Pervasive distribution of polyester fibres in the Arctic Ocean is driven by Atlantic inputs

The study addresses how microplastics (MPs) are distributed, transported, and transformed across the Arctic Ocean, where they have been detected in sea ice, seawater, and sediments but with limited understanding of sources and fate. MPs may settle to sediments over time, and ingestion by diverse marine taxa is widely reported, yet ecological and health consequences remain uncertain. Potential transport mechanisms to and within the Arctic include Atlantic thermohaline circulation, wave-driven Stokes drift, riverine inputs, sea-ice incorporation and release, and atmospheric deposition. Identifying sources is complicated by the diversity of MP forms and the prevalence of secondary MPs generated by fragmentation. Fibres are a notable and common MP shape in marine samples. Weathering alters polymers and their infrared (IR) signatures, complicating identification but potentially serving as indicators of environmental aging and transport. Methodological constraints, especially the challenge of sampling and analyzing small particles (<250 µm), hinder cross-study comparisons, despite evidence that smaller particles may be more abundant and potentially more bioavailable. The study aims to characterize MP abundance, size, and polymer identity across the Arctic’s near-surface waters and through the water column, and to use IR spectral signatures to infer source and weathering processes.

Prior work shows MPs present in Arctic sea ice, seawater, and sediments, implicating multiple pathways including Atlantic circulation, Stokes drift, riverine contributions, and incorporation/release by sea ice. Atmospheric transport of MPs to remote regions, including the Arctic, is plausible by analogy with other pollutants and emerging observations of MPs in snow and air. MPs have been found across marine food webs and habitats, raising concerns for indigenous communities reliant on marine foods. Fibre-shaped particles are frequently reported in seawater and sediments, with some studies confirming synthetic identity via FTIR. Weathering processes (UV, oxygen, biological activity) modify plastic properties and IR spectra, complicating polymer identification while offering potential indicators of environmental aging. Methodological differences, particularly minimum particle size captured and analyzed, limit comparability and may bias against smaller, more abundant particles with greater potential for tissue translocation. Together, these studies motivate comprehensive Arctic-scale surveys integrating polymer identification and weathering metrics.

Sampling design: Near-surface seawater (3–8 m depth) was collected via ship seawater intake loops at 71 stations across four 2016 expeditions: CCGS Sir Wilfrid Laurier (North Pacific, Bering, Chukchi Seas), CCGS Louis S. St-Laurent (UNCLOS transect Tromsø–North Pole–northern Canada Basin), JOIS (Canada Basin), and RV Akademik Ioffe (western Greenland through the Canadian Arctic Archipelago). Water column profiles (n=26) were collected at six Beaufort Sea stations using a CTD/rosette (24×10 L Niskin bottles) down to 1015 m. Volumes filtered per sample were recorded (near-surface: mean ~68.6 L; range ~28.6–460.3 L; depth profiles: 29–67 L). Sample processing: Seawater was sieved through a 63 µm brass sieve. Retained particles were rinsed into 50 mL glass vials and stored at 4 °C. MPs were extracted using a density-independent oil extraction method; a 95% ethanol soak removed residual oil to improve FTIR spectra. Extracts were vacuum-filtered onto 10 µm polycarbonate filters for microscopy and FTIR. Contamination control: Field and lab blanks (air blanks; procedural blanks approximately 1 per 10 samples) were used to assess contamination. Processing occurred in HEPA-filtered labs, using cotton lab coats, metal/glass equipment rinsed with 1 µm-filtered water, with equipment covered and handling in a biological safety cabinet or laminar flow bench. Visually similar particles recurrent across samples were conservatively removed as likely contamination; blank fibres (often orange, likely from lab coats) averaged 9 ± 5.42 per blank. No cruise-specific differences in contamination were detected (ANOVA p>0.05). Enumeration and identification: A two-step approach was used: (1) stereo microscopy to identify suspected microplastics (SMPs) based on published visual criteria for fibres and fragments; particles were categorized as not MPs (N), uncertain (U), or suspected (Y). (2) μFTIR (micro-ATR with Ge crystal) confirmed polymer identity for a subset: 590 of 1570 SMPs (37.6%) across 20 near-surface samples plus all depth-sample particles and blanks. Spectra (3800–900 cm−1; 128 co-added scans; 8 cm−1 resolution) were matched to a commercial library; identifications required all major peaks present and >80% spectral overlap. Validation showed 10.7% of N, 18.2% of U, and 39.8% of Y were plastic, underscoring the need for spectroscopic confirmation. A weighted calculation corrected total MPs per sample (per m³) using category-specific confirmation rates and excluding confirmed non-plastics. IR weathering metric: A Peak Ratio Index for polyester (PET) was derived from controlled laboratory weathering of commercial polyester fibres, using the ratio of absorbance peak heights at ~970 cm−1 (variable) to 1241 cm−1 (reference). Station-level mean indices for PET fibres were mapped to assess spatial patterns. Oceanographic data: Thermosalinograph (Seabird SBE21) and CTD (Seabird SBE911+) provided temperature, salinity, and depth; TSG data were binned at 30 s and CTD at 1 dbar. Data were normalized to particles per m³ and summarized by region and water mass.

