The International Maritime Organization (IMO) has gradually applied stricter regulations on the maximum sulphur content permitted in marine fuels and from January 1, 2020, the global fuel sulphur limit was reduced from 3.5% to 0.5%. An attractive option for shipowners is to install exhaust gas cleaning systems, also known as scrubbers, and continue to use high sulphur fuel oil. In the scrubber, the exhausts are led through a fine spray of water, in which sulphur oxides are easily dissolved. The process results in large volumes of acidic discharge water, but while regulations are focused on sulphur oxides removal and acidification, other pollutants e.g. polycyclic aromatic hydrocarbons, metals and nitrogen oxides can be transferred from the exhausts to the washwater and discharged to the marine environment. The aim of the current study was to investigate how different treatments of scrubber discharge water (1, 3 and 10%) affect a natural Baltic Sea summer microplanktonic community. To resolve potential contribution of acidification from the total effect of the scrubber discharge water, “pH controls” were included where the pH of natural sea water was reduced to match the scrubber treatments. Biological effects (e.g. microplankton species composition, biovolume and primary productivity) and chemical parameters (e.g. pH and alkalinity) were monitored and analysed during 14 days of exposure. Significant effects were observed in the 3% scrubber treatment, with more than 20% increase in total biovolume of microplankton compared to the control group, and an even greater effect in the 10% scrubber treatment. Group-specific impacts were recorded where diatoms, flagellates incertae sedis, chlorophytes and ciliates increased in biovolume with increasing concentrations of scrubber water while no effect was recorded for cyanobacteria. In contrast, these effects was not observed in the “pH controls”, a suggestion that other parameters/stressors in the scrubber water were responsible for the observed effects.

In the Baltic Sea, water is stratified due to differences in density and salinity. The stratification prevents water from mixing, which could affect sinking rates of microplastics in the sea. We studied the accumulation of microplastics to halocline and thermocline. We sampled water with a 100 μm plankton net from vertical transects between halo- and thermocline, and a 30 L water sampler from the end of halocline and the beginning of thermocline. Thereafter, microplastics in the whole sample volumes were analyzed with imaging Fourier transform infrared spectroscopy (FTIR). The plankton net results showed that water column between halo- and thermoclines contained on average 0.92 ± 0.61 MP m⁻³ (237 ± 277 ng/m⁻³; mean ± SD), whereas the 30 L samples from the end of halocline and the beginning of thermocline contained 0.44 ± 0.52 MP L⁻¹ (106 ± 209 ng L⁻¹). Hence, microplastics are likely to accumulate to thin layers in the halocline and thermocline. The vast majority of the found microplastics were polyethylene, polypropylene and polyethylene terephthalate, which are common plastic types. We did not observe any trend between the density of microplastics and the sampling depth, probably because biofilm formation affected the sinking rates of the particles. Our results indicate the need to sample deeper water layers in addition to surface waters at least in the stratified water bodies to obtain a comprehensive overview of the abundance of microplastics in the aquatic environment.

Decades of intensive discharge from industrial activities into coastal systems has resulted in the accumulation of a variety of persistent organic pollutants (POPs) in marine waters and sediments, having detrimental impacts on aquatic ecosystems and the resident biota. POPs are among the most hazardous chemicals originating from industrial activities due to their biotoxicity and resistance to environmental degradation. Bacterial communities are known to break down many of these aromatic compounds, and different members of naturally occurring bacterial consortia have been described to work in syntrophic association to thrive in heavily contaminated waters and sediments, making them potential candidates as bioindicators of environmental pollution. In this study environmental, sampling was combined with chemical analysis of pollutants and high-resolution sequencing of bacterial communities using Next Generation Sequencing molecular biology tools. The aim of the present study was to describe the bacterial communities from marine sediments containing high loads of POPs and to identify relevant members of the resident microbial communities that may act as bioindicators of contamination. Marine sediments were collected from a coastal bay area of the Baltic Sea historically influenced by intense industrial activity, including metal smelting, oil processing, and pulp and paper production. Different types of POPs were detected at high concentrations. Fiberbank sediments, resulting from historic paper industry activity, were found to harbour a clearly distinct bacterial community including a number of bacterial taxa capable of cellulolytic and dechlorination activities. Our findings indicate that specific members of the bacterial communities thrive under increasing levels of POPs in marine sediments, and that the abundances of certain taxa correlate with specific POPs (or groups), which could potentially be employed in monitoring, status assessment and environmental management purposes.

