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, their integral impact on wildlife is scientifically not well established yet.
There are two main sources of microplastics:
The abundance and global distribution of microplastics in the oceans has steadily increased over the last few decades with rising plastic consumption worldwide.[2]
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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:
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)[4] 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:
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.[5] The dispersal of aggressive alien and invasive species is as much a topic as the dispersal of cosmopolitan species.[6]
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.
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.[7] 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[8] suggest this to be a potential portal for entering food webs. Not only do POPs raise 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.[9]
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.