B. THE WARNING SIGNS OF THE RISKS THAT PARTICULATE PLASTICS POSE TO HUMAN HEALTH ARE MULTIPLYING
· Microplastics are present - and accumulating - in all human organs
People are exposed to plastics in three ways: through food, breathing and the skin. Exposure can be direct, through the use of everyday products, but also through inhalation. In the Paris region, 3 to 10 tonnes of airborne plastics are deposited every year, mostly fibres, and we inhale up to 30 million plastic particles a year. As many microplastics are inhaled as ingested.
Exposure can also be indirect: micro- and nanoplastics are present in all ecosystems and affect the animal and plant species we consume - salt, beer, fruit and vegetables, tea, eggs, meat, etc.
The organs that absorb them are numerous - the lungs, the colon, the skin. It has been shown that plastics can be transported by the blood and by the nerves and reach distant organs such as the testicles, placenta, kidneys and brain. One study21(*) estimated the concentration of plastic in the brain at 5 milligrams per gram: this would mean that 0.5% of the brain's mass is made up of plastic.
Microplastics also accumulate in the organs. The quantity of plastics in the lungs increases with age, which suggests that these particles can persist in the body without being eliminated.
The accumulation of plastics in both the physical and living environments and their consequences for human health therefore raise legitimate concerns under the One Health principle, which identifies the links between animal health, human health and the quality of the environment.
· Worrying correlations between the presence of plastics and the alteration of certain organs and their functions, and even the appearance of pathologies
· Plastics have an impact on the digestive system
Exposure to plastics appears to change the composition of the intestinal microbiota. Bacteria appear in both adults and children, such as pathobionts, which can contribute to dysbiosis of the intestinal microbiota. In addition, a reduction in butyrate, a highly beneficial short-chain fatty acid (SCFA), has been observed in children.
Currently unpublished work on mice has shown that adding microplastics to their diet leads to a loss of beneficial bacteria and an increase in bacteria that are harmful to the intestinal microbiota when the rodents are fed a Western-style diet rich in fat and sugar.
Abrasive phenomena linked to the transit of large microplastics cannot be ruled out, particularly in areas not covered by mucus. This abrasion could lead to inflammation.
· Inhaled plastics have an impact on health
Depending on their size, plastic particles can penetrate deeply into the respiratory tract.
The largest particles, over 300 micrometres in diameter, cannot pass through the nasopharynx. Those between 2.5 and 10 micrometres can travel down into the bronchi. Only the finest inhalable particles, less than 2.5 micrometres in diameter, can enter the bronchi and reach the alveoli.
The respiratory system is equipped with elimination mechanisms such as mucociliary clearance and alveolar macrophages. However, nanoparticles can bypass clearance mechanisms, cross the epithelium and enter the bloodstream to reach secondary organs. Some nanoparticles can travel up nerves, such as the olfactory nerves, and reach the brain.
The toxicity of inhaled plastic particles was demonstrated in the 1970s in workers in the flocking industry. Some of them developed impaired lung function, breathlessness, inflammation, fibrosis and even lung cancer. The same symptoms have been observed in workers in the textile and PVC industries.
In addition to particulate plastics, additives, contaminants and monomers can also have an impact on health. In the polystyrene industry, for example, it is mainly the monomers (styrenes), which are known to be toxic and carcinogenic, that cause these diseases.
An increase in stomach cancer could also be due to swallowing inhaled particles.
Other studies have shown a correlation between respiratory diseases and the presence of plastics in the lungs. There are more particles and fibres present in tumours than in normal tissue.
There is also a link between the presence of microplastics and impaired lung function. There are more plastics in the bodies of people with allergic rhinitis. Blood parameters are also altered when plastics are detected in the lung.
· The presence of microplastics in carotid artery plaque is correlated with an increased risk of myocardial infarction
A recent study published in the New England Journal of Medicine22(*) measured the quantity of microplastics removed from such plaque in over 300 patients who underwent surgery on their carotid artery. This study showed that there was a 4.53 times greater risk of myocardial infarction, and potentially of stroke and even death, in people with the highest levels of micro and nanoplastics.
* 21 Matthew Campen et al., « Bioaccumulation of microplastics in decedent human brains assessed by pyrolysis gas chromatography-mass spectrometry », Research Square (Preprint), May 2024.
* 22 Raffaele Marfella, « Microplastics and nanoplastics in atheromas and cardiovascular events », The New England Journal of Medicine, 6 March 2024, Vol 390 N° 10.