20
Aug
Modes of Action of Persistent Pesticides Documented, with Ongoing Poisoning and Multigenerational Effects
(Beyond Pesticides, August 20, 2024) A study published online in the journal Environmental Toxicology and Pharmacology raises continuing concern about residual exposure to organochlorine pesticides (OCPs) and the disruption that they and their metabolites and isomers cause to biological systems. For the most part, OCPs, including dichlorodiphenyltrichloroethane (DDT), are no longer used worldwide, but the legacy of their poisoning and contamination persists. A 2022 article in Environmental Science & Technology cites California condors and marine mammals along California’s coast contaminated with several dozen different halogenated organic compounds (hazardous, often-chlorinated chemicals) related to DDT, chlordane, and other now-banned legacy chemicals. Other research finds DDT in deep ocean sediment and biota. And, more research finds multigeneration effects from DDT exposure with grandmothers’ exposure to DDT increasing granddaughters’ breast cancer and cardiometabolic disorder risk.
This study may be the first compilation of research regarding the modes of action for distinct types of organochlorine pesticides (OCPs). The findings raise the significant danger of legacy chemicals that persist for generations and call for a precautionary regulatory standard that is focused on preventing harm and advancing alternative nontoxic practices and products. In tracking the ongoing scientific literature on a broad spectrum of adverse effects daily, Beyond Pesticides has urged the U.S. Environmental Protection Agency (EPA) to recognize that under the “unreasonable adverse effects†standard of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), the viability, productivity, efficacy, and profitability of organic practices and organic-compatible products, make the current use of toxic pesticides violative of the statutory standard.  (See Pesticides and You.)
The authors aim to highlight differences and common behavioral reactions for three groups of OCPs—dichlorodiphenyltrichloroethane (DDT), hexachlorocyclohexane (HCH), and chlordecone (CLD)—in humans and animals by collecting data on their modes of action. A ‘mode of action’ is the chemical mechanism by which a chemical causes changes to an organism. Relevant studies from 1970 to 2024 on the mode of action for various classes of OCPs are compiled in the research, then translated into a series of detailed graphic flow charts.
Each pesticide, as well as its metabolites and isomers, exhibit different abilities to disrupt natural biological processes in mammals, according to the authors. In addition, each OCP differs in where they accumulate in the body and which types of protein they bind with most effectively. For example, DDT and HCH tend to accumulate in fat cells while CLD is most prevalent in the liver. However, DDT is more likely to bind to high-density lipoproteins (HDLs), while one of its metabolites DDE binds more readily to low-density lipoproteins (LDL). Furthermore, certain OCPs disrupt biological processes by mimicking hormones and filling a cell’s hormone receptor sites so that the cell is no longer able to receive natural signals from the body. Other compounds change the permeability of cell walls by binding with calcium or sodium, thereby changing the ability of cells to function properly. In some cases, the exact mode of action still has not been determined.
However, although each OCP has different modes of action, their biological impacts are mostly the same. For example, all compounds were found to be endocrine disruptors. The endocrine system creates and releases the hormones that regulate body function, such as metabolism, growth and development, and sexual function. Each of the OCPs mimics different hormones, creating different methods for disrupting the natural hormone systems. Similarly, all OCPs tested were found to disrupt the nervous system. The nervous system is responsible for blood pressure, heart rate, and breathing, as well as all sensation, movement, emotions, communication, thought processing, and memory among many other biological functions. In addition, each compound was found to contribute to oxidative stress—an imbalance of oxidants causes cell death and is linked to cancer, Alzheimer’s disease, heart disease, and many other diseases.
What are organochlorine pesticides?
OCPs are primarily made up of chlorine atoms, classified as persistent organic pollutants (POPs) due to their toxic longevity in the environment. The study notes that chemicals enter the environment through (1) their employment in farming as pest control, (2) the release of contaminated waste into landfills and dumpsites, and (3) emissions from industrial plants synthesizing these compounds.Â
Although many countries ban most organochlorine compounds, OCPs remain in soils, water (solid and liquid), and the surrounding air at levels exceeding EPA standards. While EPA has ended pesticide registration for virtually all of the original POPs, the United States has not joined over 150 countries in ratifying a 2001 United Nations treaty known as the Stockholm Convention on Persistent Organic Pollutants, which requires the elimination of persistent organic pollutants’ (POPs) production, use, and/or release. (See here and here for Beyond Pesticides coverage).
OCPs are largely insoluble in water but easily dissolve in fats and oils, which makes them exceptionally persistent in the environment by binding readily to soils, plants, and animals. When OCPs enter an animal through ingestion or dermal absorption, the organochlorine pesticides may break down into metabolites or transform into isomers. Together, this affinity enables OCPs to move around the body with ease by attaching to lipoproteins and passing through the bloodstream. Additionally, as the study documents, prior epidemiological research clearly focuses on “the carcinogenicity of OCPs with a significant occurrence of acute myeloid leukaemia [leukemia], multiple myeloma, myelodysplastic syndrome, and hematopoietic bone marrow cancer (Bassil et al., 2007)†and their neurotoxicity “due to their toxicity towards insect nervous systems (Casida, 2009, Costa et al., 2008).†For Beyond Pesticides’ latest reporting on OCPs, see here.
This research highlights the complexity of the interactions associated with the adverse impacts of OCPs on biological systems. In her groundbreaking book, Silent Spring, Rachel Carson illuminated the severe and systemic collateral damage to wildlife, soil health, and water quality from the widespread use of pesticides, particularly DDT, but also organophosphate pesticides. Four decades after pesticides entered the scene, scientists are still only scratching the surface of the tangled web of interactions, reactions, and counteractions that can result from their use.
The evidence is clear: OCPs pose serious health and environmental risks, and the U.S. regulatory system has repeatedly failed to address these threats preventively or in a timely manner (see here and here). The continued persistence and use of fossil fuel-based pesticides and fertilizers is contributing to a trifecta of existential crises: human illness exacerbated by pesticide exposure, the collapse of biodiversity, and the accelerating climate emergency. We must take urgent action to eliminate their continued use. To learn more about the negative health effects of OCPs and other pesticides, please see the Gateway on Pesticide Hazards and Safe Pest Management and the Pesticide-Induced Disease Database. Â
Organic practices offer a viable and necessary alternative. Grounded in the preservation of healthy ecosystems, these practices not only ensure food productivity and resilient land management but also safeguard our food, air, and water. The data supporting organic agriculture creates a compelling case for phasing out pesticides within the next decade. [Meeting Existential Challenges, the latest issue of Pesticides and You, underscores this stark reality.]  To learn more about why organic is the best choice for both consumers, farmworkers who grow our food, and those living in ‘fence-line communities’ near farms, visit the Beyond Pesticides webpages on the Health Benefits of Organic Agriculture and Agricultural Justice.
Now is the time to act. The work being done by Beyond Pesticides, along with our network and allies, demonstrates the potential for change through community-based efforts and initiatives See Beyond Pesticides’ Action of the Week and join your voice in the call for action. To become an advocate in your local community for organic public parks, learn more about our Parks for a Sustainable Future program. Together, we can build a future where organic solutions can thrive, protecting our health and the environment from unnecessary toxicants for generations to come.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources:
The mode of action of different organochlorine pesticides families in mammalians, Environmental Toxicology and Pharmacology, September 2024 (print release)
