Plastic bottles lying in the gutter. Grocery bags tangled in branches. Food wrappers scuttling across the ground on a windy day. Although such examples of litter easily come to mind, they only hint at the serious and growing problem of plastic pollution — a problem mostly hidden from view.
The problem with plastics is they do not easily degrade. They may break down, but only into smaller pieces. The smaller those pieces get, the more places they can go.
Many pieces wind up at sea. Tiny bits of plastic float throughout the world’s oceans. They wash up on remote islands. They collect in sea ice thousands of kilometers (miles) from the nearest city. They even meld with rock, creating a whole new material. Some scientists have proposed calling it plastiglomerate (pla-stih-GLOM-er-ut).
Fish net and yellow rope melded with volcanic rock to create this plastiglomerate — a completely new type of “rock.”
P. CORCORAN ET AL/GSA TODAY 2014
Exactly how much plastic is out there remains a mystery. Scientists are hard at work trying to find out. So far, though, experts haven’t found as much plastic floating in the oceans as they expected. All that missing plastic is worrisome, because the smaller a plastic bit becomes, the more likely it will make its way into a living thing, whether a tiny plankton or an enormous whale. And that may spell some real trouble.
Into the soup
Plastics are used to make countless everyday products — from bottles to auto bumpers, from homework folders to flowerpots. In 2012, 288 million metric tons (317.5 million short tons) of plastic were produced worldwide. Since then, that amount has only grown.
Just how much of that plastic winds up in the oceans remains unknown: Scientists estimate about 10 percent does. And one recent study suggests as much as 8 million metric tons (8.8 million short tons) of plastic wound up in the ocean in 2010 alone. How much plastic is that? “Five plastic bags filled with plastic for every foot of coastline in the world,” says Jenna Jambeck. She’s the researcher from the University of Georgia, in Athens, who led the new study. It was published February 13 in Science.
Of those millions of tons, as much as 80 percent had been used on land. So how did it get into the water? Storms washed some plastic litter into streams and rivers. These waterways then carried much of the trash downstream to the sea.
Different types of plastic litter a remote beach in northern Norway. The plastic washed ashore after being swept into the ocean or dumped at sea. People have collected more than 20,000 pieces of plastic from this beach over the last three years.
The other 20 percent of plastic ocean trash enters the water directly. This debris includes fishing lines, nets and other items lost at sea, dumped overboard or abandoned when they become damaged or are no longer needed.
Once in the water, not all plastics behave the same way. The most common plastic — polyethylene terephthalate (PAHL-ee-ETH-ill-een TEHR-eh-THAAL-ate), or PET — is used to make water and soft-drink bottles. Unless filled with air, these bottles sink. This makes PET pollution tough to track. That’s especially true if the bottles have drifted to the ocean depths. Most other types of plastic, however, bob along the surface. It’s these types — used in milk jugs, detergent bottles and Styrofoam — that make up the abundance of floating plastic trash.
Abundant, indeed: Evidence of plastic pollution abounds across the world’s oceans. Carried by circular currents called gyres (JI-erz), discarded pieces of plastic can travel thousands of kilometers. In some areas, they amass in huge quantities. Reports on the largest of these — the “Pacific Garbage Patch” — are easy to find online. Some sites report it to be twice the size of Texas. But defining the actual area is a difficult task. That’s because the garbage patch is actually quite patchy. It shifts around. And most of the plastic in that area is so tiny that it’s hard to see.
Millions of tons… gone missing
Recently, a group of scientists from Spain set out to tally just how much plastic floats in the oceans. To do so, the experts traveled the world’s oceans for six months. At 141 locations, they dropped a net into the water, dragging it alongside their boat. The net was made of very fine mesh. The openings were only 200 micrometers (0.0079 inch) across. This allowed the team to collect very small bits of debris. The trash included particles called microplastic.
The team picked out the plastic pieces and weighed the total found at each site. Then they sorted the pieces into groups based on size. They also estimated how much plastic might have moved deeper into the water — too deep for the net to reach — due to wind churning up the surface.
