Tiny plastic debris is accumulating far beneath the ocean surface

Vast swathes of litter floating on the ocean, like the great Pacific garbage patch, may just be the tip of the trash heap.

Divers have reportedly spotted plastic bags and candy wrappers as deep as the Mariana Trench. Now, a survey of microplastics at various depths off the coast of California suggests that this debris is most common several hundred meters below the surface, scientists report online June 6 in Scientific Reports.

Using remotely operated underwater vehicles, researchers sampled microplastics in Monterey Bay at depths from five to 1,000 meters. The team also measured pollutants in the guts of 24 pelagic red crabs and eight mucus filters from giant larvaceans — both of which eat organic particles about the same size as microplastics (SN Online: 8/16/17).

The concentration of particles 1,000 meters deep was roughly the same as it was five meters deep, averaging about three particles per cubic meter. Plastic in water from 200 to 600 meters deep was more concentrated, with 10 to 15 particles per cubic meter.

Chemical analyses of these particles revealed most to be plastics used in consumer products, such as disposable bottles, packaging and textiles. Plastics used to make fishing gear, the source of many larger hunks of ocean pollution, were far less common (SN Online: 1/4/19).

Every giant larvacean mucus filter and pelagic red crab contained microplastics. These particle-feeding creatures may be spreading contaminants to other predatory animals, from tuna to turtles, says study coauthor Anela Choy, a biological oceanographer at the Scripps Institution of Oceanography in La Jolla, Calif.

“It’s really important that this study be replicated … at different depths and in different regions of the world,” Choy says. Better understanding the distribution of deep-sea microplastic could help inform cleanup strategies beyond scooping up surface trash (SN Online: 9/7/18). “I think we’re going to find that the deep sea might be one of the biggest reservoirs of plastic pollution on the planet,” she says.