Marine litter is defined as any persistent, manufactured, or processed solid material that has been discarded, disposed of, or abandoned within the marine and coastal environment. Originating from human activity, this pollution affects every ocean basin, from surface waters to the deepest trenches. The durability of materials like plastic means marine litter poses a serious threat to ocean ecosystems and accumulates relentlessly, persisting in the environment for hundreds of years. The scale of this persistent human waste is so immense that projections suggest the weight of plastic in the ocean could outweigh the weight of all fish by the middle of the century.
Composition and Scale of Marine Litter
The majority of debris found in the ocean is plastic, accounting for 85% to 95% of all marine litter. Plastic pollution is categorized by size: macroplastics are visible pieces of debris, and microplastics are fragments smaller than five millimeters. Because polymers are non-biodegradable, larger macroplastics like bottles do not disappear but degrade through fragmentation.
Sunlight, friction, and wave action break these items into progressively smaller pieces, creating secondary microplastics. These tiny particles, along with primary microplastics such as microbeads and microfibers, penetrate the entire water column and settle on the seafloor. Estimates suggest hundreds of trillions of pieces of plastic are currently suspended or submerged in the world’s oceans. Some common plastics can endure in the marine environment for periods ranging from 100 to over 1,300 years.
Pathways: How Litter Enters the Ocean
Litter enters the ocean through land-based and sea-based sources. Mismanaged municipal waste is a primary driver, where inadequate collection and disposal systems allow waste to leak into the environment through illegal dumping or littering. Rivers serve as significant conduits, transporting vast amounts of plastic from inland areas to the sea. Studies indicate that over a thousand rivers worldwide are responsible for the majority of plastic emissions entering the ocean.
Stormwater runoff and wastewater discharge represent another pathway, carrying street litter, microfibers from synthetic clothing, and particles from tire wear directly into waterways. Coastal tourism also contributes by concentrating littering activities near the shoreline, where waste is easily swept into the sea.
A significant portion of marine litter comes from sea-based activities, predominantly the fishing industry. Abandoned, lost, or otherwise discarded fishing gear (ALDFG), known as “ghost gear,” poses a severe threat as it continues to trap and ensnare marine life. Other sea-based sources include waste discharged from commercial shipping vessels and debris lost from offshore aquaculture operations.
Ecological and Biological Impacts
The consequences of marine litter span the entire marine food web, inflicting physical and chemical harm on organisms and their habitats. Larger pieces of debris cause physical injury through entanglement and suffocation, particularly affecting marine mammals, seabirds, and sea turtles. Animals ensnared in lost fishing nets or packing straps suffer restricted movement and feeding, often leading to drowning, starvation, or severe lacerations and infection.
Ingestion is a major pathway of harm, as many marine species mistake plastic pieces for prey. Once consumed, the plastic creates a false sense of satiation, causing the animal to stop eating and suffer starvation due to a lack of nutrients. Sharp edges on fragmented plastics can also cause internal injuries, leading to gut perforation and blockage.
At a chemical level, plastics pose a dual threat, acting as both a source and a vector for toxic substances. The polymers themselves contain various chemical additives, such as flame retardants and plasticizers, that can leach into the animal’s system upon ingestion. Microplastics also effectively absorb and concentrate ambient pollutants from the surrounding seawater, including persistent organic pollutants. When consumed, these concentrated toxins are transferred up the food chain, potentially affecting reproductive, neurological, and developmental health.
Beyond individual organisms, marine litter causes habitat degradation, especially in benthic environments and coral reefs. Large debris, such as ghost gear, physically damages coral structures through abrasion and entanglement, increasing the risk of disease. Debris that settles on the seafloor can smother the environment, creating low oxygen conditions that alter community structure and degrade spawning grounds.
Global Strategies for Reduction
Addressing marine litter requires a shift from reactive clean-up efforts to prevention and mitigation strategies. Central to this is the adoption of the Circular Economy model, which seeks to keep materials in use by changing how products are designed, manufactured, and managed. This approach prioritizes designing out waste and pollution, ensuring plastics are reusable, recyclable, or compostable from the outset. Technological solutions are also being deployed, such as automated systems positioned in major rivers to capture plastic debris before it reaches the open ocean.
Policy mechanisms are driving systemic change through targeted regulations implemented by national governments and international bodies. A key policy tool is Extended Producer Responsibility (EPR), which legally requires manufacturers to finance the collection, sorting, and recycling of their products. By shifting responsibility to producers, EPR schemes incentivize companies to design products that are more durable and easier to recycle. Many nations have also implemented bans or fees on single-use plastic items, such as bags and straws, to reduce the volume of problematic plastic entering the waste stream. International agreements and regional action plans coordinate these efforts, establishing a framework for cooperation and shared accountability.