Course:EOSC270/2021/Macroplastics in our Oceans

What is the problem?

Plastics are the most common marine waste found in our oceans. Plastic debris can come in various shapes and sizes. Debris larger than 5 mm in length are called "macroplastics". The degradation rate of plastics is very slow and cannot be biodegraded by itself. When a large number of plastics enter the marine system, it has impacts on the environment and ecosystem. Marine animals mistakenly believe that macroplastic waste is part of their natural diet, and the harm caused by eating them is frequent. Especially for large predators at the top of the food chain, the harm of macroplastics is fatal. In 2019, scientists found a young whale off the coast of the Philippines. It had 40 kilograms of plastic in its stomach, which made it unable to eat and swim back to the sea. Finally, it died of dehydration and starvation.

Figure 1: Model results for global count density in four size classes.  Model prediction of global count density (pieces km−2; see colourbar) for each of four size classes (0.33–1.00 mm, 1.01–4.75 mm, 4.76–200 mm, and >200 mm).

Macroplastics are the products of human activities.  They are synthesized from coal, oil, or natural gas and dumped into the marine system mainly through the land. Research shows that transportation and fishing cause about 20% of macroplastic pollution. Fishing nets, ropes, and abandoned boats are some of the main sources. In addition, about 80% of macroplastics come from the land. A large number of pollutants from factories and garbage from cities enter rivers and lakes through rainwater channels and sewers, and finally into the sea. The plastic bottles, plastic bags, fishing lines and so on, used by human beings will form macroplastic, which poses a threat to the marine ecosystem .

Plastic is the most common marine waste. They can be found in almost any ocean, lake, river or even arctic glacier, in the world. Most macroplastics sink to the bottom of the ocean after entering the ocean.  It is estimated that there are about 11.1 billion pieces of plastic in the coral reefs in the Asia Pacific region, and one-third of the coral reefs are covered with plastic waste, a proportion that may increase by 40% in the next seven years . Figure 1: Model results for global count density in four size classes.  Model prediction of global count density (pieces km−2; see colorbar) for each of four size classes (0.33–1.00 mm, 1.01–4.75 mm, 4.76–200 mm, and >200 mm).

It is estimated that by 2019, there will be at least 5.25 trillion macroscopic plastic debris in the global ocean, 50 times the number of stars in our galaxy, and the total weight is about 269,000 tons. Now half of all plastics produced around the world are disposable, which means it will only be used once and then discarded. In fact, only a small part of the plastic currently used is recycled, and the large amounts of waste plastic that isn't, may eventually go into the ocean. Macroplastic is known as the "ghost killer" of marine life, and it is also the killer of the top predators in the ocean. In 2016 alone, more than 100 whales were found dead due to dehydration caused by eating a lot of macroplastics.

How do Macroplastics impact marine ecosystems?

Figure 2: The following figure from Our World in Data in 2010, showcases the annual percentage of plastics usage and mismanagement of waste and approximately 8 million tons of macroplastic waste enters the ocean annually.  

Figure 3: This infographic from the NOAA showcases how macroplastics are moved into the oceans and how entanglement and ingestion of plastic waste impact marine life.

The ocean is home to a large variety of aquatic species but as a result of anthropogenic processes, it is now also a home to waste such as macroplastics that have accumulated in oceanic habitats affecting marine life. Macroplastics are used worldwide because of their durability and low-cost production and enter oceans through lost cargo, illegal waste dumping, and waste accumulation on beaches. Large plastic items build up on beaches and are transported across the oceans by surface winds, waves, and the earth’s rotation where they can either float on the surface or sink to the bottom of the ocean floor.Macroplastics that enter the marine ecosystem persist because of their durability causing a build-up of plastics in the ocean. Figure 2 depicts how macroplastics enters the ocean through mishandling of waste and how tidal movement and other oceanic processes at the ocean surface contribute to the continual accumulation of plastics.

A primary way large plastic waste affects marine life such as sea turtles, marine mammals, and seabirds are through entanglement and ingestion of macroplastics as shown by Figure 3. As plastic accumulation in the ocean continues to rise, plastic ingestion has become a repeated occurrence all across the marine food chain. It is also common for sea turtles, fish, and mammals to get entangled in plastic floating within the water column, which can often cause drowning and suffocation of the animals. The percentage of affected species because of plastic ingestion has increased to 100% in sea turtles, 66% in marine mammals and 50% in sea birds, all of whom ingest macroplastics by mistaking the plastic for prey. For example, albatross seabird parents mistakenly feed their chicks macroplastic thinking it is food, affecting the health of their chicks.

A study in the Greek and east Mediterranean seas has reported the ingestion of plastics in the odontocetes (toothed) whale species. The study conducted 34 dissections on 7 different species of odontocetes that had died due to various causes. Large macroplastics such as plastic bags were found in the stomachs of nine individuals, concluding a possible cause of death was gastric blockage because of plastic ingestion. It is common for odontocetes species to swallow their prey whole by suction, this increases the likelihood of digesting plastic found near their prey, due to high plastic accumulation in seas near Greece. This is one example of many, where plastic digestion occurs in organisms by mistaking macroplastics for prey or accidental digestion when catching prey, ultimately being lethal to the marine organism. Overall, anthropogenic macroplastic waste accumulation driven by oceanic tidal movement and surface winds, can result in the entanglement and ingestion of plastics by marine life thereby causing detrimental effects on the organisms and environment.

