Microplastics in sea ice: A fingerprint of bubble flotation

Sea ice is heavily contaminated with microplastics (MPs), with the repeatedly confirmed increased number of larger-sized particles, deficit of fibers, and prevalence of materials denser than the surrounding water. To get insight into the drivers behind such a specific pattern, sets of laboratory experiments were performed on the formation of ice by cooling from the surface of fresh and salty (NaCl, 34 g/L) water, with particles of different sizes from heavy plastics (HPP) distributed initially over the bottom of the experimental volume. After freezing, about 50-60 % of HPP were trapped in ice in all the runs. Vertical distribution of HPP, plastic mass distribution, ice salinity (in saltwater experiments), and bubble concentration (in freshwater experiments) were recorded. Formation of bubbles on hydrophobic surfaces was the main cause of the entrapment of HPP into ice, with convection playing a secondary role. Supplementary bubble formation experiments with the same particles in water demonstrated that at larger fragments and fibers, several bubbles grow at the same time, so particle rising and residing at the surface is stable. Smaller HPP experience rising/sinking cycles with minimum time spent at the surface: one bubble is enough to cause a particle rising, but it is most often lost when colliding with the water surface. Application of the results to oceanic conditions is discussed. Oversaturation with gases due to various physical/biological/chemical processes and liberation of bubbles from methane seeps and melting permafrost are common in Arctic waters. Convective water motions are able to relocate HPP in vertical. Based on applied research, the bubble nucleation and growth, the hydrophobicity of weathered surfaces, the effectiveness of flotation methods for plastic particles are discussed. Interaction of plastic particles with bubbles is an important feature, still completely overlooked in the context of MPs behavior in marine environment.

Microplastics in the first-year sea ice of the Novik Bay, Sea of Japan

Sea ice is heavily contaminated with microplastics particles (MPs, <5 mm). First-year sea ice cores (38-41 cm thick) were taken in the beginning of spring in a narrow populated bay of the Sea of Japan. Two ice cores were examined (layer-by-layer, excluding surface) for MPs content: one using μ-FTIR for 25-300 μm (SMPs), and another one - with visual+Raman identification for 300-5000 μm particles (LMPs). The integral (25-5000 μm) bulk mean abundance of MPs was found to be 428 items/L of meltwater, with fibers making 19 % in SMPs size range and 59 % in LMPs. Integral mean mass of MPs was estimated in 34.6 mg/L, with 99.6 % contribution from fragments of LMPs. Comparison with simple fragmentation models confirms deficit of SMPs (especially of fibers in size range 150-300 μm), suggested to result from their leakage with brine. Multivariate statistical analysis indicates strong positive correlation of large fiber (>300 μm) counts and ice salinity.

Microplastic contamination of sandy beaches of national parks, protected and recreational areas in southern parts of the Baltic Sea

The distribution of small (0.5-2 mm, S-MPs) and large (2-5 mm, L-MPs) microplastics and mesoplastic particles in 51 samples of surface beach sands at 7 locations along the southern shore of the Baltic Sea was investigated. MPs particles (3267 in total) were found at all the sites and in all the beach zones. The bulk mean MPs (0.5-5 mm) contamination is 68 ± 117 (median 33) items/kg DW (n = 51). The results were confirmed by μ-Raman spectroscopy analysis. National park areas did not differ substantially from other beaches. Expanded polystyrene fragments accounted for about 38% of the total collected particles. Fibres were the predominant type of MPs (55%). The highest contamination was found within the current wrack line (60.1 ± 36.6 items/kg DW of S-MPs). A consistent picture for S-MPs was observed at the beach face, where the mean values in different locations varied between 21.0 and 58.1 items/kg DW, with a bulk mean of 30.4 ± 13.7 items/kg DW.

From macro to micro, from patchy to uniform: Analyzing plastic contamination along and across a sandy tide-less coast

In search of an effective method to evaluate plastic contamination, macrolitter (>25 mm), mesolitter (5-25 mm), large microlitter (2-5 mm), large and small microplastics (2-5 mm and 0.5-2 mm) abundances in surface beach sands were simultaneously determined by two methods in four beach zones at six locations along the 100-km-long marine coast of the Curonian Spit National Park and the neighboring cities. Mean (median) content of plastic items per m² is 0.85 (0.33) for macro-, 1.48 (0.40) for meso-, 3.35 (0.68) for large microlitter, and 3235 (1800) for microplastics (0.5-5 mm). The distribution of litter and microplastics (0.5-5 mm) is highly variable along and across the beach. The abundance of small-microplastics (0.5-2 mm) at the beach face is similar for all the locations and replicates. Swash-zone mixing, water percolation, importance of sediment pore size (rather than grain size), natural sorting of plastic particles at the beach face are considered.