Toxicity of Microplastics to Aquatic Organisms

Plastic is used in products that span from cutlery to the main components in automobiles, and airplanes. Both municipal solid waste streams and marine debris are comprised of largely plastic products, and as annual global plastic production and use is unlikely to decrease, the presence of plastic in the environment will likely increase. Microplastics (MPs) are plastic fragments that have at least one dimension that is less than 5 mm, and have been found throughout water bodies around the world. MPs are in the same size fraction as most sediment particles and microorganisms, allowing them to be easily ingested by a variety of organisms. The potential for MPs to alter the bioavailability of contaminants, and whether MPs and adsorbed contaminants can undergo trophic transfer, have been investigated in very few studies. Fluoranthene (FLU) is one of the US Environmental Protection Agency's 16 priority polycyclic aromatic hydrocarbons; and its hydrophobic nature allows it to sorb easily to sediment and organic matter, which suggests FLU will sorb to the hydrophobic surfaces of most MPs. While most studies conducted have focused on acute MP exposures to marine organisms, little is known regarding the toxicological chronic effects of MP exposures. Recent studies have demonstrated that MP concentrations in freshwater water bodies are comparable to those found in the ocean; even less information is available regarding MP toxicity to freshwater organisms. The first objective of my research was to characterize the physical toxicity of MPs to aquatic invertebrates and fish. After establishing a baseline for acute MP toxicity, the second objective focused on the determination of whether fluoranthene that is adsorbed to MP surfaces is bioavailable to aquatic invertebrates and fish. Finally, the third objective evaluated whether MPs and the adsorbed fluoranthene can undergo trophic transfer between prey and predatory organisms in both freshwater and marine ecosystems. My results demonstrated that acute exposures to polyethylene spherical MP do result in mortality at environmentally relevant concentrations. Specifically, 10- and 7-day LC50s of approximately 4.6 x 104 and 7.9 x 104 MPs/mL for spherical polyethylene MPs were quantified for amphipods and copepods, respectively. No mortality was observed for either fathead minnows or mummichogs at MP exposures used during these bioassays. Interestingly, polypropylene MP fibers were more toxic to exposed amphipods than the polyethylene MP spheres, where mortality was observed at concentrations as low as > 22.5 MPs/mL. When polyethylene spherical MPs are contaminated with FLU, acute exposures can result in an increase in FLU bioavailability to both fish and invertebrates. Chronic polyethylene spherical MP exposures resulted in significant growth reductions in both Hyalellla azteca and Amphiascus tenuiremis, and decreased reproduction in exposed H. azteca. In comparison to polyethylene spherical MPs, fibrous polypropylene MP exposures to H. azteca resulted in significantly greater mortality and reductions in both growth and reproduction. Exposure to FLU-contaminated MPs resulted in an increase in FLU bioavailability to invertebrates and fish, where more than 90% of the invertebrate FLU body burdens were due to MP exposure. Finally, my results demonstrated that FLU that was adsorbed to MP surfaces can undergo trophic transfer using both freshwater and marine invertebrates and fish. Approximately 1.5 mg fluoranthene was bioavailable to fathead minnows and mummichogs that had ingested amphipods, and copepods that had been pre-exposed to fluoranthene-contaminated MPs, respectively. Hybrid striped bass that has consumed fathead minnows that were pre-exposed to fluoranthene-contaminated MPs resulted in an average bile concentration of approximately 1.3 mg fluoranthene. MPs represent another route of exposure for ubiquitous persistent organic pollutants in the environment for lower and higher trophic level organisms. My research provided a platform on which the acute and chronic toxicological effects due to MP exposures of freshwater and marine invertebrates and fish can be compared because similar methods were used in all the bioassays. Generating data that resulted from the use of similar exposure methods allows the scientific community to make cross-species comparisons that are difficult to determine with the currently available microplastic toxicity data. My results demonstrate that microplastics can have both acute and chronic toxicological effects on aquatic organisms, and that the presence of microplastics in the environment needs to be taken into consideration when evaluating the exposure to environmental contaminants.