Mining activities and the processing of ores have left a legacy of environmental contamination. Radionuclides can migrate into surrounding aquifers and soils, thus represent a human health risk. Conventional technologies based on physicochemical treatments are traditionally used to remediate contaminated mine water. However, these approaches are cost-intensive and ineffective for instance for low uranium concentrations. Findings from the present study suggest a promising method to support or outperform the physico-chemical treatments. By harnessing the magnetic properties of magnetotactic bacteria, it appears possible to bio-remediate uranium-contaminated mine water, even at low-uranium concentrations.

Magnetospirillum magneticum AMB-1 cells were treated in laboratory experiments with 24 mg/L uranium in tap water at different pH (3.5–7.5) under aerobic conditions. In a unique combination of analytical methods and transmission electron and fluorescence microscopy as well as various spectroscopic techniques, the ability of these bacteria of adsorbing uranium was tested. Significant hints were gained on possible binding sites in the bacteria cell`s wall.

The removal efficiency of dissolved uranium(VI) by Magnetospirillum magneticum AMB-1 cells from contaminated water appears to be very effective, independent of the pH. High amounts (86–96%) of uranium were removed from the suspension already in the first hours of exposure and bound in the bacteria`s cell wall showing a stable immobilization of uranium. Parallel factor analysis of time-resolved laser-induced fluorescence spectra reveals that peptidoglycan, a key ligand in the cell wall, plays a crucial role in uranium adsorption. This discovery regarding magnetotactic bacteria is both novel and unexpected for Gram-negative bacteria. M. magneticum AMB-1 cells also show a high level of tolerance towards uranium. In an aqueous environment containing 24 mg/L uranium(VI), most of the bacteria were still alive after one day's exposure.

An outstanding feature however, is the formation of nanoscopic magnetic crystals within the cell of magnetotactic bacteria, which were proved by transmission electron microscopy. These magnetic properties could be harnessed for straightforward magnetic separation of uranium-loaded bacteria from contaminated water. Thus, a simple technical water purification process could be realized, not only for uranium(VI), but probably also for other metals with the objective of potential industrial applications in the field of microbiological purification of water.

Nickel extraction through open-pit mining presents crucial environmental challenges, especially in regions with high annual precipitation, such as Indonesia, a tropical nation which has the world's largest nickel reserves. The entry of mine water into rivers severely effect aquatic ecosystems, as these water bodies serve as critical pathways for the transport and biochemical transformation of pollutants. Given the essential role that rivers play in maintaining ecological balance and supporting communities, it is crucial to find effective, sustainable solutions to manage and mitigate mining-related water contamination. This study explores the potential of aquatic plants to naturally remediate metal-contaminated water, offering an eco-friendly approach to managing mine runoff.

This study introduces a novel application of the Bioaccumulation Factor (BAF) and Translocation Factor (TF) to evaluate the phytoremediation potential of aquatic plants in nickel-contaminated rivers. By identifying and analyzing the metal uptake and translocation capabilities of local plant species, specifically the grass family Poaceae (Echinochloa sp.) in the Akelamo River of Obi Island, the research sheds light on the natural resilience of these plants in mitigating metal pollution. This dual assessment provides insight into the plant's ability to accumulate and translocate metals such as Fe, Mn, Cr, Ni, Zn, and Cu, contributing to the advancement of phytoremediation strategies.

The results indicate that Echinochloa sp. shows high potential as a hyperaccumulator of metals, particularly for Fe, Mn, and Ni, with bioaccumulation levels (%BAF) peaking at 541.03 for Fe. The translocation sequence from roots to stems (%TF) for metals was determined to be Ni > Zn > Cu > Fe > Cr > Mn. These findings highlight the plant's ability to concentrate and move metals within its structures, making it a promising candidate for removing metals from contaminated environments and reducing environmental risks associated with nickel mining.

The hyperaccumulation and translocation properties of Echinochloa sp. have essential implications for post-mining land restoration and erosion control. Their natural abundance and effectiveness in absorbing and redistributing metals make them suitable for phytoremediation applications, particularly in nickel mining regions. The study's outcomes pave the way for implementing sustainable environmental management practices in tropical mining regions, contributing to ecosystem restoration and improving water quality in nickel-contaminated rivers.

The uranium (U) contamination from mining activities in East Germany is a major concern. This study introduces an ecological and scalable approach that offers an effective microbiological technology to complement conventional remediation techniques, which are often more costly and less sustainable. This innovative microbiological solution is a promising response to environmental challenges associated with low-level U contamination.

A comprehensive investigation was conducted in the laboratory using microcosms filled with water samples from former U mines and supplemented with glycerol as an electron donor to stimulate the growth of bacteria involved in U(VI) reduction. A multidisciplinary approach was employed, integrating analytical, spectroscopic, and microscopic techniques. For the first time, High Energy-Resolution Fluorescence Detection Spectroscopy (HERFD) was used to obtain quantitative information about the oxidation state of U in mine water samples amended with an electron donor. Information about the structure of U species was given by Extended X-Ray Absorption Fine Structure (EXAFS) analyses. Advanced microscopic techniques, such as High-Resolution Transmission Electron Microscopy (HRTEM), localized U species in the samples. The findings demonstrated the reduction of U(VI) to U(V) and U(IV) within the anoxic microcosms supplemented with 10 mM glycerol.

