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Marine sediments play a significant role as reservoirs for mercury (Hg), a bioaccumulative toxic pollutant that poses risks to human and ecosystem health. Iron (Fe) has been recognized as an influential factor in the complexation and bioavailability of Hg in sediments. However, limited studies have investigated the interactions between the chemical fractions of these elements in natural settings. This study aims to examine the fractions of Hg and Fe in sediments of the Baltic Sea, a region historically impacted by Hg pollution. The Hg fractions were determined using the thermodesorption technique, while sequential extraction was employed to identify the Fe fractions. The findings confirm the crucial role of Fe in the formation, as well as the horizontal and vertical distribution of labile and stable Hg in marine sediments. Factors such as the contribution of organic matter, the presence of reactive Fe, and Fe associated with sheet silicates emerged as significant drivers that positively influenced the content of the most labile Hg fractions, potentially affecting the mobility and bioavailability of Hg in the marine environment.
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Since the 1970s, the amount of aquatic plants and algae debris, called beach wrack (BW), has increased along the shores of industrialised regions. The strong ability of primary producers to accumulate pollutants can potentially result in their deposition on the beach along with the BW. Despite that, the fate and impact of such pollutants on sandy beach ecosystems have not been investigated so far. This study examines the fate of neurotoxic mercury and its labile and stable fractions in BW on sandy beaches of the Puck Bay (Baltic Sea). In addition to BW, beach sediments and wrack-associated macrofauna were also analysed. Rough estimations showed that Puck Bay beaches (58.8 km) may be a temporary storage of 0.2-0.5 kg of mercury, deposited on them along with the BW annually. A large proportion of Hg (89 ± 16%) in a BW was labile and potentially bioavailable. The contribution of Hg fractions in the BW was conditioned by the degree of its decomposition (molar C:N:P ratio). With the progressive degradation of BW, a decrease in the contribution of Hg adsorbed on its surface with a simultaneous increase in the proportion of adsorbed (intracellular), mercury was observed. BW accumulation decreased oxygen content and redox potential and increased methylmercury content in underlying sediments, indicating methylation. Hg concentrations in the studied fauna were up to 4 times higher than in the BW. The highest values occurred in a predatory sand bear spider and the lowest in a herbivorous sand hopper. Regardless of trophic position, most of Hg (92-95%) occurred as an absorbed fraction, which indicates about a 30% increase in relation to its share of BW. These findings suggest the significant role of BW as a mercury carrier in a land-sea interface and increased exposure of beach communities to the adverse effects of mercury in coastal ecosystems.
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Mercúrio , Poluentes Químicos da Água , Animais , Mercúrio/análise , Monitoramento Ambiental , Ecossistema , Poluentes Químicos da Água/análise , PeixesRESUMO
In this study, we investigate how salinity, oxygen concentration and catchment area characteristics impact the dynamics of Fe-P-S cycling in the continental shelf sea sediments. Samples were collected from three sites representing different environmental conditions: Gdansk Deep (southern Baltic Sea), Gotland Deep (central Baltic Sea) and Bothnian Sea (northern Baltic Sea). Sediments were analysed for their mineral composition and speciation of iron and phosphorus. The main groups of Prokaryota involved in Fe-P-S cycling in sediments were indicated. Concentrations of sulphate, hydrogen sulphide, alkalinity, chloride, calcium, phosphate and iron were measured in pore waters. We demonstrated that in the eutrophicated southern region with moderate salinity and oxygen deficit in bottom water, sediments had high potential for retaining Fe and releasing P as indicated by high concentrations of pyrite and labile forms of phosphorus, respectively. Strong salinity stratification and intermittent pelagic redoxcline in the central Baltic Sea resulted in a clearly higher rate of pyrite deposition. Sediment was enriched with Mn due to the formation of Ca-Mn carbonates driven by intensive Mn redox cycling and sulphate reduction. Because of high availability of Mn oxides connected with episodic inflows of oxic seawater from the North Sea, sulphate was present in the entire profile of the studied sediments in the Gotland Deep. Sediments in the well-oxygenated, virtually fresh and rich in land-derived iron northern Baltic Sea retained significant amounts of P in authigenic minerals. Organic matter mineralisation in the surface sediment of this area was dominated by iron reduction. The variability of environmental conditions and consequent availability of electron acceptors were the cause of regional differences in the composition of Prokaryota communities - the number of sulphate reducers in the Gdansk and Gotland Deeps was greater than in the Bothnian Sea, where there were more Fe reducers and bacteria that oxidise Fe and S.
