"If you don't stop plastics from flowing into the ocean, it will be a Sisyphean task," Leonard said, citing the Greek myth of a task never completed. He added that on Sept. 15 about 1 million volunteers around the world will collect trash from beaches and waterways as part of the Ocean Conservancy's annual International Coastal Cleanup. Volunteers last year collected about 10,000 tons of plastics worldwide over two hours, he said.