Microplastics

Primary microplastics

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.

Secondary microplastics

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: 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.

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:

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 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, increasing the chances of mortality.

It was found that zooplankton ingest microplastics beads (1.7–30.6 μm) and excrete fecal matter contaminated with microplastics. Along with ingestion, the microplastics stick to the appendages and exoskeleton of the zooplankton. Zooplankton, among other marine organisms, consume microplastics because they emit similar infochemicals, notably dimethyl sulfide, as phytoplankton and other organic materials. Plastics such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) produce dimethyl sulfide odors. These types of plastics are commonly found in plastic bags, bleach, food storage containers, and bottle caps.

It can take at least 14 days for microplastics to pass from an 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 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. Microplastics also absorb chemical pollutants that can be transferred into the organism's tissues. Furthermore, small animals are at risk of reduced food intake due to false satiation and resulting starvation or other physical harm from the microplastics.

Humans

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.

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.

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

On April 11, 2013 in order to create awareness, artist Maria Cristina Finucci founded The Garbage patch state under the patronage of UNESCO and the Italian Ministry of the Environment.