More than 79 thousand tonnes of ocean plastic are floating inside The Great Pacific Garbage Patch, a figure up to 16 times higher than previously estimated, according to a study published in Scientific Reports.
Laurent Lebreton and colleagues examined a major ocean plastic accumulation zone between California and Hawaii known as the Great Pacific Garbage Patch. The results suggest that there is a greater amount of plastic in this area than previously thought, and that microplastics are rapidly accumulating— from 0.4 kg km-2 in the 1970s to 1.23 kg km-2 in 2015.
The authors found that plastics made up 99.9% of all debris in this part of the ocean. At least 46% of plastic consisted of fishing nets, and over three quarters of the plastic in this zone was debris larger than 5cm, including hard plastics, plastic sheets and film. Microplastics accounted for 8% of the total mass of plastic but 94% of the estimated 1.8 trillion pieces floating in the area.
Although most large items had broken down into fragments, the researchers were able to identify a small number of objects, including containers, bottles, lids, packaging straps, ropes, and fishing nets. 50 items in the sample had a readable production date: 1 from 1977, 7 from the 1980s, 17 from the 1990s, 24 from the 2000s and 1 from 2010.
The authors observed that only certain types of debris that were thick enough to be buoyant stayed and accumulated in this zone, such as the common plastics polyethylene and polypropylene, which are used in packaging.
The authors assessed aerial images alongside data from 652 net tows carried out by 18 vessels. The aerial imaging allowed for a more accurate count and measurement of larger debris than previous studies that used only vessel-based visual surveys, which could partly explain why their estimates are higher than those made by other researchers. The differences between estimates could also be attributed to increasing levels of ocean plastic pollution in the area in the time since the previous studies were carried out, particularly following the 2011 Tohoku tsunami.
The authors caution that more research is needed to quantify sources of ocean plastics in the Great Pacific Garbage Patch and to better assess how long plastics stay in this area.
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Evidence that the Great Pacifc Garbage Patch is rapidly accumulating plastic. L. Lebreton, B. Slat, F. Ferrari, B. Sainte-Rose, J. Aitken, R. Marthouse, S. Hajbane, S. Cunsolo, A. Schwarz, A. Levivier, K. Noble, P. Debeljak, H. Maral, R. Schoeneich-Argent, R. Brambini & J. Reisser. Scientific Reports, (2018) 8:4666, DOI:10.1038/s41598-018-22939-w.