Microplastic (MPL) contamination in the marine environment is extensively studied yet little is known about the extent of MPL abundance in seagrass beds. The aim of this study was to evaluate MPL accumulation in coastal seagrass (Zostera marina) beds in the Baltic Sea, Estonia.Surface water was sampled by pumping using 40 μm plankton net, and sediments by trowel. MPL was extracted with NaCl, identified by microscopy and ATR-FTIR on selected samples.Surface water in the seagrass beds had 0.04–1.2 (median 0.14) MPL/L, similar to other areas of the Baltic Sea. Sediments had 0–1817 (median 208) MPL/kg (dwt), much higher than previously recorded from adjacent unvegetated and offshore sediments, thereby suggesting a strong ability of the sediments in seagrass beds to retain MPL. Of identified MPL, blue fibres were dominant in both the sampled media. Sediment characterization showed a correlation between MPL counts with poorly sorted sediments.

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.

Microplastics (MPs, 0.2-5 mm) contamination of water outside/inside thickets of macrophytes in the Baltic Sea was studied. The amount of MPs particles in water samples taken within thickets is on average 1.7 times higher than in water samples taken in the areas outside thickets. Fibres are the predominant type of MPs (92.5%). For algae growing on boulders, the abundance of MPs is 1245 ± 1020 items/m². Per kilogram of dry algae mass the MPs abundance is 376 ± 404 items/kgDW for all shapes of MPs particles. This value is one order of magnitude higher than in sands of the swash zone in the given area. It is shown that filamentous algae retain more fibres than cartilaginous ones: 1.9-8.5 versus 1-1.1 items/l on average. Obviously, areas covered by sea grasses are much more contaminated than water and sediments in the given region.

A webcam was installed on the shore of the South-Eastern Baltic (Kaliningrad Oblast, Russia) to monitor the beach dynamics and beach-cast (BC) daily from November 1, 2019, to October 31, 2020. The beach was formed not the whole year (77%). The most frequent BC residence time was one day (1–21, 4.1 on average, and 1–19, 4.3 on average days to the west and east of the groin, respectively). The BC consisted primarily of algae. Fresh BC occupied smaller area, and its layer was thicker than that of long-discarded and trampled BC. The specific amount of material (per m²) in a fresh BC was 3.7 times higher in volume and 2.6 times higher in weight than in long-discarded and trampled BC. For fresh and old BC, the specific volumes were 63 and 17 l per m², respectively, and the specific masses were 48 and 18 kg per m², respectively.

Effects of household post-consumer plastics and tyre rubber on a Baltic Sea copepod Limnocalanus macrurus were assessed. Fragments of commercial recycled low-density polyethylene vegetable bags and rubber originating from recycled car tyres were incubated in seawater, and the copepods were exposed to the filtrate of the water. L. macrurus experienced erratic swimming behaviour and increased mortality in the filtrate of unwashed vegetable bags, containing elevated concentrations of alcohols, organic acids and copper. Responses of the antioxidant defence system (ADS) were recorded in copepods exposed to rubber treatments containing high concentrations of zinc. Significant responses in the ADS enzymes indicate that reactive oxygen species (ROS) formation was exceeding the detoxification capacity of the ADS which may further lead to prolonged state of oxidative stress. Observed effects of exposure on the biochemical level coincide with impaired swimming activity of the copepods, indicating possible irreversible cellular responses leading to behavioural changes and mortality.

Neuston samples were collected with a Manta trawl in the rim of the Arctic Ocean, in the Northern Atlantic Ocean and the Baltic Sea at eleven coastal and open-sea locations. All samples contained plastics identified by FTIR microscopy. Altogether, 110 microplastics pieces were classified according to size, shape, and polymer type. The concentrations at the locations were generally low (x̅ = 0.06, SD ± 0.04 particles m⁻³) as compared to previous observations. The highest concentrations were found towards the Arctic Ocean, while those in the Baltic Sea were generally low. The most abundant polymer type was polyethylene. Detected particle types were mainly fragments. The number of films and fibers was very low. The mean particle size was 2.66 mm (SD ± 1.55 mm). Clustering analyses revealed that debris compositions in the sea regions had characteristic differences possibly reflecting the dependences between compositions, drifting distances, sinking rates, and local oceanographic conditions.

Different litter types accumulate in all marine environments. Plastics are of special interest because of their high abundance and possible threats to marine organisms. Polymer type is crucial for their distribution and fate in marine environments. Seafloor litter abundance and composition in the Baltic and North Sea were analysed based on three sampling campaigns according to the protocol of ICES International Bottom Trawl Survey. Polymers were identified via attenuated total reflection-Fourier transform infrared spectroscopy. General litter abundances differed significantly between the Baltic and North Sea with 9.6 items/km² and 70.7 items/km², respectively. Plastic built the dominating litter group in both seas (62.2% and 91.3%, respectively). Polymer identification revealed clear dominance of polyethylene, polypropylene and polyamide. Most polymers were positively buoyant in seawater (89.5%), thereby excluding polymer density as the main driver of vertical plastic litter transportation. Plastics at the seafloor basically reflected the entirety of polymers entering marine environments.