During our daily activities, we are exposed to tiny fragments of plastic, which insidiously infiltrate our bodies. The effects of this contamination on our bodies are still poorly understood. Worrying data suggests it could affect respiratory, digestive, reproductive, and neurological functions.
Where Do Micro And Nanoplastics Come From?
Plastic is omnipresent in our lives, and its overall production has continued to increase, from 15 million tonnes in 1964 to 359 million tonnes in 2018. However, plastic is a material that is not durable: as soon as it is manufactured, it slowly begins its aging process. During everyday use and over time, all plastic objects release small, completely invisible particles.
They are qualified as microplastics when they measure from 1μm to 5mm, and nanoplastics below this threshold. For comparison, the size of nanoplastics is close to that of viruses, which measure around 100 nm. These microplastics, derived from large plastics, are called secondary. Primary microplastics correspond to small pieces of plastic added voluntarily to certain products.
The cosmetic industry uses them widely, mainly because of their exfoliating properties. Micro and nanoplastics contaminate all environments – oceans, soils, and even the air – and living beings. Man is no exception. Data is accumulating on their presence within our bodies.
Pathways Of Contamination
Microplastics contaminate us in several ways. We first ingest these small particles during meals. Studies carried out around the world have revealed their presence in table salt, sugar, tea bags, seafood (fish, mollusks, crustaceans, etc.), milk, honey, fruits . and vegetables … Different types of microplastics have also been identified in bottled water. More worryingly, they also contaminate water taken from groundwater.
Researchers have estimated that, on average, a human being ingests between 0.1 and 5g of microplastics per week. Due to their small size, micro- and nanoplastics can also be directly inhaled. The air in buildings is more loaded with particles than the air outside. They emanate from surrounding objects, furniture, and materials. Microplastics could finally contaminate us through dermal contact via the skin’s pores.
Microplastics In Our Body
Microplastics have thus been found in various parts of our bodies. An analysis of lung tissue identified their presence in 13 samples out of the 20 studied. They are also found in the bronchial secretions of people with respiratory infections. In a study carried out on human placentas, they were detected in all 17 samples examined. Fabrics had an average of 2.7 of these particles per gram, with eleven different types of plastics. Microplastics also contaminate breast milk, blood, and stools, male semen, etc.
Nanoparticles Invite Themselves Into The Heart Of Cells
Laboratory experiments with fluorescent nanoplastics have shown that these particles can penetrate inside human cells. These were intestinal cells, where nanoplastics accumulated on the surface and entered in modest quantities, and macrophages, which got massive. This internalization phenomenon has also been described for red and lung cells. Cell plastic fragments are not attached to the membrane and, therefore, free to interact with its internal components.
The Harmful Action Of Microplastics On The Body
It is currently difficult to understand the consequences of exposure to these micro and nanoplastics on our health. For obvious ethical reasons, it is impossible to voluntarily expose human subjects to these contaminants to observe their direct effects. In addition, all human beings are contaminated, so creating “control groups” in such a study becomes impossible!
On the other hand, we have a solid literature based on in vitro studies – in the laboratory, using cell cultures – and in animals. If the research were initially mainly on aquatic species far removed from our physiology, much work would be devoted to mammals closer to us today.
Effects On The Respiratory System
Inhaling microplastics damages the respiratory system. When mice receive a nasal spray containing these fine particles, they disperse throughout the lungs. They reach the pulmonary alveoli and the tissue that supports them, the interstitium.
Their presence disrupts the structure of the bronchial epithelium, which represents the organ’s protective physical barrier. Experiments carried out on cultures of these cells have shown that microplastics curb their proliferation and can even destroy them.
Inflammation And Oxidative Stress
Microplastics stimulate the production of various pro-inflammatory messengers in these cells. These include TGF-β, the overproduction observed in the context of various respiratory pathologies such as pulmonary fibrosis, emphysema, asthma, or lung cancer. They also increase the production of free radicals and alter antioxidant defenses, making the respiratory system vulnerable to the harmful effects of oxidative stress.
