Health Effects of Herbicides & Insecticides

Lettuce Plant Herbacide Insecticide

In August, the world stood watch as the first trial against multinational agricultural biotechnology corporation Monsanto unfolded. A jury from San Francisco, CA, awarded Dewayne Johnson $289 million in damages, ruling that Monsanto’s Roundup weed killer was a substantial contributing factor to his development of non-Hodgkin’s lymphoma.

According to reports in the media, Johnson claimed he applied Roundup 20 to 30 times per year while he worked as a groundskeeper for a school district near San Francisco; during his work, he said he had two accidents where he was soaked with the product. Now, lesions cover as much as 80% of his body.

While court findings are not proof of causation, the ruling set a precedent for thousands of other cases claiming that glyphosate, an herbicide used in Monsanto’s Roundup, causes cancer. The herbicide is registered in 130 countries and approved for use on more than 100 crops, but in 2015, the World Health Organization’s international agency for research on cancer classified glyphosate as “probably carcinogenic to humans.”

Monsanto continues to maintain that Roundup does not cause cancer.

Insecticides & Herbicides

Organophosphates (carbon- and phosphate-containing molecules) are the most commonly used insecticides and herbicides in the US in all market sectors (i.e., agriculture, home and garden, industrial, commercial, and government).1 The International Agency for Research on Cancer classifies malathion and diazinon as probably carcinogenic to humans and dichlorvos, parathion, and tetrachlorvinphos as possibly carcinogenic to humans. The US Environmental Protection Agency also classifies parathion as a possible human carcinogen. Increased cancer risk has been associated with several organophosphate insecticides in case-controlled studies in the US, Canada, and Italy.1

Epidemiologic and case-controlled studies have linked the organophosphates diazinon, chlorpyrifos, and terbufos use to lung cancer; diazinon, terbufos, fonofos, and malathion use to leukemia; and terbufos use to non-Hodgkin’s lymphoma in pest control and farm workers.1 While the majority of studies into organophosphates have been in male populations, a provocative study published in 2016 looked at cancer incidence among female spouses of pesticide applicators in the Agricultural Health Study. Researchers tracked approximately 30,000 women for 15 years; 718 of those women were diagnosed with cancer during the follow-up period. Any organophosphate exposure was associated with an elevated risk of breast cancer in these women. Malathion, the most commonly used organophosphate in the US, was associated with an increased risk of thyroid cancer, and diazinon was associated with ovarian cancer.1

Use of the herbicide glyphosate began in the 1970s, and the chemical swiftly attained widespread use in modern agriculture, becoming the most commercially successful and widely used herbicide of all time as of 2016.2 Total worldwide glyphosate use (agricultural plus non-agricultural) rose more than 12-fold from about 67 million kg in 1995 to 826 million kg in 2014 (0.15–1.8 billion pounds).3 Levels of glyphosate and its primary metabolite, aminomethylphosphonic acid (AMPA), have been detected in the air, soil, water,3 and food.4

A number of studies suggest that glyphosate stimulates breast cancer growth via estrogen receptors.5 A 2018 study published in Food and Chemical Toxicology investigated the effect of glyphosate on the estrogen signaling pathway involved in the induction of cholangiocarcinoma (CCA) cell growth, cell cycle, and molecular signaling pathways. The data suggests that glyphosate can induce cell growth in estrogen receptor alpha positive CCA cells through the non-genomic estrogen receptor/ERK1/2 signaling pathway.5

In addition to glyphosate, malathion, parathion, and dimethoate are known for their endocrine-disrupting potential.6 They have been associated with effects on the function of cholinesterase enzymes, a decrease in insulin secretion, disruption of normal cellular metabolism of proteins, carbohydrates, and fats, genotoxic effects, and effects on mitochondrial function, which can lead to cellular oxidative stress and problems with the nervous and endocrine systems.6

A 2018 case-control study suggests that the occurrence of diabetes among Thai farmers was associated with pesticide exposure.7 Lifetime pesticide exposure and other relevant data were collected from 866 participating cases with diabetes mellitus and 1,021 healthy controls. Of the 35 individual pesticides investigated, those found to show a statistically significant increased risk of diabetes were endosulfan, mevinphos, carbaryl/Sevin, and Benlate. Cell studies suggest that organochlorine pesticide and some other persistent organic pollutants may reduce cell metabolic functions.7

In May 2018, the Ramazzini Institute, a nonprofit social cooperative that has dedicated more than two decades to fighting cancer, initiated a pilot study of glyphosate’s health hazards that will be followed on an ongoing basis by an integrated experimental research project.8 The evaluation, independent of industry support and sponsored by worldwide crowdfunding, will explore the effects of exposures to glyphosate-based herbicides at current real-world levels on several toxicological endpoints, including carcinogenicity, long-term toxicity, neurotoxicity, endocrine-disrupting effects, prenatal developmental toxicity, the microbiome, and multi-generational effects.8

