Release Of Trace Elements Research Articles

Chemical analysis and performance evaluation of ClearCorrect® aligners as received and after intraoral use: Implications for durability, aesthetics, and patient safety

BackgroundOrthodontic treatment with transparent aligners is popular with patients. Any alteration of the plastic material, as subjected to the oral environment, could influence the treatment's durability, the aligner's aesthetic appearance, and the patient's safety. PurposeThis study concerns the physicochemical properties of ClearCorrect® aligners before and after intraoral use, focusing on transparency, surface topography, leachable, polymer glass transition temperature, and viscoelastic properties. MethodsAligners were collected after two weeks of intraoral use. Unused samples were obtained from the manufacturers. Transparency was measured by UV–visible spectroscopy. Chemical modifications were studied using infrared and Raman spectroscopies. Thermal degradation, glass transition (Tg), and storage modulus (E') were characterized by thermal analysis (DSC, TGA, DMA). Surface morphology and roughness were studied thanks to SEM and AFM. Aligners were immersed in water-based solutions to identify and quantify organic leachable by HPLC chromatography and trace elements by atomic absorption spectroscopy. ResultsClearCorrect® aligners have a three-layer structure (outer PETG/inner PU layers). Slight chemical alterations occurred after aging. There was also no significant evolution in Tg and thermal degradation temperatures and only a minimal evolution of E'. Surface and transparency alterations occurred. A difference in organic compound and trace element release levels between new and used aligners was evidenced, suggesting an intraoral release during use. SignificanceIntra-oral aging mainly impacts the aligner transparency and surface. The leachable study suggests significant ingestion of organic and non-organic compounds by the patient: investigations are needed to assess the impact of the long-term use of trays on patient health.

Impact of sediment mobilization on trace elements release in Galician Rías (NW Iberian Peninsula): insights into aquaculture

In the latest years, the concentration levels of certain metals and metalloids in the sediments of the Galician Rías have shown an increasing trend (e.g., As, Zn, Cu, Pb, Hg). These areas are also characterized by their richness in nutrients and their great aquaculture or mariculture activity, with the presence of more than 3500 mussel rafts in the Rías Baixas. The inner areas of the Galician Rías are subjected to activities that resuspend the sediment such as high levels of maritime traffic and dredging or cleaning operations. It is likely that a transfer of these elements to the water column happens during the resuspension of sediments caused by natural events or anthropogenic activities. In this study, selected samples of surface sediments of the Ría de Pontevedra (NW Spain) were subjected to a procedure of aerobic oxidation to determine the concentration of some elements (Fe, Mn, Cu, Cr, Pb, Hg, and Zn) released from the sediment to the aqueous phase. The experiment was carried out within 5 days. Measurements of pH and total concentration were taken both in water and sediment samples. Furthermore, speciation of trace elements was carried out in the sediment samples. Trace element concentrations were lower in the sediments during aerobic oxidation, being released to the aqueous phase. From an environmental point of view, Cu was the only trace element released in quantities that may be toxic for the organisms in the area. This problem of sediment oxidation related to dredging activities or natural storm conditions should be considered in environmental impact studies and transferred to stakeholders.

Organic carbon, major and trace element release from and adsorption onto particulate suspended matter of the Ob River, western Siberia