What is the extent of the problem?

In order to look at the extent of macroplastics and their problematic effects, it is important to focus on the ecosystem changes occurring because of them. Within the many ecosystems in the oceans, plastics are ubiquitous. Macroplastics are altering the ecosystems in different ways, and in some environments the changes are still unknown. In the open ocean, larger macroplastics are compiling together as they drift along with circular currents called ocean gyres. As seen in Figure 4, the North Pacific Ocean has three large areas where garbage has accumulated due to ocean gyres. These areas are now commonly known as the Great Pacific Garbage Patch. These accumulations are problematic since the plastics can kill many marine organisms by ingestion and suffocation. Coral reefs are receiving harmful impacts due to marine debris and lost fishing gear. They cause entanglement and damage to stony corals and other benthic reef organisms, potentially introducing parasites and pathogens. Mangroves and salt marshes that are contaminated by macroplastics are acting as a trap and filter for the debris, which is causing serious threats to the sustainable use of the region’s marine and coastal resources. In addition to these, deep-sea and Arctic regions are seeing growing numbers of macroplastics. However, it is still unknown exactly what ecosystem changes this will bring. Much more research is still to be done in order to assess the extent of effects and alterations macroplastics are causing in these two marine environments.

Figure 4: This image depicts the ocean currents and where the largest plastic Pacific Garbage Patches are in the ocean.

Examining the extent of this problem must also include comparing the present situation to the past situation. Looking back, the issue was discovered shortly after the popularity of commercial plastic production skyrocketed in the 1950’s. Plastics in the ocean were first reported more than 50 years ago when less than 50 million metric tons were produced per year. At this time, our oceans were relatively unobserved, and in particular, little was known about the deep-sea floor. Since the seafloor was portrayed as a huge, near lifeless desert at this time, it appeared to be a suitable place to dump waste. Fortunately, at the London Convention in 1970, all large-scale waste disposal at sea was banned. However, macroplastics in the ocean continued to increase as the production of plastics increased substantially. Currently more than 320 million tons of plastics are produced globally each year and this rate does not seem to be slowing down. The increase of macroplastics in the ocean has grown exponentially and this reflects the exponential growth of plastic production.

These marine macroplastics polluting our oceans need to be addressed. If they are not, the prognosis for the future is not good. Plastic production is expected to triple by 2050 from what it is today. The amount of plastic entering the oceans is expected to triple. Our current trajectory is grim, however, more research effort is needed to quantify ocean plastic sources, transport and loss processes that are currently happening. It is important to have an accurate estimate of what is occurring in order to predict what the future will most likely be.

Given the impact, what are the solutions?

Figure 5 This flowchart illustrates different courses of action that can be taken to combat plastic pollution on global, national, and local levels .

Plastic waste continues to be found more and more prevalently in our oceans in recent years. Additionally, with single use plastics on the rise since COVID-19 hit, there has been a large increase in single use plastic waste in the ocean over the course of this global pandemic . One of the main ways to tackle the issue of plastic pollution on a local level is through a restructure of city plans and policies regarding water, plastic, and cleanup management. One way of tackling the issue while also keeping citizens engaged is by involving them in the process in some way. Creating regional committees in cities and involving them in creating new policy increases likelihood that citizens will uphold such standards and enforce repercussions upon violation, since they helped create the policy themselves . Though COVID-19 safety precautions have ramped up the need for single use plastics, in the future, cities can look at establishing tax credits when individuals use greener alternatives (e.g. reusable cups, cloth bags) that can be claimed annually . As such, cities could tailor a list of acceptable green alternatives based on their communal demographic. Cities may also look at developing a dedicated waste management and cleanup team within their local government that involves and educates citizens rather than solely relying on larger scale efforts (e.g. Shoreline Cleanup) so that plans can be more locally targeted and strategized . The sad reality is that although most people are aware of the plastic waste problems, many neglect to actively implement tackling the issue in their daily lives, simply due to convenience. As such, even greater emphasis can be placed on educating citizens in more detail about the seriousness of the issue, such as ramping up ads that highlight the importance of recycling .

Figure 6 The leftmost pie chart illustrates the plastic collection methods currently in use compared to those that are still available. The rightmost pie chart illustrates the plastic prevention methods currently in use compared to those available. Evidently, though many mechanisms are in use, there are still more out there that can help combat this issue.

Plastic pollution is harder to tackle on a global scale since every country has unique environmental conditions. Ultimately, a global success at beating plastic pollution would require united fronts and collective efforts across all countries, amalgamating to an overall global reduction of marine plastic pollution. Over time, countries can work together to develop strategies for plastic recycling that implement novel technology. National campaigns, such as the Great Canadian Shoreline Cleanup, have previously been effective in directly involving citizens nation-wide, but more of these efforts would increase citizen awareness and education on a larger scale. On an international level, it is ultimately up to higher levels of the global government to come together and campaign within their entity for more aggressive international agreements that impede plastic pollution .

It is understood that macroplastics ultimately decompose into microplastics but in terms of research studies and data analysis, there are still many information gaps to fill about understanding how exactly these plastic particles make their way into animals. As such, conducting further studies is a sort of continual intermediate solution to uncover new information and identify more concrete long term solutions. Further studies should aim to develop methods to identify different plastic variants, their contributing environmental factors, correlate their effects on marine life accordingly, and track their movement through trophic pyramids, since there is already evidence as to how plastics travel into marine organisms initially.