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Daily News Blog

30
Jun

Implications for Human Health: Pesticides and Other Environmental Contaminants Alter Gut Microbiome

(Beyond Pesticides, June 30, 2020) A review of scientific literature on the toxic effect of environmental contaminants—including pesticides—published in the journal Toxicological Science, “The Impact of Environmental Chemicals on the Gut Microbiome,” associates these chemicals to changes in the gut microbiome and other adverse health implications. The review, by researchers at the University of Illinois, looks at how environmental contaminants adversely effects and reinforce chemical disruption of the gut microbiome. It highlights the importance of evaluating how environmental contaminants, like pesticides, impact body regulation by gut microbiota. The study has significant implications for considerations that should be, but are not currently, a part of pesticide review and registration by the U.S. Environmental Protection Agency (EPA).

Gut microbiota plays a crucial role in lifelong digestion, immune, and central nervous system regulation, as wells as other bodily functions. Through the gut biome, pesticide exposure can enhance or exacerbate, the adverse effects of additional environmental toxicants on the body. Since the gut microbiome shapes metabolism, it can mediate some toxic effects of environmental chemicals. However, with prolonged exposure to various environmental contaminants, critical chemical-induced changes may occur in the gut microbes, influencing adverse health outcomes. Karen Chiu, Ph.D., a graduate research fellow at the University of Illinois, states, “All of these data together suggest that exposure to many of these environmental chemicals, during various stages of life, can alter the gut microbiome in ways that influence health.” 

Over 300 environmental contaminants and their byproducts, including pesticides, bisphenols, phthalates, persistent organic pollutants (POPs), and heavy metals, are all chemicals commonly present in human blood and urine samples. These toxicants can alter hormone metabolism, which adversely affects health outcomes. Adverse health effects of environmental contaminants include reproductive and developmental defects, diabetes, cardiovascular disease, liver disease, obesity, thyroid disorders, and improper immune operation. Although studies show how chemical exposures affect human health, more research is now questioning how these chemicals influence gut microbiota.

The review details manufacturing compounds in customer goods, like bisphenols (BPA) in plastic packaging, and phthalates in anything from vinyl flooring to plastics packaging. Additionally, the paper examines the science behind the exposure to POPs like pesticides, polychlorinated biphenyl (PCBs), perfluorochemicals (PFCs) in non-stick cookware, polybrominated diphenyl ethers (flame retardants), and dioxins (byproducts of pesticide manufacturing and burning organic material like fossil fuels). Various research in the review looks at the impacts of these chemicals in rodents (e.g., rats, mice), aquatic organisms (e.g., fish, amphibians), birds (e.g., chickens), larger mammals (e.g., dogs, cows, human adults, and infants), insects (e.g., honey bees), and other organisms.

A plethora of studies finds detectable levels of bisphenols in the urine of over 90% of all U.S. adults, in addition to an increase in Methanobrevibacter gut bacteria only in males. Human studies find that newborn exposure to high levels of phthalates alters the gut microbiome and immune response to vaccinations. Additionally, phthalate exposure during puberty compromises the microbial formation of the vital regulatory metabolite, butyrate, in mice. Recent studies find that exposure to persistent organic pollutants, like PCBs, shift microbes in the gut, thus increasing gut porousness, inflammation in the intestines, and cognitive dysfunction. Furthermore, another study links PFCs (a POP) exposure to a genetic shift in the gut microbiome and weakened lipid metabolism in female fish and offspring. There is extensive research surrounding gut dysbiosis associated with exposure to heavy metals like mercury, cadmium, lead, and arsenic in aquatic organisms, rodents, birds, and larger mammals. Dioxins also increase the formation of antibiotic resistant genes and disrupt gut microbiome, as well as lipid and glucose metabolism. According to multiple studies, exposure to the weed killer glyphosate (which is patented as an antibiotic) changes the bacterial composition of the gut microbiome in cattle, rodents, and honey bees. Chlorpyrifos pesticides alter gut microbe populations in developing and adult male rodents and fish. New findings suggest exposure to the pesticide atrazine, diazinon, glyphosate-based herbicides, and trichlorfon cause sex-specific shifts in gut microbiota, as well.

Dr. Chui concludes, “The pathologies associated with altered microbiomes after exposure to environmental chemicals include immune dysfunction, altered carbohydrate and lipid metabolism, and neurological and behavioral impairments. We are also seeing that these effects highly depend on an individual’s sex and age.”

Similar to gut microbes, soil microbiotas are essential for the normal functionality of the soil ecosystem. Toxic chemicals damage the soil microbiota by decreasing and altering microbial biomass and soil microbiome composition (diversity). Pesticide use contaminates soil and results in a bacteria-dominant ecosystem as these chemicals cause “vacant ecological niches, so organisms that were rare become abundant and vice versa.”  The bacteria outcompete beneficial fungi, which improves soil productivity and increases carbon sequestration capacity. The resulting soil ecosystem is unhealthy and imbalanced, with a reduction in the natural cycling of nutrients and resilience. Thus, plants grown in such conditions are more vulnerable to parasites and pathogens. The implications of climate change only exacerbate threats on soil health as studies show a link between global climate change and a high loss of microbial organisms in the soil ecosystem.

This review showcases commonality among the aforementioned environmental contaminants via their endocrine-disrupting capabilitiesBisphenols (BPAs) increase the presence of Methanobrevibacter, bacterial microbes, in humans and mice. Methanobrevibacte boosts their host’s ability to extract more energy from food, leading to BPA-induced weight gain and obesity. Phthalates in plastics leach onto foods and, ingestion of the chemical inhibits the formation of the metabolite, butyrate. This metabolic molecule is essential in human intestinal health, immunological health, and neurological function. PFC exposure induces genetic changes in gut health, and those offspring exhibiting a shift in their microbiome have a higher mortality rate. Multi-species evaluations find that various pesticides (i.e., insecticides, herbicides, and fungicides) alter the gut microbiome, lipid metabolism, and cause intestinal inflammation and oxidative stress. Specifically, the review mentions that exposure to pesticides glyphosate and chlorpyrifos, as well as other registered pesticides, increases anxiety and depression symptoms in mice, pathogenic bacteria in cattle, and inflammation and oxidative stress in the gut.

Environmental contaminants, like pesticides, are of specific concern as the Trump administration  dismantles many environmental regulations.Additionally, the administration has waived the requirement of the multinational chemical company Syngenta-ChemChina to continue monitoring Midwest waterways for the presence of the weed killer atrazine, through 2020. Even with prior monitoring of water systems, atrazine was present in 78% of drinking water across the U.S., and several Midwestern communities have seasonal exceedances up to three to seven times the legal limit of atrazine in drinking water. With evidence, it is apparent that the federal government should implement strong safeguards that avoid harmful impacts of pesticide exposure on human, animal, and environmental microbiomes.

To improve and sustain our gut microbiome health, the use of toxic pesticides must stop. Instead, emphasis on converting to regenerative-organic systems and using least-toxic pest control to mitigate harmful exposure to pesticides, restore soil health, and reduce carbon emissions, should be the main focus. Public policy must advance this shift, rather than continue to allow unnecessary reliance on pesticides. Learn more about soil microbiota and its importance via Beyond Pesticide’s journal Pesticides and You. Additionally, learn more about the effects of pesticides on human health by visiting Beyond Pesticides’ Pesticide-Induced Diseases Database. This database supports the clear need for strategic action to shift away from pesticide dependency. 

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

Sources: Toxicological Sciences, University of Illinois

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