Microplastics are small plastic particles in the environment that are generally smaller than 1 mm (0.039 in) down to the micrometre range. They can come from a variety of sources, including cosmetics, clothing, and industrial processes. Two classifications of microplastics currently exist: primary microplastics are manufactured and are a direct result of human material and product use, and secondary microplastics are microscopic plastic fragments derived from the breakdown of larger plastic debris like the macroscopic parts that make up the bulk of the Great Pacific Garbage Patch. Both types are recognized to persist in the environment at high levels, particularly in aquatic and marine ecosystems. Because plastics do not break down for many years, they can be ingested and incorporated into and accumulated in the bodies and tissues of many organisms. The entire cycle and movement of microplastics in the environment is not yet known, but research is currently underway to investigate this issue.
- 1 Classification
- 2 Sources
- 3 Potential impacts on the environment
- 4 Persistent organic pollutants
- 5 Policy and legislation
- 6 Action for creating awareness
- 7 See also
- 8 Literature
- 9 References
- 10 External links
These are particles of plastics that are purposefully manufactured to be microscopic. They are usually used in facial cleansers and cosmetics, or in air blasting technology. In some cases, their use in medicine as vectors for drugs was reported. 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 often become contaminated with heavy metals such as cadmium, chromium, and lead.
These are described as 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 smaller in size, although the smallest microparticle reportedly detected in the oceans at present is 1.6 micrometres (6.3×10−5 in) in diameter. The prevalence of microplastics with uneven shapes suggests that fragmentation is a key source.
Other Sources: Microplastic as a by-product/dust emission during wear and tear
Examples of these include dust from synthetic textiles, ropes, paint and waste treatment. These sources of microplastics are quite recently recognized and are somewhere between primary and secondary microplastics. A Norwegian Environment Agency review report about microplastics published in early 2015 states it would be beneficial to classify these sources as primary, as long as microplastics from these sources are added from human society at the "start of the pipe", and their emissions are inherently a result of human material and product use and not secondary defragmentation in nature.
The existence of microplastics in the environment is often proved via aquatic-related studies. These include taking plankton samples, analyzing sandy and muddy sediments, observing vertebrate and invertebrate consumption, and evaluating chemical pollutant interactions. Through such methods, it has been recognized that there are a variety of microplastics in the environment from multiple sources.
Estimates of emissions of microplastics to the environment in Denmark are between 5,500 and 14,000 tonnes (6,100 and 15,400 tons) per year. Secondary microplastics (e.g. from tyres or footwear) are more important than primary microplastics by an order of magnitude. The formation of microplastics from the degradation of larger plastics in the environment is not accounted for in the study.
Some companies have replaced natural exfoliating ingredients with microplastics, usually in the form of "microbeads" or "micro-exfoliates". These products are typically composed of polyethylene, a common component of plastics, but they can also be manufactured from polypropylene, polyethylene terephthalate, and nylon. They are often found in face washes, hand soaps, and other such personal care products, so the beads are usually washed into the sewage system immediately after use. Their small size prevents them from being retained by preliminary treatment screens at wastewater plants, thereby allowing them to enter rivers and oceans.
Studies have shown that many synthetic fibers, like nylon and acrylics, can be shed from clothing and persist in the environment. One load of laundry can contain more than 1,900 fibers of microplastics, with fleeces releasing the highest percentage of fibers.
The manufacture of plastic products uses granules and small resin pellets as their raw material. In the United States, production increased from 2.9 million pellets in 1960 to 21.7 million pellets in 1987. Through accidental spillage during land or sea transport, 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 per m3; in a harbor adjacent to a plastic production facility, the concentration was 102,000 per m3.
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. Marine debris observed on beaches also arises 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 has significantly contributed to marine pollution. Some statistics indicate that in 1970, commercial fishing fleets around the world threw over 23,000 tons of plastic waste into the marine environment. In 1988, an international agreement (MARPOL 73/78, Annex V) was implemented and prohibited the dumping of waste from ships into the marine environment. However, due to non-implementation of the agreement, shipping remains a dominant source of plastic pollution, having contributed around 6.5 million tons of plastic in the early 1990s.
Floods or hurricanes can accelerate transportation of waste from land to the marine environment. A Californian study revealed that after a storm, the transport of plastics increased from 10 to 60 microplastics per m3. The study showed 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 showed an increase of microplastics from 1 to 18 pieces per m3 after a storm. The abundance and global distribution of microplastics in the oceans has steadily increased over the last few decades with rising plastic consumption worldwide.
Potential impacts on the environment
The first International Research Workshop on the Occurrence, Effects and Fate of Microplastic Marine Debris at the University of Washington Tacoma campus in Tacoma, Washington, USA, from September 9–11, 2008, 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 therefore can cause serious threats.
