Lake Donuzlav, located in the western part of the Crimean Peninsula is a water body undergoing anthropogenic load, which cannot but affect the state of its bottom sediments.  The content and composition of polycyclic aromatic hydrocarbons (PAH) are representative indicators of the degree and character of an anthropogenic impact in natural habitats. The aim of the work was to assess the level of PAH content in the bottom sediments, to identify potential sources and to assess the toxicity of bottom sediments. It was established that the average content of ∑PAH in the sediments amounted to 806±380 ng/g, with the values of this parameter ranging over 34–4036 ng/g. At five out of ten stations in Lake Donuzlav, PAH values, average for the Black Sea, were exceeded. These stations were grouped along both banks in the inner part of the reservoir. Fourteen PAHs were identified: Nap, 2mNap, Flu, Phe, Ant, Fla, Py, TrPhe, Chr, BbF, BkF, BaP, DBA, BghiP. The main share falls on the binuclear Nap and 2mNap, which indicate the presence of fresh oil pollution. The average share of these compounds over the water area was 60±5%, and at stations with elevated levels of ∑PAH it was 74±4%. There was a close correlation between the content of all polyarenes, which coefficient averaged 0,88. The presence of geochemical relationships between polyarenes entering from different sources was probably due to the functioning of natural mechanisms aimed at the transformation of pollutants, which served to restore the dynamic balance of the system.

Shelf areas of the seas and oceans characterizing high productivity are the spawning sites of many aquatic organisms. However, they are strong impacted for anthropogenic pollution, including oil contamination, which negatively influence on marine organisms. The effects of mazut and diesel fuel in the concentrations of 0.05, 0.1 and 0.2 ml/l on the activity of antioxidant enzymes which are recognized as biomarkers of the oxidative stress namely superoxide dismutase (SOD), catalase (CAT), peroxidase (PER) and glutathione reductase (GR) in the developing embryos of two marine blennies Parablennius sanguinolentus and Salaria pavo (Perciformes: Blenniidae) on the V - VI developmental stages were studied. The results demonstrated higher mazut toxicity as compared with diesel fuel. In P. sanguinolentus embryos exposed to mazut the activity of key anti-oxidant  enzymes SOD and CAT were significantly higher (+413% and +100% as  compared with the control, p<0.05), while in the case of diesel fuel the enzymes level varied insignificantly. In the embryos of S. pavo SOD and CAT activities were also increased at mazut incubation (256% and 103% respectively, p<0.05), while the differences between enzymes level in embryos exposed to diesel fuel were lower. In contaminated S. pavo embryos enzyme activities varied less as compared with the embryos of P. sanguinolentus, therefore they are more resistant and adaptive to oil contamination. The possible mechanisms of fish embryos antioxidant system response to oil pollution are discussed.

The authors propose a methodology for assessing the sources of microplastic pollution (particles 0.5-5 mm in size), which makes it possible to differentiate coastal recreational areas according to the degree of vulnerability to microplastic accumulation. The methodology takes into account the sources of microplastics coming to the beach directly from vacationers - factors of recreational activities, as well as the influence of factors of the adjacent territory: the type of adjacent territory, saturation with transport infrastructure, etc. An analysis of the results of monitoring the microplastic concentration in beach and bottom sediments of seven beaches of the Sevastopol region with varying degrees of anthropogenic load during 2018–2020, as well as an assessment of the sources of microplastic pollution on these beaches using the proposed methodology, made it possible to differentiate these coastal recreational areas according to the degree of vulnerability to accumulation of microplastic pollution. The most vulnerable are the beaches that are actively visited by tourists and located in close proximity to large blocks of apartment buildings and extensive transport infrastructure (Pesochniy and Omega). The beaches Konstantinovsky and Goryachka (placed close tothe thermal power station), located in the zone of active navigation of ships of various tonnage, are confined to areas of low and moderate pollution. The main stream of vacationers on them are local residents with a high turnover rate. The least vulnerable are the beaches with park areas: Uchkuevka, Solnechny and Zolotoy. The source of microplastic pollution on these beaches is mainly vacationers.

International audience | The Don River is among the largest rivers in the Eastern Europe and is heavily polluted. This river inflows into small and semi-isolated Sea of Azov, which is connected with the Black Sea by a narrow strait. Generally, the Sea of Azov is a large choked lagoon, which serves as a barrier for river-borne constituents. Using numerical modeling, we reveal that presence of the choked lagoon significantly slows down the estuary-seawater flux of dissolved pollutants and slackens its discharge-induced seasonal variability. In particular, the Sea of Azov delays the 5 % and 95 % of the total flux of riverine pollution to the Black Sea by 9 and 36 months, respectively. The obtained results are important for assessment the influence of background and emergency pollution accidents at the Don River on water quality in the study region. Moreover, these results could be applied to many other chocked lagoons in the World Ocean.

The red mullet (Mullus barbatus Linnaeus, 1758) is a keynote species for the Bulgarian Black Sea ecosystem and fisheries; nevertheless, existing knowledge on population status is very scarce. The present study was intended to assess the health status and adaptive potential of M. barbatus populations inhabiting the Bulgarian waters of the Black Sea. Our findings revealed that populations of M. barbatus are exposed to a variety of anthropogenic and environmental stressors. The species’ status was assessed using representative genetic, morphological, biochemical and chemical biomarkers from specimens obtained in the research area’s northern and southern regions. Based on mtDNA markers, genetic analysis revealed low haplotype and nucleotide diversity, typically observed in overexploited or “threatened” populations. Examining the morphology of the specimens revealed no discernible pattern of differentiation. Except for aluminium and chrome, metal and PAH concentrations in fish were below the regulatory thresholds. The specimens from the southern region ingested more microplastics than those from the northern region. The majority of specimens collected from the southern region also exhibited elevated levels of oxidative stress and decreased antioxidant defence, which can be interpreted as an early indication that they had reached the limits of their adaptive potential. Further research on the composite effects of the stressogenic environment on the Black Sea biota are critically needed, as well as the introduction of new indicators and thresholds at molecular and cellular levels for adequate monitoring of both the ecological state of the marine environment and its biota.