IMPACTS OF PLASTIC POLLUTION ON A PELAGIC MARINE MAMMAL, THE NORTHERN ELEPHANT SEAL

As plastic pollution increases, top marine predators such as marine mammals are becoming increasingly susceptible to plastic particles and their additives. Plastic particles have been found in gastrointestinal tracts and scat of many marine mammals, and quantifying plastic pollution in those that are pelagic can provide insight into plastic pollution in mesopelagic ecosystems that are just beginning to be analyzed. Adapting well-developed laboratory techniques for microplastic (MP) isolation (i.e. density separation and chemical digestion), I isolated MPs from the scat of the deepest diving pinniped, the northern elephant seal (NES), and found that100% of scat samples (n=11) contained high counts of MPs compared to other pinnipeds. Further, as plastic particles move through the digestive tract and potentially translocate into the circulation, body cells may be exposed to these plastic particles. Nanoplastics (NPs;\u3c1μm) have been shown to affect cell viability and redox homeostasis in fish and human cells, while the lipophilic additives bisphenol-a (BPA) and bisphenol-s (BPS) used in plastics production are known endocrine disruptors. However, the effects of plastics (NPs) and plastics additives (BPA and BPS) have not been well-studied in marine mammals. To assess the direct impacts of NPs on marine mammal cells, I exposed fibroblasts isolated from NES skin (n=6 experiments) to polystyrene NPs of two different sizes (0.05μm and 0.5μm) and concentrations (3.64x109 and 3.64x1010 particles/mL) and did not find consistent effects on morphology and viability. Cell viability, which was quantified by an MTT assay, decreased as a result of NP exposure in two experimental replicates, but these results were not reproducible. I found that NPs did not have consistent effects on the morphology or viability of NES fibroblasts, regardless of their size or concentration. Lastly, I examined the effects of plastic additives on the physiology of marine mammal blubber tissue, the primary energy depot and reservoir of lipophilic pollutants. Precision-cut NES blubber slices were exposed to BPA and BPS, alone and in combination with the lipolytic hormone epinephrine, and I assessed their effects on the blubber transcriptome. I found that while BPA and BPS treatments alone did not have a pronounced effect on gene expression, they altered the expression of several genes associated with lipid homeostasis and adipogenesis. These data suggest that NES likely ingest MPs and maybe physiologically affected by exposure to plastic particles and their associated contaminants