Depression and one of its possible sequelae, death by suicide, are particular problems for farmers everywhere.  Any families that deal with depression and death by suicide of a loved one are all too familiar with these behavioral health issues.

Last week’s column identified five factors that research has strongly implicated as contributing to depression and suicide, including exposures to certain pesticides.  This week we take a more in-depth look at the culprit pesticides and relevant research methods.  

This article summarizes only the conclusions about pesticides that have extensive scientific confirmation of deleterious effects, so their users and others who are potentially affected can make informed determinations about using these chemicals.

A substantial and growing body of research indicates that toxic exposures to most organophosphate and organochlorine pesticides are positively correlated with the development of depression.    

Organophosphate pesticides kill their intended target insects by reducing the metabolism, or breakdown, of transmitter chemicals in the nervous system, thereby causing an overabundance of the transmitter chemical, acetylcholine, and disabling the insects that ingest or absorb these insecticides.  Organochlorine insecticides also disable nerve signal transmission, but through a different mechanism with somewhat similar symptoms.  

These chemical compounds affect humans similarly.  Human victims report feeling highly agitated, unable to think clearly or to sleep, and terribly ill at ease physically and mentally.  Definitive diagnosis of toxic reactions is based on blood levels of these transmitter chemicals.    

Acute high-level exposures, whether absorbed through the skin or by inhaling or ingesting the substances, usually lead to severe nausea and often convulsions.  Erratic thinking and depressive torpor may set in as the nervous system becomes overwhelmed.

The risk for developing depression is greater if the exposure is an acute poisoning that results in the need for detoxification treatment, but a lengthy period of low grade exposures can also lead to depression.  A significant amount of these substances is stored in fat cells and can be reabsorbed into the bloodstream that supplies the nervous system when the toxic substance accumulates.

In addition to farmers, persons exposed through pesticide drift such as agricultural field workers, as well as insecticide merchants, family members and anybody for that matter can unwittingly become exposed gradually if they do not use personal protective equipment and always take careful means to avoid the substances, tainted clothing and so forth.  

Persons who are agitated because exposure to organophosphate or organochlorine pesticides is suspected, should not take antidepressant medications that contain serotonin because medications that contain serotonin can intensify nervous system overstimulation and worsen uncontrollable negative reactions.  

The Agricultural Health Study, an ongoing longitudinal study of 89,000 farmers and pesticide applicators in Iowa and North Carolina, has yielded informative data concerning the use of many farm chemicals.  A subset of 19,000 subjects was selected from the Agricultural Health Study sample for extensive analyses.  

The selected sample study showed that the fumigants aluminum phosphide and ethylene dibromide, the herbicide 2,4,5-T, the organochlorine insecticide dieldrin and the organophosphate insecticides diazinon, malathion and parathion all were positively correlated with diagnosed depression.  The Environmental Protection Agency currently allows only the use of aluminum phosphide, diazinon and malathion.  

A newer class of nervous system activator insecticides, neonicotinoids, are widely used as crop seed treatments, usually by coating the seed.  Neonicotinoids have been suggested as a contributing factor to recent reductions of bees, butterflies and other beneficial insects.
While neonicotinoids are claimed by their manufacturers to be less toxic to humans–and mammals in general–than to insects, there are too few independent studies of the effects of neonicotinoid poisonings and their long-term usage on humans to be certain.  

Most studies of the effects of pesticides on humans do not prove they cause depression.  Correlations are associations and do not verify that these chemicals cause depression in humans, but animal testing suggests this is possible.

Most studies of exposures to pesticides of various types rely on verbal reports of the study subjects, such as self-ratings and questionnaire scores, or clinical diagnoses based on reported and observable symptoms and not on biological assays of the tested substances in blood or tissue.  

Because of ethical considerations, it is usually not possible to expose a test group of subjects to the pesticides that have been implicated and to compare them to an unexposed control group.  

However, much useful information could be obtained from autopsies if State Medical Examiners routinely include blood level analyses of commonly used pesticides, whenever a coroner suspects suicide as the cause of death of a farmer or anyone else who has likely been exposed to such agents.  

The next two weeks’ columns will consider how farmers can modify the factors that are known to contribute to depression and suicide.  Our behaviors make a difference in protecting our health and well-being.

Michael Rosmann is a Harlan, Iowa clinical psychologist (and fly-fisherman) who lives on the farm he shares with his wife.  Contact him at: