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Daily News Blog

02
Jul

Recent Studies Continue To Highlight Connection Between Depression and Suicide in Pesticide-Exposed Farmers

The risk of depression and suicide in pesticide-exposed male farmers continues to be documented in three new studies.

(Beyond Pesticides, July 2, 2024) Men’s Mental Health Awareness Month, which took place last month, evokes concern about the growing body of science linking pesticide exposure to neurological effects linked to depression. Recent studies reveal elevated rates of psychiatric disorders, including suicide, among farmers, with problems more common for males. 

Through systematic reviews, meta-analyses, surveys and interviews, and blood sampling, these three studies add to the growing body of science linking pesticide exposure to neurological impacts. First, in the Journal of Agromedicine, researchers from Greece and the United Kingdom review eight studies and find a significant positive association between pesticide poisoning and depression in agricultural populations.1 Second, a study in Toxicology shows a link between depression in Brazilian farmers and pesticide exposure, most notably with glyphosate usage.2 Third, the latest study in Environmental Toxicology and Pharmacology focuses on work by researchers from Spain in identifying farmers exposed to chlorpyrifos, mancozeb, and malathion that have higher rates of depressive symptoms and suicide attempts.3 

Through a meta-analysis of published research, the authors of the Agromedicine journal article identify pesticide poisoning as a risk factor of depression. With depression affecting more than 264 million individuals worldwide, this is a field of interest with increasing importance. The authors conclude that “farm workers represent a high-risk population for the development of depression.”1 The studies they analyze are throughout the United States, Korea, United Kingdom, and France with a focus on acute effects. While previous “epidemiological studies have reported higher prevalence of depression in particular occupational groups of individuals,” such as farmers, this review “confirmed a positive association between both pesticide exposure and pesticide poisoning and depression… [with] male agricultural workers [having] the highest incidence of depression compared to non-agricultural workers.”1      

Depression can have harmful effects on physical, mental, and cognitive functioning and increases suicidal risk. As the researchers state, “Disturbances in neurotransmitter functioning and genetic factors have been implicated in the etiology of anxiety disorders and depression.”1 They continue, saying, “High level acute poisoning involves inhibition of the enzyme acetylcholinesterase (AChE), causing neurotoxic effects and disturbances in peripheral, autonomic and central nervous system function (the cholinergic crisis) and resulting in a constellation of physical, cognitive, and psychiatric symptoms. AChE is used as a biomarker for exposure to organophosphates (OPs). Many neurotransmitters, few of which are responsible for mood regulation such as serotonin, are disrupted by OPs, which indicates the link between pesticide exposure and mood disorder, becoming in fact stronger in cases of acute poisoning.”1  

The researchers of the study in Toxicology link occupational pesticide exposure to depression among rural workers from Maravilha, Brazil by assessing “the mental health, oxidative, and inflammatory profiles of farmers exposed to pesticides and compared them to an urban control group without occupational exposure to pesticides.”2 This was performed through blood sampling and interviews with over 50 survey participants. 

The rates of mental disorders are higher in Brazil than the world average, “with an estimated 5.8% of the population diagnosed with depression and 9.3% with anxiety disorders, ranking the country as having the highest rates in the Americas region,” according to the World Health Organization (WHO). Brazil is also one of the largest food producers in the world, which raises concerns about pesticide usage and exposure. Beyond Pesticides has previously covered a study that links neurotoxic effects of the herbicides 2,4-D and glyphosate to the impairment of behavioral performance (i.e., attention/inhibitory control, memory/learning, language, visuospatial processing, and social perception). Another study links glyphosate to adverse impacts on the gut microbiome, which plays a pivotal role in regulating both physical and mental health. Exposure to glyphosate is widespread, as “glyphosate-based products have consistently maintained their dominance in the market, representing more than half of the total volume of pesticides sold in the country,” the authors say.2 Glyphosate is the predominant pesticide used by the farmers in the study in Toxicology, with 100% of them having reported using the herbicide, as well as other commonly used chemicals such as atrazine, simazine, paraquat, and permethrin. 

This study finds that farmers exhibit more severe cases of depression than non-farmers. “Our findings revealed an elevated prevalence of depressive disorders among farmers exposed to pesticides, along with an increased self-reported prevalence of depression in this population,” the researchers state.2 They also find that suicide rates are higher in regions dedicated to agriculture with intensive pesticide usage. The data reveals that of their participants, 57% of the farmers exhibit depressive symptoms. Of those, “7% presented severe symptoms, carrying a potential risk of suicidal behavior. Conversely, within the control group comprised of individuals from urban region of Maravilha, a substantial 80% showed no signs of depressive symptoms, with only 20% experiencing just mild indications of depression.”2 

The blood sampling reveals that, “Oxidative stress markers, such as increased lipid peroxidation and superoxide dismutase (SOD) activity, along with decreased catalase (CAT) activity and ascorbic acid levels, were noted in the pesticide-exposed group compared to controls.”2 The authors also determine that, “Redox imbalance, mitochondrial dysfunction and neuroinflammation were described as key factors on the mechanism underlying the neurotoxic impacts of pesticides… In addition, inflammatory processes were ascribed as one of the putative biological pathways associated with the neurobiology of both depressive mood and suicidal behavior.”2 With these findings, the authors conclude that inflammation and oxidative stress may be associated with depression in pesticide-exposed farmers and warrants further study, and that  “occupational exposure to pesticides, especially glyphosate, compromises antioxidant defense mechanisms and induces inflammatory processes that may compromise neural circuits and may be associated with the pathophysiology of anxiety and/or depression disorders in pesticide-exposed farmers.”2 

The third study, in Environmental Toxicology and Pharmacology, adds to the findings of pesticide exposure correlating with depressive symptoms as 453 participants in AlmerĂ­a, Spain were surveyed and sampled. Of those participants, 225 were pesticide-exposed farmers that showed “significantly increased risk of moderate/severe depression and suicide attempts compared to non-farmers” with risks particularly observed with chlorpyrifos, mancozeb, and malathion exposure.3 33.3% of the farmers had made a suicide attempt compared to only 18.4% of non-farmer participants.  

