New Study Links Suicidal Thoughts to Pesticides

(Beyond Pesticides, October 26, 2009)

A new study conducted in China finds that people with organophosphate pesticides in their homes are more likely to have suicidal thoughts. According to the study, “Pesticide exposure and suicidal ideation in rural communities in Zhejiang province, China,” published in the October issue of the WHO Bulletin, there is biological evidence that chronic low-grade exposure to organophosphate pesticides, which are very easily absorbed into the body through the skin and lungs, may have adverse effects on mental health.

The study was carried out in the central/coastal region of China, a relatively wealthy area with a rapidly developing economy. In a very large survey of mental health in rural community residents, participants were also asked about how they stored pesticides. The study found that people who stored pesticides at home, i.e. those with more exposure, were more likely to report recent suicidal thoughts. Supporting this, the survey also found suicidal thoughts to be associated with how easily accessible these pesticides were in the home and that the geographic areas with highest home storage of pesticides also had highest levels of suicidal thoughts in their populations.

“Organophosphate pesticides are widely used around the world. They are particularly lethal chemicals when taken in overdose and are a cause of many suicides worldwide,” stated one of the study researchers, Dr. Robert Stewart. “Our research findings that suggest that higher exposure to these chemicals might actually increase the risk of suicidal thoughts provides further support for calls for tighter international restrictions on agricultural pesticide availability and use.”

The analysis involved data from a survey of a representative sample of 9,811 rural residents in Zhejiang province who had been asked about the storage of pesticides at home and about whether or not they had considered suicide within the two years before the interview. The Chinese version of the 12-item General Health Questionnaire (GHQ) was administered to screen for mental disorder.

According to the study findings, the odds ratio for the association between pesticides stored at home and suicidal ideation over the 2 years prior to the study was more than double. Of the pesticides stored at home, nearly 87 percent comprised or included organophosphates. The most commonly stored pesticide was methamidophos, which was present in 63 percent of households that stored pesticides.

Previous studies have shown that farmers often have higher rates of depression than other population groups. A study published in 2008, “Depression and pesticide exposures among private pesticide applicators enrolled in the Agricultural Health Study,” found that both acute high-intensity and cumulative pesticide exposure contribute to depression in pesticide applicators. Another 2008 study “A cohort study of pesticide poisoning and depression in Colorado farm residents,” found adverse effects on mental health such as irritability were associated with pesticide poisoning.

A 2002 study found that farmers poisoned by agricultural pesticides containing organophosphates are nearly six times as likely to suffer depression in their lifetimes as compared to their counterparts. The study showed that populations exposed to the agricultural pesticides also face long-term risks of anxiety, irritability, restlessness and depression. In the study, 69 participants reported having been sickened by pesticide poisoning. 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 and younger farmers were more likely to have high depressive symptoms compared to older farmers.

Organophosphates are a family of insecticides that are derived from World War II nerve agents. They are cholinesterase inhibitors, meaning that they bind irreversibly to the active site of an essential enzyme for normal nerve impulse transmission, acetylcholine esterase (AchE), inactivating the enzyme.