Microplastics in Arctic waters threaten spotted seals and humans

Microplastic pollution is already reaching the farthest corners of the globe – including the remote Arctic. A recent study conducted on spotted seals(Phoca largha) reveals that even wild marine mammals from Pacific Arctic regions have been regularly ingesting plastic particles for more than a decade. The effects of this phenomenon may affect not only the animals themselves, but also the indigenous communities for which the seals are a food source.

Microplastics in the Arctic food chain

Microplastics – plastic particles smaller than 5 mm in diameter – are one of the most common and disturbing contaminants of the Anthropocene era, also present in remote Arctic waters. Recent studies confirm its presence in the bodies of wild marine mammals such as spotted seals(Phoca largha), which inhabit the Bering, Chukchi and Beaufort Seas.

These seals play a key role in Arctic ecosystems as an indicator species – their health, diet and pollution accumulation levels make it possible to assess the overall health of the marine environment, including the extent of its contamination, changes in the structure of trophic networks and the effects of climate warming. These animals are also of great cultural and nutritional importance to Alaska’s indigenous communities, who have been harvesting them through traditional hunting for generations.

The study by a team from the Alaska Department of Fish and Game included analysis of 34 stomachs of spotted seals harvested through traditional hunting in Gambell (Bering Sea) and Shishmaref (Chukchi Sea). The samples came from two years – 2012 and 2020 – and were collected in autumn, which means that even the juveniles had time to switch to a diet based mainly on fish. In 97 percent of the cases, microplastics were detected in the stomachs.

How was the presence of microplastic tested?

Samples of spotted seal stomachs, obtained from traditional subsistence hunts conducted by indigenous communities, were used for analysis. In the laboratory, the contents of the stomachs were thawed (after storage at -20 °C) and accurately weighed. It was then sifted through 1 mm and 0.125 mm mesh sieves to separate larger food debris from finer particles, including potential microplastics. The contents were subjected to enzymatic digestion, which breaks down organic components, leaving intact plastics and hard prey fragments such as fish otoliths and crustacean shells. Finally, the samples were vacuum-passed through filters with a pore diameter of 0.7 µm.

The filters were analyzed in detail under a stereomicroscope, identifying plastic particles based on their shape (e.g., fibers, fragments), color and size. All identified microplastics were measured, photographed and cataloged.

At the same time, the age of the seals (based on analysis of their teeth), their sex, the place and year of obtaining the sample, and the composition of their diet based on the preserved food remains were determined. It should be noted that only the contents of the stomachs were analyzed – the study’s authors suggest that the next step should be to see whether microplastics can penetrate body tissues (e.g., liver, kidney or adipose tissue), which would allow a better assessment of the potential health effects, both for the animals and for humans consuming their meat.

Spotted seals’ diet affects pollution levels

Of the 34 stomachs examined, a total of 211 plastic particles were detected in 33, of which 190 were classified as microplastics (<5 mm) and 21 as macroplastics (≥5 mm). The identified microplastics were mostly thin fibers – only one particle was in the form of a fragment. This may suggest that their source is textiles or fishing nets.

The number of particles in the stomachs ranged from 0 to 23, with a median of 4, and the concentration ranged from 0 to 60 particles per gram of wet weight (median: 0.059). There were no significant differences between juveniles and adults, or between locations and years of harvest.

Clear differences, however, were revealed according to the type of food. Seals that fed on both pelagic and benthic organisms had significantly more microplastic in their bodies than those that consumed only pelagic prey. Higher concentrations were also observed in individuals that hunted species from higher trophic levels.

Steady presence of microplastics in Arctic waters

The lack of differences between age, location and time of capture indicates that spotted seals have been exposed to constant and widespread microplastic exposure since at least 2012. The highest concentrations were recorded in individuals feeding near the bottom – this is where microplastic accumulates in the sediment.

Although the hydrological conditions of the Bering Sea and the Chukchi Sea differ in terms of currents and sediments, the study found no differences in pollution levels between the two bodies of water. This may indicate the widespread presence of microplastics in the Arctic marine environment.

Threats to seal and human health

Microplastics not only mechanically irritate the digestive system, but can also carry toxic substances, heavy metals and endocrinally active compounds. Potential effects on seals include metabolic disorders, reproductive problems and weakened immunity. The implications for Alaska Native communities, which have obtained seals as a food source for generations, are also significant. Contamination of the organisms of these animals could also pose a risk to human health.

MAIN PHOTO: NOAA Fisheries