Only a year ago, streams of lava gurgled from Hawaii's Kilauea volcano, blocking roads and inching across fields. It eventually reached the ocean where the intensely hot lava hit cold seawater and burst into tiny shards of glass and rubble: brand new sand.

Eventually, new beaches formed, like Pohoiki, a black sand beach that stretches for 1,000 feet on Hawaii's Big Island. Scientists based in the area aren't sure if the beach formed quickly after the volcano began erupting in May 2018 or slowly as the lava began to simmer down in August, but based on samples taken from the newborn beach, they know it's already polluted—covered with hundreds of tiny pieces of plastic.

Pohoiki adds to the growing body of evidence that plastic is most likely ubiquitous on beaches: even ones that look virgin.

Testing the waters

Microplastics are smaller than five milimeters and rarely larger than a grain of sand. To the naked eye, Pohoiki looks pristine.

“It's gorgeous,” says Nic Vanderzyl, the University of Hawaii at Hilo student who discovered the beach's plastic.

Vanderzyl saw the new beach as an opportunity to study new sediment that was perhaps untouched by human influence. He collected 12 samples from various beach spots. Using a solution of zinc chloride, which is more dense than plastic but less dense than sand, he was able to separate the two by forcing plastic to float to the top while the latter sank. The separation method was published in the journal Environmental Pollution in 2017.

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On average, Vanderzyl found 21 plastic bits per every 50 grams of sand. Most of them, he says, were microfibers, the hair-thin fibers that shed from commonly used synthetic textiles like polyester or nylon. They enter the water via wastewater flushed from washing machines or simply from swimmers plunging into the sea.



Steven Colbert, a marine ecologist and Vanderzyl's academic mentor, says the plastic would have likely washed up with waves and been left on the beach as tiny grains of sand comb through it. Compared with samples taken from two other neighboring beaches that were not formed by volcanoes, Pohoiki has about 30 to 50 percent of the plastic they have.

Vanderzyl and Colbert plan ongoing monitoring of Pohoiki to measure whether the amount of plastic increases or stays the same.

An end to pristine beaches

“I didn't want to find it,” Colbert says of the microplastic in Vanderzyl's samples, “but I really wasn't surprised.”

“There's this romantic idea of the remote tropical beach, clean and pristine like the beach Tom Hanks washed up on [in the movie Castaway],” says Colbert. “That kind of beach doesn't exist anymore.”

Plastic, including microplastics, has washed ashore on some of the world’s most remote beaches, uninhabited by humans.

Scientists have often likened the current state of the ocean to a plastic soup. Microplastics are so prolific that they rain down from the sky in remote mountain locations and turn up in most of our table salt.

Plastics 101

And unlike larger plastic items like bags and straws that might be grabbed and tossed in the trash, microplastics are is simultaneously abundant and invisible. One study published earlier this month found that beach clean-ups often leave behind millions of pieces of plastic.

Conservation groups like the Hawaii Wildlife Fund have teamed up with universities to develop beach cleaning contraptions that essentially act like a vacuum, sucking up sand and separating out the microplastics. But the machines’ bulk, cost, and the tendency to scoop up microscopic life as well all mean they can be used to clean only the most polluted beaches.

Though already filled with plastic, Pohoiki has a long way to go before it can rival places like Hawaii's famous “trash beach.”