "We all thought that, if anything, it should be lower than that," says Edward Loechler, a molecular biologist at Brandeis University in Boston who served on the scientific review panel.

Instead, the DPR risk managers have settled on 96 parts per billion — far more than the panel recommended, although still roughly half of the 193 ppb permitted by the EPA. "That's not policy — that's meddling with the science," says panel member Dr. Paul Blanc, head of the occupational and environmental medicine division at UC San Francisco.

Pesticide reform groups are opposed to registration of the chemical for agricultural use. "The Pesticide Action Network has not objected to the registration of any new pesticide in the last 15 years — but methyl iodide is so toxic that it's worth going to the mat on this one," says chemist Susan Kegley, who consults for the organization. Usually, newer pesticides are less toxic than the old ones, she says.

In a statement, Department of Pesticide Regulation Director Mary-Ann Warmerdam said that, with the use restrictions her agency is recommending, which are more stringent that those of the EPA, "methyl iodide can be used safely."

Here's a closer look at the health effects of methyl iodide and who is at risk.

What is methyl iodide?

Methyl iodide, also called iodomethane, is a small, highly reactive chemical that kills a wide range of tiny animals, weeds and fungi that live in soil, many of which are detrimental to strawberry growth. The pesticide is applied to fields before planting and is so chemically reactive that it does not remain in the soil for long. More than half of the applied fumigant evaporates into the air, where it breaks down within 12 days; what remains in the soil also breaks down quickly, according to the EPA.

Methyl iodide was developed as an alternative to methyl bromide, which has similar pest-killing actions. However, agricultural use of methyl bromide is being slowly phased out because it lasts longer in the atmosphere (as long as two years) and contributes to depletion of the ozone layer.

Who is at risk?

The main people at risk of methyl iodide exposure are farmworkers — those who apply the chemical — and anybody who lives or works near treated fields.

There's no methyl iodide risk in eating strawberries that were grown in treated fields, according to EPA and DPR assessments. Tests have shown that no residual methyl iodide exists on the fruit.

So strawberries are clear of pesticides?

Conventionally grown strawberries still contain residues of other pesticides. According to data collected by the U.S. Department of Agriculture, as many as 54 pesticides have been found on American strawberries, although rarely at levels above what the EPA considers safe. The Environmental Working Group, an advocacy group, ranks strawberries as one of the three worst fruits and vegetables with regard to pesticide exposure. (Peaches and celery are the other two.)

What are the health risks with methyl iodide?

In animal studies, exposure to sufficient quantities of methyl iodide causes thyroid cancer, neurotoxicity and fetal death.

"We're talking about an extremely reactive chemical that binds to key biological molecules, including — but not limited to — DNA," Blanc says. "In fact, if you're working in the laboratory and you want to modify DNA experimentally, methyl iodide is one of your chemicals of choice."

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