FREQUENTLY ASKED QUESTIONS
What we actually know about common
marine debris factoids
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Are there really 46,000 pieces of plastic per square kilometer of the world's oceans?
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Is it true that 80% of marine debris comes from land and 20% comes from the ocean?
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How long do various marine debris items take to degrade in the marine environment?
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Is it true that marine debris kills a million seabirds each year?
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What happens when albatross or other seabirds ingest debris?
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What happens to marine debris once it is removed from the marine environment?
- What is being done to address marine debris in the US and around the world?
How much debris enters the ocean?
There is currently no up-to-date, accurate answer to this question. A figure that has been cited came from a 1975 study by the National Academy of Sciences that estimated 6.4 million metric tons (equivalent to approximately 14 billion pounds) of trash per year enters the ocean (NAS, 1975). Important items to note about this figure:
- This study was published in 1975, 13 years before the implementation of MARPOL Annex V prohibited the dumping of plastics and restricting the dumping of other wastes in the oceans, and thus is quite dated.
- This study only took into account debris from maritime sources and estimates “the total amount of litter generated in the world’s oceans.” Data were collected from vessels’ Garbage Record Books.
NOAA is working with other agencies and groups to investigate the best available information to work towards a more current estimate. While the NAS (1975) study estimated then-legal dumping of waste from ocean vessels, an accurate, current estimate of debris entering the oceans would need to measure debris entering from rivers, storm sewers, beach litter, illegal dumping at sea, and many other avenues. A comprehensive, global study like this has not yet been done.
Are there really 46,000 pieces of plastic per square kilometer of the world's oceans?
We were unable to find a reference for this figure. The closest we could find was a UNEP report published in 2005 that mentions a figure of 13,000 pieces of litter per square kilometer; however there is no source or referenced study for that figure (UNEP, 2005).
We found a couple of potential explanations. One came from a UNEP report published in 2005 that mentions 13,000 pieces of litter per square kilometer; however, there is no source or referenced study to explain that figure (UNEP, 2005). A second potential source is from the Sea Education Association's 22-year data set in the Atlantic Ocean. Law et al. (2010) enumerated 64,000 plastic particles in surface waters from October 1986 to December 2008. This figure represents twenty two years of collecting particles over a large swath of the North Atlantic from Massachusetts to Bermuda.
Is it true that 80% of marine debris comes from land and 20% comes from the ocean?
This statement is possible, but unknown. We have been looking into the origin of that figure. It's frequently quoted in the press, but doesn't appear often in scientific literature. A few times the results from the International Coastal Cleanup were cited as the source for these percentages; however if you take a look at the results from any given year, you will notice percentages differing from one place to another. Additionally, this event surveys primarily beach debris, and thus may overestimate land-based sources because of beachgoers’ litter.
Another cited source has been: Faris, J. and Hart, K., Seas of Debris: A Summary of the Third International Conference on Marine Debris, N.C. Sea Grant College Program and NOAA, 1994, 54p. Here's the quote from the paper that the 80% comes from (and the only place where 80% is mentioned). There are no studies or publications referenced for this percentage: "Marine debris pollutes all of the world's oceans, but the problem hardly starts there. Close to 80 percent is washed, blown or dumped from shore. In the entire marine debris debate, no other point is so straightforward."
We know relatively little about what is lying on the ocean floor or suspended in the water column. Because of this we truly can't say what the land- and ocean-based percentages are with any certainty or accuracy. Just begin to think of all the debris types that sink (e.g., metal, dense plastics) in addition to all the ships on our ocean floor and you get the picture.
How long do various marine debris items take to degrade in the marine environment?
Bottom line: Most debris items take a long time to degrade in the marine environment. However, the more natural/organic the material composition of the item is, the less time it generally takes to degrade.
Figures on the amount of time it takes for durable debris items to break down in the environment are many and varied (e.g., Aluminum can: 100 years (The Coral Reef Alliance and Worldwise) vs. 80-200 years (Mote Marine Laboratory)). It is unknown where the numbers listed in degradation timelines for these durable items originated or how they were estimated. Likely that the numbers listed on posters and pamphlets are estimates intended to raise awareness of the very long life of marine debris items rather than provide exact degradation rates.
Basically, degradation time depends upon numerous factors including material type, size, and thickness, temperature, wave action, exposure to sunlight, and location (e.g., on the beach, in the surf, floating at sea, etc).
For more information on the degradation of plastic debris, please visit our page on plastics.
Is it true that 100,000 marine mammals and/or sea turtles die each year due to marine debris/plastics?
This statement is possible, but difficult to say with certainty. To date there are no published studies specifically researching how many marine mammals die each year directly due to marine debris. Regardless of the exact number that die each year due to marine debris, each death is one too many. Marine debris doesn’t belong in our oceans and waterways.
Below is the closest figure that we could find. These statements were made in a paper presented at the 1984 Workshop on the Fate and Impact of Marine Debris by Wallace (1985). The manuscript does not state that marine mammals are dying from plastic pieces, but rather that mortality is caused by entanglement from lost fishing gear and other unknown causes.
“Debris entanglement is estimated to cause 50,000 to 90,000 deaths per year in the northern fur seal. The population in 1983 was dropping on the main rookery in Alaska at about 8% per year. At least 50,000 deaths are thought to be due to entanglement; the other 40,000 deaths possible entanglement or possibly some unknown factor such as disease (Fowler, 1983).”
In the conclusions: “Up to one hundred thousand marine mammals and possibly more die each year. Half or more of the individuals of certain marine reptile species are affected by the plastic litter, and beachcombing land mammals become snarled in nets and die. ...”
