Microplastics

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Polyethylene based microspherules in toothpaste
Microplastic fibers identified in the marine environment

Microplastics are small plastic particles in the environment and have become a paramount issue especially in the marine environment. Not unequivocally defined, some marine researchers define microplastics as all plastic particles smaller than 1 mm pertaining to their microscopic size range[1] while others in turn define them as smaller than 5 mm[2] recognizing the common use of 333 μm mesh neuston nets for field sampling.[3] However, scientifically, their integral impact on wildlife and human health is not well established.

Classification[edit]

  • Primary microplastics are the plastics that are manufactured to be of a microscopic size. They are usually used in facial cleansers and cosmetics, or in the air blasting technology. In some cases, their use in medicine as vectors for drugs was reported.[4] Microplastic ‘‘scrubbers’’, used in exfoliating hand cleansers and facial scrubs, have replaced traditionally used natural ingredients, including ground almonds, oatmeal and pumice. Primary microplastics have also been produced for use in air blasting technology. This process involves blasting acrylic, melamine or polyester microplastic scrubbers at machinery, engines and boat hulls to remove rust and paint. As these scrubbers are used repeatedly until they diminish in size and their cutting power is lost, they will often become contaminated with heavy metals (e.g. Cadmium, Chromium, and Lead)[5]
  • Secondary microplastics describe microscopic plastic fragments derived from the breakdown of larger plastic debris, both at sea and on land. Over time a culmination of physical, biological and chemical processes can reduce the structural integrity of plastic debris, resulting in fragmentation. It is considered that microplastics might further degrade to be nanoplastic in size, although the smallest microparticle reportedly detected in the oceans at present is 1.6 µm in diameter.[5]

Sources[edit]

There are several suspected sources of microplastics:

  • Natural calamities, such as floods or hurricanes can accelerate transportation of waste from land to the marine environment. A study realized in California revealed that after a storm, the transport of plastics has increased from 10 microplastics/m3 to 60 microplastics/m3. The study has shown how the waste was transported and deposited at much greater distances from the river mouth than usual. A similar study conducted near the southern coast of California shows an increase of microplastics from 1 pcs/m3 to 18 pcs/m3 after a storm.
  • Coastal tourism, recreational and commercial fishing, marine vessels and marine-industries are all sources of plastic that can directly enter the marine environment, posing a risk to biota both as macroplastics, and as secondary microplastics following long-term degradation. Tourism and recreational activities account for an array of plastics being discarded along beaches and coastal resorts, although it is worth noting that marine debris observed on beaches will also arise from beaching of materials carried on in-shore- and ocean currents. Fishing gear is one of the most commonly noted plastic debris items with a marine source. Discarded or lost fishing gear, including plastic monofilament line and nylon netting, is typically neutrally buoyant and can therefore drift at variable depths within the oceans.
  • Shipping have significantly contributed to marine pollution. Some statistics indicate that in 1970, commercial fishing fleet in the world has thrown over 23,000 tons of plastic waste in the marine environment. In 1988, an international agreement (MARPOL 73/78, Annex V) has been implemented, and prohibited the dumping of waste from ships in the marine environment. However, due to non-implementation of the agreement, shipping remains a dominant source of plastic pollution, contributing around 6.5 million tons of plastic in the early 1990s. [6]
  • The manufacture of plastic products that use granules and small resin pellets, as their raw material. In the United States, the production increased from2.9 million pellets in 1960 to 21.7 million pellets in 1987. Through accidental spillage during transport, both on land and at sea, inappropriate use as packing materials and direct outflow from processing plants, these raw materials can enter aquatic ecosystems. In an assessment of Swedish waters using an 80 µm mesh, KIMO Sweden found typical microplastic concentrations of 150–2, 400 microplastics/m3, but in a harbor adjacent to a plastic production facility, the concentration was 102,000/m3.[5]
  • Laundry.Wastewater, collected after washing synthetic blankets, fleeces or shirts in a washing machine, contained more than 100 fibres per litre of water. Fleeces released 180% more fibres than blankets or shirts. On average, more than 1900 fibres of microplastic can be discarded by a synthetic item during one wash.[7]
  • Cosmetics industry which have replaced natural exfoliating ingredients with microplastics, is another source of marine pollution. The most of the facial cleansers in New Zealand contain polyethylene as an ingredient, described as "micro exfoliates" or “micro-beads”. Once used in face washing, microplastics reach into the sewage system, but because of their small size, they are not retained by the preliminary treatment screens on wastewater plants, and end up in rivers, seas and oceans.[8]

The abundance and global distribution of microplastics in the oceans has steadily increased over the last few decades with rising plastic consumption worldwide.[2]


Potential impacts on the marine environment[edit]

The scientists that participated in the first International Research Workshop on the Occurrence, Effects and Fate of Microplastic Marine Debris, held September 9–11, 2008 on the University of Washington Tacoma campus in Tacoma, Washington, USA, agreed that microplastics may pose problems in the marine environment based on the following:

  • the documented occurrence of microplastics in the marine environment,
  • the long residence times of these particles (and, therefore, their likely buildup in the future), and
  • their demonstrated ingestion by marine organisms.

So far, research has mainly focused on larger plastic items. Widely recognized problems are associated with entanglement, ingestion, suffocation and general debilitation often leading to death and/or strandings. This raises serious public concern.
In contrast, microplastics are not as conspicuous, being less than 5 mm. Particles of this size are available to a much broader range of species and have been shown to be ingested by deposit-feeding lugworms (Arenicola marina) and filter-feeding mussels (Mytilus edulis),[9] to name just two examples. Ingestion of microplastics by species at the base of the food web causes concern as little is known about its effects.[2] It remains unknown if microplastics may be transferred across trophic levels.
Possible effects of microplastics on marine organisms after ingestion are threefold:

  • physical blockage or damage of feeding appendages or digestive tract,
  • leaching of plastic component chemicals into organisms after digestion, and
  • ingestion and accumulation of sorbed chemicals by the organism.