These tiny plastic fragments broke off of larger items that had washed into the ocean.
GIORA PROSKUROWSKI/SEA EDUCATION ASSOCIATION
What the scientists found came as a complete surprise. “Most of the plastic is lost,” says Andrés Cózar. This oceanographer at the Universidad de Cádiz in Puerto Real, Spain, led the study. The amount of plastic in the oceans should be on the order of millions of tons, he explains. However, the collected samples lead to estimates of just 7,000 to 35,000 tons of plastic floating at sea. That’s just one-hundredth of what they had expected.
Most plastic that Cózar’s team fished out of the seas was either polyethylene or polypropylene. These two types are used in grocery bags, toys and food packaging. Polyethylene is also used to make microbeads. These tiny plastic beads can be found in some toothpastes and facial scrubs. When used, they wash down the drain. Too small to be trapped in filters at wastewater treatment plants, microbeads continue to travel into rivers, lakes — and eventually down to the sea. Some of this plastic would have been too small to have been caught in Cózar’s net.
Most of what Cózar’s group found were fragments broken from larger items. That comes as no surprise.
In the oceans, plastic breaks down when it’s exposed to light and wave action. The sun’s ultraviolet (UV) rays weaken the otherwise strong chemical bonds within the plastic. Now, when waves smash the chunks against each other, the plastic breaks into smaller and smaller pieces.
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Almost every sample of ocean water collected by a Spanish team contained at least a few small pieces of plastic. On this map, the dots show the average concentration of plastic in hundreds of locations. Red dots mark highest concentrations. The gray areas denote gyres, where plastics accumulate.
CÓZAR ET AL/PNAS 2014
When the Spanish team began sorting its plastic by size, the researchers expected to find larger numbers of the very smallest pieces. That is, they figured that most of the plastic should have been tiny fragments, measuring just millimeters (tenths of an inch) in size. (The same principle applies to cookies. If you were to smash a cookie, you would wind up with many more crumbs than you would large pieces.) Instead, the scientists found fewer of these tiny bits of plastic.
What had happened to them?
Entering the food web
Cózar proposes several possible explanations. The tiniest bits might have broken down quickly into particles too small to catch in his net. Or maybe something caused them to sink. But a third explanation seems even more likely: Something ate them.
Unlike the organic matter found in living things, plastics do not provide energy or nutrients to growing animals. Still, critters do eat plastic. Sea turtles and toothed whales gulp down plastic bags, mistaking them for squid. Sea birds scoop up floating plastic pellets, which can resemble fish eggs. Young albatross have been found dead from starvation, their stomachs full of plastic garbage. While feeding, adult seabirds skim floating trash with their beaks. Parent birds then regurgitate the plastic to feed their young. (These plastic bits eventually can kill them.)
Yet such large animals wouldn’t eat pieces just millimeters in size. Zooplankton might, however. They are much smaller marine creatures.
“Zooplankton describe a whole range of animals, including fish, crab and shellfish larvae,” explains Matthew Cole. He is a biologist at the University of Exeter in England. Cole has found that these tiny critters are just the right size to snap up the millimeter-size bits of plastic.
His research team has collected zooplankton from the English Channel. In the lab, the experts added polystyrene beads to tanks of water holding the zooplankton. Polystyrene is found in Styrofoam and other brands of foam. After 24 hours, the team examined the zooplankton under a microscope. Thirteen of the 15 zooplankton species had swallowed the beads.
In a more recent study, Cole found that microplastics limit the ability of zooplankton to consume food. Zooplankton that had swallowed polystyrene beads ate smaller bits of algae. That cut their energy intake nearly in half. And they laid smaller eggs that were less likely to hatch. His team published its findings January 6 in Environmental Science & Technology.
“Zooplankton are very low on the food chain,” Cole explains. Still, he notes: “They are a really important food source for animals like whales and fish.” Reducing their population could have a widespread impact on the rest of the ocean ecosystem.
This image shows zooplankton that has swallowed polystyrene beads. The beads glow green.
