The oceans may contain much, much more plastic than previously thought

In the oceans, the most widespread type of plastic pollution may be the kind you can’t see.

A new study published Wednesday in the journal Nature estimates that the North Atlantic Ocean alone contains 27 million metric tons of nanoplastic — plastic particles 100 times smaller than the width of a human hair. That figure is 10 times higher than previous estimates of plastic pollution of all sizes across all the world’s oceans, according to the study’s authors. 

The research represents one of the first attempts to quantify marine nanoplastic pollution; previous efforts were constrained by limitations in detection technology. The study suggests that the mass of nanoplastics in the North Atlantic is greater than that of their much larger counterparts, microplastics and macroplastics. Microplastics range in width between 0.001 millimeters and 5 millimeters, making them up to 5 million times bigger than nanoplastics. Macroplastics are even larger.

Helge Niemann, a researcher at the Royal Netherlands Institute for Sea Research, a professor of geochemistry at Utrecht University, and one of the study’s authors, said the findings are concerning for marine biology and human health. Nanoplastics are “not conducive, generally, for life,” he told Grist. He emphasized that the study’s findings are limited to the North Atlantic, but said it is “likely the case” that nanoplastics are widespread across other oceans as well.

Studies suggest that nanoplastics cause inflammation to living cells when ingested, though it’s unclear whether this is because of the particles themselves, the plastic chemicals they can release, or pathogens that they pick up while floating around in the environment. Due to their tiny size, nanoplastics can more easily traverse biological membranes than their larger counterparts. 

Tracey Woodruff, a professor of reproductive health and the environment at the University of California, San Francisco, who was not involved in the new research, said she expects that nanoplastics will be linked to many of the same health risks as microplastics. In animals, these include reproductive issues, intestinal problems, and colon and lung cancer. Microplastics also bioaccumulate, meaning they travel up the food chain as larger animals eat smaller ones. 

“Our hypothesis is that … nanoplastics could travel more widely in the body even than microplastics, and therefore could have more adverse health consequences,” Woodruff said. It’s also possible that future research will discover that nanoplastics are present in the human body at even higher concentrations than microplastics.

The study’s authors obtained their data during a research cruise in 2020. They collected water samples at 12 locations of varying depths across the North Atlantic Ocean. Five samples were taken from within the North Atlantic gyre, one of the world’s five circular ocean currents that has become famous for its “garbage patch,” an enormous collection of plastic trash and other waste.

The researchers looked at nanoplastic concentrations at three different depths at each location: a layer just 10 meters below the surface, a middle layer at 1,000 meters deep, and 30 meters above the seafloor. Back in the lab, they used a novel type of mass spectrometry — an analysis that can identify different kinds of plastic — to distinguish between three polymers. Polyethylene terephthalate, or PET, the type of plastic used in water bottles, was the most widespread at every depth, followed by polyvinyl chloride, used in water pipes, upholstery, children’s toys, and other products; and polystyrene, used in plastic foam. 

Overall, nanoplastic concentration was the highest closer to the surface at 18 milligrams per square meter and lowest near the seafloor at about 5.5 milligrams per square meter. The researchers suspect that this distribution is due to the deterioration of bigger pieces of plastic that are suspended near the surface, which may sink slowly unless transported downward by, for example, animals that have eaten plastic and then died.

Eighteen milligrams per square meter might not seem like much. But, it’s the equivalent of containing seven mosquitoes in a 3-foot by 3-foot box, assuming each mosquito weighs roughly 2.5 milligrams. Multiply that by the vast volume of an ocean, and you end up with a whole lot of plastic. 

“I would argue as a toxicologist that if you see something in micrograms per liter in the open ocean, that’s quite a high concentration,” said Martin Wagner, a biology professor at the Norwegian University of Science and Technology who was not involved in the study.

Wagner cautioned that the study’s major extrapolation — that there are 27 million metric tons of nanoplastic in the North Atlantic, more than the weight of 26,000 Eiffel towers — relies on “very few samples.” Still, Wagner said it makes sense that there would be an exorbitant amount of nanoplastic given the high volume of larger plastic fragments that end up in the oceans each year. According to the United Nations, roughly 20 million tons of plastic enter aquatic ecosystems each year. This includes lakes, rivers, and streams, as well as oceans, but for much of that pollution, the ocean is the final destination.

“We’ve basically been dumping plastic in the ocean for decades,” Woodruff said. “It doesn’t go away, it just breaks down into smaller plastics, so it does make sense that you would find more nanoplastics than macro and microplastics.”

Notably, the type of analysis that the study’s authors used was unable to detect the world’s two most common plastic polymers: polyethylene and polypropylene, meaning their estimate for overall nanoplastics is likely conservative. Still, the study’s findings could provide more realistic data for researchers who are trying to model the real-world impacts and toxicity of nanoplastic pollution.

Niemann said more research is needed on nanoplastics, including on their prevalence globally. He recently won a grant to research what happens to nanoplastics once they’re in the ocean, including whether any types of bacteria can naturally break them down. Manually trying to clean them from the global oceans’ more than 330 million cubic miles of water is “not really a good idea,” he said.

Both Wagner and Woodruff said the research adds to the growing body of  evidence supporting limits on global plastic production — rather than allowing it to triple by 2050, as projected by the United Nations Environment Programme. World leaders are expected to continue debating plastic production limits during the next round of negotiations over the U. N.’s plastics treaty, scheduled to take place next month in Geneva, Switzerland. 

“This reinforces how important it is to cap [plastic production], leave fossil fuels in the ground, and look to alternatives,” Woodruff said.