For centuries, people have used the oceans as a dumping place. Many cities take tons of garbage out to sea and dump it there. The quantity of garbage that ends up in the water is incredible. Five million plastic containers are thrown into the world,s oceans every dayl Aside from plastics, many other dangerous substances are dumped in oceans. These inciude human waste and chemicals used in agriculture. And every year, oil tankers accidentally spill millions of gallons of oil into the sea