When the search teams combing the ocean for the lost Air France flight last week mistook floating garbage for plane wreckage, it raised a question. Is ocean debris so widespread that it turns up in a search for a plane? Just how much garbage is floating in the ocean, anyway?
The simple answer, say marine experts, is lots.
Oceans are full of abandoned fishing gear, junk thrown overboard from ships, and plastic washed out to sea from land. A report [PDF] released this week by the United Nations Environment Program (UNEP) and the Ocean Conservancy found that marine litter was a growing problem worldwide.
The wooden pallet pulled out of the Atlantic by Brazilian search teams during the search was likely discarded by a passing ship, says Keith Criddle, professor of marine policy at the University of Alaska.
"Pallets are common out there,” says Professor Criddle, though he adds that often garbage is concentrated in certain areas. “You’ve got shipping going all the way across the ocean regularly. A lot of that stuff is loaded onto pallets,” which end up getting dumped when they’ve outlived their usefulness.
Wooden pallets – along with shipping and packing materials, glass, metal, paper, and food waste – fit into the categories of debris that ships can lawfully dump into the ocean as long as they're certain distances from shore. Those distances vary according to the type of material they're dumping.
“You just have to be 12 nautical miles offshore to get rid of cargo residue,” says Criddle. “That’s not very far out.”
Ocean debris can entangle wildlife, harm habitats, and damage or pose navigational hazards to ships. The junk can also cause economic losses by deterring tourism or hampering fishermen.
Criddle led the National Research Council committee that produced a report on marine debris last year. The report, which found that current measures to reduce marine debris aren’t working and the problem is likely to worsen, called for a “zero discharge” policy for dumping waste at sea.
He says that one factor contributing to the problem is that the International Convention for the Prevention of Pollution from Ships (MARPOL) allows dumping except in certain circumstances and regions. Instead, he says, it should prohibit all dumping, except for certain exceptions.
“Societies evolve, and our standards we set ought to evolve as we evolve,” Criddle says. “Historically it was technically not possible to retain all the garbage on board [ships]. We now have the ability to be able to hold the garbage onboard and get it to the shore system where we can dispose of it properly.”
UNEP says that economic incentives are essential to encourage ship operators not to dump their waste at sea. According to the report, some ports, particularly in the East Asian Seas region, charge ships a fee for disposing of certain waste onshore, so the ship operators choose to dump the garbage at sea instead. Doing away with those fees, says the report, would discourage dumping in the ocean.
In 1988, MARPOL did prohibit dumping all plastics, which account for much of the trash filling the ocean. But up to 80 percent of it comes from land, not ships – flowing from rivers, storm drains, sewage outflows, or even blown from beaches by the wind.
Plastics aren’t biodegradable, but they do break down into smaller and smaller pieces. Those tiny pieces, which scientists say attract and concentrate toxins, can be mistaken for food and ingested by fish and seabirds. The toxins then leech into the animals’ tissue. Numerous studies have shown plastic bits in the bellies of fish and seabirds.
Another common source of ocean debris is lost or abandoned fishing gear, particularly nets and “fish aggregating devices,” which are sometimes heaps of debris lashed together by fishermen and then left to float out in the open seas where fish often congregate underneath them. Fishermen can attach satellite beacons to find the devices later, but those that drift too far away or are no longer useful can end up as just another piece of trash floating in the ocean.