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  • Are Microplastics Toxic to the Environment? Literature Review

    Posted on October 24th, 2019 Microsphere Expert

    by Nathan Garnica, Cospheric LLC

    What are microplastics?

    Microplastic is a broad term used to describe microscopic plastics with sizes ranging from 1µm to 3mm1. The shapes of microplastics can vary from fragments, fibers, pellets, film, and spheres2. Anything less than that can be considered nanoplastic, which is also prevalent in the ocean. The properties such as the size, shape, and charge are constantly changing which affects the bioavailability, or circulation into living organisms1. The plastic production generated in 2016 was estimated at 335 million metric tons and the demands continue to increase2. It is estimated that over 5 trillion plastic particles weighing over 250,000 tons resides in the ocean1. The most common forms of polymer microplastics are polyethylene (PE), polystyrene (PS), polypropylene (PP), polyester (PES), polyvinylchloride (PVC), polyamide (PA), acrylic polymers (AC), polyether (PT), cellophane (CP), polyurethane (PU), and others that are not specified2.

    How are microplastics being accumulated in the ocean?

    Microplastic accumulated in the ocean can be divided into two categories. The primary means of accumulation of microplastic is released directly into the environment via domestic use, industrial effluents, spills, and sewage discharge2. The secondary means involves the gradual degradation and fragmentation of larger plastic particles already present in the environment. About 80% of marine plastic debris derives from land-based sources including beach litter4. Roughly 18% of marine plastic debris comes from the fishing industry4. These particles can continue to degrade into nanoparticles that can range from 1nm to 100nm2.

    Are microplastics toxic?

    The toxicity of microplastics in living organisms has been largely debated in scientific literature. Research has shown conflicting results regarding entry and harm to organisms.

    Clear Polyethylene Microspheres from Cospheric LLC, 0.96g/cc - Various Sizes 1um to 1700um (1.7mm)

    Clear Polyethylene Microspheres from Cospheric LLC, 0.96g/cc – Various Sizes 1um to 1700um (1.7mm)

    A recent article published in Marine Pollution Bulletin utilized a wide range of sizes of polyethylene microspheres, such as those produced by Cospheric LLC (USA), and showed that polyethylene microplastics used in this study were not toxic to the unicellular marine organisms exposed at environmentally relevant concentrations or even at higher concentrations6.  In this study non-fluorescent low-density and high-density polyethylene microparticles were used in sizes from 1micron to 500micron in diameter. The authors state that ”in this study, bacteria luminescence inhibition and micro algal growth were not affected by either the virgin or the oxidized PE-MPs at concentrations of up to 25 mg/L. These results confirm previous data on the absence of ecotoxicological effects included in standard test guidelines in decomposers and primary producers exposed to MPs.” The authors refer to prior publications by other researchers who also investigated ecotoxicological effects of plastic microparticles in the same bacterium as well as several microalgae and did not find any toxic effect at environmental concentrations.

    Due to limited number of studies in this area, the questions remain. For example, would nanoplastics (particles smaller than 1um in diameter) would behave differently and have a stronger effect? Are we measuring the right parameters? Do we need to investigate alternative responses to detect the potential risk and influence on plastics on unicellular organisms?

    It is important to note that, as they disperse and degrade in the ocean, polymer microparticles undergo changes which can alter their bioavailability and access into living organisms.

    The dispersal determines which depth and area of the ocean and which organisms are impacted. The density, size, and surface properties determine the depth and distance microplastics particles travel. Any given microparticle can take weeks to years to reach the ocean floor1. This dispersal directly impacts the marine communities inhabiting that area.

    Factors that influence degradation of microplastics include chemical additives, water permeability chemical composition, molecular weight, morphology, porosity, size, and more3. Additives define the outer surface which change the overall properties of particles. Porous particles allow cells to migrate into the pores which can help in the degradation process3. Nonporous particles degrade more slowly than porous particles3.

    Do microplastics alter the ocean ecosystem?

