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Insecticide Use Linked to Neurological Problems for Farmers

May 2005

A new NIEHS study shows that farmers who used agricultural insecticides had increased neurological symptoms - like headaches, fatigue, dizziness, nausea, hand tremors and numbness - even when they were no longer using the chemicals.

NIEHS researchers, as part of the ongoing, multi-agency Agricultural Health Study, looked at data collected in nearly 19,000 questionnaires that asked North Carolina and Iowa farmers about their exposure to herbicides, fungicides and fumigants. Some of those products are still on the market, while others, like DDT, have been banned or restricted.

Unlike many past studies, which focused on high-dosage exposure, the study looked at levels that are common for farmers, according to NIEHS researcher Freya Kamel. They found that nearly 3,000 participants had a high lifetime exposure to insecticides, defined as more than 500 days, and nearly 800 of them reported more than 10 neurological symptoms than the farmers who reported less than 50 days of exposure.

The study showed no significant association between neurological symptoms and other chemicals, including herbicides or fungicides, and only a weak association between fumigant exposure and neurological symptoms.

The study is available at and will appear in the June issue of the NIEHS journal, Environmental Health Perspectives.

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