Background and Aims: Bioremediation of soils contaminated with metal(loid)s is an attractive research area due to its sustainability and economic benefits. In the Slovak Republic, there are several abandoned mines containing high concentrations of arsenic (As) and antimony (Sb). This calls for new options for removing these hazardous metalloids from contaminated substrates. Studies on bioleaching of soils co-contaminated with both metalloids are very rare. This study aimed to test the effectiveness of bioleaching of soils heavily co-contaminated with As and Sb (up to 1463 mg.kg^–1 and 5825 mg.kg^–1, respectively) at a former stibnite mining site (Poproč, eastern Slovakia) through biostimulation and bioaugmentation. Methods: Bioleaching of As and Sb from four soils was induced by biostimulation of autochthonous microflora with Sabouraud medium (SAB) and SAB+glucose, and bioaugmentation of the soil with bacterial strains Cupriavidus oxalaticus and Cupriavidus metallidurans. Soil samples were subjected to determination of physico-chemical properties, microbiological parameters, and additional mineralogical analysis. Results: An inverse relationship between the total metalloid concentration and the microbial diversity was confirmed. In experiments with Cupriavidus metallidurans and Cupriavidus oxalaticus, mean bioleached As fractions were 37.6% and 41.3%, while Sb bioleaching was significantly lower, ranging between 17.0–26.2%. The mean bioleached fraction of As and Sb using SAB was 40.7% and 14.4%, respectively. The addition of glucose to SAB increased As bioleaching (50.7%) but not that of Sb. Conclusion: Collectively, the results highlighted a role of microorganisms in the mobility of metalloids in soils with their prospective applications in remediation of contaminated sites.

It is known that nanoiron has a high reducing activity, due to which it can effectively dechlorinate organic pollutants and reduce toxic metals. Presently, nanoparticles are being synthesized by physical and chemical methods that use toxic substances and require high energy supply. The increasing global demand for sustainable and green technologies drives the development of biological methods that might overcome those limitations. In the case of nanoparticles, phytogenic synthesis using plants or plant tissues can be carried out. The key role is played by bioactive substances present in plants and their interaction with iron precursors (ferric/ferrous salt). The present article provides a current insight into the process of the "green" synthesis of nanoparticles, with the focus on the key parameters that should be taken into account during both the synthesis and environmental application.

Removing polychlorinated biphenyls (PCBs) from the environment is an important process for the protection of biota. This work examines three different approaches to the degradation of such contaminants. The first involves the use of iron bionanoparticles (Fe-BNPs) prepared through green synthesis from selected plant matrices. The second approach entails the use of the bacteria Stenotrophomonas maltophilia (SM) and Ochrobactrum anthropi (OA) isolated from a PCB-contaminated area, Strážsky canal, located in the Slovak republic, which receives efflux of canal from Chemko Strážske plant, a former producer of PCB mixtures. The third approach combines these two methods, employing a sequential hybrid two-step application of Fe-BNPs from the plant matrix followed by the application of bacterial strains. Fe-BNPs are intended to be an eco-friendly alternative to synthetic nanoscale zero-valent iron (nZVI), which is commonly used in many environmental applications. This work also addresses the optimization parameters for using nZVI in PCB degradation, including the pH of the reaction, oxygen requirements, and dosage of nZVI. Pure standards of polyphenols (gallic acid, GA) and flavonoids (quercetin, Q) were tested to produce Fe-BNPs using green synthesis at different concentrations (0.1, 0.3, 0.5, 0.8, and 1 g.L⁻¹) and were subsequently applied to the PCB degradation experiments. This step monitored the minimum content of bioactive substances needed for the synthesis of Fe-BNPs and their degradation effects. Experimental analysis indicated that among the selected approaches, sequential nanobiodegradation appears to be the most effective for PCB degradation, specifically the combination of Fe-BNPs from sage and bacteria SM (75% degradation of PCBs) and Fe-BNPs from GA (0.3 g.L⁻¹) with bacteria OA (92% degradation of PCBs).

Over past decades, the rapid increase of industrial activities has caused vast environmental pollution by different types of contaminants. Groundwater sources belong to the most vulnerable parts of the environment. Zones, especially aquifers with low hydraulic-conductivity (mainly clayey, silty soils with gravels) represent a considerable challenge for scientists to remediate due to their low transmissivity values. Conventional remediation methods (i.e. pump and treat) are ineffective in such conditions; therefore, new and effective methods are required. Electroremediation appears to be a suitable technique in aquifers with low-hydraulic conductivity. Although, this method has been known for decades, there is still a lack of field applications. This article summarizes the current stage of knowledge in electrokinetic remediation of contaminants (e.g. hydrocarbons, metals) in low-hydraulic conductivity aquifers and presents information from certain available field application studies. The aim was to focus on optimizing and enhancing approaches in the electroremediation method and summarily bring useful information to future researchers in their practical utilization. Furthermore, a small-scale laboratory experiment was conducted to prove the efficiency of electroremediation of chlorinated hydrocarbons in groundwater from the model locality (environmental burden), intended for large-scale pilot decontamination by this approach.