Understanding the occurrence and fate of microplastics in coastal Arctic ecosystems: The case of surface waters, sediments and walrus (Odobenus rosmarus)

The Arctic ecosystem receives contaminants transported through complex environmental pathways - such as atmospheric, riverine and oceanographic transport, as well as local infrastructure. A holistic approach is required to assess the impact that plastic pollution may have on the Arctic, especially with regard to the unseen microplastics. This study presents data on microplastics in the Arctic fjords of western Svalbard, by addressing the ecological consequences of their presence in coastal surface waters and sediment, and through non-invasive approaches by sampling faeces from an apex predator, the benthic feeder walrus (Odobenus rosmarus). Sample locations were chosen to represent coastal areas with different degrees of anthropogenic pollution and geographical features (e.g., varying glacial coverage of catchment area, winter ice cover, traffic, visitors), while also relevant feeding grounds for walrus. Microplastics in surface water and sediments ranged between <LOD (limit of detection)-3.5 particles/m³ and <LOD-26 particles/kg dry weight, respectively. This study shows that microplastics may also enter the Arctic food web as the microplastic concentration in walrus faeces were estimated at an average of 34 particles/kg. Polyester was identified by Fourier transformation infrared spectroscopy (FT-IR) as the most common plastic polymer (58% in water, 31% in walrus), while fibres were the most common shape (65% water, 71% in sediment, 70% walrus). There was no significant difference in microplastic occurrence between water samples from populated or remote fjords, suggesting that microplastics are a ubiquitous contaminant which is available for interaction with Arctic marine animals even at distances from settlements. The present study contributes to our understanding of microplastics in the remote Arctic ecosystem. It also identifies the potential of non-invasive sampling methods for investigating Arctic pinnipeds. This approach will need further development and standardisation before utilisation to monitor plastic pollution in other marine mammals.