To complement these findings, Ocean Cleanup used data on winds and currents to show that when pieces of plastic come out of, say, rivers, they tend to stick around the coastline. Maybe they’re washing out a little ways, then washing back ashore. Perhaps they bury in coastal sediments, then resurface due to erosion.
Ocean Cleanup reckons that in total, just .06 percent of plastics from the shore and coastline make their way into gyres. But the plastics that do make it there can stick around for perhaps decades—the researchers say they’ve pulled out plastics from the 1970s. They even found a Game Boy.
“Plastic fragments mostly by layers,” says Lebreton. “We call it the onion peel.” But different kinds of plastic polymers, in varying shapes, degrade at different rates. A Game Boy, for instance, has a better chance of surviving for years than a plastic bag.
But a problem with this study, says Marcus Eriksen, who studies ocean plastic and directs the 5 Gyres Institute, is that the observations are based on only 50 pieces of plastic that could be dated as old. “For this paper to come out and say hey, we found 50 objects with dates on them, and we think trash is in the ocean for decades and therefore we must continue this cleanup narrative, is wrong,” he says. “That’s my personal opinion.” An old piece of trash could have fallen off a boat a month ago, for instance, instead of starting its ocean journey from shore decades ago. (Ocean Cleanup says it collected 83,000 pieces, of which 50 had production dates, but only found one object dated past 2010. The group contends that if the sampled debris had been recently discarded, it should have found more new pieces.)
Scripps oceanographer Jennifer Brandon agrees that just because a piece of plastic in the gyre is old doesn’t mean it’s been adrift for a long time. And even if .06 percent of plastics from the shore and coastline make their way into gyres, Ocean Cleanup’s device isn’t equipped to capture microplastics. “One sticking point that I’ve always had with the people at Ocean Cleanup is I think personally they always underestimate the microplastic,” says. The group notes that because it would be difficult to collect microplastics in the sea, it’s important for them to collect macroplastics before they fragment into smaller pieces.
The science of ocean plastic pollution is so new, it’s still hard to tell what’s doing the most harm, and what most needs fixing. Macroplastics like single-use bags get into sea turtle stomachs, but microplastics are small enough to embed in organisms like shellfish. Scientists still don’t know how the chemicals that leach off plastics might affect marine organisms like the bacteria that produce our oxygen.
If this new study is correct in that plastics ejected at the coast tend to stick to the coast, as other modelers have generally found, you might argue that cleanup efforts should focus on those areas. After all, biodiversity is especially high around the coasts—think of bustling reefs. “I’m really less concerned environmentally about this nasty garbage patch than I am about all the plastics that are right along the coastline,” says University of Michigan eco-toxicologist Allen Burton, who studies plastic pollution.
Photograph: The Ocean Cleanup