Microplastic: The Invisible Pollutant
In recent years, plastic consumption has grown immensely. Because plastic is inexpensive to produce and versatile, it is used in a large variety of products. Many of these plastic products make their way into landfills and, when disposed of incorrectly, into the ocean. A study conducted in 2010 calculated that 275 million metric tons of plastic waste were generated by 192 coastal countries. 4.8 to 12.7 million metric tons of this plastic waste ended up in the ocean [3].
Once disposed of, plastic waste can break down into microplastics. Microplastics can be defined as particles smaller than 5mm in size which are produced through the degradation of bonds in plastics [2]. This degradation can occur through forces generated from waves and wind, from sunlike, as well as from microorganisms. Unlike larger debris, microplastics are not as readily visible to the naked eye, which makes it difficult to detect the actual amount present in the environment. In 2014, the Atlantic Ocean was found to have a microplastic density of 2.46 particles per cubic meter, likely an underestimate due to incomplete sifting [4]. Clearly there are an abundance of microplastics in our oceans, which threaten the aquatic ecosystem.
Due to these small dimensions, microplastics become available for ingestion by organisms not commonly affected by larger marine debris. A 2016 report by the United Nations Food and Agriculture Organization found microplastics in up to 800 species of fish, crustaceans, and mollusks [2]. Many of these animals will end up ingesting microplastics because they confuse them for food, or from the intake of water. Of fish larvae tested in the Western English Channel, 2.9% were found to have ingested microplastics [7]. In addition, zooplankton have been seen to readily consume microplastics in laboratory settings. Experiments using both zooplankton and marine worms have demonstrated the adverse effects of microplastic exposure, which include increased mortality, decreased growth rates, and decreased hatching. [7].
As more organisms ingest microplastics, these particles are passed through the food chain, and can eventually find their way onto our plates. Researchers at John Hopkins University found that Europeans consuming seafood on a regular basis ingest approximately 11,000 pieces of microplastics per year [2]. Once ingested, these microplastics may enter the bloodstream and cause damage to different parts of the body.
There are ongoing efforts to prevent more microplastics from being produced and entering our environment. Some of the more obvious strategies include moving to reusable products to produce less waste, as well as encouraging recycling of plastic products people do use. There is also promising research being conducted on biopolymers which could be used in place of plastic products. Plastics produced from natural sources would not only reduce waste, but also come from cleaner, more renewable sources.
In addition to preventing more microplastics from being produced, strategies to remove existing microplastic pollution from our waters are being developed. For one, wastewater treatment facilities are looking into improving separation efficiency to prevent microplastics from entering surface waters. Because microplastics produced from washing clothing are a significant portion of microplastic pollution, the implementation of effective filters in washing machines could be a simple and effective way to prevent these substances from making their way into sewers, and eventually the ocean. Research is also being conducted on microbial biodegradation of petroleum-based plastics [8]. With proper and controlled introduction of bacteria and fungi to the environment, existing plastics such as PE, PS, and PET could be degraded into less problematic substances.
When trying to remove microplastics that have already made their way into the ocean, it is important to determine where cleanup would be the most effective. Utilizing an oceanographic model to estimate movements and density of microplastics, one 2016 study concluded that cleanup efforts would be most effective when focused on microplastics near the coasts [5]. This would prevent debris from making its way to more ecologically significant areas of the ocean.
Once locations for cleanup are identified, removal strategies must be implemented. One very promising technology is a membrane bioreactor. This device utilizes porous membranes and biological processes to reduce the concentration of microplastics in water, with a removal efficiency of 99.9% [1]. Another, simpler device consists of an elongated polymer coated mesh screen between opposing poles. The advantages of this device are its easy fabrication and absence of electrical power, which is useful when trying to collect microplastics away from an electric source [1].
A conscious effort must be made on the part of companies, governmental agencies, and consumers if the amount of microplastic in our environment is to be decreased to an acceptable level. To achieve this goal, we not only need to reduce the amount of microplastics being produced, but also remove microplastics already in our environment.
Sources and References:
1. Ahmed, T., et al. “Removal of Microplastics from the Environment. A Review.” Environmental Chemistry Letters, Springer International Publishing, 1 Jan. 1970, link.springer.com/article/10.1007/s10311–020–00983–1.
2. Iberdrola Corporativa. “How Do Microplastics Affect?” Iberdrola, www.iberdrola.com/environment/microplastics-threat-to-health.
3. Jambeck, Jenna R., et al. “Plastic Waste Inputs from Land into the Ocean.” Science, American Association for the Advancement of Science, 13 Feb. 2015, science.sciencemag.org/content/347/6223/768.abstract?ijkey=BXtBaPzbQgagE&keytype=ref&siteid=sci.
4. Lusher, Amy L., et al. “Microplastic Pollution in the Northeast Atlantic Ocean: Validated and Opportunistic Sampling.” Marine Pollution Bulletin, vol. 88, no. 1–2, 2014, pp. 325–333., doi:10.1016/j.marpolbul.2014.08.023.
5. “Researchers Uncover Highest-Ever Amount of Microplastics on Ocean Floor.” CBS News, CBS Interactive, www.cbsnews.com/news/highest-ever-concentration-microplastic-ocean-floor-plastic-pollution/.
6. Rochman, Chelsea M. “IOPscience.” Environmental Research Letters, IOP Publishing, 23 Mar. 2016, iopscience.iop.org/article/10.1088/1748–9326/11/4/041001.
7. Steer, Madeleine, et al. “Microplastic Ingestion in Fish Larvae in the Western English Channel.” Environmental Pollution, vol. 226, 2017, pp. 250–259., doi:10.1016/j.envpol.2017.03.062.
8. Wu, Wei-Min, et al. “Microplastics Pollution and Reduction Strategies.” Frontiers of Environmental Science & Engineering, vol. 11, no. 1, 2016, doi:10.1007/s11783–017–0897–7.
