There May Be Almost a Million Times More Microplastics in the Oceans Than We Thought
The amount of plastic in the oceans around California may be almost a million times more abundant than previously calculated.
Scientists writing in Limnology and Oceanography Letters estimate the true number of microplastics per cubic meter is 8.3 million—not ten as previously stated.
Researchers at the University of California, San Diego, developed a new method of counting plastic. It shows more traditional methods may be missing some of the smaller microplastics, with the effect of underestimating the degree to which plastic is contaminating the world's oceans.
These traditional methods involve trawling a mesh net below water. The bulk of studies use a mesh fine enough to separate plankton from seawater but not fine enough, it appears, to capture microplastics smaller than 333 micrometers, or one-third of a millimeter—a microplastic is considered anything that is smaller than 5 millimeters.
But by using surface seawater samples and salps, the team at UC Diego were able to collect microplastics just 10 micrometers in size. The thickness of a piece of paper, for perspective, is 100 micrometers.
"For years we've been doing microplastics studies the same way (by) using a net to collect samples. But anything smaller than that net mesh has been escaping," lead author Jennifer Brandon, a biological oceanographer with UC San Diego, said in a statement. Brandon developed the method when she was a graduate student at the university.
Salps are a group of gelatinous and often transparent creatures that can vary in size from a few millimeters to a few meters. They frequently group together to form longer chains (or wheels) when they reach maturity. They are filter feeders, taking in food (and microplastics) from the surrounding water. Because the size of the pores on their filters are just 5 micrometers they can absorb infinitesimally small particles.
"They are passive filter-feeders, meaning they don't select what particles they eat based on anything but size," Brandon told Newsweek. "So if there are microplastics in the water, they will eat them."
Using specimens collected at the Scripps Pelagic Invertebrate Collection, the researchers were able to study samples of salps collected over the years during expeditions in the North Pacific to find out how much microplastic they were ingesting. The team found that the mini-particles included in the study were five orders of magnitude more common than particles 333 micrometers or more.
"We were surprised at how high the numbers were," said Brandon. "But we expected the mini-microplastics to be higher than the previous recorded numbers of microplastics, because as microplastics break down, they make more and more smaller pieces"
When compared to seawater samples collected at surface level, the team found the microplastics discovered in the salps were "significantly smaller." They also observed particles were more abundant in samples collected closer to the land than they were in samples collected near the garbage patch, something that may be explained by runoff pollution.
While the effect of microplastic pollution on human health is not widely understood, research has shown that it has a detrimental effect animals further down the food chain. For example, a study has shown exposure to polystyrene microplastics affects oyster reproduction.
"[Plastic] keeps breaking down but stays chemically plastic and doesn't go back into the ecosystem," said Brandon.
The article has been updated to include comments from lead author Jennifer Brandon.
