Abstract
Plastics are ubiquitous contaminants that are increasingly found in aquatic ecosystems. These synthetic polymers range in size from visible macroplastics (>25 mm) to smaller-sized micro- (<5 mm) and nanoplastics (<100 nm).1-3 Smaller-sized plastic is not only produced through industry but also as a byproduct of plastic degradation in the environment.1,2,4 Currently, plastic occupies the greatest proportion of marine debris, with most particles estimated to be on the micro- and nano-scale.3,4,6 Due to their size, micro- and nanoplastics can easily assimilate within marine organisms and have been observed to disrupt normal physiological processes, including immune function.5-9 Nanoplastics, in particular, are hypothesized to pose the greatest threat.2,8 The effects of nanoplastics on the immune system have been studied for marine invertebrates, fish, murine models, and even human cell lines, though have yet to be assessed for marine mammals.5-9
Beluga whales (Delphinapterus leucas) are charismatic odontocetes that inhabit the world’s arctic and subarctic waters. Despite being remote, these regions face growing concerns about plastic pollution from increasing anthropogenic access and global transport of particles. Recent studies have identified microplastics in both beluga whales and their prey species, suggesting that nanoplastics are also present.10 This study is the first to explore the effects of nanoplastics on marine mammals, particularly using aquarium beluga whales as a study species. Here, we investigated how in vitro exposure to polystyrene nanoplastics (PS NP) affects the immune function of beluga whales. Specifically, we aimed to 1) measure the effects of PS NP alone on lymphocyte proliferation and phagocytosis with respiratory burst activity and 2) measure the effects of PS NP on these immune functions in response to mitogenic or bacterial stimulation. We hypothesized that the presence of PS NP alone would elicit an immune response in beluga leukocytes and would impair the cellular response to an immunological challenge.
Blood samples were collected behaviorally from three resident beluga whales at Mystic Aquarium in Mystic, CT. Isolated leukocytes were exposed to 40 nm PS NP at varying concentrations (0.01, 1, and 100 µg/mL), both with and without simultaneous exposure to concanavalin A for lymphocyte proliferation or Staphylococcus aureus for phagocytosis and respiratory burst. Comparisons were made using a t-test or a generalized linear mixed model. Initial analyses suggest that exposure to lower concentrations of PS NP alone may not elicit an immune response as only exposure to 100 µg/mL PS NP appeared to induce lymphocyte proliferation (t=0.668, p=0.026). Similarly, no apparent differences in phagocytosis and respiratory burst were observed following exposure to 0.01 µg/mL PS NP as compared with controls. Finally, no significant changes in the proliferative response to mitogen stimulation were detected for any concentration of PS NP. Further evaluation is needed, and analyses are ongoing. The results of this study provide preliminary insight as to how marine mammal immune cells are affected by exposure to smaller-sized plastics. Such knowledge can inform future studies needed to understand and address the potential toxicity of these microscopic yet presumably omnipresent contaminants.
Acknowledgments
This work was made possible through the support and assistance of the Mystic Aquarium and the University of Connecticut, Avery Point. From Mystic Aquarium, we thank Drs. Maureen Driscoll and Ebru Unal, as well as Danielle Lavoie, for their help with laboratory work, data review, and troubleshooting. We thank the beluga whale husbandry team and veterinary department for blood sample training and collection. Moreover, our gratitude extends to the University of Connecticut, Marine Sciences Department, particularly department head Dr. Evan Ward and doctoral candidate Kayla Mladinich Poole for providing guidance on working with nanoplastics. This research was funded as part of a supplemental grant for Mystic Aquarium’s National Science Foundation (NSF) Research Experience for Undergraduates (REU). Author Rachel Bonney conducted this work through an NSF Research Experience for Post-Baccalaureate Students (NSF Award # 1950480).
*Presenting author
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