Where can we best tackle the ocean plastics problem?

plastic bottles on the beach
Image credit: epSos.de [CC BY 2.0], via Wikimedia Commons
Following recent research suggesting that 90% of seabirds have eaten plastic,  Department of Physics undergraduate Peter Sherman investigates how we could clean up our oceans.

There is a lot of plastic in the ocean, and the situation is only getting worse. Within the next decade, oceanographers predict that there will be ten times more plastic debris in the ocean than today.

Marine plastic is known to have many ecological and economical impacts. There are also associated human health risks. So what’s the best way of tackling this issue?

Ideally, we would simply stop polluting. Putting an end to plastic pollution will however be a lengthy and arduous task due to the massive behavioural shifts and infrastructural changes required. In the meantime, we should look to technological innovations, such as Boyan Slat’s plastic extraction method in The Ocean Cleanup project. Slat proposes placing floating barriers – booms – in areas of high plastic concentration in the North Pacific to collect surface debris.

My summer research project at the Grantham Institute revealed that Slat’s booms could indeed play a pivotal role in mitigating the ocean plastics problem, but that they are most effective when placed closer to shore, particularly around major sources of plastic such as East China and the Indonesian Archipelago. These results agree with a recently published paper that says seabirds are more affected by plastic close to shore than in the gyres.

Determining the best boom locations

Grantham Lecturer Dr. Erik van Sebille based his computer simulations on satellite-tracked buoy data from the Global Drifter Program. I then used these simulations to determine the optimal plastic removal locations.

A large fraction of the plastic on the ocean surface is located in the ocean gyres, the five rotating currents in Earth’s oceans. Somewhat counterintuitively, however, my research found that solving the problem might not be as simple as targeting these gyres with a set of clean-up booms. Although the highest concentration of plastic is in the gyres, plastic closer to the coast has much greater ecological and economical impacts on its surroundings. Once the plastic is out there in the open ocean, it has done most of its harm already.

Using this idea, I searched for the optimal removal locations for 29 of Boyan Slat’s plastic cleaners for two scenarios: reducing the impact on ecosystems as much as possible, and removing the most plastic.

The results

Below are maps of optimal boom locations for each scenario, assuming they were left in the water for 10 years.

Sherman-fig1

The locations for 29 booms (Left) to remove the most plastic; (Right) to save the most plankton. Each dot’s colour represents how effective the boom is: lighter-coloured dots represent more effective booms than darker dots.

These maps share some common locations for possible boom positions off the coast of Eastern China and around Malaysia. These regions have extremely high coastal population densities, which explains why they are projected to input so much plastic over the next decade. If we were to start ocean plastic removal processes, it makes sense that we would begin by placing booms around the major contributors to the world’s largest garbage patch.

These booms would be quite efficient in capturing any new ocean plastic, as shown below.

Over a 10-year span, the graphs represent (Left) the mass of the cumulative ocean plastic without booms, with booms in the North Pacific, and with booms near coastlines; (Right) plastics’ impact on ecosystems without booms, with booms in the North Pacific, and with booms near coastlines (a greater impact is worse for plankton). [click to enlarge image]

Not only do these boom locations remove a large amount of plastic (although still only a tiny fraction of global ocean plastic pollution) and reduce pressure on ecosystems, they are also more economically viable than placing them in the middle of the North Pacific because of transportation and production costs. Seldom do monetary and environmental incentives align, which makes results like this particularly inspiring.

So what?

These solutions give us a first estimate of the optimal placement of clean-up booms, which can be implemented in a variety of scenarios.

While these sinks will be effective in reducing the impacts of plastics, ocean plastic pollution is still expected to grow as the world population rises. We must find a way to minimise the amount of plastics entering our oceans, whether it be through substantial fines for plastic pollution, engineering plastics that degrade in the ocean faster, or through some other form of technological innovation or government policy.

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