NEW YORK – Recent headlines have raised concerns about microplastics in people’s bodies and the harm they may be doing.

Scientists say it could be years before there is a full understanding of how these tiny plastic particles are affecting human health. But it is known they have been found from the depths of the Mariana Trench to the heights of Mount Everest. And it is known that plastic is accumulating in people’s bodies too.

“The air we breathe, the water we drink, the food we eat – it’s in it,” said professor of marine biology Richard Thompson at the University of Plymouth, who coined the term “microplastics” in a 2004 paper. “We’re exposed.”

What are microplastics?

Scientists generally define microplastics as pieces less than 5mm long. Nanoplastics, which measure less than 1 micrometre, are the smallest of these and the most likely to get into one’s blood and tissues.

Microplastics mostly come from larger plastics, which degrade with use or when they are not disposed of properly, said Dr Jeffrey Farner, an assistant professor of civil and environmental engineering at the Florida A&M University-Florida State University College of Engineering.

“We use plastics in areas or in ways that lend themselves to the production of microplastics or to the breakdown over time,” Dr Farner said. For example, in construction materials that are weathered outdoors; in tubing that generates microplastics when it is cut; and in agriculture, as plastic mulch or in irrigation systems.

More than one-third of plastic produced today is for packaging, including single-use items such as food containers that largely end up as waste. A discarded plastic bag or bottle that makes its way to the ocean or a beach gets hit with ultraviolet light, heat and sand abrasion. From there, the bag or bottle “is going to break down into just an enormous number of micro- and nanoplastics”, Dr Farner said.

How do they get into one’s body?

These micro- and nanoplastics end up in the air, soil, water and food. The wear and tear on car tyres, for example, produces particles that pollute the air and water.

Microplastics filtered out of wastewater end up in sludge that is then used as fertiliser. Plastic cigarette filters make their way to lakes and oceans, where they degrade over time.

Humans breathe in these particles and ingest them. Some research suggests plants directly take them up from the soil and incorporat...