Pesticide Exposure Linked to Depression Among Ag Workers, Says Report

This article was first published in Earth Island Journal.


It is not clear if farmer suicides are linked to pesticide use, says coauthor of study that’s being cited in news reports connecting the two

Is routine exposure to pesticides responsible for the global outbreak of suicides on farms? One might think so after reading a recent report that was published in several popular science and environment magazines and websites that suggested researchers have linked pesticide exposure with farmer suicides.

The pesticide-suicide meme gained currency on in early October with the publication of the article, “Pesticide use by farmers linked to high rates of depression, suicide,” in the online magazine Environmental Health News. The article noted that “recent research has linked long-term use of pesticides to higher rates of depression and suicide.” Versions of the article were published by the Scientific American and other publications. But a closer look into the issue reveals that so far, no direct link has been established between pesticide exposure and farmer suicides.

It’s true that suicides on farms are occurring with alarming frequency, not only in developing countries like India and China, but also in the United States, France, England, Canada, and Australia. Prolonged drought, failed crops, mounting debt, and poor economics on the farm have been offered as possible reasons, in addition to depression caused by pesticide exposures. (According to an investigation published in 2012 in the medical journal The Lancet, a person living in a rural area is twice as likely to commit suicide as a person in an urban area.)  But, as Dr Freya Kamel, a senior researcher at the National Institutes of Health says, there’s no evidence that exposure to pesticides is a direct cause of farmer suicides.

Kamel is one of the eight co-authors of a study cited by in the media reports as evidence of the link between pesticides and suicides. The study, “Pesticide Exposure and Depression among Male Private Pesticide Applicators in the Agricultural Health Study,” was published in the September 2014 issue of the scientific journal Environmental Health Perspectives (EHP). Kamel says that while research shows that pesticide exposure does affect mental health, some people are misreading the study as evidence of a pesticide-suicide connection.

“Everybody who has been talking to me about our recent publication has wanted to conflate the two things,” she told me. “In our study, we found absolutely no association of pesticides with suicide.”

The EHP study does not even mention the word “suicide.” “It is not at all clear to me that suicide has anything to do with pesticides.” If pesticides are involved, she added, it’s in the event of an intentional overdose. In the US, farmer suicides are more likely to be the result of gunshot wounds. In other countries, the methods are often far more gruesome.

However, Kamel and her colleagues did find a strong link between pesticide usage and mental depression.

“Suicide and depression are not the same thing,” she said. “We did a paper earlier on suicide, and only 15 percent of people who committed suicide have reported depression, so it’s not a strong link. It is clear that depression is a risk factor for suicide, but there are other psychological characteristics that increase the risk of suicide much more, like hostility and aggression. Suicide is a form of aggression directed inward. “

Apart from the EHP study, the Environmental Health News article cites only two other studies that it said “have linked suicide to pesticide use,” but in each case the link was tenuous. Neither of the two studies mentioned pesticide exposure as a cause for suicide, but merely pesticide use and possession. One study from Brazil found higher rates of suicide and suicide attempts in areas where pesticides are intensively used, and the other one, a World Health Organization survey of 9,800 people in China’s rural Zhejiang province revealed that those who stored pesticides in their homes had more than double the risk of having suicidal thoughts.

That pesticides are linked to depression among farmers and agricultural workers is a serious matter in itself and it deserves more attention.

Many studies have linked pesticide exposure to depression in the past, including 10 cited in the EHP report. The EHP research is significant because it identifies, for the first time, the names of specific pesticides that “may be positively associated with depression.” Few previous studies have looked into the impacts of individual pesticides.

The study, which analyzed data for 10 pesticide classes and 50 specific pesticides used by 21,208 applicators in Iowa and North Carolina, and found that seven individual pesticides were most closely associated with depression. (The research was part of a federal Agricultural Health Study, a collaborative effort involving investigators from National Cancer Institute, the National Institute of Environmental Health Sciences, the Environmental Protection Agency, and the National Institute for Occupational Safety and Health.)

The seven pesticides found to be linked to depression were: the fumigants aluminum phosphide and ethylene dibromide; the phenoxy herbicide (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T); the organochlorine insecticide dieldrin; and the organophosphate insecticides diazinon, malathion, and parathion.

The US Environmental Protection Agency no longer allows farmers to use ethylene dibromide, 2,4,5-T, dieldrin, and parathion. But aluminum phosphide, diazinon, and malathion have been legal to use for many years and are now undergoing an EPA regulatory process known as “re-registration review.”

The EPA has published fact sheets about the potential health effects of exposure to these three  legal pesticides (you can view them here, here and here). None of the fact sheets mention mental depression as among their health effects.

There are 23 products registered as pesticides in the US that contain aluminum phosphide as the active ingredient. Aluminum phosphide is registered as fumigants on a wide variety of raw agricultural commodities including stored grain and vegetable crops, stored processed foods and nonfood commodities. Typical storage structures include silos, bins and railcars. The EPA lists aluminum phosphide in Toxicity Category I, the highest (most toxic) of four categories, for acute effects via inhalation. Symptoms of mild to moderately acute toxicity include nausea, abdominal pain, tightness in the chest, excitement, restlessness, agitation, and chills.

The EPA’s final decision in its aluminum phosphide re-registration review is not expected until 2020.

The EPA says diazinon can cause cholinesterase inhibition in humans, a condition that can overstimulate the nervous system, causing nausea, dizziness, and confusion; and at very high exposures (e.g. accidents or major spills) respiratory paralysis and death. The EPA’s final decision in its diazinon re-registration review is due this year.

Malathion, also a cholinesterase inhibitor, can have health effects that are similar to those of diazinon. The EPA’s final decision in its malathion re-registration review is due in 2015.

Since 1999, at least 10 peer-reviewed studies have found a link between pesticides and mental depression among their cohorts, including:

A 1999 study of 51 women employed in gardening enterprises. The exposed workers had longer reaction times and reduced motor steadiness compared to unexposed workers. In addition, increased tension, greater depression and fatigue, and more frequent symptoms of central nervous system disturbances were observed in the exposed women compared to the controls.

A 2000 study of one of the worst human-induced chemical disasters in history examined 1,800 homes and businesses in Jackson County, Miss., that had been contaminated with methyl parathion over a 10-year period. More than half the victims interviewed reported symptoms at levels suggesting probable clinical depression. Those at greatest risk of depressive symptoms were people who had been exposed to the neurotoxin for the longest period of time, among whom there was an overrepresentation of women and African Americans.

A 2010 study found that more than 40 percent of a group of sheep farmers exposed to organophosphate insecticides reported clinically significant levels of anxiety and depression compared to less than 23 percent of a control group who were not exposed.

A 2010 study in Costa Rica examined symptoms of psychological distress, including suicidal thoughts, among banana workers in Costa Rica previously exposed to a cholinesterase inhibiting pesticide. Organophosphate-poisoned workers reported significantly more symptoms than non-poisoned workers.

None of these, or similar studies, mention suicide as a consequence of pesticide poisoning, although one found that pesticide exposure might induce suicidal thoughts This study, “Symptoms of psychological distress and suicidal ideation among banana workers with a history of poisoning by organophosphate or n-methyl carbamate pesticides,” found a relationship between acute occupational poisoning with organophosphates and psychological distress including suicidal ideation, or thoughts.

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