- Ubiquity and abundance: Near-surface SMPs averaged 186 ± 15.4 particles m−3. FTIR-confirmed MPs averaged 40.5 ± 4.4 m−3 Arctic-wide, demonstrating that visual counts substantially overestimate MPs without spectroscopic confirmation. - Particle type and polymers: Fibres dominated MPs (92.3%). Polyester accounted for 73.3% of synthetic fibres, with mean fibre widths (~14.1 µm) resembling PET textile fibres. Polymers typical of fishing gear were a minor fraction of MPs: nylon 8.3%, polypropylene 3.3%, polyethylene 0%. - East–west gradient: MP concentration increased eastward and correlated with longitude (regression p≈1.6×10−4). The Atlantic-influenced eastern Arctic (east of 105°W) had significantly higher MP concentrations than the Pacific-influenced western Arctic (Kruskal–Wallis p<0.001; Dunn’s p<0.001). The North Pole region did not differ from the eastern Arctic but exceeded the western Arctic (Dunn’s p=0.011). - Fibre size: Confirmed MP fibre length showed no significant longitudinal trend (not significant), whereas SMPs exhibited significant differences among regions (Kruskal–Wallis p<0.001; Dunn’s p<0.001). - IR weathering metric: PET Peak Ratio Index varied with longitude (R²=0.235; p=0.042) and differed between eastern and western Arctic (Kruskal–Wallis p=0.044; East–West Dunn’s p=0.02). Indices indicated less-weathered (newer) polyester fibres in the east and more-weathered fibres in the west. - Depth distribution: MPs were detected throughout the Beaufort Sea water column to 1015 m. Depth-profile SMPs averaged 174 ± 21.2 m−3 (range 26–427), and FTIR-confirmed MPs averaged 37.3 ± 6.9 m−3 (range 0–200). Polyester dominated at depth (71% of confirmed MPs; 66% of plastic microfibres). Concentrations were higher in the Polar Mixed Layer and near the Atlantic-origin core (450–500 m), lower around the Pacific-origin core (~200 m). - Cellulosic fibres: Of visually identified fibre SMPs, 41% were FTIR-identified as cellulosic, indicating a substantial presence of human-made (e.g., textile) cellulosic materials alongside synthetics. - Source context: Prior measurements by the authors indicate large releases of textile microfibres via domestic laundry and wastewater, including up to ~21 billion microfibres annually from a single secondary WWTP and an estimated 3.5×10^15 fibres per year from households in Canada and the USA, consistent with a substantial anthropogenic source of polyester fibres to the ocean.

Findings reveal pervasive microplastic fibre contamination across the Arctic Ocean, with dominance of polyester consistent with textile sources. The strong east–west gradient in MP abundance and PET IR indices indicates relatively fresh fibres entering the eastern Arctic, plausibly via Atlantic inflow and possibly atmospheric transport from lower latitudes, with more weathered fibres prevalent in the western, Pacific-influenced Arctic. Detection of MPs throughout the water column, and elevated concentrations near Atlantic-origin water at ~450–500 m, suggest coupling between circulation and MP distribution. While polymer density-based expectations might predict segregation with depth, environmental weathering and biofouling likely alter particle properties, contributing to observed vertical distributions and polyester dominance even at depth. The presence of substantial cellulosic fibres underscores the need to account for both natural and human-made cellulosics in Arctic particle budgets. Collectively, results support a scenario where widespread releases of textile-derived fibres, transported by oceanic inflows and potentially the atmosphere, reach even the most remote Arctic regions, aligning with tracer evidence for efficient mixing and contaminant transport from coastal sources into the open ocean.

This Arctic-wide survey demonstrates widespread microplastic contamination dominated by polyester fibres, with significantly higher concentrations and less-weathered IR signatures in the Atlantic-influenced eastern Arctic. MPs are present from the near-surface to 1015 m depth, with distributions broadly consistent with known water masses. The integration of FTIR confirmation and a PET weathering metric provides insight into both polymer identity and environmental aging, strengthening inferences about sources and transport. The evidence points to substantial inputs of textile-derived fibres, likely from domestic wastewater and potentially atmospheric pathways, contributing to pervasive contamination in the Arctic. Future work should expand temporal and spatial coverage, include standardized sampling of smaller size classes, develop larger weathering spectral libraries, integrate 3-D ocean–atmosphere transport models, and further quantify riverine and atmospheric contributions to constrain sources and inform mitigation focused on textile shedding and wastewater management.

- Source attribution remains inferential: oceanographic associations and IR weathering metrics suggest, but do not prove, Atlantic and atmospheric inputs; distinguishing local versus remote sources requires additional sampling and 3-D modelling. - Partial spectroscopic confirmation: Only 37.6% of SMPs underwent FTIR in near-surface samples; weighted corrections reduce but do not eliminate uncertainty. - Size selectivity: Use of a 63 µm sieve biases against particles <63 µm, limiting assessment of the smallest and potentially most abundant/biologically relevant MPs. - Spectral libraries and weathering effects: Weathering alters IR spectra and library matches; limited reference libraries and environmental coatings (biofouling/organics) may affect identifications and the PET Peak Ratio Index generality. - Potential contamination despite controls: Although extensive blanks and conservative exclusions were applied, residual contamination cannot be entirely ruled out. - Temporal coverage: Sampling was limited to 2016 summer–autumn cruises; seasonal and interannual variability were not assessed.