The unsustainable settlement and high industrialization around the catchment of the Baltic Sea has left records of anthropogenic heavy metal contamination in Baltic Sea sediments. Here, we show that sediments record post-industrial and anthropogenic loads of Cd, Zn, and Pb over a large spatial scale in the Baltic Sea. We also demonstrate that there is a control on the accumulation of these metals in relation to oxic/anoxic conditions of bottom waters. The total concentrations of Cd, Zn, and Pb were obtained with the near-total digestion method in thirteen cores collected from the Bothnian Bay, the Bothnian Sea, and the west and central Baltic Proper. The lowest average concentrations of Cd, Zn, and Pb were observed in Bothnian Bay (0.4, 125, 40.2 mg kg⁻¹ DW, respectively). In contrast, the highest concentrations were observed in the west Baltic Proper (5.5, 435, and 56.6 mg kg⁻¹ DW, respectively). The results indicate an increasing trend for Cd, Zn, and Pb from the early nineteenth century until the 1970s, followed by a decrease until 2000–2008. However, surface sediments still have concentrations above the pre-industrial values suggested by the Swedish EPA (Cd is 0.2, Zn is 85, and Pb is 31 mg kg⁻¹ DW). The results also show that the pre-industrial Cd, Zn, and Pb concentrations obtained from 3 cores with ages < 1500 B.C. were 1.8, 1.7, and 1.2 times higher, respectively, than the pre-industrial values suggested by the Swedish EPA. To conclude, accumulations of metals in the Baltic Sea are governed by anthropogenic load and the redox conditions of the environment. The significance of correct environmental governance (measures) can be illustrated with the reduction in the pollution of Pb, Zn, and Cd within the Baltic Sea since the 1980s.

This study established background (pre-industrial) values of copper (Cu), arsenic (As), cobalt (Co), and uranium (U) in Baltic Sea sediments. The indicated background values could help identifying the spatial and temporal anthropogenic loads of these elements (metals and metalloids) in the Baltic Sea. In this study, 137 sediment samples were collected from cores obtained from 13 monitoring stations in the Gulf of Bothnia (Bothnian Bay and Sea) and the entire Baltic Proper. To understand the extent of contamination, we used direct and combined methods to define the geochemical background values as inputs for the geochemical index (Igeo) calculation. The obtained values were then compared with the background values established by the Swedish Environmental Protection Agency. From the direct method, Cu, Co, As, and U had background values of 39, 21.5, 12.4, and 6.3 mg kg−1 DW. Copper and U exhibited concentrations above the background values in surface sediment in the western and eastern Baltic Proper (maximum Igeo indicates moderate contamination). Arsenic was above background concentrations in the Baltic Sea and highest in the Gulf of Bothnia (maximum Igeo indicates strong contamination). Cobalt concentrations were within the range of background values (no contamination).

Extensive red/brown precipitates of unknown origin and composition have caused ecological degradation of a wetland nature reserve (the Water Kingdom Biosphere Reserve) in the hemiboreal zone in south Sweden. Chemical analyses of samples containing the precipitates showed strong dominates of Fe and elevated levels of rare earth elements (REEs), Be, and U. In addition, synchrotron-based analyses indicated that the Fe in these precipitates was bound largely in akageneite and/or schwertmannite. Under nearby farmlands, acid sulfate soils, developing on sulfide-bearing sediments and notorious for abundant export of metals, were identified and found to be widespread, deep (down to the sampling depth of 180 cm or deeper), and very acidic (minimum pH range for soil profiles: 2.8–3.5). In-between the farmland and wetland was a central drain that can act as both a transporter and sink of elements leached from the acid sulfate soils. In the drain had accumulated sediments that had strongly elevated concentrations of Al (15%), ∑REE (2725 mg/kg), Be (15 mg/kg), and U (37 mg/kg). Based on these data and features, a conceptual model for the areas was proposed. The acid sulfate soil releases several major and trace elements, including Fe2+, which are transported in acidic waters via drainpipes to the central drain where pH increases, causing extensive precipitation of Al, REEs, Be, and U as well as Fe2+ oxidation and formation of Fe oxyhydroxides and oxyhydroxysulfates. A substantial part of the Fe2+ in the drain water, however, remains in solution, so when this water is ultimately pumped to the wetland, large amounts of Fe2+ together with significant amounts of Al, REEs, Be, and U and transported to the wetland where Fe2+ is finally oxidized, precipitated and retained. Yet several other metals, leached abundantly from the acid sulfate soils (Mn, Zn, Ni, Co, and Cd), were not found in elevated levels in any of the recipients and therefore most likely have been transported beyond our sampling sites and has thus reached further out in the ecologically sensitive wetland.

To bring life back to anoxic coastal and sea basins, reoxygenation of anoxic/hypoxic zones has been proposed. This research focuses on the metals released during the oxidization of sediments from two locations in the anoxic Eastern Gotland Basin under a laboratory-scale study. Triplicate experimental cores and reference cores were collected from the North and South Eastern Gotland Basins. The oxygenation of the water column took place over a 96-hour experiment in a dark and 5 °C environment. In 12 and 24 hour intervals, the surface waters were exchanged and, over time, analyzed for pH, electroconductivity (EC), total organic carbon (TOC), soluble metal concentrations, and the top samples (0–10 cm) were analyzed with 3-step (E1: water-soluble, E2: exchangeable, and E3: organic-bound) sequential chemical extraction (SCE). Results show stable pH and decreasing EC in the column waters. The EC indicates that metals are released in the initial phases (12 h) of reoxygenation for both sites. Arsenic, Ba, Co, Mn, Rb, U, K, Sr, and Mo are released into the water column during the 96 hour experiment, and based on the calculations for the entire East Gotland Basin, would mean 8, 50, 0.55, 734, 53, 27, 347,178, 3468, and 156 μg L−1 are released, respectively. Elements Mn, Mo, U, and As are released in higher concentrations during the experiment than previously measured in the Eastern Gotland Basin, which provides vital information for future proposed remediation and natural geochemical processes with their known environmental impacts. The SCE results show that redox-sensitive metals (Mn, U, and Mo) are released in the highest concentrations into the solution. The relationship between the highest released metals (beside redox-sensitive) into solution over the oxygenation and their initial abundant phase is noticed, where the smallest released concentrations belong to K < Rb < Sr in E2, and As<Ba in E3, respectively.

This study explores the reuse of spent coffee-grounds (SCGs) and the use of dissolved humic acid (DHA) to remediate acid sulfate (AS) soil drainage using adsorption and precipitation experiments, with changing pH,weight/volume, and concentrations (mg/L of dissolved organic carbon). In addition, this study aims to extend the usability of the SCGs, after being reacted with AS soil drainage, by identifying the potential recovery of incinerated SCGs from the ash of the SCGs produced incineration. As compared to DHA, the SCGs had greater efficiency in removing metals, such as Al (98%), Ca (96%), Co (94%), Fe (88%), Mn (100%), Ni (93%), and Zn (96%). However, the removal of Fe was significantly reduced when higher weight/volume of SCGs were introduced. In addition, SCGs could not bind sulfur, while DHA had removed up to 25% of S from the solution.This suggests the simultaneous use of SCGs and DHA could restrict the formation of problematic Fe(III) secondary compounds (e.g., schwertmannite/akaganeite) which are problematic in some AS soil settings. The results show that Co (69%), Ni (58%), Mn (60%), Fe (59%), Zn (55%), and Al (34%) had the highest recovery percentage by sequential chemical extraction, respectively. The recovery of metals, as well as the removal of dissolved metals from the drainage water, illustrates the effectiveness of the proposed approach for SCGs reuse.