Biological integration of microplastics into organisms
Microplastics often become embedded in animals' tissue through ingestion or respiration. Various annelid species, such as deposit-feeding lugworms (Arenicola marina), have been shown to have microplastics embedded in their gastrointestinal tracts. Many crustaceans, like the shore crab Carcinus maenas have been seen to integrate microplastics into both their respiratory and digestive tracts.
Additionally, bottom feeders like benthic sea cucumbers, who are non-selective scavengers that feed on debris on the ocean floor, ingest large amounts of sediment. It has been shown that four species of sea cucumber (Thyonella gemmate, Holothuria floridana, H. grisea and Cucumaria frondosa) ingested between 2- and 20-fold more PVC fragments and between 2- and 138-fold more nylon line fragments (as much as 517 fibers per organism) based on plastic to sand grain ratios from each sediment treatment. These results suggest that individuals may be selectively ingesting plastic particles. Since this suggestion opposes the previously determined indiscriminate feeding strategy of sea cucumbers, this trend may be something which could potentially occur in all non-selective feeders when presented with microplastics.
Not only fish and free-living organisms can ingest microplastics. Scleractinian corals, which are primary reef-builders, have been shown to ingest microplastics under laboratory conditions. While the effects of ingestion on these corals has not been studied, corals can easily become stressed and bleach. It was also noted that microplastics were present stuck to the exterior of the corals after exposure in the laboratory. The adherence to the outside of corals can potentially be harmful, because corals cannot handle sediment or any particulate matter on their exterior and slough it off by secreting mucus, and they expend a large amount of energy in the process and increasing the chances of mortality.
It can take at least 14 days for the microplastics to pass from the animal (as compared to a normal digestion periods of 2 days), but enmeshment of the particles in animals' gills can cause a prolonged presence. When these microplastic-laden animals are consumed by predators, the microplastics are then incorporated into the bodies of higher trophic-level feeders. For example, scientists have reported plastic accumulation in the stomachs of lantern fish which are small filter feeders and are the main prey for commercial fish like tuna and swordfish. Furthermore, small animals are at risk of reduced food intake due to false satiation and resulting starvation or other physical harm from the microplastics. Thus, the known 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.
As fish is the primary source of protein for nearly one-fifth of the human population, it is important to consider that the microplastics ingested by fish and crustaceans can be subsequently consumed by humans as the end of the food chain. In a study done by the State University of New York, 18 fish species were sampled and all species showed some level of plastics in their systems. Many additional researchers have found evidence that these fibers had become chemically-associated with metals, polychlorinated biphenyls, and other toxic contaminants while in water. The microplastic-metal complex can then enter humans via consumption. It remains unclear how much of an impact this has directly on the health of humans, but research on this issue continues.
Microplastics as a dispersal of biota
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. The dispersal of aggressive alien and invasive species is as much a topic as the dispersal of cosmopolitan species. By spreading species to regions that they normally do not inhabit, disruptions in local ecosystems can occur. The fact that microplastics can negatively perpetuate the dispersal of biota is notable, especially when policies and laws are being implemented about the usage of plastic.
Effects on buoyancy
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. Buoyancy changes in relation to ingestion of microplastics have been clearly observed in autotrophs because the absorption can interfere with photosynthesis and subsequent gas levels. However, this issue is of more importance for larger plastic debris.
Persistent organic pollutants
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. 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 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.
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.
Plastics, polymers derived from mineral oils, 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.
|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|
Policy and legislation
With increasing knowledge of the detrimental effects of microplastics on the environment, many groups are now advocating for the removal and ban of microplastics from various products. One of the most prominent campaigns is the "Beat the Microbead" movement, which focuses on removing plastics from personal care products. The Adventurers and Scientists for Conservation are running a Microplastics Project that is working to pass a national ban on microbeads in household items and cosmetics. Even UNESCO has sponsored research and global assessment programs due to the trans-boundary issue that microplastic pollution constitutes. These environmental groups will seemingly keep pressuring companies to remove plastics from their products in order to maintain healthy ecosystems. Statewide action has also been taken to mitigate the negative environmental effects of microplastics as Illinois was the first U.S. state to ban cosmetics containing microplastics. New Jersey Congressman Frank Pallone proposed the Microbead-Free Waters Act of 2014, which calls for a nationwide ban on the creation and sale of products that contain microbeads by 2018. The Microbead-Free Waters Act of 2015 was enacted after being signed by the President on December 28, 2015. It is effective from July 1, 2017 with respect to manufacturing, and July 1, 2018 with respect to introduction or delivery for introduction into interstate commerce.
Action for creating awareness
- Plastic particle water pollution (Nurdles)
- Plastic pollution
- Endocrine disruption
- Biodegradable plastic
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- NOAA Marine Debris Program
- Algalita Marine Research Foundation
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- International Pellet Watch
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