Marine debris refers to any persistent solid material manufactured or processed and then intentionally or unintentionally released into the marine environment or Great Lakes. This human-made material is found globally, from remote shorelines to the deepest ocean trenches, making marine debris one of the most pervasive environmental challenges facing the world’s oceans and waterways.
The Pervasiveness of Plastic Debris
Plastic constitutes the largest portion of marine debris, accounting for an estimated 60% to 80% of all items found in marine environments. Its widespread use, coupled with its slow degradation rate, allows plastic to persist in oceans for centuries. This durability contributes to its accumulation across various marine habitats.
Single-use plastics are a major component of this pollution, including items like plastic bottles, bags, straws, and food packaging. A plastic water bottle, for example, can take approximately 450 years to decompose in the marine environment. Bottle caps are frequently found and rank among the most harmful marine debris items for sea life due to ingestion risks.
Derelict fishing gear, often called “ghost gear,” is another major plastic contributor. This includes abandoned, lost, or discarded nets, lines, and traps. Ghost gear continues to “ghost fish,” indiscriminately catching marine animals for years after it is lost. Between 500,000 and 1 million tons of this gear are estimated to enter the ocean annually, making up at least 10% of marine litter.
Beyond larger items, industrial plastic pellets, known as “nurdles,” also contribute to plastic debris. These lentil-sized plastic granules are the raw material used to manufacture nearly all plastic products. Nurdles are the second largest source of microplastics in the ocean and can be mistaken for food by marine wildlife, posing an ingestion hazard.
Other Significant Debris Categories
While plastic dominates, various other materials also become marine debris, posing distinct threats to ocean ecosystems. Glass items, such as bottles and jars, are commonly found. Although glass does not break down chemically, it can fragment into sharp pieces that may injure marine life or beachgoers.
Metal debris, including beverage cans, discarded ship parts, and industrial waste, also enters marine environments. An aluminum can, for example, can take between 200 to 500 years to dissolve. These items can injure animals with their sharp edges or pose a risk if ingested.
Rubber materials, such as tires and balloons, contribute to the debris load. These items can persist for extended periods and, like other debris, can entangle or be ingested by marine animals. Textiles, including clothing and fabric scraps, particularly synthetic fibers, are also prevalent. These materials can break down into smaller fibers, adding to pollution.
The Unique Nature of Microplastics
Microplastics are a distinct category of marine debris defined as plastic pieces less than five millimeters in size. Their diminutive size allows them to permeate marine ecosystems, entering food chains from the smallest organisms to larger marine animals. This widespread presence makes their removal from the ocean challenging with current technology.
Microplastics originate from two main sources. Primary microplastics are those intentionally manufactured at a small size, such as microbeads in cosmetics, plastic pellets (nurdles), and microfibers shed from synthetic textiles during washing. Microfibers from synthetic clothing alone account for approximately 35% of primary microplastics in the oceans.
Secondary microplastics form from the breakdown of larger plastic debris, such as bottles, bags, and fishing nets, through natural weathering processes like sunlight exposure and wave action. These secondary fragments are estimated to make up a substantial majority, between 69% and 81%, of all microplastics found in the oceans. Once ingested, microplastics can cause physical damage, accumulate in tissues, and carry pollutants, which can transfer up the food chain.