Particulate suspended matter (PSM) of rivers is a significant factor for carbon, nutrient, and trace metal transfer from land to ocean. Towards better understanding the role that PSM exerts on major and trace elements in riverine systems, here we report the results of an experimental study which utilizes a two-fold approach to assess interaction between PSM and riverine solutes. First, we measured element leaching (via desorption and dissolution in distilled water, simulating snow melt) from PSM of the largest Siberian river, the Ob River. Second, we quantified the capacity of PSM to adsorb dissolved organic carbon (DOC), macro- and micronutrients and trace elements from organic-rich waters of the river floodplain. We documented sizable desorption of organic carbon, some major and trace metals, oxyanions and insoluble elements from PSM; the majority (>50 %) of elements were released over the first hour of reaction. In contrast, PSM of the Ob River was capable of removing 20 to 90 % of dissolved OC, nutrients (Si, P), and trace elements from the tributary and floodplain fen. Our experiments demonstrated preferential adsorption of aromatic compounds large molecular size colloids. Taken together, the adsorption of solutes by PSM can sizably decrease the concentration and modify the molecular size distribution, and therefore the potential bioavailability of major (DOC, P, Si) and trace micronutrients. Overall, the PSM of the Ob River exhibited high reactivity with respect to natural waters and was capable of modifying the elemental composition of the tributary and floodplain fen waters. This transfer of organic carbon and nutrients in the surface-adsorbed (particulate) form is especially important during spring flood and requires specific consideration in short-term biogeochemical cycles of elements in continental waters.

Cd(II) and Zn(II) adsorption on lignite‐derived humic substances and cattle manure biochar

AbstractExcessive industrial release of trace elements may pose a great risk to the environment. Conventional remediation treatments have considerable limitations, making less expensive new technologies an important research area. Batch experiments were conducted at room temperature to investigate the use of two lignite‐derived humic products (nano‐humus and humic powder) and a cattle manure biochar as adsorbents in the removal of cadmium and zinc from laboratory synthesized water. Nano‐humus was most effective in adsorbing Cd(II), wherein 89% adsorption was rapidly achieved in 15 min. The adsorbed amount of Cd(II) and Zn(II) both increased with initial metal ion concentrations from 25 to 125 mg L−1. Despite being produced from the same sources, nano‐humus and humic powder showed different properties and adsorption behaviors. The adsorption mechanism of nano‐humus followed the Freundlich isotherm model and pseudo‐second‐order kinetic model, indicating multilayer chemisorption. Humic powder followed the pseudo‐second‐order kinetic model, although it had a low isotherm model fit, implying chemisorption‐dominated adsorption. Cattle manure biochar followed the Freundlich isotherm and pseudo‐first‐order kinetics model, suggesting diffusion‐dominated multilayer adsorption. Of the three adsorbents tested, nano‐humus had greatest potential as an effective and inexpensive material for metal remediation.

Mesozoic orogenic gold metallogenesis at the Bangong–Nujiang suture belt, central Tibet: Constraints from pyrite textures, composition and sulfur isotope of the Shangxu gold deposit

Pyrite is a good carrier to provide gold within a hydrothermal mineralization system. Under prograde metamorphism, recrystallization of sedimentary and diagenetic pyrite and transformation of pyrite into pyrrhotite in a metamorphic terrane lead to the release of trace elements from the pyrite carrier into an upward migrating liquid phase carrier. In this case study, we report the in situ trace element and δ34S compositions of the pyrite from four different stages, which chronologically comprise sedimentary Py1, diagenetic Py2, metamorphic Py3a, Py3b and hydrothermal Py4a, Py4b, Py5, and the dominant sulfides from the hydrothermal stage at Shangxu, an Early Cretaceous turbidite-hosted orogenic gold deposit in the middle Bangong–Nujiang suture belt (BNSB) in central Tibet, in order to decipher the ore-forming material source and the metallogenesis of the Mesozoic orogenic gold mineralization in the BNSB. Concentrations of trace elements, i.e., Au, Co, Cu, Zn, Mo, Ag, Sb, Te, Hg, Tl, Pb and Bi, that are easy to dissolve during pyrite recrystallization, show a general progressive decline from Py1 to Py4b (excepting in Py3b and Py4a, which have a sudden rise in trace element composition) and a plunge in Py5, indicating that Py1 and Py2 supply the parent source minerals for mineralization, and that the main ore-forming stage are contemporary with the deposition of Py3b and Py4a, ending up with the precipitation of Py5. The δ34S values of pyrite narrow from −46.7 ‰–19.3 ‰ (Py1, Py2), through −7.6 ‰–0.2 ‰ (Py3a, Py3b), to − 3.6 ‰–5.7 ‰ (Py4a, Py4b) and −7.7 ‰–5.6 ‰ (Cp, Gn), indicating that a probable coeval seawater sulfate sulfur source for Py1 and Py2 (by bacterial sulfate reduction), and an inherited sulfur source from Py1 and Py2 for Py3 and Py4. We highlight that contributions from the magmatic materials to the hydrothermal gold mineralization are limited at Shangxu, and the widely distributed Lower–Middle Jurassic pyrite-rich turbidite of the Mugagangri Group is a highly potential primary source rock for the regional gold mineralization.