    The effect on the ecosystem could potentially happen indirectly by altering the environment around marine life.

    Polystyrene Microspheres from Cospheric LLC, Crosslinked, 1.07g/cc - Diameters between 9.5um and 105um

    Polystyrene Microspheres from Cospheric LLC, Crosslinked, 1.07g/cc – Diameters between 9.5um and 105um

    A study shown in “Interactions of Microplastics throughout the Marine Ecosystem” by Galloway et al. observed the digestion effects of polystyrene microspheres in zooplankton. The fecal pellets of zooplankton are a vital carbon source for marine life in the deep depths of the ocean1. The polystyrene fecal pellets took 53 days longer to reach the bottom of the ocean1. This delay in carbon supply impacted deep ocean life that is dependent on this maintenance of carbon flux. The experiment used polystyrene microspheres but polyethylene and polypropylene, which are more abundant in the ocean, are less dense and may take even longer to sink1.

    Fertility and fecundity were greatly reduced in oysters during an 8-week exposure experiment to polystyrene microparticles 1.  The findings showed a decrease in sperm motility, oocyte production, and size of oocytes1. Similar effects were found in offspring not exposed to microspheres1. The study suggested that the microspheres were present where the food should have been and had adverse biological impacts1. A similar result in Daphnia magna led to immobilization1. The energy production was most likely inhibited using the 1µm polyethylene experimental particles 1.

    Biofilms, which are communities of bacteria surrounded by their extracellular matrix, colonize microplastics1. A typical colonizer of microplastics are the ubiquitous Vibrios1. Vibrio crassostrea is a common pathogen that can colonize microplastics which can then be ingested by oysters1. The bacteria can then cause infections to the oysters1.

    It is difficult to define a specific threshold of harmful microplastics due to the changing nature of material properties over time. A harmless microplastic may degrade to become toxic or a toxic microplastic may degrade to become passive.

    How can we limit microplastic pollution?

    There are many strategies to help reduce the amount of microplastic accumulation. The public can reuse, recycle, and recover plastics5. Alternatives to biodegradable products can be made such as polylactatide (PLA), polyhydroxyalkanoates (PHA)5. Laundry balls can help catch microfibers from falling off clothes in the washer.

    There is also research that shows great promise towards reducing microplastic through new technologies or through bioremediation strategies. Improved water filters can help catch microplastics in wastewater treatment facilities before the water enters rivers and the ocean5. Several species of microbes and fungi have been found to degrade polymers5. Polyethylene, polypropylene, polystyrene, and Polyethylene terephthalate have been found to be degraded by Bacillus and Enterobacteria along with several different fungi5. Polyethylene, polypropylene, polystyrene are considered nonbiodegradable5. These promising developments demand collective support from industry, government, and the general public if we are to move away from a plastic ocean.

    1. Galloway, T S, et al. “Interactions of Microplastics throughout the Marine Ecosystem.” Nature Ecology and Evolution, vol. 1, no. 5, 20 Apr. 2017, doi: 10.1038.
    2. Sá, Luís Carlos De, et al. “Studies of the Effects of Microplastics on Aquatic Organisms: What Do We Know and Where Should We Focus Our Efforts in the Future?” Science of The Total Environment, vol. 645, Dec. 2018, pp. 1029–1039., doi:10.1016/j.scitotenv.2018.07.207.
    3. Sá, Luís Carlos De, et al. “Studies of the Effects of Microplastics on Aquatic Organisms: What Do We Know and Where Should We Focus Our Efforts in the Future?” Science of The Total Environment, vol. 645, Dec. 2018, pp. 1029–1039., doi:10.1016/j.scitotenv.2018.07.207.
    4. 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.
    5. 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.
    6. Gambardella, Chiara, et al. “Microplastics Do Not Affect Standard Ecotoxicological Endpoints in Marine Unicellular Organisms.” Marine Pollution Bulletin, vol. 143, 2019, pp. 140–143.

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