Humans produce almost 300 million tons of plastic each year. There's ~40,000 tons of plastic currently bobbing along in the ocean, travelling the currents or spinning around in gyres. And that has scientists worried since there should be a lot more.
"A conservative first-order estimate of the floating plastic released into the open ocean from the 1970s (10^6 tons) is 100-fold larger than our estimate of the current load of plastic stored in the ocean," Cozar wrote. "Large loads of plastic fragments with sizes from microns to some millimeters are unaccounted for in the surface loads. The pathway and ultimate fate of the missing plastic are as yet unknown."
Andres Cozar, of Spain's University of Cadiz, offered up some suggestions to how the plastic is unaccounted for from
shore deposits to nano-fragmentation to
biofouling. While it's likely a combo of processes, Cozar and other scientists think
ingestion by wildlife is the most likely way plastic is being removed from the oceans.
[Carlos Duarte, an oceanographer at the University of Western Australia, Crawley] suspects that a lot of the missing plastic has been eaten by marine animals. When plastic is floating out on the open ocean, waves and radiation from the sun can fragment it into smaller and smaller particles, until it gets so small it begins to look like fish food—especially to small lanternfish, a widespread small marine fish known to ingest plastic.
“Yes, animals are eating it,” says oceanographer Peter Davison of the Farallon Institute for Advanced Ecosystem Research in Petaluma, California, who was not involved in the study. “That much is indisputable.”
If it didn't die from it, the digested plastic would likely have been passed by sea critter and has since sunk to the bottom of the ocean. We don't know a lot about the ecosystems of the ocean floor to know the extent of the impacts. Maybe the plastic is carried (eventually) into a subduction zone and is melted in the Earth's mantle.
Plastic is already creating new types of rocks.
A bigger worry though is that plastic will allow pollutants to bio-accumulate in the food chain.
[R]esearchers soaked small pellets of polyethylene in the waters of San Diego Bay for three months, then tested them and discovered that they’d absorbed toxins leached into the water from nearby industrial and military activities. Next, they put the pollution-soaked pellets in tanks (at concentrations lower than those found in the Great Pacific garbage patch) with a small, roughly one-inch-long species called Japanese rice fish. As a control, they also exposed some of the fish to virgin plastic pellets that hadn’t marinated in the Bay, and a third group of fish got no plastic in their tanks at all.
...
“We saw significantly greater concentrations of many toxic chemicals in the fish that were fed the plastic that had been in the ocean, compared to the fish that got either clean plastic or no plastic at all,” Rochman says. “So, is plastic a vector for these chemicals to transfer to fish or to our food chain? We’re now fairly confident that the answer is yes.”
...
One particular plastic-fed fish had even developed a liver tumor during the experimental period.
Even
plastics supposedly chemical free still contain suspect chemicals that can influence hormones.
“There is potential for this plastic to enter the global ocean food web,” explains Duarte. “And we are part of this food web.”