Fluxes of dissolved trace metals (Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn) via groundwater discharge along the southern Baltic Sea have been assessed for the first time. Dissolved metal concentrations in groundwater samples were less variable than in seawater and were generally one or two orders of magnitude higher: Cd (2.1–2.8nmolL−1), Co (8.70–8.76nmolL−1), Cr (18.1–18.5nmolL−1), Mn (2.4–2.8μmolL−1), Pb (1.2–1.5nmolL−1), Zn (33.1–34.0nmolL−1). Concentrations of Cu (0.5–0.8nmolL−1) and Ni (4.9–5.8nmolL−1) were, respectively, 32 and 4 times lower, than in seawater. Groundwater-derived trace metal fluxes constitute 93% for Cd, 80% for Co, 91% for Cr, 6% for Cu, 66% for Mn, 4% for Ni, 70% for Pb and 93% for Zn of the total freshwater trace metal flux to the Bay of Puck. Groundwater-seawater mixing, redox conditions and Mn-cycling are the main processes responsible for trace metal distribution in groundwater discharge sites.

The need to detect and monitor introduced marine species has increased with the increasing number of marine invasions. To complement standard detection and monitoring techniques, new approaches using environmental DNA (eDNA) have recently been developed. However, most of the eDNA work has focused on vertebrate species in spatially limited freshwater habitats while benthic invertebrates in coastal environments have received much less attention. Here, we evaluated the suitability of the eDNA approach for detecting benthic, hard-shelled, crustacean mud crab species in a brackish water environment. We demonstrated for the first time that eDNA from an introduced mud crab Rhithropanopeus harrisii can be successfully amplified in aquarium water samples and detected in the brackish water environment. However, the detection rate was rather low. This suggests that in contrast to freshwater vertebrates, it may be more challenging to develop a highly sensitive eDNA method for detecting crustacean species in a marine environment.

Muscle and liver tissues of nine fish species were analyzed to assess butyltin and phenyltin contamination. The samples were collected from three basins located in the Southern Baltic Sea coastal zone that each represent different potential for organotin pollution. Maximum total concentrations of butyltin compounds (BTs) in the fish muscles and livers were 715 and 1132ng Sn g−1 d.w., respectively, whereas triphenyltin (TPhT) was not detected. In the muscle samples, the predominant compound in the sum of butyltins was tributyltin (TBT), while in the liver samples, tributyltin degradation products were found in the majority. The results demonstrate that 6–7years after the implementation of the total ban on harmful organotin use in antifouling paints, butyltins remain present in fishes from the Polish coast of the Baltic Sea. According to the HELCOM recommendation, eight samples exceeded the good environmental status boundary for tributyltin in seafood.

The combination of the sensitive characteristics of the Baltic Sea and the intense maritime traffic makes the marine environment vulnerable to anthropogenic influences. The theoretical scenario calculated in this study shows that the annually generated food waste onboard ships in traffic in the Baltic Sea contains about 182tonnes of nitrogen and 34tonnes of phosphorus. Today, all food waste generated onboard can be legally discharged into the marine environment at a distance of 12NM from the nearest land. The annual load of nitrogen contained in the food waste corresponds to 52% of load of nitrogen from the ship-generated sewage. Future regulations for sewage discharge in the Baltic Sea will require significant reduction of total nitrogen and phosphorus released. The contribution of nutrients from food waste compared to sewage will therefore be relatively larger in the future, if food waste still can be legally discharged.

Parallel studies on organic and elemental carbon in PM1 and PM2.5 aerosols and in wet deposition in various forms of its occurrence were conducted in the urbanised coastal zone of the Baltic Sea. The carbon load introduced into the sea water was mainly affected by the form of precipitation. Dry deposition load of carbon was on average a few orders of magnitude smaller than wet deposition. The suspended organic carbon was more effectively removed from the air with rain than snow, while an inverse relationship was found for elemental carbon. However the highest flux of water insoluble organic carbon was recorded in precipitation of a mixed nature. The atmospheric cleaning of highly dissolved organic carbon was observed to be the most effective on the first day of precipitation, while the hydrophobic elemental carbon was removed more efficiently when the precipitation lasted longer than a day.