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SalinidadeRESUMO
The study aimed to determine the level of mercury (Hg) and its labile and stable forms in the surface sediments of the Baltic Sea. The work considers the impact of current and historical sources of Hg on sediment pollution, together with the influence of different environmental parameters, including water inflows from the North Sea. Surface sediments (top 5 cm) were collected in 2016-2017 at 91 stations located in different areas of the Baltic Sea, including Belt Sea, Arkona Basin, Bornholm Basin, Gdansk Basin, West Gotland Basin, East Gotland Basin, and the Bothnian Sea. Besides, the particulate matter suspended in the surface and near-bottom water was also collected. The analysis of total Hg concentration and individual Hg forms in collected samples was carried out using a 5-step thermodesorption method. This method allows for the identification of three labile and thus biologically available, fractions of Hg, which are mercury halides, organic Hg, mercury oxide and sulphate. Two stable fractions, mercury sulphide and residual Hg, were also determined. The highest Hg concentrations, reaching 341 ng g-1, were measured in the highly industrialised Kiel Bay, which was additionally a munition dumping site during and after World War II. High Hg level, ranging from 228 to 255 ng g-1, was also recorded in the surface sediments of the Arkona Basin, which was a result of the cumulative effect of several factors, such as deposition of Hg-rich riverine matter, favourable hydrodynamic conditions and military activities in the past. The relatively elevated Hg concentrations, varying from 60 to 264 ng g-1, were found in the Gdansk Basin, a region under strong anthropopressure and dominated by soft sediments. The sum of labile Hg in sediments was high and averaged 67% (with the domination of organic Hg compounds), which means that a large part of Hg can be released to the water column. It was found that the water inflows from the North Sea intensify the remobilisation of Hg and its transformation into bioavailable labile forms. As a consequence, the load of Hg introduced into the trophic chain can increase. Despite the significant reduction of Hg emission into the Baltic in the last decades, surface sediments can be an important secondary Hg source in the marine ecosystem. This is especially dangerous in the case of the western Baltic Sea.
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Mercúrio , Poluentes Químicos da Água , Países Bálticos , Disponibilidade Biológica , Ecossistema , Monitoramento Ambiental , Sedimentos Geológicos , Mercúrio/análise , Mar do Norte , Poluentes Químicos da Água/análiseRESUMO
High-resolution bathymetric data were collected with a multi-beam echosounder in the southern part of the Baltic Sea (region MET1, Gulf of Gdansk) revealing the presence of a 10 m deep and 50 m in diameter pockmark (MET1-BH) on the sea bottom (78.7 m). To date, no such structures have been observed to reach this size in the Baltic Sea. The salinity of the near-bottom water in the pockmark was about 2 PSU (about 31.22 mmol/l Cl-), which clearly indicated the presence of a submarine groundwater discharge (SGD). Water column, sediments and the seabed structure were investigated in the MET1-BH area using various hydroacoustic devices: multi-beam and splitbeam echosounders and a sub-bottom profiler. Geochemical analyses of sediment pore waters (CH4, Cl-, Br-, F-, SO42-, Ca2+, Mg2+, K+, Na+, ∑H2S, dP, dSi, NH4+, DIC, DOC) and microbiological analysis of sediments (16S rRNA) were performed. The content of CH4 and CO2 in the outflowing gas and its origin (δ13C-CH4 and δ2D-CH4) were determined. Hydroacoustic data showed that gas was emitted intensively from the inside of the structure. The height and intensity of the gas flares varied depending on the hydrostatic pressure. The gas contained 76.1% of CH4, 17.6% of CO2 and 0.39% of He. Methane source was microbial. Geophysical investigation revealed the presence of dislocations in sub-surface sediment layers in the MET1 region, which could have created a passage for groundwater and gas. Geochemical analyses pointed to intensive processes of organic matter decomposition in this area, active methanogenesis in the surface sediment layer, lack of the sulphate-methane transition, and freshwater seepage at a depth of ~88 m (bottom of the pockmark), probably from Upper Cretaceous deposits. The Prokaryota composition, atypical for marine surface sediments, resulted from the combination of freshwater and high organic matter content, and reflected active in situ methanogensis.
