What is Microplastic?

In the last decade, microplastic residues in both marine and freshwater systems have become an emerging problem. There is a growing interest in understanding the effects of microplastics on aquatic wildlife, as their effects are still not fully understood. Microplastics first appeared as spheres in plankton shoots off the coast of New England in North America in the 1970s. Since then, microplastics have been found in most large bodies of water (oceans, seas, lakes and rivers).

Microplastics are plastic particles smaller than 5.0 mm in size. The lower limit (size) of microplastics is not defined; however, it is common practice to use the mesh size of Neuston meshes (333μm or 0.33mm) used to collect samples. There are two main ways microplastics form and enter a body of water: primary and secondary microplastics. Primary microplastics consist of manufactured raw plastic material such as untreated plastic pellets, scrubbers and microbeads that enter the ocean via land runoff. Secondary ingress of microplastics occurs when larger plastics (meso and macroplastics) enter a beach or ocean and undergo mechanical, photo (oxidative) and/or biological degradation. This degradation breaks larger pieces into increasingly smaller pieces of plastic that eventually become undetectable to the naked eye.

Microplastics have many uses. For example, microbeads are used in personal care products such as exfoliants in facial peels. Microplastics are also used to deliver drugs in some medical applications. Also, fibers shed from synthetic clothing and string are microplastics, as are particles used in "media spraying" processes to clean boat hulls and large machinery. Many of these microplastics, microbeads and fibers are small enough to pass through wastewater treatment plants and enter a watershed.

The effects of microplastics on wildlife are currently not well understood. However, a number of organisms, both vertebrates and invertebrates, have been found to ingest microplastics. These samples represent a large number of organisms with different feeding mechanisms, including detritivores, sediment feeders, and filter feeders. Examples include scleractin corals, mussels, fish, as well as lugworms, amphipods, and mussels.

Scientists are also concerned that organisms ingesting plastic debris may be exposed to pollutants absorbed into the plastic. Plastic debris provides a sink and a source for chemical contaminants. Additives used in the manufacture of plastics can leach from plastics into the marine environment. On the other hand, hydrophobic pollutants present in water can absorb plastic particles. Thus, microplastics can provide a mechanism to transport concentrated pollutants to organisms.

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