Effects of Persistent Organic Pollutants (POPs) on Gut Microbiota

This article is about the effects of Persistent Organic Pollutants (POPs) on gut microbiota.

Persistent organic pollutants (POPs) are a series of toxic compounds characterized by high chemical stability originating mainly from human activities.

These pollutants can remain in the environment for a long time, hence their nickname forever chemicals. They can also spread far from where they were used or produced.

As a result, they have also been found in regions remote from human activities, such as the Antarctic, Arctic, Alpine, and Baltic regions.

Effects of Persistent Organic Pollutants (POPs) on gut microbiota: Introduction

Human exposure to persistent organic pollutants (POPs) occurs primarily through contaminated food.

As such, these substances have an impact on the gut and, therefore, on the intestinal microbiota.

Numerous studies have been conducted and have demonstrated the negative impact of POPs on the gut bacterial population and their danger to human health.

This article presents the harmful effects of these persistent organic pollutants, or POPs, on our intestinal microbiome.

Persistent Organic Pollutants (POPs): Definition

Persistent organic pollutants are halogenated compounds that are resistant to environmental degradation.

Because of their lipophilicity (i.e., tendency to dissolve in fat), they accumulate in the fatty tissue of living organisms and concentrate along the food chain.

Exposure to these substances can also have severe consequences for human health with chronic and long-term effects.

More than 90% of human exposure to persistent organic pollutants is due to consuming contaminated food, especially of animal origin and, more specifically, through fish.

Once released into the environment by industrial and agricultural activities, these compounds can contaminate soil, drinking water, crops, livestock, and fish.

Numerous research studies have shown that the most common persistent organic contaminants found in foods are:

• pesticide residues,
• benzene,
• polychlorinated biphenyls (PCBs), and
• dioxins.

History of persistent organic pollutants

Around the 1970s, there was a peak in the release of persistent organic pollutants into the environment.

A few years later, developed countries defined regulations after discovering the considerable danger to human health.

In May 2001, a convention on POPs was adopted to reduce and eliminate their emissions into the environment.

Many of them have been banned in Europe, although some products containing them are still in circulation.

In some countries, persistent organic pollutants are still used, especially in developing countries where there is not yet adequate regulation.

Since 2020, European regulation has banned the manufacture, marketing, and use of PFOA (perfluorooctane sulfonate), its salts, and related compounds.

The three main types of persistent organic pollutants

Three types of persistent organic pollutants are most present in the environment. They can be categorized as follows:

Industrial chemicals

They mainly include:

• Polybrominated diphenyl ethers (e.g., PBDEs) are used as flame retardants. Since 2004, they have been banned in Europe and the United States.
• PFAS, impermeable perfluoroalkyl substances, oil and heat-resistant, including perfluorooctanesulfonic acid (PFOS), which is frequently used in food paper, perfluorooctanoic acid (PFOA), used in non-stick cookware.
• Polychlorinated biphenyls (PCBs) are used as coolants and lubricants.

Pesticides

When discussing pesticides, mainly “organochlorines” are concerned, such as DDT.

By-products of industrial processes

This category includes:

• Polyaromatic hydrocarbons, generated by the incomplete combustion of natural or artificial sources, or by specific cooking or food preparation methods
• Polychlorinated dibenzofurans
• Polychlorinated dibenzo-p-dioxins

What are the harmful effects of chronic exposure to persistent organic pollutants?

Chronic exposure to persistent organic pollutants adversely affects:

• development and behavior,
• reproduction, and
• immunological, dermatological, and even cancerous diseases.

These pollutants also substantially impact the composition of the intestinal microbiota.

Namely, they modify the balance of the intestinal mucosa and the stabilization of bile acids and cause dysbiosis.

In addition, some studies suggest that their toxicity is specifically through gut dysbiosis.

Many of these pollutants, such as PCBs, Bisphenol A, phthalates, organophosphate pesticides, and PFOS, can act as endocrine disruptors.

This means they can interact with the body’s endocrine (hormonal) system with harmful consequences, especially for fetal development and child growth.

Research has shown that endocrine disruptors also interact with the gut microbiota.

PFAS (Per- and Polyfluoroalkyl Substances)

Some of these substances, such as PFAS (perfluoroalkyl compounds), are everywhere.

For example, they are used in food and kitchenware packaging, outdoor tools, furniture such as outdoor rocking chairs and camping chairs, and carpeting.

They are also used for their hydrophobic and oil-repellent properties and as components in firefighting film foams at airports and military bases. In addition, they can resist high temperatures.

As a result, this widespread use has made it one of the primary contaminants of our drinking water.

Movie tip: The eye-opening, must-see legal thriller Dark Waters is based on the true story of pollution of drinking water in West Virginia by the DuPont chemical company. The chemical in question is called C8, also known as PFOA or perfluorooctanoic acid.

A study on the effects of some PFAS on the gut microbiome showed that they could:

• cause disruptions in the bacterial ecosystem,
• with changes in the metabolites of the gut microbes, and
• disruption of glucose and lipid metabolism.

PCBs (polychlorinated biphenyls)

PCBs are a class of stable and persistent fat-soluble substances that like to accumulate in the fatty tissues of animals and remain in the environment for a long time.

Cases of meat and egg contamination have been discovered due to the use of PCB-containing paints on the inner walls of barns and on egg conveyor belts.

Due to their diffusion in the environment, many studies have been conducted on the dangers of PCBs.

For example, researchers have found that the composition of the microbiota in a pregnant mother is altered after exposure to PCBs.

Consequently, this also led to variations in the composition of the fetal microbiome.

It has also been observed that prenatal exposure to PCBs or through breast milk leads to dysbiosis in newborns and disturbances in the microbiota development in children, with negative consequences later in life.

In addition, exposure to PCBs also creates a risk of developing behavioral and neurological disorders, including autism spectrum disorders.

In other research, PCB exposure in mice during development has been shown to:

• increase intestinal permeability,
• alter inflammatory cytokine levels, and
• alter gut microbiome composition.

Other cases of POPs

Dioxins and furans are among the most dangerous persistent organic pollutants and are mainly produced by industrial processes.

In developing countries, one of the primary sources is the burning of waste in the open air, so much so that they have been found in high concentrations in the milk and meat of cattle raised near incineration plants.

Both types of POPs are mainly present in fish, meat, milk, and eggs. Animals can absorb these substances from contaminated soil and water or via contaminated feed.

In addition, calves can absorb dioxins through breast milk.

Chronic exposure causes various adverse effects in humans, with reproductive, developmental, and behavioral damage, and has even been shown to be carcinogenic.

Effects of Persistent Organic Pollutants (POPs) on gut microbiota: Conclusion

Persistent organic pollutants are toxic compounds originating mainly from human activities.

These pollutants remain in the environment for a long time and are capable of spreading over great distances.

Human exposure to persistent organic pollutants occurs primarily through contaminated food.

Therefore, these substances have an impact on our intestinal microbiota, on our health as well as on our bodies.

Currently, regulations exist in some countries to reduce and limit their emissions into the environment.