Microplastics, science studies tolerance threshold

Microplastics are now everywhere, even inside the human body, but their impact on health has been studied for less than a decade, so politicians, regulators, companies and the public continue to make decisions on the use of plastics on a still limited scientific basis. What is certain is that humans today ingest and inhale more microplastics than at any other time. In a study conducted by a team at Cornell University, it was calculated that the consumption of microplastics in our diet has increased sixfold since 1990. These indestructible particles have been found in all organs, from the brain to the liver, from the lungs to the bone marrow and even in the bones, but to understand precisely how they affect our health much remains to be studied, although researchers basically agree on their inflammatory action.

One way to investigate this further is what is known in medical circles as a 'human challenge trial', usually conducted in connection with infectious diseases with human 'guinea pigs' agreeing to be deliberately infected with a pathogen to help scientists better understand its effects. The first such experiment is underway at Imperial College London, where eight brave volunteers ingested a cocktail of microplastics in exchange for a small fee. "We want to work out how many are left in our system, compared to those ingested," explains Stephanie Wright, who is leading the experiment, trying to best replicate the microplastic content we unintentionally ingest in normal life. "The biggest concern is where they end up and if they accumulate. It is very unlikely that our body is able to break them down and this can lead to chronic inflammation and tissue damage that compromises organ function," Wright adds.

The other challenge for scientists is that some microplastics absorb environmental toxins and heavy metals, transporting them into our bodies, while chemicals added to plastics can interact with the body's hormonal network as endocrine disruptors. It has also been discovered that some microplastics act as hubs for so-called antimicrobial resistance genes and can therefore induce resistance to drugs administered, for example, to cancer patients. In particular, nanoplastics (smaller than a micrometre) could be even more harmful than microplastics (5 millimetres and below), as they are small enough to cross cell membranes and accumulate inside cells. These are the most pressing questions, and in fact several studies have emerged in the last two years that have caused a stir in the medical community.

The most recent is a study by a team from the University of New Mexico, based on dozens of autopsies performed between 1997 and 2024, in which researchers found an increasing presence of micro- and nanoplastics in brain tissue. Most notably, dementia sufferers had up to 10 times more plastic in their brains than those who did not suffer from the condition. "We were shocked by the results," confesses Matthew Campen, who led the study and considers the brain "the ideal environment" for the accumulation of microplastics, given its notoriously slow disposal mechanisms.

Another study that has attracted a lot of interest is the one conducted by an Italian team led by Raffaele Marfella from the University of Campania Luigi Vanvitelli, in which researchers discovered microplastics in plaques lining the carotid arteries of people with early-stage cardiovascular disease, linking their presence to worsening disease progression. According to the study, patients whose plaques contained microplastics were almost five times more likely to suffer a stroke, heart attack or die from other causes in the next 36 months than patients without contamination.