How does microplastic affect our brain?

Tiny plastic particles called microplastics have been found accumulating in the human brain, but there is not enough evidence to say whether they are harmful to us, experts have said.

These nearly invisible plastic particles are found everywhere, from mountain tops to the seabed, in the air we breathe and the food we eat. They have also been found scattered throughout the human body, in the lungs, heart, placenta and even crossing the blood-brain barrier.

The growing ubiquity of microplastics has emerged as a key issue in the development of the world's first treaty to combat plastic pollution, with the next round of UN talks set to take place in Geneva next week.

The impact of microplastics and even smaller nanoplastics on human health is not yet fully understood, but scientists are already studying this relatively new issue in science.

The most prominent study of microplastics in the brain was published in the journal Nature Medicine in February.

Scientists analysed brain tissue from 28 people who died in 2016 and 24 people who died last year in New Mexico, US, and found that the amount of microplastics in the samples increased over time.

The study made headlines around the world when its lead author, American toxicologist Matthew Campen, told the media that they had found the equivalent of a microplastic spoon in the brain.

Campen also told Nature that he estimates that scientists could recover about 10 grams of plastic from a donated human brain — comparable to an unused crayon.

"Speculation far outpaces evidence"

But other researchers urged caution in treating the small study's findings.

"While this is an interesting finding, it should be interpreted with caution until independent verification," toxicologist Theodore Henry of Heriot-Watt University in Scotland told AFP.

"At present, speculation about the potential health effects of plastic particles far outpaces the evidence," he added.

Oliver Jones, a professor of chemistry at Australia's RMIT University of Technology, told AFP that "there is not enough data to draw firm conclusions about the presence of microplastics in New Mexico, let alone on a global scale."

He also found it "rather unlikely" that the brain could contain more microplastics than the amount found in raw sewage estimated by the study authors.

Jones noted that the study participants were in perfect health before their deaths, and the scientists themselves acknowledged that there was insufficient data to show that microplastics were causing harm.

"If (and that's a big 'if' in my mind) we do have microplastics in our brains, there's no evidence yet that they're harmful," Jones added.

Additionally, the study, according to Neuroscience News website The Transmitter, noted duplicate images, but experts stressed that this does not affect the main findings of the work.

"We can't wait for the full data set"

Most studies on the health effects of microplastics are observational in nature and therefore cannot establish a cause and effect relationship.

One such study, published last year in the New England Journal of Medicine, found that the accumulation of microplastics in blood vessels was associated with an increased risk of heart attack, stroke and death in patients with atherosclerosis.

Experiments have also been conducted on mice, including a study published in Science Advances that found microplastics in their brains.

Chinese scientists have reported that microplastics can cause rare blood clots in the brains of mice by blocking blood vessels, but stressed that small mammals are very different from humans.

A 2022 World Health Organization review concluded that “evidence is insufficient to determine the risks to human health” from microplastics.

However, many health experts cite the precautionary principle, saying the potential threat of microplastics requires action.

A report by the Barcelona Institute for Global Health on the health risks of microplastics, published this week ahead of treaty negotiations, notes that “policy decisions cannot wait for a full set of data.”

“By acting now to limit exposure, improve risk assessment methods and identify vulnerable groups, we can address this urgent problem before it becomes a broader public health threat,” it said.

Global plastic production has doubled since 2000 and is expected to triple by 2060.