Small animals are at risk of reduced food intake due to false satiation and resulting starvation or other physical harm. However, long term impacts on marine organisms are currently unknown.
Plastic debris has also been shown to serve as carrier for the dispersal of biota, thus greatly increasing dispersal opportunities in the oceans, endangering marine biodiversity worldwide.[10] The dispersal of aggressive alien and invasive species is as much a topic as the dispersal of cosmopolitan species.[11]

Approximately half of the plastic material introduced to the marine environment is buoyant, but fouling by organisms can induce the sinking of additional plastic debris to the sea floor, where it may interfere with sediment-dwelling species and sedimental gas exchange processes. However, this is of more importance for larger plastic debris.

Persistent organic pollutants[edit]

Furthermore, plastic particles may highly concentrate and transport synthetic organic compounds (e.g. persistent organic pollutants, POPs) commonly present in the environment and ambient sea water on their surface through adsorption.[12] It still remains unknown if microplastics can act as agents for the transfer of POPs from the environment to organisms in this way, but evidence[6] suggest this to be a potential portal for entering food webs. Of further concern, additives added to plastics during manufacture may leach out upon ingestion, potentially causing serious harm to the organism. Endocrine disruption by plastic additives may affect the reproductive health of humans and wildlife alike.[13]

At current levels, microplastics are unlikely to be an important global geochemical reservoir for POPs such as PCBs, dioxins, and DDT in open oceans. It is not clear, however, if microplastics play a larger role as chemical reservoirs on smaller scales. A reservoir function is conceivable in densely populated and polluted areas, such as bights of mega-cities, areas of intensive agriculture and effluents flumes.

Oil based polymers ('plastics') are virtually non-biodegradable. However, renewable natural polymers are now in development which can be used for the production of biodegradable materials similar to that of oil-based polymers. Their properties in the environment, however, require detailed scrutiny before their wide use is propagated.

Synthetic Organic Chemicals that have been Detected in the Ocean
Name Major Health Effects
Aldicarb (Temik) High toxicity to the nervous system
Benzene Chromosomal damage, anemia, blood disorders, and leukemia
Carbon tetrachloride Cancer; liver, kidney, lung, and central nervous system damage
Chloroform Liver and kidney damage; suspected cancer
Dioxin Skin disorders, cancer, and genetic mutations
Ethylene dibromide (EDB) Cancer and male sterility
Polychlorinated biphenyls (PCBs) Liver, kidney, and lung damage
Trichloroethylene (TCE) In high concentrations, liver and kidney damage, central nervous system depression, skin problems, and suspected cancer and mutations
Vinyl chloride Liver, kidney, and lung damage; lung, cardiovascular, and gastrointestinal problems; cancer and suspected mutations

See also[edit]

References[edit]

  1. ^ Browne, Mark A: "Ingested microscopic plastic translocates to the circulatory system of the mussel, Mytilus edulis (L.)", Environmental Science & Technology, 42(13), pp. 5026–5031, 2008
  2. ^ a b c Moore, C J: "Synthetic polymers in the marine environment: A rapidly increasing, long-term threat", Environmental Research, 108(2), pp. 131–139, 2008
  3. ^ Moore, C J: "A comparison of plastic and plankton in the North Pacific central gyre", Marine Pollution Bulletin 42(12), pp. 1297–1300, 2001
  4. ^ Patel, M.M., Goyal, B.R., Bhadada, S.V., Bhatt, J.S., Amin, A.F., 2009. Getting into the brain: approaches to enhance brain drug delivery. CNS Drugs 23, 35–58.
  5. ^ a b c Cole Matthew, 2011, Microplastics as contaminants in the marine environment: A review, Marine Pollution Bulletin, Nr. 62, pp. 2588-2597
  6. ^ a b Derraik, José G: "The pollution of the marine environment by plastic debris: a review", Marine Pollution Bulletin, 44(9), pp. 842–852, 2002; Teuten, E L: "Transport and release of chemicals from plastics to the environment and to wildlife", Philosophical Transactions of the Royal Society B – Biological Sciences, 364(1526), pp. 2027–2045, 2009
  7. ^ Browne A., 2011, Accumulations of microplastic on shorelines worldwide: sources and sinks, Environmental Science and Technology.
  8. ^ Fendall S. Lisa, Mary A. Sewell, 2009, Contributing to marine pollution by washing your face: Microplastics in facial cleansers, Marine Pollution Bulletin, Nr. 58, pp.1225 - 1228
  9. ^ Thompson, Richard C. (2004-05-07). "Lost at Sea: Where is All the Plastic". Science 304 (5672): 838. doi:10.1126/science.1094559. PMID 15131299. 
  10. ^ Barnes, David K: "Accumulation and fragmentation of plastic debris in global environments", Phil. Trans. R. Soc. B, 364, pp. 1985–1998, 2002, doi:10.1098/rstb.2008.0205 PMID 19528051
  11. ^ Gregory, M R: "Environmental implications of plastic debris in marine settings – entanglement, ingestion, smothering, hangers-on, hitch-hiking and alien invasions", Philos Trans R Soc Lond B Biol Sci, 364(1526), pp. 2013–2025, 2009
  12. ^ Mato Y: "Plastic resin pellets as a transport medium for toxic chemicals in the marine environment", Environmental Science & Technology 35(2), pp. 318–324, 2001
  13. ^ Teuten, E L: "Transport and release of chemicals from plastics to the environment and to wildlife", Philosophical Transactions of the Royal Society B – Biological Sciences, 364(1526), pp. 2027–2045, 2009

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