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.

From macro to micro: dataset on plastic contamination along and across a sandy tide-less coast (the Curonian Spit, the Baltic Sea).

The contamination by macrolitter (>25 mm), mesolitter (5-25 mm), large microlitter (2-5 mm), large and small microplastics (L-MPs (2-5 mm) and S-MPs (0.5-2 mm), accordingly) in the surface beach sand at 6 locations along the 100-km-long marine coast of the Curonian Spit UNESCO National Park and the neighboring city beaches is quantified. In total, 55 samples obtained during 1-2 May 2018 are analyzed. Primary data is provided, along with exhaustive information on sampling dates and coordinates, sampling methods, extracting procedures, control measures, detection techniques, and µ-Raman spectroscopy verification. The number of items per m2 and items per kg dry weight (for MPs) is determined separately for fibres, films, and fragments. Distributions by size and plastic type are presented. Standard protocols, a modified NOAA method, and µ-Raman spectroscopy were applied to obtain the data, thus they can be used for comparative analyses.