Study detects synergistic effect making substances more dangerous, raising alarm since humans are exposed to both

Few human-made substances are as individually ubiquitous and dangerous as PFAS and microplastics, and when they join forces there is a synergistic effect that makes them even more toxic and pernicious, new research suggests.

The study’s authors exposed water fleas to mixtures of the toxic substances and found they suffered more severe health effects, including lower birth rates, and developmental problems, such as delayed sexual maturity and stunted growth.

The enhanced toxic effects raise alarm because PFAS and microplastics are researched and regulated in isolation from one one another, but humans are virtually always exposed to both. The research also showed those fleas previously exposed to chemical pollution were less able to withstand the new exposures.

The findings “underscore the critical need to understand the impacts of chemical mixtures on wildlife and human health”, wrote the study’s authors, who are with the University of Birmingham in the United Kingdom.

PFAS are a class of about 15,000 compounds typically used to make products that resist water, stains and heat. They are called “forever chemicals” because they do not naturally break down and accumulate, and are linked to cancer, kidney disease, liver problems, immune disorders, birth defects and other serious health problems.

Microplastics are tiny bits of plastic that are either intentionally added to products or are shed by plastic goods as they deteriorate. They have been found throughout human bodies, and can cross the blood-brain barrier. Research has linked them to developmental harms, hormone disruption cardiovascular disease and other health issues.

Plastic is often treated with PFAS, so microplastics can contain the chemical.

Researchers compared a group of water fleas that had never been exposed to pollution with another group that had been exposed to pollution in the past. Water fleas have high sensitivity to chemicals so they are frequently used to study ecological toxicity.

Both groups were exposed to bits of PET, a common microplastic, as well as PFOA and PFOS, two of the most common and dangerous PFAS compounds. The mixture reflected conditions common in lakes around the world.

The study’s authors found the mixture to be more toxic than PFAS and microplastics in isolation. They attributed about 40% of the increased toxicity to a synergy among the substances that makes them even more dangerous. The authors theorized the synergy has to do with the interplay in the charges of microplastics and PFAS compounds.

The remainder of the increased toxicity was attributed to simple addition of their toxic effects. Fleas exposed to the mixture showed a “markedly reduced number of offspring”, the authors said. They were also smaller at maturation and showed delayed sexual growth. The effects they observed “significantly advance” the understanding of exposure to multiple chemicals and substances, the authors wrote.

“It is imperative to continue investigating the toxicological impacts of these substances on wildlife to inform regulatory and conservation efforts,” they said.