10
Sep
More Scientific Evidence that Endocrine-Disrupting Pesticides Disrupt Thyroid Function
(Beyond Pesticides, September 10, 2021) Research conducted in Thailand shows that exposures to pesticides, even at low levels, can impact the human endocrine system and distort thyroid function. The study looked specifically at interactions of genetics and environment: it investigated associations between variations in genes involved in pesticide metabolism and altered thyroid hormone concentrations in agricultural workers. This research underscores some of the complexity and difficulty of determining human vulnerability to impacts of pesticide exposures, given genetic variables. Beyond Pesticides believes that this very complexity is a cogent argument for anchoring regulation of pesticides in the Precautionary Principle. If exposure to a pesticide can cause damage to human (or environmental) health, it sometimes will do so. Thus, to protect people’s health, agriculture and other land management practices must transition from the use of synthetic pesticides to broad adoption of organic regenerative approaches that obviate the need for such chemicals.
This research is part of a longitudinal study that seeks to evaluate sub-chronic impacts, on thyroid hormone levels, of repeated exposures to a variety of pesticides. The farmworkers studied in this phase comprise two groups: those working on organically managed farms (216 subjects), and those working on conventional farms that use pesticides (229 subjects). Participants were recruited from an area of Thailand whose agricultural activity is broadly representative of that throughout the country — primarily, rice, fruit, vegetable, and sugarcane production. Those in the chemical pesticide–using group most commonly employed, from greater to lesser amounts used, herbicides (largely glyphosate, paraquat, and 2,4-D), insecticides (chlorpyrifos, cypermethrin, carbaryl, and carbosulfan), and fungicides. Workers in the “chemicals” group had used pesticides in their work for an average of 25 years; however, more than 35% of them had worked with the chemicals for more than 30 years.
The study furthers understanding of how pesticides can disrupt or distort endocrine function. The thyroid gland is an important part of the human endocrine system, which comprises a number of glands and the hormones they produce and secrete. Those hormones travel through the circulatory system to organs and tissues to transmit important regulatory messages regarding metabolism, stress response, reproduction, development, and other functions. The other major glands of the endocrine system are the hypothalamus, pituitary, parathyroids, adrenals, ovaries, testes, and the pineal body.
Beyond Pesticides has long covered the roles of synthetic chemical pesticides, including endocrine-disrupting (ED) ingredients in them, in endocrine dysfunction. Beyond their ED impacts: a May 2021 Daily News Blog entry reported on a U.S. National Institutes of Health (NIH) study showing that exposures to either of the pesticides lindane and metalaxyl increases the risk of developing thyroid cancer.
A recent Daily News Blog article said, “The ingredients in many pesticides (and in many consumer products) act as endocrine disruptors in humans and other animals in several ways. They may: (1) mimic actions of hormones the body produces (e.g., estrogen or testosterone), causing reactions similar to those generated by the naturally produced hormones; (2) block hormone receptor cells, thereby preventing the actions of natural hormones; or (3) affect the synthesis, transport, metabolism, and/or excretion of hormones, thus altering the concentrations of natural hormones in tissues or at receptor sites.” Pesticides acting as EDs can, through disruption of the activities in #3, distort hormone levels in the body. The research paper concurs that there is increasing evidence of pesticides acting as ED chemicals to disrupt thyroid function.
Human susceptibility to harmful pesticide impacts can be influenced and mediated by multiple factors, including age, sex, health status, lifestyle features, and genetic factors, among others. The study notes, “Genetic polymorphisms are one determinant of pesticide-induced adverse health effects, especially polymorphisms of genes related to pesticide metabolism.” Genetic polymorphisms — variations in phenotypes caused by expression of different alleles of a given gene, such as happens with the human blood groups O, A, B, and AB, for example — can alter reactions in the multiple steps of pesticide metabolism.
This research investigated disruptions of the HPT (hypothalamic-pituitary-thyroid) axis or pathway of the endocrine system — a set of interacting hormones and transporter enzymes that regulate metabolism and some of the body’s stress responses. The metabolism of ED pesticides that impact the thyroid gland is regulated in part by the activity of this axis.
Hormone levels and specific genetic SNPs (single nucleotide polymorphisms — variations at single positions in DNA sequences) were determined from blood samples taken after a 12-hour, overnight fast. The study assessed thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) in the farmworkers, and found significant differences in the TSH and FT3 concentrations between the chemical pesticide and the organic worker groups; however, the nature of those differences was highly correlated to the presence of specific SNPs.