The distribution of alkali and heavy metals in coastal sediments of three Polish beaches was assessed. In all locations there are sandy beaches of different characteristics according to the anthropogenic impact and degree of sheltering. Core sediments collected in Czołpino and Ustka were characterized by the highest concentration of Cd, Ag, Ba, and Al, Cu, Cr, Bi, Na, respectively. Among the alkaline metals core sediments were the most abundant with Ca, Bi, Mg and Na, presenting almost stable decreasing order in all beaches. The majority of dredge material collected can be classified as light or trace contaminated by Cr, Cu, Zn, Cd and Hg. An abundance of mineralogical components in core sediments in Ustka increases in Summer and Autumn, while in Puck is stable throughout the year. The content of studied metals in core sediments collected in three Polish beaches changes both in the vertical and horizontal profiles of the beach.

Plastic ingestion by marine biota has been reported for a variety of different taxa. In this study, we investigated 290 gastrointestinal tracts of demersal (cod, dab and flounder) and pelagic fish species (herring and mackerel) from the North and Baltic Sea for the occurrence of plastic ingestion. In 5.5% of all investigated fishes, plastic particles were detected, with 74% of all particles being in the microplastic (<5mm) size range. The polymer types of all found particles were analysed by means of Fourier transform infrared (FT-IR) spectroscopy. Almost 40% of the particles consisted of polyethylene (PE). In 3.4% of the demersal and 10.7% of the pelagic individuals, plastic ingestion was recorded, showing a significantly higher ingestion frequency in the pelagic feeders. The condition factor K was calculated to test differences in the fitness status between individuals with and without ingested plastic, but no direct effect was detected.

Marine litter is one of the problems marine ecosystems face at present, coastal habitats and food webs being the most vulnerable as they are closest to the sources of litter. A range of animals (bivalves, free swimming crustaceans and benthic, deposit-feeding animals), of a coastal community of the northern Baltic Sea were exposed to relatively low concentrations of 10μm microbeads. The experiment was carried out as a small scale mesocosm study to mimic natural habitat. The beads were ingested by all animals in all experimental concentrations (5, 50 and 250beadsmL−1). Bivalves (Mytilus trossulus, Macoma balthica) contained significantly higher amounts of beads compared with the other groups. Free-swimming crustaceans ingested more beads compared with the benthic animals that were feeding only on the sediment surface. Ingestion of the beads was concluded to be the result of particle concentration, feeding mode and the encounter rate in a patchy environment.

The frequencies of micronuclei (MN), nuclear buds (NB) and nuclear buds on filament (NBf) were examined in 660 specimens of herring (Clupea harengus) collected in 2009–2014 at 65 study stations located mainly along the chemical munition transport routes in the Baltic Sea. The frequency of nuclear abnormalities was strongly increased in herring caught at four stations located close to chemical munition dumping sites, or CWAs — substances (chemical warfare agents) in sediments. Significant increase of MN, NB and NBf was observed in fish caught November 2010–2013 compared to 2009. The most significantly increased genotoxicity responses were recorded in fish caught at stations along CW (chemical weapons) transport routes, close to the Bornholm CW dumping area, in zones with CWAs in sediments and with oil–gas platforms.

Simplified physical models and geometrical considerations reveal general physical and dynamical properties of microplastic particles (0.5–5mm) of different density, shape and size in marine environment. Windage of extremely light foamed particles, surface area and fouling rate of slightly positively buoyant microplastic spheres, films and fibres and settling velocities of negatively buoyant particles are analysed. For the Baltic Sea dimensions and under the considered idealised external conditions, (i) only one day is required for a foamed polystyrene particle to cross the sea (ca. 250km); (ii) polyethylene fibres should spend about 6–8months in the euphotic zone before sinking due to bio-fouling, whilst spherical particles can be retained on the surface up to 10–15years; (iii) for heavy microplastic particles, the time of settling through the water column in the central Gotland basin (ca. 250m) is less than 18h. Proper physical setting of the problem of microplastics transport and developing of physically-based parameterisations are seen as applications.