Exacerbation Of Respiratory Allergies
These contaminants could increase sensitivity to respiratory allergens, facilitating their passage through the protective membrane of the alveoli. Joint exposure of asthmatic mice to dust mites and microplastics worsens their situation. It leads to increased production of a protein involved in allergies, MALT1, in lung tissues.
Impact On The Digestive Sphere
When microplastics are ingested, these tiny particles pass along the digestive tract and reach the intestine, where they cause numerous upheavals. A study carried out in mice first showed that they cause a reduction in mucus secretion. Intestinal mucus plays an essential role in the protection and proper functioning of the intestine.
It forms a protective layer that prevents pathogens, toxins, and unwanted particles from damaging the intestinal wall. It also promotes lubrication and regulation of nutrient absorption. The essential genes’ expression in mucus formation decreased in animals exposed to microplastics.
An Increase In Intestinal Permeability
The researchers then noted a decrease in the production of some proteins that formed tight junctions, zonulin- 1 and claudin-1. These guarantee the intestinal barrier’s integrity, preventing unwanted molecules from entering the bloodstream. Microplastics could increase the permeability of the intestine and play a role in the appearance of food intolerances.
Microbiota Imbalance
These pollutants also damage the ecosystem that populates the intestine. In mice, exposure to microplastics for six weeks causes changes in microbiota populations. The abundance of 13 genera of bacteria, including the beneficial Bifidobacterium, decreased, while populations of 2 genera ( Coprococcus and Anaeroplasma ) increased.
Additionally, the metabolism of specific amino acids and bile acids was altered in these animals. Other types of metabolic disruption have been observed with exposure to microplastics. They lead to an increase in fasting blood sugar and insulin concentration and could promote the development of non-alcoholic fatty liver disease.
Pro-Inflammatory Effects On The Intestine
Imbalances in the microbiota result in increased levels of inflammation in the gut. Indeed, certain allied bacteria facilitate the appearance of regulatory white blood cells (Tregs) and the production of anti-inflammatory messengers. They thus help to control the intensity of the immune response, preventing it from getting out of control and causing damage.
An increase in blood levels of IL-1α, a pro-inflammatory messenger, and a decrease in the proportion of Tregs were observed in mice fed with different doses of microplastics, 6, 60, and 600 μg/day for five weeks. The intestine showed apparent inflammation in animals that received the most microplastics.
While there is insufficient data to link microplastics to human inflammatory bowel disease, there are some concerns. A study has highlighted a higher concentration of microplastics in the stools of people suffering from pathology of this type compared to healthy people (41.8 particles per gram compared to 28). The intensity of the symptoms went hand in hand with the degree of contamination.
Impairment Of Reproductive Function, With A Transgenerational Impact
Several abnormalities in reproductive function have been observed in animals exposed to microplastics. In male mice, they cause impaired sperm quality, inflammation in the testicles, and a drop in testosterone levels. In females, they induce inflammation of the ovaries and decrease the survival rate of eggs.
Exposure of mothers during gestation results in a reduction in the number of pups per litter. The birth weight of the young mice is lower than usual. Even without having directly received microplastics, they present alterations in the white blood cells of their spleen, just like their mothers. The harms of microplastics can thus be transmitted to the next generation, at least partially.
A Neurological Risk?
No natural barrier in the body seems able to block plastic particles, not even one of the most selective: the blood-brain barrier. The administration of nanoplates with a size of 50 nm for seven days to mice increases the permeability of this envelope which protects the brain. They accumulate in the organ and cause activation of microglial cells, the brain’s first line of immune defense, and damage to neurons.
In the second part of the study which highlighted this phenomenon, the researchers used human cells commonly used as a model for studying the blood-brain barrier. They were able to verify that the nanoplastics penetrated these cells.
They trigger oxidative stress, promote cell death, and disrupt the formation of the tight junctions that unite them. The size of the particles determines possible access to the brain. During work that examined the passage of fragments of 9.55 µm, 1.14 µm, and 0.293 µm, only the smallest were able to cross the blood-brain barrier, and this very quickly, 2 hours after ingestion.
