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Microplastics in the Deep Ocean

Paul Kando

The first comprehensive effort to estimate how much plastic pollution is going into the world's oceans has come up with as much as 13 million tons per year. And this annual number could get 10 times bigger over the next decade.

Whale chasing a plastic bag
photo credit: DeeperBlue.com

Based on tonnage, China is the biggest plastic polluter among 192 coastal countries surveyed, followed by No. 2 Indonesia and No. 3 the Philippines. The US ranks No. 20. Many others in the top 20 have fast-growing populations and economies.

The survey, results of which were published in the journal Science, combined country-by-country estimates for plastic production and disposal, as well as levels of waste mismanagement and litter, to come up with an estimate for the amount of plastic debris finding its way from land to sea. The middle of the range is currently 8 million tons annually.

Plastic waste, ranging from grocery bags and soft-drink bottles to toys and the micro-beads washed off cosmetics, is a fast-growing environmental problem. Plastics accounted for 1% of municipal solid waste in 1960, but more than 10% today.

Most of that plastic ends up in landfills — but a good portion of it eventually makes its way to the ocean. According to one estimate over 270,000 tons of plastic is floating on the ocean surface and much more beneath it — mostly as broken-up bits that are ingested by marine life.

There have been efforts to skim plastic off the first couple of meters of the ocean’s surface. For instance, two years ago, Dutch inventor Boyan Slat, attempted to use a 2,000-foot-long screen deployed more than 1,000 miles off the California coast to trap plastic debris from the surface of the ocean. But punishing winds and waves broke apart his Ocean Cleanup Device, sidelining his project.

Now it turns out that at depths of 200 to 600 meters, the concentration of plastic particles is roughly four times what it is near the surface. This raises questions about whether it is even possible to reach a significant portion of the plastic floating in the ocean.

Scientists using underwater robots in the waters off California’s central coast found that plastic debris has infiltrated the deep ocean, with evidence of microscopic plastic particles extending from the surface all the way to the sea floor. A new study by Scripps Institution of Oceanography scientists at the University of California, San Diego, published in the journal Scientific Reports was conducted at two locations within the Monterey Bay National Marine Sanctuary. It sought to account for the significant discrepancy researchers have found between the total amount of plastic produced and the amount of plastic accounted for in the environment.

The Scripps team used remotely operated vehicles (ROVs) designed to sample the water at depths ranging from 5 to 1,000 meters. They found evidence of microplastics throughout the water column, with the highest concentration of the particles seen at depths between 200 to 600 meters. The concentration at those depths was roughly four times what it was near the surface.

To find plastic in the deep sea Is no surprise. What is surprising is that the highest concentrations are not at the surface nor at the deepest depths sampled, but somewhere in the middle, where plastic particles were found in crabs and other marine animals that live at those depths.

Scientists don’t yet know the implications for humans who eat that seafood. In the last couple of years, the Environmental Protection Agency has conducted studies to determine if there is a concern for human health but they haven’t yet been able to find evidence that is cause for concern. Obviously much more research is needed.

Previous research has shown plastic in the ocean to be a worldwide problem. The Scripps study, by revealing new dimensions of the plastic pollution, could help guide more effective cleanup efforts. Similar studies should be done in other bodies of water to better understand the true extent of the problem and how to deal with it.

This study is a wake-up call for people across the globe. Whether or not we live near the ocean, we impact that environment. The deep sea is not a garbage dump. It is critically important for all of nature, including human society. We all, but especially those who make plastics, must take responsibility for their safe disposal. If that increases the price of plastic items, so be it.