The study asserts, “Thyroid dysfunction has long been recognized as abnormal TSH, FT4, and FT3 concentrations, which can result from exposure to endocrine-disrupting pesticides. The[se] results suggest that the long-term use of pesticides by the chemical workers may have contributed to their significantly higher concentrations of TSH and FT3 compared with the organic workers. . . . Changes in thyroid hormone concentrations may involve the effects of insecticides, herbicides, and/or fungicides on the molecular regulation of the HTP axis.”
The researchers believe that theirs is the first study to explore whether genetic polymorphisms are associated with pesticide-induced alterations in thyroid hormones, and the first to investigate “a large number of SNPs in agricultural workers to assess the potential risk of thyroid dysfunction.” The co-authors write, “The genetic analysis of enzymes involved in pesticide metabolism provides valuable information regarding individuals or populations that may have an increased health risk because of their polymorphism profile. Genetic variations of these genes can lead to pesticides forming highly toxic intermediates and ultimately damaging various molecular targets.”
The researchers note that such variations in individuals’ genetic polymorphisms may explain, at least in part, why people can differ in their response to pesticide exposure. The study asserts: “These findings support a possible role of pesticide exposure in adverse thyroid function and should focus public and environmental health concerns regarding the occupational risk associated with pesticide use.”
The bottom line for farmworkers — who would virtually never know anything about their “polymorphism profile” — is that they are at significant risk of thyroid dysfunction or/and disease from their chronic exposures to ED pesticides. Frontline agricultural workers have been the canaries in the coalmine for many decades — since agricultural production shifted in the mid-20th century to chemical-intensive management. Those working in conventional farming are exposed chronically to multiple toxic pesticide compounds, many of which have been registered for use by the U.S. Environmental Protection Agency (EPA) without evidence of their safety. Many agricultural workers in the U.S. are people of color, making pesticide use not only a health and environmental morass, but also, a major environmental justice issue.
Beyond Pesticides and other advocates have repeatedly called attention to the ED impacts of many pesticides, and especially, their negative human health impacts. See these recent articles: “Ban Endocrine Disrupting Pesticides Now,” and “Tell EPA: It Must Ban Pesticides Unless Shown Not to Be Endocrine Disruptors.” For years advocates have worked to bring ED (and many other) pesticide issues to the public’s attention, persuade policymakers, and enter into litigation to get EPA to act protectively on human and environmental health. But the people and their representatives, whether elected or in advocacy, should not have to fight against their own government to secure the protections that EPA is tasked with providing.
Just days ago, Beyond Pesticides wrote, in a commentary on the EPA announcement on ending chlorpyrifos use on food: “Does a science-based, public health–oriented, occupational safety–focused, children-concerned, ecologically protective society allow the use of toxic pesticides that are unnecessary to achieve land management, quality of life, and food productivity goals? Should victims of poisoning have to plead with regulators to protect them? Should organizations have to fight, chemical by chemical, to achieve basic levels of protection from individual neurotoxic, cancer causing, endocrine disrupting pesticides? Of course not. But . . . EPA’s announcement that it is stopping food uses of the insecticide chlorpyrifos, after being registered 65 years ago, provides us with an important opportunity for reflection. The collective effort to remove this one chemical is a tremendous feat in eliminating one exposure to a hazardous material for children. That is the point. The action we’re celebrating required an amazingly resource-intensive effort at a time in history when we are running against the clock in an urgent race to transition our society and global community away from the use of petroleum-based, toxic pesticides [and] to . . . meaningful practices that sustain, nurture, and regenerate life.” Those practices happen in approaches that respect Nature, exercise precaution, and take seriously their stewardship role.
Beyond Pesticides believes that organic regenerative agriculture and land management must be the future. And EPA must do better — now — to get us there.
Source: https://www.dovepress.com/risk-management-and-healthcare-policy-journal
ISSN: 1179-1594
Risk Management and Healthcare Policy is an international, peer-reviewed, open access journal focusing on all aspects of public health, policy, and preventative measures to promote good health and improve morbidity and mortality in the population. It is a member of and subscribes to the principles of the Committee on Publication Ethics (COPE).
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