MATTHEW COLE/UNIVERSITY OF EXETER
And, it turns out, not just tiny zooplankton are eating the plastic bits. Larger fish, crabs, lobster and shellfish do too. Scientists have even found plastic in the guts of marine worms.
Once there, the plastic tends to stick around.
In crabs, microplastics remain in the gut six times longer than food does, says Andrew Watts. He is a marine biologist at the University of Exeter. What’s more, eating plastic causes some species, such as marine worms, to store less fat, protein and carbohydrate, he explains. When a predator (such as a bird) now eats those worms, it gets a less nutritious meal. It also ingests the plastic. With each meal consumed, more and more plastic makes its way into a predator’s body.
That’s cause for concern. “Plastics might pass up the food chain,” says Cole, “until it gets into food that ends up on our own dinner plates.”
An accumulating problem
The thought of eating plastic isn’t pleasant. But it isn’t just the plastic that’s cause for concern. Scientists also worry about a variety of chemicals found on the plastic. Some of those chemicals come from the manufacturing process, explains Kara Lavender Law. She is an oceanographer at the Sea Education Association in Woods Hole, Mass.
Plastics also attract a variety of dangerous pollutants, she notes. That’s because plastic is hydrophobic — just like oil, it repels water.
But plastic, oil and other hydrophobic substances are attracted to each other. So oily contaminants tend to glom onto pieces of plastic. In a way, plastic acts like a sponge, soaking up hydrophobic contaminants. The pesticide DDT and polychlorinated biphenyls (or PCBs) are two such toxic contaminants that have been found in ocean-going plastics.
Even though both contaminants have been banned for decades, they are slow to break down. So they persist in the environment. To this day, they hitch a ride on trillions of pieces of plastic floating in the oceans.
Scientists found 47 pieces of plastic in the stomach of this triggerfish. It had been caught near the surface in the North Atlantic subtropical gyre.
DAVID M. LAWRENCE/SEA EDUCATION ASSOCIATION
One reason these contaminants were banned is because of the way they affect animals and people. When eaten, the chemicals work their way into an animal’s tissues. And there they stay. The more of these chemicals a critter consumes, the more that gets stored in its tissues. That creates a constant exposure to the pollutants' toxic effects.
And it doesn’t stop there. When a second animal eats that first critter, the contaminants move into the new animal’s body. With each meal, more contaminants enter its tissues. In this way, what had started as trace amounts of a contaminant will become increasingly concentrated as they move up the food chain.
Whether contaminants hitching a ride on plastic work their way into the body tissues of marine animals in the same way remains unknown. But scientists are concerned that they might. Just how much of these chemicals in marine organisms came from eating contaminated plastic and how much from eating contaminated food is a big question, says Law. And no one yet knows whether the problem affects people.
The very nature of microplastics makes cleanup impossible. They are so tiny and so widespread that there is no way to remove them from the seas, notes Law.
The best solution is to prevent more plastic from reaching the ocean. Trash traps and litter booms can snag garbage before it enters waterways. Even better: Reduce plastic waste at its source. Be aware of packaging and buy items that use less of it, Law suggests. Skip the plastic bags, including zippered ones used for foods. Invest in reusable water bottles and lunch containers. And say no to straws.
This trash trap in Washington, D.C., stops litter before it can enter the Anacostia River. About 80 percent of the plastic that ends up in the world’s oceans gets its start on land.
MASAYA MAEDA/ANACOSTIA WATERSHED SOCIETY
Law also recommends asking restaurants to stop using polystyrene foam containers. These break up quickly and are not recyclable. Talk to friends and parents about the problems of plastic, and pick up litter when you see it.
Law recognizes that reducing plastic use won’t be an easy change. “We live in an era of convenience,” she says. And people find it convenient to throw things away when they are done with them.
That’s not to say that we should do away with plastic altogether. “Plastic has a lot of beneficial uses,” says Law. But people need to stop looking at plastic as disposable, she argues. They need to view plastic items as durable things to hold on to and reuse.