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Água Subterrânea , Sedimentos Geológicos , Metano/análise , RNA Ribossômico 16S , NaviosRESUMO
Due to changing climate conditions, such inland seas as the Baltic are expected to become more eutrophicated and less saline (causing lower availability of sulphates). This may promote methanogenesis as the main process of organic matter (OM) degradation in marine sediments. Presence of methane, in turn, may affect biogeochemical cycling of many elements, including iron. Thus, in the present study we attempted to investigate the influence of CH4 on the Fe forms in marine sediments. Sediment cores were collected from three physico-chemically different stations within the Southern Baltic, taking into account such parameters as water depth, OM content, bottom zone oxygenation and distance from the Vistula River (main source of anthropogenic material). At two sampling stations methane was present in shallow sediments (P1, MET2) and at one station (W6) any traces of this gas were not determined. Iron species (FeCARB, FeOX1, FeOX2, FeMAG, FePRS, FeT, FeFeS2, FeFeS) in sediments were investigated using the sequential extraction. Pore water was analysed to obtain vertical profiles of hydrogen sulphide, sulphate and dissolved inorganic carbon (DIC). Additionally, such parameters as water and OM content, CH4 and Eh in sediments were determined. Results showed that methanogenesis affects the biogeochemical iron cycling in sediments of the Southern Baltic, leading to the increase of carbonates containing ferrous iron (as a result of DIC production during intensive OSR, AOM and methanogenesis) and decrease of ferric iron compounds used in the AOM. Moreover, in the areas of lower salinity, pyrite formation is limited by an insufficient amount of hydrogen sulphide, leading to the situation when a significant part of Fe is accumulated in the form of monosulphides. In turn, in the areas of higher salinity, where oxygen deficiencies occur more often, more hydrogen sulphide is present in pore water. Pyrite formation is then limited by iron, not by sulphur.
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Dissolved organic carbon (DOC) concentration and fluxes from four rivers draining the catchment of the Puck Lagoon in southern Baltic are presented. Water samples from rivers and coastal zone close to the rivers' mouth were collected from April 2015 to March 2017. DOC was measured using high temperature catalytic oxidation with an NDIR detection. DOC concentration in rivers as well as area specific load discharged to the lagoon reflected variations of land use along their course. Area specific load of DOC discharged by rivers with high proportion of forests, meadows, and pastures in the catchment was significantly higher as compared to rivers with catchment dominated by arable land. However, the main controlling factor of the total discharged loads of DOC was the water flow. The highest loads were observed during the downpour. That was due to the larger volumes of water transported with rivers and the higher concentration of DOC resulting from increased leaching from the catchment area. The obtained results are especially important in the light of climate change in the southern Baltic region. According to the forecasts, we can expect increased precipitation and flooding and consequently increased leaching from the catchment and transport of DOC to the sea via rivers.
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Carbono/análise , Monitoramento Ambiental , Rios/química , Movimentos da Água , Mudança Climática , Inundações , Florestas , Meteorologia , Polônia , ChuvaRESUMO
BACKGROUND: We compared concomitant cisplatin and irradiation with radiotherapy alone as adjuvant treatment for stage III or IV head and neck cancer. METHODS: After undergoing surgery with curative intent, 167 patients were randomly assigned to receive radiotherapy alone (66 Gy over a period of 6 1/2 weeks) and 167 to receive the same radiotherapy regimen combined with 100 mg of cisplatin per square meter of body-surface area on days 1, 22, and 43 of the radiotherapy regimen. RESULTS: After a median follow-up of 60 months, the rate of progression-free survival was significantly higher in the combined-therapy group than in the group given radiotherapy alone (P=0.04 by the log-rank test; hazard ratio for disease progression, 0.75; 95 percent confidence interval, 0.56 to 0.99), with 5-year Kaplan-Meier estimates of progression-free survival of 47 percent and 36 percent, respectively. The overall survival rate was also significantly higher in the combined-therapy group than in the radiotherapy group (P=0.02 by the log-rank test; hazard ratio for death, 0.70; 95 percent confidence interval, 0.52 to 0.95), with five-year Kaplan-Meier estimates of overall survival of 53 percent and 40 percent, respectively. The cumulative incidence of local or regional relapses was significantly lower in the combined-therapy group (P=0.007). The estimated five-year cumulative incidence of local or regional relapses (considering death from other causes as a competing risk) was 31 percent after radiotherapy and 18 percent after combined therapy. Severe (grade 3 or higher) adverse effects were more frequent after combined therapy (41 percent) than after radiotherapy (21 percent, P=0.001); the types of severe mucosal adverse effects were similar in the two groups, as was the incidence of late adverse effects. CONCLUSIONS: Postoperative concurrent administration of high-dose cisplatin with radiotherapy is more efficacious than radiotherapy alone in patients with locally advanced head and neck cancer and does not cause an undue number of late complications.