A particularly compelling first-of-its-kind study in September 2018 examined the unusually high number of cancer cases in the agricultural community of India, finding a significantly elevated relative risk of lower antioxidant defense mechanism (glutathione catalase, superoxide dismutase, glutathione peroxidases, and glutathione reductase) in the exposed group as compared to the unexposed group.9 The data show pesticide exposure to be a major risk factor for increased oxidative stress inside the body. Gas chromatographic analysis revealed the residues of organophosphates (chlorpyriphos, dichlorvos, ethoprophos) and herbicides (atrazine, butachlor, alachlor, metolachlor) in the blood samples of the exposed population.9

In addition to cancer, studies suggest that organophosphates may be tied to a wide variety of other negative health effects. A 2010 study of 1,139 children representative of the general US population suggested that organophosphate exposure at levels common in the US may contribute to ADHD prevalence.10 In 2017, a cross-sectional study of farmers and non-farmers in Thailand suggested that a long-term, low-level exposure to organophosphates may be associated with breathlessness, chest pain, dry throat, cramping, headache, dizziness, eye irritation, white/red rash, white/red pimple, and an increasing prevalence of muscle weakness and numbness.11 A 2018 study provides some of the first evidence that preconception exposures to organophosphates are associated with decreased fertility in Chinese couples.12


How can Functional Medicine practitioners recognize the diseases and dysfunctions potentially associated with chronic toxicity? What is the relationship between chronic toxic insult and neurotoxicity, immunotoxicity, autoimmunity, mitochondrial dysfunction, endocrine disruption, and carcinogenesis? What can practitioners do to help their patients lower their risk to these toxic insults? Find out answers to these questions and much more in IFM’s Biotransformation (formerly Detox) Advanced Practice Module. Clinicians will learn to develop personalized dietary treatments using the IFM Elimination Diet and Detox Food Plan suites, as well as how to apply various nutraceuticals, botanicals, pharmaceuticals, and lifestyle interventions to increase the mobilization, biotransformation, and elimination of toxic compounds in the body.

Learn More About Biotransformation Pathways and Toxic Exposures

  1. Lerro CC, Koutros S, Andreotti G, et al. Organophosphate insecticide use and cancer incidence among spouses of pesticide applicators in the Agricultural Health Study. Occup Environ Med. 2015;72(10):736-744. doi:10.1136/oemed-2014-102798.
  2. Davoren MJ, Schiestl RH. Glyphosate-based herbicides and cancer risk: a post-IARC decision review of potential mechanisms, policy and avenues of research [published online July 28, 2018]. Carcinogenesis. doi:10.1093/carcin/bgy105.
  3. Benbrook CM. Trends in glyphosate herbicide use in the United States and globally. Environ Sci Eur. 2016;28(1):3. doi:10.1186/s12302-016-0070-0.
  4. Myers JP, Antoniou MN, Blumberg B, et al. Concerns over use of glyphosate-based herbicides and risks associated with exposures: a consensus statement. Environ Health. 2016;15:19. doi:10.1186/s12940-016-0117-0.
  5. Sritana N, Suriyo T, Kanitwithayanun J, Songvasin BH, Thiantanawat A, Satayavivad J. Glyphosate induces growth of estrogen receptor alpha positive cholangiocarcinoma cells via non-genomic estrogen receptor/ERK1/2 signaling pathway. Food Chem Toxicol. 2018;118:595-607. doi:10.1016/j.fct.2018.06.014.
  6. Nicolopoulou-Stamati P, Maipas S, Kotampasi C, Stamatis P, Hens L. Chemical pesticides and human health: the urgent need for a new concept in agriculture. Front Public Health. 2016;4:148. doi:10.3389/fpubh.2016.00148.
  7. Juntarawijit C, Juntarawijit Y. Association between diabetes and pesticides: a case-control study among Thai farmers. Environ Health Prev Med. 2018;23(1):3. doi:10.1186/s12199-018-0692-5.
  8. Landrigan PJ, Belpoggi F. The need for independent research on the health effects of glyphosate-based herbicides. Environ Health. 2018;17(1):51. doi:10.1186/s12940-018-0392-z.
  9. Kaur G, Dogra N, Singh S. Health risk assessment of occupationally pesticide-exposed population of cancer prone area of Punjab. Toxicol Sci. 2018;165(1):157-169. doi:10.1093/toxsci/kfy140.
  10. Bouchard MF, Bellinger DC, Wright RO, Weisskopf MG. Attention-deficit/hyperactivity disorder and urinary metabolites of organophosphate pesticides. Pediatrics. 2010;125(6):e1270-1277. doi:10.1542/peds.2009-3058.
  11. Hongsibsong S, Sittitoon N, Sapbamrer R. Association of health symptoms with low-level exposure to organophosphates, DNA damage, AChE activity, and occupational knowledge and practice among rice, corn, and double-crop farmers. J Occup Health. 2017;59(2):165-176. doi:10.1539/joh.16-0107-OA.
  12. Hu Y, Ji L, Zhang Y, et al. Organophosphate and pyrethroid pesticide exposures measured before conception and associations with time to pregnancy in Chinese couples enrolled in the Shanghai Birth Cohort. Environ Health Perspect. 2018;126(7):077001. doi:10.1289/EHP2987.

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