Oceans of plastic waste

Net gain: The schooner Tara, on an expedition around the Mediterranean to monitor microplastic pollution, drags a so-called manta net to collect floating debris. (Photo © A. Deniaud Garcia Tara Expéditions.) The research vessel Tara, a schooner built for marine and polar research, spent seven months of the last year cruising the Mediterranean Sea on an expedition to collect an unglamorous material that is becoming more and more of a problem — microplastics. Particles of less than five millimetres in length arise from the photochemical decay of larger plastic items, including both land-based waste and nautical equipment, but there are also those that were manufactured at that size, as microbeads in cosmetics, or as pellets for the production of plastic items. An ever-changing cast of visiting scientists spent time on board the schooner to assist with sampling and to study various aspects of microplastic, from its distribution through to its impact on animals that ingest the particles and on microbes that may settle on them. During the seven-month trip around the Mediterranean, scientists and crew took more than 300 samples, which will be dispatched to 12 laboratories for detailed analyses. Results are expected to come out by the end of this year. These results will be very welcome, as the plastic pollution of the oceans is a growing problem about which far too few details are known with any certainty (Curr. Biol. (2013) 23, R135–R137). What is clear so far is that plastic waste that, for some reason or another, escapes the orderly processing of waste streams into recycling, combustion or landfill facilities is likely to end up in the oceans sooner or later. Plastics that are heavier than sea water, like PVC, will end up in the sediments near the shores where they were released. Most bulk plastics, including polyethylene and polypropylene, however, are buoyant and will drift out to the open ocean. Floating debris tends to accumulate in the large oceanic whirls, such as the North Pacific gyre (also known as the North Pacific garbage patch, for obvious reasons) and the corresponding gyres in the subtropical areas of the other oceans. What happens then is still an open question very much in need of investigation. Options include degradation down to small molecules and ultimately carbon dioxide, biofouling leading to sinking and incorporation into the sediment, and, most worryingly, ingestion by animals and thus entry into the food web. And if significant amounts of microplastics enter the food web, what effects will they have on the organisms that swallow them, and will they end up in our stomachs as well? All these questions need to be addressed, along with policy issues regarding how to stop the stream of plastics flowing into the oceans. It is a big challenge and science is only just beginning to rise to it.