A massive amount of the world’s garbage has found its way to the central Pacific Ocean. Plastic debris churns in ocean currents and breaks down into microscopic particles that form a chemical sludge.

The particles “are eaten by things like jellyfish, who turn out to be one of the favorite foods of larger fish, and then you go through the food chain to tuna” and other large marine creatures, says Allen Clark of Hawaii’s East-West Center. “All of this material … gets concentrated in the fatty tissues of the fish.”

Some chemical components of plastic are known to cause cancer. So that’s dangerous for marine life and humans higher up the food chain.

This map shows how Pacific currents force debris to converge in the ocean’s center. (NOAA)

It’s easy to see mountains of garbage on land, but broken-down ocean debris is hard to measure and map. U.S. scientists are working to better understand how this saltwater sludge moves around the Pacific and vertically through the water column.

Ocean pollution is an urgent issue recognized by a consortium of political and environmental leaders that Secretary of State John Kerry has invited to Washington September 15 to 16 for a conference called “Our Ocean, One Future.”

Don’t wait for governments to act. You can do a lot of things yourself to reduce the flow of garbage in the oceans.