Scientists on toxic impact of microplastics

Plastic pollution is a grave and growing concern, but the biggest problems that it poses may just come from its smallest forms.

Tiny fragments of the stuff are now strewn across the entire globe and are beginning to show up in different parts of the human body, New Atlas reports.

But what are the health risks associated with ingesting and inhaling this now omnipresent synthetic material? While early studies do offer some cause for concern, they also show there is much still to learn before we truly start to sound the alarm.

Microplastics are smaller pieces of plastic measuring less than 5 mm in size (0.2 in), and can wash into the environment in ready-made forms, such as the microbeads used in cosmetic products or the tiny fibres used in synthetic textiles. Alternatively, microplastics can come via the breakdown of larger plastic products in the environment, such as plastic bags or soda bottles that are weathered and corroded by forces like UV light and ocean currents.

In recent years, scientists have intensified their focus on the behaviour of microplastics, exposing the many ways they move through the environment. This has led to a string of important discoveries as groundbreaking as they are concerning, showing that plastics can be driven into the deep ocean, spread through the air with the wind, drift back to Earth with snowfall in the Arctic and Antarctic, and even turn up near the summit of Mount Everest. Further, we know that disposable coffee cups release trillions of plastic particles into their liquid, and that plastic bottles can shed particles and chemicals into drinking water during use.

Meanwhile, scientists have also dialled up their efforts to understand the presence of microplastics in the human body. This includes a 2018 study that found microplastics in human stool samples all around the world and a 2020 study that unearthed plastic particles in every human tissue it sampled. More recently, significant discoveries have shown for the first time that microplastics can exist in living lung tissue, and also that they can enter the bloodstream.

"We already knew that microplastic is present in excrements of humans, but it is toxicologically relevant to check what might be circulating in the human blood," Heather Leslie, lead author of that study, explained to New Atlas. "We went from expecting there to be microplastic in human blood to knowing it is there. It’s the first real-world evidence plastic particles are actually absorbed in the human bloodstream."

Studies have shown that microplastic exposure can cause aneurysms and reproductive changes in fish, impair cognitive function in hermit crabs, lead to swimming abnormalities in shrimp and weaken the grip of mussels and potentially hamper their growth. We've also seen efforts to extrapolate these kinds of findings to humans through studies that use the genetically similar fruit fly as a model, which showed that microplastics can alter gene expression associated with stress response and oxidative damage.

"Much of what we know about microplastics has come from the marine environment research and it is only more recently that human impacts have come under scrutiny," Jeanette Rotchell, principal investigator of microplastic impacts on human health at the University of Hull, told New Atlas.

Last December, scientists at the University of York published research investigating the toxic effects of microplastic exposure on human cells. The first study of its kind, it built on previous work in this area such as research demonstrating that microplastics have the ability to alter the shape of human lung cells. It did so by taking into account how much we are likely taking in through food and water consumption, and subjecting those plastic concentrations to cells in the lab.

Among the toxic effects, the team observed were cell death, impacts on the cell membranes, oxidative stress and characteristics akin to allergic reactions. The research showed, according to lead author Evangelos Danopoulos, that we are ingesting microplastics at "levels consistent with harmful effects on cells, which are in many cases the initiating event for health effects." Though clearly not good news, there is an important distinction to be made between what occurs in laboratory experiments, and what we know for sure to be taking place in the human body.