All participants in this study were males, and all farmers reported having direct and indirect means of pesticide exposure. Blood samples were collected, and enzyme markers such as erythrocyte AChE and butyrylcholinesterase (BChE) were analyzed in the blood samples. The authors find that, “The AChE activity was lower in farmers than in non-farmers, as was BChE activity. When comparing AChE and BChE activity in farmers and non-farmers, according to the level of depression and whether they had had any suicide attempts, a significant decrease in AChE activity was observed in farmers with moderate/severe depression with respect to those with minimal/mild depression symptoms… Farmers who had had a suicide attempt showed significantly lower AChE and BChE activity relative to those who had not had suicidal attempts.”3 

This study is focused in Spain, where “approximately 10% of the surveyed population acknowledges experiencing psychiatric disorders, with depression (6.7%) being a prominent factor.”3 The importance of highlighting the connection between depression and pesticides in this country is particularly important since Spain led pesticide sales in the European Union in 2021, with transactions of “approximately 76,448 tons. Of these, 10,091 tonnes (13.2 percent) were used in the southern Spanish region of Almería, recognized for its intensive agricultural practices, both in greenhouses and outdoors,” the authors share.3 

Worldwide agricultural dependence on petrochemical pesticides and fertilizers puts everyone at risk. “This widespread application of pesticides has come at a considerable cost, impacting both environmental and human health, particularly among farmers occupationally involved in pesticide application,” the researchers say. “The adverse effects of pesticides can manifest acutely through high-concentration pesticide intoxication or chronically as a result of repeated exposure to lower concentrations… While factors like physical injuries and chemical exposures often take center stage, it’s crucial to recognize that mental health is an equally significant concern.”2 

These studies, proving a connection between pesticide exposure and mental health disorders in various parts of the world, highlight the lack of extensive research on the neurological impacts of pesticide exposure, specifically for those with disproportionate risk, as well as the need for alternative agricultural methods that do not cause unreasonable harm. “These findings,” the researchers conclude, “underscore the importance of investigating the neurotoxic effects of pesticides and their relationship with mental disorders, emphasizing the need to implement appropriate preventive and protective measures in agriculture to preserve the mental health of farmers.”3  

While Beyond Pesticides has been reporting on mental health effects of pesticides since its founding, this area of research is still limited. In recent years, more studies have emerged that highlight the link between acute and chronic pesticide exposure and the prevalence of depression, especially in farmworkers. (See further previous coverage here, here, and here.) Additional research still needs to be conducted, though, to assess variations in types of exposure regarding time, amount, and type of pesticides, as well as how they correlate to mental health symptoms. The researchers comment that, “ongoing research efforts to safeguard the health of those who play a vital role in our agricultural communities” are still needed.2  

As the scientists share, “Suicide is a serious global public health issue that takes the lives of more than 700,000 people each year… Furthermore, since suicide in the agricultural population is widespread and constitutes a significant public health issue, it is imperative to comprehend the risk and protective factors associated with it to design and implement specific interventions targeting those with higher vulnerability.”3 

Farmworkers that are exposed to pesticides through the application process, as well as through direct or indirect contact with any targeted crops, are among those with a higher risk. According to the latest survey from the National Center for Farmworker Health (NCFH) for 2019-2020, 66% of crop workers are male. Based on the science presented in these studies, as well as many others, this leaves males more likely to experience depressive symptoms resulting from occupational pesticide exposure. 

The solution to these harmful effects is the transition to organic agriculture. By eliminating the need for petrochemical pesticides and fertilizers, the disproportionate risk to agricultural workers, especially males, for neurological impacts will be reduced. The Safer Choice, for all individuals, is to avoid hazardous home, garden, community, and food use pesticides. There are many health benefits to organic agriculture, specifically for farmworkers and their children, as well as environmental benefits. To learn more, see Beyond Pesticides’ Resources and subscribe to the Daily News Blog.      

All unattributed positions and opinions in this piece are those of Beyond Pesticides.  

Sources: 

[1] Frengidou, E., Galanis, P. and Malesios, C. (2024) Pesticide Exposure or Pesticide Poisoning and the Risk of Depression in Agricultural Populations: A Systematic Review and Meta-Analysis, Journal of Agromedicine. Available at: https://www.tandfonline.com/doi/full/10.1080/1059924X.2023.2278801. 

[2] Zanchi, M.M. (2024) Redox imbalance and inflammation: A link to depression risk in Brazilian pesticide-exposed farmers, Toxicology. Available at: https://www.sciencedirect.com/science/article/abs/pii/S0300483X23002937?via%3Dihub.  

[3] Zheng, R. et al. (2024) Depressive symptoms and suicide attempts among farmers exposed to pesticides, Environmental Toxicology and Pharmacology. Available at: https://www.sciencedirect.com/science/article/pii/S1382668924001017?via%3Dihub.

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