Overexposure to agricultural pesticides may lead to severe depression among farm residents, according to a recent Colorado State University study.

"The study’s findings support evidence of an association between mental health and pesticide poisoning," said Colorado State psychology professor Lorann Stallones, lead author of the study. "Farmers poisoned by agricultural pesticides containing organophosphates are nearly six times as likely to suffer depression in their lifetimes as compared to their counterparts."

Organophosphates are highly toxic compounds found in industrial-strength agricultural pesticides that are easily absorbed through the skin, mucus membranes, lungs and intestines. Immediately after being poisoned, a person can experience nausea, vomiting, abdominal pain, headaches, respiratory problems and blurred vision. However, the study shows that populations exposed to the agricultural chemicals also face long-term risks of anxiety, irritability, restlessness and depression.

Previous studies have shown that farmers often have higher rates of depression than other population groups. Additional studies have reported that farm workers have a higher risk of suicide compared to other workers.

"However, little work had previously been undertaken to investigate the effects of exposure to pesticides on depressive symptoms among the farming population," Stallones said.

To investigate the relationship, Stallones and study co-author Cheryl Beseler recruited 761 farmers and their spouses from eight counties in northeastern Colorado living and farming in the state between 1992 and 1997. Participants provided details about aspects of their physical and mental health, farm operations, pesticide exposure and other information.

In the study, 69 participants reported having been sickened by pesticide poisoning. Factoring in other dynamics such as age, education level, marital status and alcohol use, farmers who reported organophosphate poisoning were 5.8 times more likely to score high on tests measuring level of depression than farmers not poisoned by the chemicals.

Other study findings include that the Colorado farm population was more likely to have high depressive symptoms if they were female and in poor physical health; younger farmers were more likely to have high depressive symptoms compared to older farmers; and educational achievement and income were not associated with depressive symptoms.

Perhaps the most controversial finding was that those who live on farms and actively involved in agricultural work were less likely to have high depressive symptoms than their counterparts not actively involved in farm work. This finding is contrary to a longstanding belief that farm workers are highly stressed and therefore likely to be at a higher risk for depression.

"This study provides evidence of a link between pesticide exposure and depression," said Stallones. "However, many more questions need to be answered and further research needs to be conducted to better determine factors that affect the overall risk of depression and suicide among farm residents."

Colorado State