Microplastics in muscle and blubber of the Pacific walrus (Odobenus rosmarus divergens)

Microplastic pollution in marine environments is an increasingly important aspect of anthropogenic disturbances to ecosystems. While prior studies have demonstrated microplastics in marine mammal gastrointestinal tracts, there has been little research on translocation of microplastics in body tissues. Pacific walruses (Odobenus rosmarus divergens) are an important Arctic predator and a vital subsistence and cultural resource to Alaska Native coastal communities. As a benthic predator, the walrus may be at risk of ingesting and retaining microplastics. Muscle and blubber from 20 walruses harvested in 2016 from the Alaska Native communities of Gambell and Savoonga were processed to determine the number, nature, and color of microplastics in tissues. Fibers were the predominant shape, and most of the microplastics were blue in color. The average length of microplastics in blubber was 1047.9 μm and 1017.6 μm in muscle. Walrus muscle had a significantly greater average concentration of microplastics (0.34 MP/g) than blubber (0.13 MP/g, p < 0.001). Age was not significantly correlated to microplastics in both muscle and blubber, although the relationship was weakly positive for muscle. The only sex-based differences in microplastic concentration were in blubber, where male walruses had a greater concentration than females (0.17 and 0.11 MP/g, respectively), although not significant (p = 0.14). While the reasons behind these results are hard to define at present, expanded and continued monitoring of more tissues will help elucidate any effects of microplastics on walrus health and the potential impacts on marine mammal subsistence users.