The Role of Microorganisms in the Formation, Dissolution, and Transformation of Secondary Minerals in Mine Rock and Drainage: A Review

Mine waste rock and drainage pose lasting environmental, social, and economic threats to the mining industry, regulatory agencies, and society as a whole. Mine drainage can be alkaline, neutral, moderately, or extremely acidic and contains significant levels of sulfate, dissolved iron, and, frequently, a variety of heavy metals and metalloids, such as cadmium, lead, arsenic, and selenium. In acid neutralization by carbonate and silicate minerals, a range of secondary minerals can form and possibly scavenge these potentially harmful elements. Apart from the extensively studied microbial-facilitated sulfide oxidation, the diverse microbial communities present in mine rock and drainage may also participate in the formation, dissolution, and transformation of secondary minerals, influencing the mobilization of these metals and metalloids. This article reviews major microbial-mediated geochemical processes occurring in mine rock piles that affect drainage chemistry, with a focus on the role of microorganisms in the formation, dissolution, and transformation of secondary minerals. Understanding this is crucial for developing biologically-based measures to deal with contaminant release at the source, i.e., source control.

Assessment of the Railroad Transport Impact on Physical and Chemical Soil Properties: The Case Study from Zduńska Wola Karsznice Railway Junction, Central Poland

Contamination of the soil and water environment with harmful substances can be associated with many activities carried out on the railway. The problem is particularly relevant to liquid fuel loading and refueling facilities as well as to increased traffic at railway junctions. Studies were conducted in the area of railway junction Zduńska Wola Karsznice in central Poland (Łódź Voivodeship). Soil samples were collected from specific research points: from the inter-railway (A), 5 m from the main track (B), from the embankment—10 m from the main track (C), and from the side track (D), at the depth of 0–5 (1) cm and 20 cm (2). The following analyses were made: granulometric composition, pH in H2O, and percent content of carbonates (CaCO3). PHEs were determined in the fractions: 0.25 ≤ 0.5 mm, 0.1 ≤ 0.25 mm, and 0.05 ≤ 0.1 mm: Pb, Cd, Cr, Co, Cu, Ni, Zn, Sr by inductively coupled plasma mass spectrometry technique (ICP-MS/TOF OPTIMass 9500). The objectives of the study were (1) to assess PHEs (potentially harmful elements) contamination of the topsoil level of railway area, (2) to determine the correlation between the concentration of PHEs and the size of the fraction, and (3) to identify the areas (places) where the highest concentrations of PHEs were recorded. Based on the studied parameters, significant differentiation in soil properties of the areas in Zduńska Wola Karsznice was found. The analyses carried out showed that the accumulation of potentially harmful elements was as follows: Cu > Zn > Sr > Pb > Ni > Cr > Co > Cd. The average concentrations of Cu, Zn, Sr, Pb, Ni, Cr, Co and Cd were 216.0; 152.1; 97.8; 64.6; 15.2; 14.4; 3.1 and 0.2 mg·kg−1 d.w., respectively. These contaminations occur in the topsoil layer of the railway embankment, which suggests a railway transport origin. The highest concentrations of PHEs were recorded in samples collected from close to the rails (inter-railway, side track), and in the embankment (10 m from the track) in the very fine sand fraction (0.05 ≤ 0.1 mm). The high accumulation index of copper, cadmium and lead in the surface layer of soil indicate their anthropogenic origin. The results presented in the paper can be used in local planning and spatial development of this area, taking into account all future decisions about ensuring environmental protection, including groundwater and soils.

Global evaluation of potentially harmful elements (PHEs) in potato and carrot irrigated by wastewater: A systematic review, meta-analysis, and health risk assessment

