At the height of the summer produce season, strawberries are ubiquitous and relatively cheap. But Edward Loechler would like the public to know that such abundance comes with a potentially devastating price tag.
A new pesticide called methyl iodide will soon be approved for use by strawberry growers in California at a level that Loechler, a College of Arts & Sciences professor of biology, believes may cause cancer in field workers. Loechler, a researcher of carcinogens, was one of nine scientists who studied methyl iodide as part of a California Department of Pesticide Regulation scientific review committee formed in spring 2008. After finding the chemical to be highly toxic, he and his colleagues recommended a safe exposure level of 0.8 parts per billion for strawberry field workers.
"That’s the only sensible option,” he says. “You can’t kill and maim workers to make strawberries cheaper.”
California regulators disagreed, and issued their own number: 96 parts per billion, or 120 times the level of exposure Loechler believes is safe.
Unless California’s legislators intervene, the regulators’ recommendation for methyl iodide dosage will be approved for use on June 29. “We need some oversight here,” Loechler says. “The state’s risk managers are making a mistake.”
For years, the strawberries that flood supermarket shelves each summer — 90 percent from California — were grown with the help of a pesticide called methyl bromide. Researchers later discovered that the chemical contributed to the depletion of the ozone layer, and over the past decade methyl bromide has been phased out under the internationally recognized Montreal Protocol.
Methyl iodide, developed as a substitute pesticide, received approval from the U.S. Environmental Protection Agency in 2008 with a recommended exposure level of 193 parts per billion, a number even higher than the one Loechler is now fighting. (California requires its own safety review process for new pesticides.) Thus far, the chemical has been used only for growing strawberries.
“I just think this stuff is too dangerous,” he says. “It’s such a simple compound, but it has so many different toxicities.”
BU Today spoke with Loechler about the potential risks of methyl iodide.
BU Today: How are pesticides used in strawberry fields?
Loechler: In the soil, there are grubs called nematodes that eat strawberries and roots and make the plants not as productive. Decades ago, we developed a chemical to put into the soil to kill nematodes and increase the yield of strawberries per plant. That was methyl bromide, which turned out to be an ozone depleter. Methyl iodide, the new alternative, would work the same way on the grubs.
Why is methyl iodide considered dangerous to humans?
It causes a mutation that leads to cancer. Methyl iodide belongs in a class of compounds that fairly indiscriminately methylate things. A methyl group goes on a particular atom in DNA and leads to a modification in DNA. Then when that DNA is copied — when cells divide — you will always get a mutation.
Those genes no longer work right; the proteins don’t work right. The cell isn’t regulated properly: it grows when it wants to rather than when it should, and you get a tumor.
There’s no mystery about this. Not only do we know these methyl groups do this, but it’s a well-worked-out pathway. Two very similar compounds, methyl nitrosourea (MNU) and methyl methanesulfonate (MMS), have been studied to death. They’re recognized as probable human carcinogens by many groups, such as the International Agency for Research on Cancer.
But methyl iodide has not been studied as extensively. It’s harder to study because it’s very volatile. There are probably thousands of papers on MNU and MMS, and there are only 25 papers on methyl iodide. Still, that’s a lot of papers. In 22 of those 25 papers, methyl iodide has been shown to affect pathways similarly to MNU and MMS.
What other health risks does methyl iodide pose to workers or others exposed to it?
The panel found that the principal health risks were neurotoxicity and cancer. There are reports of individuals exposed to high levels of methyl iodide having both short-term and long-term neurological problems. They go into a coma, then seem like they’re better. Six months later, they start complaining of problems such as memory loss, tics, weakness, mood swings, and dementia.
In some cases, the toxicology had to be done in experimental animals, and we had to extrapolate the results to humans.
Methyl iodide causes fetal death in experimental animals. That was a critical aspect of the ultimate value — 0.8 parts per billion — that we decided on as safe. It also causes developmental defects. There were parts of the body that just didn’t look right in experimental animals, and the animals revealed defects in behavior. You can see abnormal areas of the brain and abnormal parts of the nervous system, and the thyroid is enlarged.
Is methyl iodide a danger to consumers who eat strawberries?
Most likely, no. Methyl iodide is put into the soil, not sprayed on the plant, and it doesn’t get into the plant very much. All the evidence suggests that the residual effect, by the time you get the strawberries to market, is virtually zero.
Why are you speaking out against the proposed regulations for methyl iodide?
First, the best decision is to not use methyl iodide or methyl bromide. It’s an industry, and the growers can still make their money, but consumers just have to pay more. I hate to be blunt about this, but if you don’t get strawberries, have blueberries.
Second, we have this idea that we can just throw chemicals into our environment in tens of millions of ways and not have it come back to haunt us. There needs to be a transformation, where we start thinking in terms of diminishing our dependence on all of these chemicals. How many of them are really essential? How many are perceived as important when in fact they aren’t?
Third, if you think it’s important to use chemicals and there are risks, then you have to put in place the proper safety measures to minimize those risks. I couldn’t help but see an analogy between the methyl iodide circumstances, where the management side is saying, we don’t have to put in that extra safety factor, and BP’s decision not to have that third auditory safety valve on the Deepwater Horizon. Sometimes you get away with it. Sometimes you don’t, and the impact is horrific.
Should consumers concerned about field workers’ safety buy organic strawberries, then?
Yes, absolutely. At our hearing, we had a number of organic farmers come to testify and say, “You can do this without harmful compounds and it works.” But as a society we’re so addicted to a chemical approach rather than a holistic approach or an organic approach. Capitalism unfettered is an ugly thing.