Fewer small pieces are found than expected and may be becoming fish food
Plastic seems to be disappearing from the ocean, and scientists are not sure why.
Exposure to waves and radiation from the sun can cause plastics to break down into micro-fragments, but scientists say those fragments are stable and durable enough to last for hundreds of thousands of years.
And yet, in a study in the Proceedings of the National Academy of Sciences, researcher reports that 10,000 to 35,000 tons of plastic debris is floating on the surface of our oceans — significantly less than the 1 million tons extrapolated from data reaching back to the 1970s.
After analyzing 3,070 samples of seawater from around the world, the researchers found that there has been no significant increase in the amount of plastic in the surface water of the world’s oceans since the 1980s, even as the amount of plastic produced has more than quadrupled.
More plastic almost certainly means more plastic in our oceans. But if the buoyant plastic is not floating, where is it?
Members of the team, lead by ecologist Andres Cozar of the University of Cadiz in Spain, don’t claim to have the answer, but they do identify a few clues for future science detectives to follow up on. They found far fewer fragments of plastic debris 5 millimeters and smaller than their computer models predicted. That led them to conclude that it is probably the smallest pieces of plastic that are making their way deeper into the water.
The authors say mesopelagic fish, which live in the hazy twilight zone 660 to 3,300 feet beneath the ocean’s surface, may be mistaking these bits of plastic for zooplankton. Perhaps the fish are gobbling them up at night when they come to the surface to feed, and then bringing the plastic back down to the deeper ocean where they spend most of their lives.
Over time, the plastic may sink deeper when excreted or when the fish dies.
The researchers also note that recent studies have shown bacterial populations growing on plastic micro-fragments, weighing them down and causing them to sink. But these are just a few possible answers to the missing plastic question, and the authors note that there are probably others.
Kara Lavender Law, who studies plastic pollution at the Sea Education Association in Woods Hole, Mass., said it provides the first global estimate for floating plastic debris. “We are putting, certainly by any estimate, a large amount of a synthetic material into a natural environment. We’re fundamentally changing the composition of the ocean.” □