Marine plastic debris

A great deal of the debris in and on the ocean ends up on beaches or the ocean floor. Especially deep-sea trenches have essentially become deposition sites for large amounts of debris. Currents transport plastic debris through the ocean, allowing it to accumulate even in remote areas like the Arctic. Unlike beach debris, the plastics in the ocean cannot be readily removed – and breaks down into smaller and smaller particles over time. Many particles are ingested by marine fauna; as a result, the concentration of plastic particles in their bodies is likely quite high, though it can’t yet be realistically quantified.

The total amount of marine plastic debris is extremely difficult to quantify; although there have been various scientific studies that have sought to estimate the volume or total weight on the basis of litter surveys conducted at sea. However, subsequent extrapolations to the ocean as a whole suffer from a high degree of uncertainty. This is due in part to the fact that scientists can only gather random samples. In addition, estimating the total amount of litter is problematic because it enters the ocean from a broad range of sources that cannot all be observed in detail. In order to capture the total amount, we would have to add up the microplastics, the floating plastics, and the plastics on the seafloor. But measuring the microplastics alone is technically extremely challenging. According to some estimates, there could be more than one hundred million metric tons of plastic debris in the ocean.

In the centre of the oceans, driven by the prevailing winds, massive patterns of circular currents form at the surface. All objects floating on the surface are slowly but surely pulled toward the centre, producing areas with exceptionally high concentrations of debris. Over the past several years, the amount of litter has grown severely so that these areas are now referred to as garbage patches. However, unlike what many images in the media suggest, the patches are not solid layers of garbage. Here, too, much of the plastics drifts through the water column as microplastics; as a result, at first glance, for the most part you simply see open water on the surface.

There are currently five major ocean gyres in which plastic debris has formed garbage patches over the past decades. They can be found in the Atlantic, Indian and Pacific Oceans. The largest is the North Pacific Gyre, which reaches from the Equator to roughly the 50^th parallel. It is difficult to determine where exactly a garbage patch starts and how large exactly it is. To do so accurately, we would have to measure the debris concentration at countless different locations. But even this method is not completely reliable, since the ocean is dynamic and the debris is in constant motion. What we do know for certain is that the patches are hundreds of kilometres in diameter. Ultimately, however, their size is not the most relevant aspect – what matters is that debris accumulates in these patches, and that marine organisms living in these regions are exposed to large amounts of garbage. 

The diverse types of marine plastic debris have equally diverse effects on the biota. Larger pieces of plastic can become deadly traps for marine fauna when the animals become entangled in them and suffocate. In this regard, seabirds, sea turtles and various marine mammals are at risk. Many animals accidentally ingest pieces of plastic because they mistake them for their natural food. Once swallowed, the foreign objects can cause internal injuries. They can also accumulate in animals’ digestive tracts, leading to malnutrition. The effects of microplastics have yet to be conclusively established. However, it has been confirmed that the smallest particles can produce inflammation in the tissues of the digestive tract. We also know that many plastics’ chemical components, due to their molecular structure, can function in the same way as natural messenger molecules of the body, influencing important metabolic functions. Microplastic particles have also been detected in humans, who e.g. ingested them along with the food. The majority of particles, however, most likely enter the body through the air we breathe.

In many sectors, marine plastic debris is already producing new costs or harming revenues. Tourism is a good example. Litter-strewn beaches scare off visitors and vacationers. As a result, coastal municipalities are forced to remove the plastic debris regularly from their beaches. The costs involved in gathering and disposing of the debris most often have to be borne by local communities. Debris also means greatly reduced revenues in the fishing industry, when fishermen have to spend part of their working hours sorting out polluted catches. Last but not least, marine litter can clog up ships’ propulsion and steering systems, increasing the risk of maritime casualties. In many regions, plastic debris is affecting municipal drainage systems, increasing the likelihood of flood-related damages. The production of plastic also consumes enormous amounts of energy and involves substantial greenhouse-gas emissions. 

Meaningfully reducing the amount of marine plastic litter will require fundamental changes in how we use plastics. One important point is that plastics need to be viewed as a raw material that can be reused over and over again. In this way, plastics could take on a value and would no longer be thoughtlessly dumped into the environment as debris – which is essential, since once it is there, it is virtually impossible to remove. Accordingly, preventing plastic debris from being released into the environment is one of the most important approaches to combating the pollution problem. The starting point for doing so would be a reduction in the worldwide production of new plastics. As such, it is above all up to the industries to take action, although politicians also need to define the corresponding legal framework. Consumers can also adapt their behaviour so as to produce as little garbage as possible. In this regard, good environmental education is required to raise awareness for the effects of excessive plastic consumption. Technological solutions represent another approach: for example, conventional plastics could be replaced by bio-based and bio-degradable alternatives. Researchers at the AWI are also working on these new plastics, investigating their degradability and their effects on the marine environment. Bio-based plastics can, at least, reduce the use of fossil carbon sources and the associated greenhouse gas emissions.