What happens to all our plastic bottles and lids and containers after we toss them out? The vast majority of plastic trash ends up in landfills, just sitting there and taking thousands of years to degrade. A smaller fraction gets recycled (about 9 percent in the United States).
But there’s another big chunk that finds its way into the oceans, either from people chucking litter into waterways or from storm-water runoff carrying plastic debris to the coasts. And scientists have long worried that all this plastic could have adverse effects on marine life.
Now we can finally quantify this problem: A new study in Science calculates that between 5 and 13 million metric tons of plastic waste made it into the ocean in 2010 alone. What’s more, the authors estimate this amount could more than quadruple by 2025 without better waste management.
So where does this ocean plastic go?
Many people have heard of the Great Pacific garbage patch — a massive patch of trash that’s accumulated in a swirling subtropical gyre in northern Pacific Ocean. Ocean currents carry trash from far and wide into this vortex.
And it turns out that there are at least five of these floating garbage patches around the world. That’s according to a separate 2014 study in The Proceedings of the National Academy of Sciences, led by Andres Cózar of the Universidad de Cadiz based on the results of a 2010 circumnavigation cruise.
These garbage patches aren’t visible from up high — or even from a passing boat — since most of the plastic is bobbing just beneath the surface, and most of the particles are smaller than 1 centimeter in diameter. Over time, the plastic bits get broken down into ever smaller pieces as they get battered by waves and degraded by the sun.
Even so, these gyres have a lot of garbage, collectively holding some 7,000 to 35,000 tons of plastic in all. The patch in the North Pacific was by far the biggest — containing about one-third of all the floating plastic found. (Much of the plastic debris from eastern China, for instance, collects here.)
And yet, what was most surprising to researchers was that these plastic garbage patches weren’t even bigger. There should be millions of tons of plastic in the oceans. But these subtropical gyres only contained up to 35,000 tons. In particular, there seemed to be much less plastic smaller than 1 millimeter in diameter than expected. So where did the rest go?
In the PNAS paper, the authors offer a couple of possible explanations for why they didn’t find nearly as much floating plastic as they expected. The most troubling is that fish and other organisms are eating all the plastic:
1) Maybe the plastic is washing back ashore.The problem with this hypothesis is that most of the “missing” plastic is less than 1 millimeter in diameter. It’s unclear why only smaller bits would have washed up ashore.
2) Perhaps the plastic somehow breaks down into really, really tiny, undetectable pieces. This is possible, although the authors note that “there is no reason to assume that the rate of solar-induced fragmentation increased since the 1980s.”
3) Maybe small organisms are growing on some of the plastic bits, causing them to get heavier and sink deeper into the ocean. This is also possible, although other studies have found that when these plastic pieces sink, the organisms on them typically die and the plastic bobs back up to the surface.
4) Plankton and fish are eating the plastic. This one’s a more plausible hypothesis. After all, the tiny plastic bits that seem to have vanished are small enough to be eaten by zooplankton, who are known to munch on plastic. The authors also argue that mesopelagic fish beneath the surface may be eating a lot of plastic too — and, perhaps, pooping it out down to the ocean bottom. This needs further testing though.
Assuming fish are eating all that plastic and it’s entering the food chain, it’s still unclear how dangerous that is. Obviously some marine organisms, like seabirds, can get digestive problems (and can die) if they eat large pieces of plastic. But what about very tiny pieces? There’s some evidence that toxic chemicals can cling to plastic in the ocean and accumulate — but there’s still scant research on how much harm this might actually do as it passes through the food chain.
5) Plastic is accumulating in the ice caps. Meanwhile, a separate 2014 study in Earth’s Future suggested that a great deal of microplastic is accumulating in the polar ice caps. As sea ice forms and expands, the argument goes, it essentially “scavenges” the plastic from the seawater. This, too, might be part of the story.
6) Someone’s estimating wrong. Alternatively, it’s always possible that scientists’ best estimates of how much plastic is actually entering the oceans are incorrect. That might help explain the discrepancy.
Either way, something doesn’t add up — the current numbers suggest that the vast majority of plastic trash in the ocean is vanishing, and no one seems to know where it went.
–Jenna Jambeck has a fascinating podcast about her research available here.
— Dianna Parker of NOAA’s Marine Debris Program talks about possible ways to clean up the Great Pacific Garbage Patch.
Source: Vox, Brad Plumer on February 12, 2015