These nanoplastics have very concrete consequences: the cognitive functions of mice decrease, particularly their short-term memory. In a context where neurodegenerative diseases affect a growing proportion of the population, it is legitimate to wonder about a possible aggravating role of exposure to these contaminants.
Entrance Doors For Harmful Elements
If microplastics cause the body to react by their simple presence, exposure to them poses another threat. They carry various substances that are dangerous for our health.
Problematic Chemical Additives
Different types of additives are used to improve their properties during the production of plastics. They represent, on average, 4% of their weight. When plastic degrades, these additives migrate from the interior to the surface, making it easier to release them into the body in the event of contamination. An analysis published in 2021 identified more than 10,000 chemicals used in plastics.
Of these, more than 2,400 are problematic due to their environmental persistence, tendency to accumulate in living organisms (bioaccumulation), and toxicity. Some of them, such as phthalates, bisphenol A, or brominated flame retardants, interfere with our hormonal system. These endocrine disruptors can cause hormonal cancers and metabolic, reproductive, and developmental disorders. A singular fact with this category of compounds is that the dose does not make the poison: low exposure can have significant effects.
Environmental Co-Contaminants
Beyond the harmful substances that are part of their composition, microplastics can fix different contaminants: heavy metals, persistent organic pollutants, pathogens, etc. Thus, they allow them to penetrate living organisms and are often qualified as Trojan horses.
Heavy Metals
A team studied the accumulation of 55 metals or semimetals on two types of common microplastics: polyethylene and polyethylene terephthalate. The tests were carried out on particles with a size varying from 63 to 250 micrometers. The researchers found that the smallest particles paradoxically accumulate the most significant quantity of metals. Some, like chromium, iron, or tin, strongly bind to microplastics.
Polyethylene particles tend to accumulate these compounds more quickly than polyethylene terephthalate particles. A final testing phase established that the metals attached to the microplastics detach under conditions reproducing those of the digestive tract. They thus have every opportunity to spread throughout the body and exert their toxicity there.
Microbes Pathogenic To Humans
A community of bacteria and other microorganisms colonizes plastic materials that drift in the ocean. A natural ecosystem is formed, which some refer to as the plastisphere. The long lifespan of microplastics provides a sustainable habitat for these species, which can drift great distances. German researchers collected and analyzed samples taken from 39 stations in the North Sea and 5 in the Baltic Sea. Almost all microplastics harbored a microbial community.
Among the residents, they identified the presence of bacteria belonging to the genus Vibrio, including species pathogenic to humans ( V. cholerae and V. parahaemolyticus ). Bacteria affecting the digestive system from the Campylobacteraceae family have also been identified in microplastics present in wastewater treatment plants. These discoveries lead us to consider microplastics as potential vectors for the spread of pathogenic microbes.
How To Limit Exposure To Microplastics?
As microplastics are massively distributed in the environment, it would be illusory to consider protecting ourselves entirely from them. However, specific daily actions can reduce our level of exposure to these contaminants:
- Choose cosmetic products free of microplastics. In the list of ingredients, many terms can suggest their presence. These include polyamide, polyethylene, polystyrene, polyurethane, acrylate, or words ending in -one, -oxane, -vinyl, -polymer. To be sure to escape them, the ideal is to select products with an organic label, which guarantees their absence;
- Favor raw and bulk foods for your daily diet. This helps reduce the risk of contamination and reduces the plastic waste generated;
- Limit your consumption of the most contaminated foods, such as seafood. Eating the whole animal, and therefore the contents of its digestive tract is a significant source of exposure;
- Ban tea in bags because they are often made of plastic (nylon or PET). One study showed that a single cup could contain 11.6 billion microplastics and 3.1 billion nano plastics;
- Avoid bottled water. There are filtration systems to eliminate unwanted products contained in tap water;
- Avoid plastic kitchen utensils, containers (water bottles, shakers), and baby bottles;
- Abandon synthetic textiles, which release microfibers, especially when washing, in favor of natural materials.
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