Plastic waste on a beach in Panama City. Scientists believe that 4.4 million to 8.8 million tons of plastic enter the sea every year. Credit...Luis Acosta/Agence France-Presse — Getty Images Plastic waste has long been a visible — and growing — problem in oceans around the world, with refuse littering the shorelines of once-pristine beaches, stretching out across a wide expanse of sea in the Great