Strategies for reducing ocean plastic debris should be diverse and guided by science (2024)

Sherman and van Sebille (2016) argue that the increasing accumulation of plastic in the oceans is an urgent issue deserving of immediate attention. Such claims are becoming common from environmental managers, activists and scientists. The complexity of this environmental issue spans both land and sea and includes a number of diverse stakeholders. As a consequence, and much like other challenging issues in conservation science, effective solutions are likely also complex and diverse (Green et al 2015). Waste management has not proven to be a 'one size fits all' solution. If we look all over the world we see a diversity of strategies to reduce, reuse, recycle and clean up our waste. Such strategies may be most effective when guided by the best available science.

The ever-increasing problem of plastic pollution is complex. On land, the production of plastic continues to increase annually (Plastic Europe 2015) and the availability and effectiveness of waste management infrastructure for plastic waste varies globally (Jambeck et al 2015). As a consequence of increasing production and leaky waste management, plastic of all sizes contaminates our oceans from the poles to the equator and from the coasts to the middle of the subtropical gyres (Barnes et al 2009). As a consequence, plastic is found in hundreds of species (Gall and Thompson 2015) and can cause a diversity of adverse impacts (Rochman et al 2016). Recently, plastic has been found in our seafood (Van Cauwenberghe and Jensson 2014, Rochman et al 2015a), reaching a level in the foodchain that affects us.

Heightened concerns have sparked ideas for mitigation and reduction, and are popularized by the media. These include a circular economy (World Economic Forum 2016), source reduction via waste management infrastructure (Ocean Conservancy 2015) and large-scale ocean cleanup (Slat et al 2014). Sherman and van Sebille (2016) took a closer look at the last of these solutions, ocean cleanup, to inform locations where cleanup will be most environmentally, ecologically and economically effective. They specifically examined a proposal by The Ocean Cleanup project to remove plastic debris from the North Pacific 'garbage patch', arguably the most famous accumulation of plastic floating in the centers of the oceans. Based on their results, Sherman and van Sebille (2016) suggest that ocean cleanup will most effectively reduce the amount of microplastic and the interaction between microplastic and wildlife when efforts are concentrated closer to shore, rather than in the middle of the ocean.

Sherman and van Sebille (2016) aimed to determine the locations where removal of microplastic would (1) remove the most surface microplastic and (2) reduce impacts on ecosystems. To address these questions, they developed a model that placed 29 plastic collectors (the number proposed by The Ocean Cleanup) in an oceanographic model that uses satellite-tracked buoy observations scaled to observations of microplastic from surface trawls to estimate movements and ultimately density of microplastic, and satellite-derived proxies of phytoplankton growth to estimate density of biota and the overlap with plastic debris. They conclude that cleanup efforts should focus on the flux (i.e. flow) of microplastics near the coasts rather than in regions where plastic debris accumulates. These efforts would remove debris before it reaches regions of high ecological significance (Sherman and van Sebille 2016). Broadly, they suggest it will be most cost-effective and ecologically beneficial to clean up plastic near the coasts, e.g., before it sinks and/or is ingested by wildlife. Specifically, they suggest that optimal removal locations are primarily located off the coast of China and in the Indonesian Archipelago—where sources are relatively large (Jambeck et al 2015) and circulation models suggest debris will disperse relatively quickly.

These suggestions for mitigation are similar to those published by Ocean Conservancy (2015), suggesting that source reduction via waste management should occur at locations where leakage is predicted to be greatest. This strategy is informed by a study published in Science by Jambeck et al (2015). Ocean Conservancy (2015) estimates that focusing efforts in 5 countries, including China, Indonesia, Philippines, Vietnam and Thailand, would reduce total global leakage by approximately 45% by 2025. Similarly, Sherman and van Sebille (2016) suggest that by focusing removal in modeled optimal locations, 31% of the modeled microplastic mass can be removed by 2025. This is in contrast to the 17% removal of plastic predicted by The Ocean Cleanup when cleanup is concentrated in the North Pacific 'garbage patch' (Slat et al 2014).