Before French marathon swimmer Benoit Lecomte began his six-month-long attempt Tuesday to become the first to swim across the Pacific Ocean, he prepared for a number of possible challenges such as sharks, extremely cold water — and “plastic smog.”

That’s the term scientists use to describe billions of pieces of microplastic in the sea.

On his way from eastern Japan to San Francisco — a distance of 5,600 miles — the 51-year-old swimmer will encounter a lot of those microplastic particles, most of which have broken down from larger plastic items or deliberately included by manufacturers in body wash or toothpaste. In the Pacific, the biggest accumulation of plastic smog is about the size of Germany, France and Britain combined and Lecomte will swim right through it.

He already swam across the Atlantic Ocean over two decades ago, but this latest attempt in the Pacific isn’t only focused on athleticism. While Lecomte will be busy swimming approximately eight hours a day, scientists on accompanying boats will take water quality probes and conduct further experiments focused on plastic pollution in the Pacific Ocean.

A new U.N. study, which was also published Tuesday for World Environment Day, suggests that plastic pollution is an increasingly serious concern across the globe.

Some plastic “can take up to thousands of years to decompose, contaminating soil and water,” write the authors, who warn that plastic pollution is already manifesting itself in ways that few people are aware of.

“Plastic bags can block waterways and exacerbate natural disasters. By clogging sewers and providing breeding grounds for mosquitoes and pests, plastic bags can increase the transmission of vector-borne diseases like malaria,” they write. Hundreds of animal species are being harmed by the toxic chemicals that are often used to produce plastics and may enter the human food chain. Last week, for instance, a whale died in southern Thailand after eating plastic rubbish and vomiting out several plastic bags. Overall, the U.N. estimates the global damage to marine ecosystems amounts to at least $13 billion annually.

National responses have varied — with the United States still lagging behind, despite sharing a significant responsibility for the problem.

North America produced 21 percent of the world’s single-use plastics in 2014 and was outranked only by Northeast Asia, where 26 percent of the world’s plastic supplies were made.

“Much plastic may be single-use, but that does not mean it is easily disposable. When discarded in landfills or in the environment, plastic can take up to a thousand years to decompose,” wrote Erik Solheim, head of the U.N. Environment Program.

Most plastic packaging waste comes from China, but the United States is the world’s biggest per capita polluter, followed by Japan and the European Union.

In the study, the U.N. authors provide the first comprehensive analysis of policies in place worldwide to counter plastic pollution. Overall, they document efforts across 50 countries, mostly focusing on Africa and Europe. Whereas African nations appear to prefer total or partial bans over economic instruments, such as artificially raising prices on plastic bags, European lawmakers have mostly relied on the latter.

Notably absent from that statistic is North America, where national legislation to decrease plastic waste does not exist.

That doesn’t mean that Americans simply don’t care about the problem, though. In fact, there are more U.S. cities or states that have banned plastic bags and put restrictions on the use of the plastic foam material in takeout coffee cups than in Europe, Africa and South America combined.

The U.N. study indicates that some global progress has been made in recent years, even though major global powers such as the United States are lagging behind poorer nations. “Rwanda, a pioneer in banning single-use plastic bags, is now one of the cleanest nations on earth. Kenya has followed suit, helping clear its iconic national parks and save its cows from an unhealthy diet,” wrote Solheim, the U.N. Environment Program chief.

While many African nations were so directly affected by the impact of plastic pollution that they decided to take action, the impact of U.S. toothpaste on marine life in the Pacific Ocean appears harder to grasp for many Americans or Europeans.

Over the next six months, Lecomte, the French swimmer, wants to show people that there’s a link between their morning routines or their takeout coffee and the plastic smog polluting millions of square miles of the world’s oceans. His decision to risk the grueling adventure was partially motivated by a similarly eye-opening experience, he said in interviews before his departure.

“I remember my father, and he was the one who taught me how to swim in the Atlantic. I remember times when we would go to the beach and walk and never see any plastic,” Lecomte said.

“Now, everywhere I go, on the beach, I see plastic everywhere.”

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