Studies show toxic chemicals impair brain function

More and more, scientists are discovering links between toxic chemical exposure and brain function. Two new studies have strengthened this connection for pesticides, one finding that pesticides can affect the behavior of mother animals toward their young, and one finding more depression among farmers exposed to pesticides.

In the laboratory, researchers in Argentina exposed mother rats to the herbicide 2,4-D for a week after they gave birth. The rats that were exposed were slower to retrieve their pups after birth and were much less likely to show normal maternal behaviors such as licking. The treated rats also took longer to get into position for nursing. In addition, they spent more time out of the nest: all treated rats left the nest, whereas only 25 percent of untreated rats did.

To get at the cause of this behavior change, the researchers tested hormones related to behavior as well as neurotransmitter levels, which would show disruptions in brain chemistry. They found greatly reduced levels of the hormone prolactin in treated animals, as well as changes in neurotransmitter balance.

A newly published study in Environmental Health Perspectives shows effects that are not limited to the laboratory. The Agricultural Health Study is a large study, of 89,000 individuals, sponsored by the National Institutes of Health and the Environmental Protection Agency. Its goal is to explore the causes of diseases including cancer among farmers, their families, and pesticide applicators; these groups have higher rates of some cancers than the general population.

In this study, the researchers examined the possibility of a link between pesticide exposure and depression. They surveyed farmers, asking about their status with regard to depression. They then compared pesticide exposure among 534 farmers who had been diagnosed with depression and 17,051 farmers who had not been diagnosed or felt depressed more than once a week in the past year.

They found that farmers who had either had a pesticide poisoning incident or high cumulative exposure were more likely to be depressed. In addition, they found that farmers who had ever used insecticides, organophosphate or organochlorine pesticides were more likely to suffer from depression. While other studies have found a link between pesticide poisonings and depression, this is the first to find an association with long-term pesticide exposure. It also includes a much larger study group that most similar studies.

The study findings linking pesticide exposure to depression were published Sept. 9 in Environmental Health Perspectives by lead author C. Beseler. The study findings on pesticides affecting maternal behavior in rats was published volume 247 of Toxicology by lead author N. Stürtz .

Erika Schreder is a staff scientist at Washington Toxics Coalition, where she leads the Coalition’s research on toxic chemicals in children’s products. In 2005 and 2006, she led the research for the Toxic-Free Legacy Coalition’s Pollution in People study. She has a Masters in Resource Ecology and Management from the University of Michigan and a B.S. in molecular biology from MIT.