California is considering legalizing the use of methyl iodide as a fumigant for crops such as strawberries. This chemical is being considered as a replacement after the ban on methyl bromide, which was banned because of its effects on the ozone layer. Methyl bromide is also poisonous but methyl iodide is worse.
Methyl iodide is selected because the larger iodine atom is heavier than bromine, so it cannot rise into the atmosphere as easily as bromine. Light also degrades methyl iodide faster than methyl bromide. As the iodine atom is larger, it is also more stable as an iodine ion, and disassociates much more easily from the methyl group. The methyl ion is what is causing the toxicity problems, since the methyl free radical can attach to chemicals in the body and react with them, as it reacts with ozone in the atmosphere.
The selling pitch is that methyl iodide is more effective at killing plant bugs and worms than methyl bromide, which is true for the reasons mentioned above. Some growers and pesticide manufacturers claim that methyl iodide is safe because of its lower vapor pressure. The heavier iodine containing molecule does not evaporate into the air as easily as bromine does, even if it is more toxic. That reduces the amount of methyl iodide in the air, but if it’s on clothing or the workers’ skin, as well as on the vegetables, it remains very dangerous.
According to the Sacramento Bee, methyl iodide is approved as a fumigant in 47 other states. This is concerning, since it means that this pesticide is sprayed in other fields where foods are harvested for shipment to California. California grows a lot of its own crops, so pesticides from other states are not a huge concern, but people who live near farms in other states and countries might want to be aware of this regulatory battle.