The figures cited here are from another study by Fowler (1983) of fur seals in the North Pacific, and not from Wallace’s research. Keep in mind that this 1983 paper predates MARPOL Annex V, an international treaty implemented in 1988, which prohibits the dumping of plastics (including fishing gear) anywhere at sea.
Many of NOAA’s marine debris projects work to help protect marine mammal and turtle populations across the nation through debris removal as well as prevention.
Is it true that marine debris kills a million seabirds each year?
This statement is currently unknown. We are so far unable to find a scientific reference for this figure. The closest we have found is “214,500 to 763,000 seabirds are killed annually incidental to driftnet fishing by Japanese fishermen in the North Pacific Ocean (US Department of Commerce, 1981)” from Laist, 1987. This refers to active fishing gear bycatch and not marine debris; it also predates the high seas driftnet ban adopted by the United Nations General Assembly in 1992.
Seabirds live much of their lives at sea or in remote locations. While the number of deaths can be estimated, it is difficult to determine causes of mortality when the carcasses can’t be retrieved.
What happens when albatross or other seabirds ingest debris?
We have all seen and been moved by photos of a seabird carcass (typically a Laysan albatross) laden with plastic debris. The detrimental effects of marine debris ingestion on Laysan albatross have been an object of research interest for many years, but like most ecological issues the answers are not straightforward. Regardless, the problem of marine debris ingestion is real; not just in seabirds, but species of fish, marine mammals, and sea turtles.
Albatross:
Ingestion of debris may cause a blockage in the digestive tract, perforate the gut, result in a loss of nutrition (due to displacement of food), or cause a false feeling of being “full”. Studies have found that ingested plastic debris is problem for seabirds; however may not be a significant direct cause of mortality (e.g., on a population level) (Sievert and Sileo, 1993; Auman et al., 1997). More research is needed to see if these results (mid-1990’s) have changed.
Other Seabird Species:
There are numerous studies on ingestion of debris in seabird species other than the Laysan albatross. The results of a recent study conducted by Ryan (2008) show the number of ingested plastic particles in five species of seabirds, sampled in the 1980s and again in 1999–2006, have not changed significantly in the southern Atlantic and southwestern Indian Oceans. He found that the proportion of pre-production plastic pellets decreased 44-79% in all five species. “More data are needed on the relationship between plastic loads in seabirds and the density of plastic at sea in their foraging areas, but the consistent decrease in pellets in birds suggests there has been a global change in the composition of small plastic debris at sea over the last two decades.”
What happens to marine debris once it is removed from the marine environment?
Depending on the type of debris, methods of disposal may include recycling, reusing, or even using debris to create electricity.
Two great examples of marine debris disposal are:
When options are limited or unavailable, debris is disposed of in a landfill.
What is being done to address marine debris in the US and around the world?
While this is a global problem, local efforts are ongoing to solve it. Together, through partnerships, work is being done nationwide to research, prevent, and reduce marine debris as well as educate the public to be better stewards of our ocean.
The NOAA Marine Debris Program has funded and helped support over 140 projects working with partners and addressing marine debris across the nation. Click here to learn about some of them.
Much is also being done on an international level to raise awareness and address this pervasive problem. One great example is the International Coastal Cleanup coordinated by the Ocean Conservancy. The event is the largest marine debris and litter cleanup event in the world. It is held on the 3rd Saturday of every September and is coordinated by the Ocean Conservancy. The NOAA Marine Debris Program is a proud sponsor of this event.
Everyone, no matter how close to or far from the ocean, can contribute to the solution. It’s simple: Reduce, Reuse, and Recycle - (1) Try to reduce the amount of trash you produce (e.g., try to purchase items with minimal additional packaging); (2) Make use of items that are reusable rather than disposable; and (3) when you do use disposable items, remember to recycle!
Literature Cited
Auman, H.J., Ludwig, J.P., Giesy, J.P., and Colborn, T. 1997. Plastic ingestion by Laysan Albatross chicks on Sand Island, Midway Atoll, in 1994 and 1995. Albatross Biology and Conservation, pp 239-44.
Fowler, C. 1983. Status of northern fur seals on the Pribilof Islands. Background paper submitted to the 26th Annual Meeting of the Standing Scientific Committee of the North Pacific Fur Seal Commission, 28th March-8th April 1983, Washington DC.
Laist, D. 1987. Overview of the Biological Effects of Lost and Discarded Plastic Debris in the Marine Environment. Mar. Poll. Bull. 18: 319-326.
National Academy of Sciences (NAS), 1975. Assessing Potential Ocean Pollutants: A Report of the Study Panel on Assessing Potential Ocean Pollutants. National Academy of Sciences, Washington DC, p. 419-422.
Ryan, P.G. 2008. Seabirds indicate changes in the composition of plastic litter in the Atlantic and south-western Indian Oceans. Mar. Poll. Bull. 56: 1406-1409.
Sievert, P.R., and Sileo, L. 1993. The effects of ingested plastic on growth and survival of albatross chicks. In: The status, ecology, and conservation of marine birds of the North Pacific. Can. Wildl. Serv. Spec. Publ, Ottawa. pg 212-217.
United Nations Environment Programme (UNEP), 2005. Marine Litter, an analytical overview.
Wallace, N. 1985. Debris entanglement in the marine environment. A review. Pp 259-277 in: R. S. Shomura, H. O. Yoshida (eds.) Proceedings of the Workshop on the Fate and Impact of Marine Debris. NOAA Technical Memorandum. NMFS, NOAA-TM-NMFS-SWFC-54.
Acknowledgements
This information was compiled with the input and assistance of the US Fish and Wildlife Service.
