Marine Debris
- A vast variety and amount of human-derived solid waste is lost, discarded or discharged daily into oceanic and coastal environments or reaches the sea through waterways and other land- based sources. While composed largely of materials made out of plastic, marine debris also includes polystyrene cups and packaging, rubber (e.g., boots, tires), sanitary and sewage-related debris (e.g., tampons, condoms, diapers, disposable syringes), metals (e.g., cans, oil drums, aerosol containers, bottle caps), cigarette filters, glass (e.g., bottles, light bulbs), ceramics, wood, cloth and cardboard, and fishing lines and gear.
- Marine debris, in particular that derived from plastics and synthetics, is a global problem. Plastic can be seen floating – often in vast amounts – on all the world’s oceans, even in extreme polar waters, and can be found on shorelines of the remotest islands.
- Marine debris poses a threat to people, kills marine life and damages or alters habitats, reduces navigation safety, and can have substantial economic impacts on local communities:
- Human health and safety is threatened by contact with pathogen-contaminated debris from medical waste and sewage, by injuries from pieces of glass or metal lying on beaches or the ocean floor, by entanglement in lines or netting during scuba diving, and indirectly by damaging and otherwise disabling vessels – e.g., by punctures, propeller and rudder entanglement, blocked intakes – and thus stranding the occupants.
- While marine debris is negatively involved with a wide spectrum of marine species the primary concern is on impacts – typically entanglement or ingestion – to those threatened with extinction. Lost and discarded fishing gear, for example, presents a continuous entanglement threat to such endangered species as the North Atlantic right whale and the Hawaiian monk seal, and to most of the world’s sea turtle species. Sea turtles can also die after ingesting even very small amounts of debris, either starving by digestive tract blockage or through the effects of gut ulceration or perforation from sharp objects. At least 111 seabird species – almost one-third of the world’s total – are now known to ingest marine debris; effects can include reduced body weight, clogged gizzards, increased risk of disease, and death.
- Changes and damage to habitats as a result of debris can also occur. Discarded sport fishing lines, debris from lost lobster traps, and derelict trawl netting and monofilament gillnets can damage and kill coral colonies. Accumulating debris on the seafloor can alter the benthic community by providing habitat for opportunistic organisms and by interfering with gas exchange between the sediment pore waters and overlying waters. Ecosystem changes may also occur when various organisms – e.g., bryozoans, hydroids, tunicates – attach to drifting debris and raft into environments where they did not previously exist.
- The aesthetic impacts of debris on beaches and beach waters can affect local communities through reduced tourism and from the often substantial financial costs associated with beach litter collection and disposal.
- It is generally considered that the majority of marine debris (~ 80%) is due to land-based pollution – primarily littering from shore and beach recreation and from storm-water discharges and combined sewer overflows. The remainder (~ 20%) is composed mainly of fishing-related debris – e.g., lines and nets, strapping bands – and garbage jettisoned or lost from ships and boats.
- It is estimated that somewhere between 60 and 80% of marine debris is made up of plastic, and that plastic is accumulating in the oceans because of its ongoing use and disposable nature, and longevity. Discarding from ships alone has been estimated at contributing some 6.5 million tons of plastic a year. While some plastics are likely able to last centuries recent research has also discovered widespread accumulation of microscopic plastic and fiber particles in coastal sediments and pelagic waters, evidently a result of the breakdown of larger items. The environmental consequences of this type of pollutant is not known.
- Almost all fishing nets and pots used outside of subsistence fisheries are constructed from synthetic fibers which are highly resistant to degradation. Besides entangling wildlife, lost or abandoned fishing gear can continue to ‘fish’ for many months and may be having an impact on some fisheries already stressed from years of overfishing. Economic losses can accrue as well: it has been estimated that in the U.S. some $250 million of marketable lobster is lost each year to ‘ghost fishing’.
- Internationally, marine debris from shipping is addressed by Annex V of the International Convention for the Prevention of Pollution from Ships (MARPOL), which prohibits all overboard disposal of plastics and limits other discharges based on the material and the vessel’s location and distance from shore. However, MARPOL’s effectiveness at reducing marine debris has been difficult to gauge.
- The U.S. ratified Annex V in 1987 and has enacted a variety of debris-related legislation over the years including the Marine Plastic Pollution Research and Control Act which prohibits any ship from dumping plastics into U.S. waters. Most recently – in December of 2006 – the Marine Debris Research, Prevention, and Reduction Act was signed into law and establishes programs to identify, assess, reduce, and prevent marine debris impacts on the nation’s marine environments and on navigation safety. Priority requirements of the Act include:
- development of alternative types of fishing gear to facilitate the tracking and recovery of lost or discarded gear; and
- improvement to the implementation of MARPOL Annex V requirements concerning the disposal of plastics and other garbage from shipping activities.
- It is likely that the amount of marine debris entering the oceans will increase simply due to human population growth – much of it projected in the coastal zone where over one-third of humankind already lives – and the rapid expansion of coastal tourism. It has been suggested by some, as well, that the increasing industrialization of lesser developed countries is likely to result in an increase in plastic and other synthetic wastes thus adding to the threat of marine debris pollution.
- While marine debris is a global transboundary problem solutions will require measures enacted at all political levels and support given to developing countries who may be particularly vulnerable to its impacts. Current programs and policy approaches generally include combinations of prohibitions, education programs, disposal facilities, tax/subsidy programs, beach cleanups, and continuing research. Various environmental organizations meanwhile continue to advocate for more efficient waste prevention strategies involving not only waste reduction, reuse, and recycling but also producer responsibility for a product’s life cycle and incentives for the design and production of environmentally-safe packaging and products. Ultimately, it would appear that the production of plastics and synthetics that do not rapidly biodegrade into a nonhazardous substance must be dramatically reduced.
Derraik, J.G.B. 2002. The pollution of the marine environment by plastic debris: a review. Marine Pollution Bulletin 44(9): 842-852
Thompson, R.C. et al. 2004. Lost at sea: Where is all the plastic? Science 304(5672): 838.
Yoshikawa, T. and Asoh, K. 2004. Entanglement of monofilament fishing lines and coral death. Biological Conservation 117(5): 557-560.
Zheng, Y. et al. 2005. A review of plastic waste biodegradation. Critical Reviews in Biotechnology 25(4): 243-250.
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