During the experiment, the monitoring of the physicochemical parameters of the water samples showed a decrease in the redox potential, accompanied by a remarkable decrease of the U, Fe, and SO₄^2- concentrations by 98%, 96%, and 68%, respectively. A black precipitate formed at the bottom of the microcosms was collected and studied by spectroscopy and microscopy. EXAFS spectra revealed the reduction of soluble U(VI) to insoluble U(IV) dioxide (uraninite) and U(VI)/U(V)-carbonates. HERFD analysis combined with Iterative Transformation Factor Analysis estimated the oxidation states in the black precipitates, revealing U(IV) as dominant oxidation state. A notable finding was the identification of U(V) in the samples with a proportion ranging from 21% to 32% and a long-term U(V) phase even under oxic conditions. By HRTEM we were able to localize U(IV) and U(V) as nanoparticles in the membrane of the bacteria.

This research gives rise to further investigations for the development of an applicable process approach for a cost-effective solution for remediating water contaminated with low U concentrations and co-contaminants such as Fe, and SO₄^2- and even As, through biostimulation of native microbial communities using glycerol. Additionally, biogenic U(V), as a reduction product, provides a noteworthy advantage over uraninite due to its greater stability and resistance to reoxidation.

The closure of pit lakes as aquatic ecosystems is a viable, sustainable and economically responsible option for post-mining land use. Riparian vegetation and littoral areas are critical ecosystem components that cannot be established before the lake is full. Pits may take decades to centuries to fill, creating a long period where the aquatic ecosystem is unlikely to meet regulator and public expectations. We aimed to investigate the potential for artificial floating islands (AFIs) to provide a source of plant propagules that could seed the lakes edges during and post filling, allowing riparian plants to become established without a need for direct planting or seeding in saline coal pit lakes.

AFIs replicate naturally occurring islands of floating vegetation, using a constructed floating base where emergent plants can grow through the island, and their roots sit in and interact with the water column. AFIs have been used to treat stormwater quality issues in lakes and provide habitat for waterbirds. In a one-year pilot study, a set of six (3 ‘vegetated’ and 3 ‘unvegetated’) small AFIs (3 m²) were installed at two saline (3 and 12 mS cm^-1) pit lakes in Queensland (Australia). Vegetated islands were planted with four local species (<1 m tall) in approximately equal proportions. Plant survival rates, growth and biomass were measured twice and sedimentation rates in the lake and under the AFIs were measured once.

Only two of the four plant species grew successfully on the islands which spread across the island via propagules. A range of terrestrial insects were noted within the plants. Evidence was found of extensive bird usage of both vegetated and unvegetated islands, yet no bird species were observed nesting on them. Multiple aquatic organisms (particularly macroinvertebrates and fish) were noted within the plant roots. The AFIs had no significant impact on the total sedimentation in the lakes with no significant difference between vegetated or unvegetated islands.

Key findings of the experiment were: 1) emergent plants can grow successfully on AFIs in pit lake 2) plants have the potential to increase aquatic and terrestrial biodiversity; 3) plants at least after less than 1 year do not alter natural sedimentation within the lake; 4) islands are used by birds. Based on these results we have commenced a full-scale trial of large (100 m²) AFIs as more intensive sources of biodiversity and propagules for pit lakes.

This work explores the role of diatoms in assessing hydrological connectivity between groundwater and surface water in wetlands affected by coal mining activities. The study aimed to establish whether phytoplankton assemblages, specifically diatoms, can improve our understanding of the interactions between terrestrial and aquatic environments in mining areas. Benthic diatoms were postulated to constitute appropriate bioindicators of groundwater-surface water connectivity, as their responsiveness to changes in water chemistry, flow, and important nutrient dynamics provides valuable insights into hydrological conditions, making them key to monitoring ecosystem health in groundwater-dependent environments.

By using field and laboratory assessments of hydrochemistry, isotopic analysis, and benthic diatom assemblages, the influence of coal mining activities on wetland ecosystems and the hydrological connectivity between wetlands and groundwater was investigated. Samples of water and diatoms were collected from wetland surface water, wetland piezometers, local boreholes and benthic vegetation, respectively. Hydrochemistry results were analyzed using standard graphical groundwater quality plots (Piper, Durov, Stiff and biplot diagrams). Cannonical correspondence analysis and cluster analysis were used to identify relationships between chemical parameters and diatom species. This multidisciplinary approach allows for result verification and generating robust findings on interactions between biotic and abiotic parameters in complex wetland ecosystems.

The study findings indicated that wetlands closer to mining operations had more acidic water (low pH), higher electrical conductivity (EC), total dissolved solids (TDS), and isotopic signatures resembling nearby boreholes. Additionally, these areas were dominated by diatom species characteristic of industrial and mining-related pollution, suggesting that the wetlands were largely supported by mine-affected groundwater. In contrast, wetlands further from mining zones were characterized by cosmopolitan diatom species associated with nutrient pollution, implying a different water source or lesser influence from mining-derived groundwater. In these wetlands, isotopic signatures were characteristic of atmospherically derived recharge.

These findings highlight the value of diatom assemblages as reliable bio-indicators of hydrological connectivity in coal mining affected landscapes. Diatoms, when combined with hydrochemistry and isotope data, provide a clearer picture of groundwater-surface water interactions. This approach is crucial for managing and conserving wetlands in coal mining regions, where understanding the influence of groundwater on surface water systems is essential for ecosystem health.