The ocean plastic problem
There are around 269,000 tonnes (269,000,000 kg) of plastic in the ocean, and this figure is growing. Put into context that means 5.25 trillion plastic particles, 580,000 fragments per square km, or the equivalent weight of over 224,000 small cars. These figures exclude nanoplastic which is invisible to the naked eye as the global concentration of these tiny particles is unknown. Many people have heard of the Pacific garbage patch, which is essentially a floating island of plastic and other rubbish which is hugely detrimental to ocean life. As plastic is positively buoyant – which means it floats – ocean plastic is driven together by wind and ocean currents and circulates around the Pacific being hugely detrimental to marine life. Some plastic is taken away from the surface due to ingestion by marine life or biofouling. Biofouling is the accumulation of organisms such as barnacles on the surface of plastic which increases the density and causes it to sink.
Plastic can make its way into the ocean a number of ways. The first thing that would come to mind for many people is littering into the ocean, like leaving rubbish on beaches. However, almost 80% of global plastic pollution is because of rivers, where plastic enters the ocean via river mouths. Plastic also enters the ocean when it is discharged from drainage systems in cities, when the handling of plastic waste is mismanaged.
The future of plastic
A paper by the University of Exeter created a model which estimated the amount of plastic in the ocean. The model assumed ocean plastic remains buoyant for 61 years, that plastic discard started in 1950, the discard rate will peak in 2029, and 2052 will be when no more plastic waste enters the ocean due to recycling and incineration of plastic on land. With these figures the model calculated that there would be 860,600 tonnes of ocean plastic by 2052, triple the figure in 2011. This is under a business as usual scenario, with no ocean plastic cleanup efforts.
Luckily for us, there are several initiatives such as the Ocean Cleanup Project which aims to cleanup the Pacific garbage patch in the next 20 years. This uses 600m floating barriers with a vertical screen to catch plastic. Once this plastic is collected it is incinerated as it is often impossible to recycle ocean plastic due to contamination. Using the model described above, the researchers calculated the efficiency of one ocean clean-up device. It was found that one device could clean a relative fraction of 0.07% of the ocean per year. With one device working continuously for 130 years until 2150, only 769 tonnes of ocean plastic would be removed from the ocean. That is 0.09% of the total amount of buoyant ocean plastic. Even deploying 200 devices for the same period, 44,900 tonnes of ocean plastic would be collected, with 816,000 tonnes remaining. This is because of the continued addition of ocean plastic until at least 2050, and after that plastic remains buoyant for a very long time.
As the paper notes, the model does assume plastic is evenly distributed in the ocean, with no areas of accumulation like the Pacific garbage patch. This assumption is purely for simplicity of the model, as there are complex interactions of factors which cause the agglomeration of ocean plastic. These are very difficult to accurately model. This means estimates of the efficiency of ocean cleanup devices is likely to be underestimated, as devices will collect more garbage in a shorter time when it is highly concentrated like in the Pacific garbage patch.
Regardless, the model suggests the goal to clean up the Pacific garbage patch within the next 20 years is very ambitious. The size of the ocean and the volume of plastic being added to the oceans means it is being added faster than we can take it away. However, the paper finds there are other ways to reduce the amount of plastic in the oceans, using surface cleanup devices in conjunction with other initiatives.
There is hope
Although surface clean up technology has received by far the most public attention, with private ventures and NGOs developing technologies, initiatives such as the Ocean Cleanup Project are also employing other methods. This includes deploying 1000 autonomous interceptors in rivers. As mentioned, this is where 80% of ocean plastic pollution originates from. These interceptors are stationed in some of the most polluted rivers in the world and funnel plastic and garbage to be collected inside the device, stopping it before it reaches the ocean. This has the added benefit of collecting plastic before it gets fragmented by wave and UV action. This means it also reduces the amount that becomes nanoplastic, preventing it being ingested by marine life. It is effectively impossible to collect and poses an issue to human health, as we also consume nanoplastic particles when we eat seafood so nanoplastic is an important part of the ocean plastic problem. Technology that reduces this as well as larger plastic particles is the best of both worlds.
Under the optimistic scenario of river barriers to collecting 100% of the plastic in rivers before it reaches the ocean. A total of 462,000 tonnes would be prevented from entering the ocean if implemented in 2020. Yet, 398,000 tonnes would remain from plastic that had entered the ocean previously. There would also be the other 20% of plastic that enters the ocean through routes other than rivers. This means the use of ocean cleanup devices is most definitely still required.
What can we do?
This paper does not ignore the significance of cleanup projects and acknowledges the benefits of initiatives like the Ocean Cleanup Project in raising public awareness of ocean plastic and the existence of the Pacific garbage patch. However, one of the aims of the paper was to outline the importance of reducing the amount of plastic waste we produce. To be more mindful about how we dispose of our plastic. Surface cleanup technology and even river barriers cannot completely solve the ocean plastic problem. Therefore, we should not treat these projects as a free pass to continue carelessly using and discarding plastic.
The best solution is still prevention rather than mitigation. This can be achieved by reducing the amount of plastic we use, and especially being more mindful about single use plastic. This could include taking reusable bags to shopping centers, banning plastic straws, and encouraging plastic free packaging. The focus by NGOs, private corporations, governments, and the public, should be to reduce plastic use and production. Projects like the Ocean Cleanup Project should simply be used to remedy the existing damage we have caused to the oceans.
This study was published in the journal Science of the Total Envrionment.
Hohn, S., Acevedos-Trejos, E., Abrams, J. F., de Moura, J. F., Spranz, R., & Merico, A. (2020). The long-term legacy of plastic mass production. Science of The Total Environment, 141115.
This is my first of hopefully many articles I plan to write and be published on Science Connected. You can find my article on their site here: https://magazine.scienceconnected.org/2020/08/ocean-plastic-mounts-despite-cleanups/. It is also a great site to keep up with other science news, especially if you don’t want to read anything too technical. Their mission is to connect the public with science, typically doing summaries of scientific papers using only primary sources of information. Science Connected aims to increase public understanding of science, believing it is the key to making informed choices, being successful members of society, and acting as responsible stewards of the planet.