Microplastics found in 90 percent of table salt: potential health impacts?

Salt is produced on Madura Island, Indonesia, by evaporating seawater, an ancient technique. A new study found that salt made in this region contains some of the highest microplastics sampled. Photograph by Ulet Ifansasti, Getty Images

In partnership with the National Geographic Society.

Microplastics were found in sea salt several years ago. But how extensively plastic bits are spread throughout the most commonly used seasoning remained unclear. Now, new research shows microplastics in 90 percent of the table salt brands sampled worldwide.

Of 39 salt brands tested, 36 had microplastics in them, according to a new analysis by researchers in South Korea and Greenpeace East Asia. Using prior salt studies, this new effort is the first of its scale to look at the geographical spread of microplastics in table salt and their correlation to where plastic pollution is found in the environment.

“The findings suggest that human ingestion of microplastics via marine products is strongly related to emissions in a given region,” said Seung-Kyu Kim, a marine science professor at Incheon National University in South Korea.

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Salt samples from 21 countries in Europe, North and South America, Africa, and Asia were analyzed. The three brands that did not contain microplastics are from Taiwan (refined sea salt), China (refined rock salt), and France (unrefined sea salt produced by solar evaporation). The study was published this month in the journal Environmental Science & Technology.

The density of microplastics found in salt varied dramatically among different brands, but those from Asian brands were especially high, the study found. The highest quantities of microplastics were found in salt sold in Indonesia. Asia is a hot spot for plastic pollution, and Indonesia—with 34,000 miles (54,720 km) of coastline—ranked in an unrelated 2015 study as suffering the second-worst level of plastic pollution in the world.

In another indicator of the geographic density of plastic pollution, microplastics levels were highest in sea salt, followed by lake salt and then rock salt.

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Sherri Mason, a professor at the State University of New York in Fredonia, who partnered with researchers at the University of Minnesota on a separate salt study, said in an interview the new findings add “another piece to the puzzle” to assessing the impact of microplastics.

“That fact that they found higher counts in Asia is interesting. While not surprising, you still have to have the data,” she says. “The earlier studies found traces of microplastics in salt products sold in those countries, but we haven’t known how much.”

close A whale shark swims beside a plastic bag in the Gulf of Aden near Yemen. Although whale sharks are the biggest fish in the sea, they're still threatened by ingesting small bits of plastic. Photograph by Thomas P. Peschak, Nat Geo Image Collection close A great bowerbird in Queensland, Australia, decorates its home with broken glass, plastic toys, and other pieces of human trash. Photograph by Tim Laman, Nat Geo Image Collection close A sponge crab wears a clear sheet of plastic over its shell in Edithburgh, Australia. Historically, sponge crabs put sponges over their shells to camouflage themselves from predators. This man-made covering is not adequate protection. Photograph by Fred Bavendam, Minden Pictures/Nat Geo Image Collection close Empty plastic and glass containers wash ashore and litter the habitat of a marine iguana on Ecuador's Santa Cruz Island. Marine iguanascan be found only on the Galápagos Islands. Photograph by Tui De Roy, Minden Pictures/Nat Geo Image Collection close A pair of curious rhesus macaques inspect a discarded plastic bottle outside the Pashupatinath Temple in Kathmandu, Nepal. Photograph by Pete Ryan, Nat Geo Image Collection close A black-footed albatross crunches down on plastic garbage on the Leeward Islands of Hawaii. Seabirds depend on the ocean for sustenance, and the ocean is littered with plastic pollution. Photograph by Frans Lanting, Nat Geo Image Collection close Marine flora mixes with plastic packaging at the water's surface. Below, a green sea turtle swims away from the trash. Photograph by Steve De Neef, Nat Geo Image Collection close A Laysan albatross and a chick rest near a mound of regurgitated trash. Some birds with smaller gizzards can't throw up undigestible plastic, so they're more susceptible to plastic pollution. Photograph by Frans Lanting, Nat Geo Image Collection close In Hawaii, a bottlenose dolphin plays with a plastic six-pack holder. Such wrapping can permanently harm young marine animals, choking or disfiguring them. Photograph by Flip Nicklin, Minden Pictures/Nat Geo Image Collection close A pack of hyenas forage through mounds of trash at the city dump in Mekelle, Ethiopia. Bits of plastic are littered among leftover food scraps and bones discarded by humans. Photograph by Karine Aigner Tap images for captions

The new study, she says, “shows us that microplastics are ubiquitous. It’s not a matter of if you are buying sea salt in England, you are safe.”

The new study estimates that the average adult consumes approximately 2,000 microplastics per year through salt. What that means remains a mystery.

A separate study by the University of York in Britain that sought to assess the risks of microplastics to the environment, published Wednesday, concluded not enough is known to determine if microplastics cause harm.

The review of 320 existing studies found “major knowledge gaps” in scientific understanding of the impact of microplastics. The studies examined different types of microplastics, including microbeads, fragments, and fibers, leading to a “mismatch” of data that makes comparisons akin to comparing “apples to pears,” Alistair Boxall, a University of York geography professor and co-author of the study, said in a statement.

“Based on our analysis, there is currently limited evidence to suggest microplastics are causing significant adverse impacts,” he said. “There is an urgent need for better quality and more holistic monitoring studies alongside more environmentally realistic effects studies on the particle sizes and material types that are actually in the environment.”

That new study, funded by the Personal Care Products Council, an industry trade group, was published in the journal Environmental Toxicology and Chemistry.

Boxall added that the focus on microplastics may divert attention from worse environmental (and more easily identifiable) pollution problems, such as small particles released from car tires.

National Geographic is committed to reducing plastics pollution. Learn more about our non-profit activities at natgeo.org/plastics. This story is part of Planet or Plastic?—our multiyear effort to raise awareness about the global plastic waste crisis. Learn what you can do to reduce your own single-use plastics, and take your pledge.