The research team reporting in 2014 that there are over 5 trillion pieces of plastic weighing over 250,000 tonnes floating in the seas – ‘The Sailing Seas of Plastic’– has released another report showing where a lot of the waste is coming from; down rivers and off beaches.
The latest report issued in Nature Communications journal in June estimated “between 1.15 and 2.41 million tonnes of plastic waste currently enters the ocean every year from rivers, with over 74% of emissions occurring between May and October. The top 20 polluting rivers, mostly located in Asia, account for 67% of the global total.”
New Zealand data visualisation company Dumpark (dumpark. com) earlier produced maps highlighting the distribution of the 5.25 trillion plastic particles being driven around the globe by the prevailing ocean currents. (see world map above)
Other studies, such as that by the 2016 Plastic Oceans campaign, estimates that of the 300 million tonnes of plastic produced globally each year, up to 8 million tonnes finds its way into the world’s oceans.
The latest report states “a significant portion of the plastics produced worldwide enters and persists in marine ecosystems. This includes shoreline, seabed, water column and sea surface environments of the world’s oceans.
“The release of plastics into the marine environment occurs through a variety of pathways, including river and atmospheric transport, beach littering and directly at sea via aquaculture, shipping and fishing activities.
“It has been estimated that between 4.8 and 12.7 million tonnes of plastic enters the ocean every year from coastal populations worldwide. Plastics within coastal areas however do not only enter the oceans through rivers. It can also reach oceans by other processes such as direct littering near beaches, followed by tidal or wind transport.
“It is also important to note that our model is calibrated against buoyant plastics found on river surface waters, whereas this previous coastal contribution assessment considers all types of plastics found in municipal waste. Finally, we only consider a section of the full plastic debris size spectrum as particles smaller than the mesh size of the sampling nets were not accounted for and debris larger than the aperture size of the trawl devices are under-represented. For these reasons our estimate should be considered conservative.”
The earlier report on Plastic Pollution in the World’s Oceans was based on 24 expeditions between 2007 and 2013 across all five sub-tropical ocean gyres, coastal Australia, the Bay of Bengal and the Mediterranean Sea. Each white dot on the map represented an estimated 20 tons of plastic of which 92% is ‘miscroplastic’, small particles measuring only a few millimetres in size which constitute a great threat to oceanic life as they are often too small to be distinguished from regular food sources and ingested by marine life.
The contribution by rivers to plastics in the oceans is derived from individual watershed characteristics such as population density, mismanaged plastic waste (MPW), production per country and monthly averaged runoff. The model was calibrated against river plastic concentration measurements from Europe, Asia, North and South America.
The original publication is at doi.org/10.1371/journal.pone.0111913
Also see: the Gyres Institute 5gyres.org