Background: We aimed to conduct a meta-analysis on the concentration of potentially harmful elements (PHEs) in carrots and potatoes irrigated by wastewater and estimate non-carcinogenic health risks among adult and children consumers. Methods: The health risk of PHEs concentration, including Pb, Cd, total Cr, Ni, Zn, Cu, and Fe, in the edible parts of carrot and potato irrigated by wastewater was investigated by a meta-analysis using a random-effects model (REM). Accordingly, the related articles were screened from international databases such as Scopus, Medline, and Embase. Results: The meta-analysis of 32 papers (38 studies) revealed that the rank order of the most accumulated PHEs in potato was Fe (86.54 mg/kg wet weight) > Zn (30.9 mg/kg wet weight) > Cu (13.7 mg/kg wet weight) > Ni (8.42 mg/kg wet weight) > Pb (5.56 mg/kg wet weight) > Cr (3.45 mg/kg wet weight) > Cd (0.58 mg/kg wet weight). This ranking for carrot was Fe (43.36 mg/kg wet weight) > Zn (36.29 mg/kg wet weight) > Ni (13.49 mg/kg wet weight) > Cu (9.79 mg/kg wet weight) > Pb (1.84 mg/kg wet weight) > Cr (1.05 mg/kg wet weight) > Cd (0.28 mg/kg wet weight). Total hazard quotient (THQ) of PHEs was higher than 1 for potato and carrot; its rank order for potato and carrot was Cu > Pb > Cd > Ni > Fe > Zn > Cr and Cd > Pb > Cu > Ni > Fe > Zn > Cr, respectively. The Cd, Pb, and Cu had also a considerable role for consumer health risk. Conclusion: According to the results, continuous monitor and control of wastewater treatment plants are necessary.

Determination of Potentially Harmful Element (PHE) Distribution in Water Bodies in Krugersdorp, a Mining City in the West Rand, Gauteng Province, South Africa

The town of Krugersdorp in South Africa is the locus of an important wildlife game reserve, the Krugersdorp Game Reserve (KGR), which is juxtaposed by the (<1000 m) down-gradient of the large-scale gold mining outfits of Mintails Mogale Gold (MMG) and Rand Uranium (RU). The aim of the study was to determine the concentration levels of potentially harmful elements (PHEs) that have accumulated due to post-mining activities in the local water bodies in Krugersdorp and to use these data as a prerequisite and basis for formulation of the most appropriate remediation measures. Thirty water samples were collected and analysed in situ for: water temperature, pH, dissolved oxygen (mgl−1), dissolved oxygen (%), total dissolved solids (TDS), oxidation/reduction potential (ORP), and electrical conductivity (EC). This was later followed by laboratory analyses of aliquots of the water samples by ICP-MS for twelve PHEs whose concentration ranges were: As (0.70–32.20), Ag (0.16–105.00), Al (1.00–41.00), Co (0.07–6.16), Cr (1.60–5.00), Cu (0.80–8.00), Fe (23.00–117.00), Mn (0.14–12 255.00), Ni (0.20–7.00), Pb (0.80–6.30), V (1.90–55.20), and Zn (2.20–783.00). Areas of the town where excessive concentration levels of these elements have negatively impacted the health of its wildlife population and surrounding ecosystems are identified, and credible mitigation measures proffered.

Potential for Biomass Production and Remediation by Cultivation of the Marine Model Diatom Phaeodactylum tricornutum in Oil Field Produced Wastewater Media

While oilfield produced water (PW) is one of the largest, unclaimed wastewater streams of the oil industry, it could potentially be used as a cultivation medium for microalgae. Microalgae could help with the remediation of this water while also delivering biomass that can be transformed into valuable byproducts such as biofuels. The coupling of these two purposes is expected to cut production costs of biofuels while aiding environmental protection. In this study, we compared the cultivation capacity of the marine model diatom Phaeodactylum tricornutum in media at varying salinities and in media composed of PW from two oilfields in the Central Valley of California that differed drastically in the concentration of inorganic and organic constituents. Specifically, we measured the carrying capacity of these media, the maximum growth rates of P. tricornutum, its cellular lipid accumulation capacity, and its capacity to remediate the most polluted PW source. Our study shows that P. tricornutum can successfully adjust to the tested cultivation media through processes of short-term acclimation and long-term adaptation. Furthermore, the cultivation of P. tricornutum in the most heavily polluted PW source led to significant increases in cell yield and improved photosynthetic capacity during the stationary phase, which could be attributed chiefly to the higher levels of nitrate present in this PW source. Chemical water analyses also demonstrated the capability of P. tricornutum to remediate major nutrient content and potentially harmful elements like fluorine and copper. Because P. tricornutum is amenable to advanced genetic engineering, which could be taken advantage of to improve its cultivation resilience and productivity in an economic setting, we propose this study as a step towards essential follow-up studies that will identify the genetic regulation behind its growth in oilfield PW media and its remediation of the PW constituents.