Threats to marine ecosystems from plastic waste vary across the world’s oceans

SEATTLE (Scrap Monster): Plastic pollution is globally ubiquitous, with wide-ranging environmental impacts. To mitigate these impacts, the EU Plastics Strategy sets out actions to reduce and manage plastic waste as part of the Circular Economy Action Plan. Internationally, efforts are also ongoing to confirm a Global Plastics Treaty addressing the entire plastics lifecycle, to prevent plastics from entering the environment and minimise their mismanagement.

Waste plastic in the ocean presents several hazards for marine wildlife and ecosystems. A wide range of animals are known to eat plastics of different types and sizes. This can cause problems, including blocking the digestive tract and reducing ingestion of nutritious food. Some potentially toxic organic pollutants can also bond to plastics and, when ingested, build up in individual animals and the wider food chain as a result. Animals such as turtles, cetaceans and sharks can also become entangled in larger plastic items, especially abandoned fishing gear.

These threats affect wildlife to different degrees in different locations. Understanding their geographic distribution is important to determine the most effective mitigation strategies and action priorities at regional and global scales.

Using existing datasets of plastic concentrations and distributions, marine biomass, and simulated plastic emission, transport and sinking processes, researchers have mapped these threats to produce a detailed analysis of global risk due to marine plastic waste. They identify varying risk distributions for different threats and project future risk trends under different plastic pollution pathways. They note that while some areas of ocean accumulate large volumes of plastic (often known as ‘garbage patches’), these may not overlap with significant animal populations, resulting in lower ecological impact. They therefore consider both these factors – accumulation of plastic pollution, and abundance of animals – in evaluating the risk level for plastic ingestion.

The findings highlight the north-eastern Atlantic Ocean as a high-risk area for plastic ingestion by larger-bodied animals, with smaller animals at greater risk in the north-western Atlantic. The study also found the North Atlantic to be at high risk from pollutants bonded to plastics – specifically methylmercury and perfluorooctane sulfonate, which they assessed as example cases. The researchers note that where high risks of ingestion and pollution overlap, as in the North Atlantic, there is a higher risk of pollutants building up within the ecosystem.

Entanglement risk is concentrated around coastlines, particularly where there are very active fisheries. The researchers report that the risk index of entanglement in coastal locations in general is more than 100 times greater than in the open ocean. They again highlight the north-eastern Atlantic as a high-risk area, along with the south-east Atlantic, subtropical Pacific and southern Indian oceans. A particularly pronounced increase in entanglement risk for larger organisms appears north of a latitude of 40°N, driven by a combination of higher biomass, more intense fishing and shipping activity, and buildup of marine debris in the Arctic Ocean.

Projections of future plastic pollution at current levels – the ‘high emissions’ scenario – estimate that by 2060 there will be 2.8 times more oceanic plastic than today, with levels rising across all oceans. Under moderate reductions the models project lower concentrations in the North Atlantic as well as the North Pacific and Indian oceans. However, even in these scenarios, higher concentrations are expected in the South Pacific and southeast Atlantic due to anticipated increases in plastic waste emissions from South America and Africa.

Risk patterns mostly change in line with plastic concentrations, say the researchers, but wildlife distribution and movement of plastic material also play a role. Even under a low plastic emissions scenario, entanglement risk reduces substantially in the open ocean but continues to rise in coastal areas due to plastic accumulation along the shoreline.

The use of relative risk probabilities for each threat presents some limitations to the study, the researchers note. It means the results do not evaluate absolute risk levels or relative risk between different threats. They suggest that further research could integrate additional factors into their model and work towards a unified framework for assessing risks. They also advocate further field research in high-risk areas including the Arctic Ocean.

The researchers highlight several implications for public policy. They argue that ocean cleanup efforts should not be overly focused on ‘garbage patch’ zones, as other areas with lower plastic volumes may present greater risks to wildlife. They also highlight the importance of beach cleanup efforts to address persistent plastic accumulation on shorelines. Tackling abandoned fishing gear is critical, they say, but they warn that ‘biodegradable’ gear, while reducing entanglement risk, may break down into particles that increase risks from ingestion and associated organic pollutant toxicity.

Geographically, they identify the North Atlantic and North Pacific as global hotspots for general plastic-related risk. However, with plastic emissions from some regions expected to increase under all scenarios, they highlight the importance of global approaches such as the UN Plastics Treaty.

Courtesy: www.europa.eu