Distribution and bioavailability of mercury in the surface sediments of the Baltic Sea

Abstract

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, Gdańsk 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 Gdańsk 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.

Mercury Sources and Fate in a Large Brackish Ecosystem (the Baltic Sea) Depicted by Stable Isotopes

“…As sediment samples were selected to represent both coastal and offshore as well as contaminated and pristine environments, the range of HgT concentrations is large, from 64 to 10 690 ng g –1 with a median value of 140 ng g –1 (interquartile range (IQR) = 167) (Table SI-2). MMHg concentrations range from 0.1 to 13.6 ng g –1 and contribute on average 0.7 ± 0.7% to HgT, similar to other coastal environments and great lakes. , Our HgT values are overall in agreement with two recent studies that demonstrated a strong anthropogenic pollution during the second half of the past century that overall increased Hg concentrations in the Baltic Sea sediments over its preindustrial background (20–50 ng g –1 ) and also led to high Hg concentrations in some local hotspots (industrial and war waste sites). , …”

Temporal trends of mercury levels in fish (dab, Limanda limanda) and sediment from the German Bight (North Sea) in the period 1995-2020

“…Mercury levels throughout the world differ quite substantially between regions. Compared to mercury levels from some other regions in the world (Table 1 in Kwasigroch et al, 2021), values for the North Sea are lower but still signi cantly exceed the ERL value of 0.15 mg/kg (OSPAR, 2021b).…”

“…Jin et al (2012) reported values for mercury in surface sediments for the Wadden sea Jade Bay ranging between 0.08-0.243 mg/kg dw. The Baltic Sea revealed similar values ranging from 0.01-0.341 mg/kg dw (Kwasigroch et al, 2021).…”

Valorization of Marine Waste: Use of Industrial By-Products and Beach Wrack Towards the Production of High Added-Value Products

“…Anthropogenic mercury release remains a problem in the aquatic environment and, based on the sedimentary records in the Baltic Sea, it exceeds Hg coming from natural sources (i.e., hydrothermal processes and rock weathering) by a factor of 5 on average. Recently, the emission of this metal to the environment has substantially decreased (Helsinki Commission, 2009, 2018Kwasigroch et al, 2021). This has resulted in a noticeable decrease of mercury concentration in macrophytes in the Polish coastal zone of the southern Baltic (Bełdowska et al, 2015(Bełdowska et al, , 2016.…”