Aquatic Microplastic Studies: A critique and suggestions for the future

, Weis Judith.

While there are numerous papers on microplastics (mps) being published every week, there is a need for improvement for the field to mature. Papers proliferate that report the numbers of mps found in water bodies, but they cannot be compared because there are no standard methods for collection and analysis. It is clear that using nets for sampling misses most of the microfibers, which are the most abundant form when whole water samples are analyzed, but which frequently go through the nets. Microfibers are released from synthetic fabrics in washing machines. Microscopic identification is common, but has a high error rate compared to chemical analytical equipment which can also identify the polymers. Microscopic analysis also can mistake cotton microfibers for plastic. Most animals studied eat mps; but it is more interesting to discover what attracts them – is it olfactory or visual? Once mps are swallowed, what proportion pass through the gut and are defecated vs get stuck and clog up the gut vs go through the gut wall and move into the tissues? Mps are considered a vector for transfer of toxic chemicals in the food chain, including chemicals that are additives in the plastic itself plus environmental chemicals that adsorb on the particle's surface. Future research should investigate what proportion of adsorbed contaminants are removed in the digestive system vs. staying bound tightly to the mps; this will vary with the chemical, and the anatomy and chemistry of the animal's digestive system. Most experimental studies to date tend to expose animals to microspheres, which can be purchased commercially but are very rare in the environment, and use concentrations that are far above environmental levels. In the future, exposure studies should use environmentally relevant concentrations and the shapes and sizes of mps that are most abundant in the environment.

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