Application of pyrite trace-metal and S and Ni isotope signatures to distinguish sulfate- versus iron-driven anaerobic oxidation of methane

The formation of authigenic pyrite in marine sediments involves multiple reactions between ferrous iron (Fe2+) and hydrogen sulfide (H2S). Ferrous iron is commonly provided through the reductive dissolution of Fe-(oxyhydr)oxides by organic matter (i.e., dissimilatory Fe reduction), dissolved sulfide (i.e., abiotic Fe reduction) or methane (i.e., Fe-AOM), whereas sulfide is supplied by organoclastic sulfate reduction (OSR) or sulfate-driven anaerobic oxidation of methane (SD-AOM). Since Rayleigh-type distillation operates widely in sediments of gas-hydrate-bearing zones, sulfur and nickel isotope compositions (i.e., δ34S and δ60Ni) cannot readily distinguish OSR- from SD-AOM-associated pyrite. However, these microbial pathways may yield different patterns of trace-element enrichment in pyrite. To better understand the linkage of trace-element patterns to specific microbial pathways (i.e., Fe reduction, Fe-AOM, OSR and SD-AOM), and to evaluate the use of S and Ni isotopic signatures as tracers for pyrite formation pathways in methane-rich sediments, we report pyrite-associated trace element and δ34S and δ60Ni isotope analyses of sediments from a gas hydrate borehole (Site GMGS4-SC-03) from the Shenhu area, Pearl River Mouth Basin, South China Sea. Pyrite formed in conjunction with Fe- and/or SD-AOM exhibits abundant framboidal overgrowths and extremely high δ34S (up to +142.8‰) and δ60Ni (up to +2.72‰), representing the highest stable S and Ni isotopic compositions of pyrite reported to date. These pyrite morphologies are enriched in Co and Ni, which may be a diagnostic signature of an SD-AOM pathway. By contrast, OSR-associated pyrite is enriched in Cu and Zn due to OSR-induced release of trace elements from decaying organic matter. In addition, the relationship of As to Cu and/or Zn can distinguish microbial Fe/Mn reduction from Fe/Mn-AOM, because microbial Fe/Mn reduction releases trace elements from both Fe/Mn-(oxyhydr)oxides (i.e., As) and organic matter (i.e., Cu and Zn), whereas Fe/Mn-AOM only releases trace elements from Fe/Mn-(oxyhydr)oxides. Furthermore, an observed covariation between As and either Co or Ni in most pyrite with high δ34S, indicates that this pyrite captured both As released during Fe/Mn-AOM and Co and Ni from SD-AOM. Thus, the high nickel isotope values measured in this study likely dominantly reflect release of isotopically heavy Ni from Fe- and Mn-(oxyhydr)oxides. Our results demonstrate that the trace-element composition of pyrite in gas-hydrate-bearing sediments can record the geochemical signature of the dominant microbial processes.

Road salt applications mobilize trace elements from roadside soil to shallow groundwater

In regions where deicers are applied to roadways, micronutrients and toxic trace elements may be mobilized from soil material into soil porewater. These elements may subsequently migrate with soil porewater to surface waters and groundwaters, potentially leaching the soil of micronutrients or introducing toxins to water resources. Our study thus aims to quantify the timing and extent of trace element releases from soil material to soil porewater and groundwater in response to deicing events. We sampled soil porewater near a road at a rural site for trace elements and compared the results to salt applications and soil porewater Na and Cl levels. We also assessed trace element, Na, and Cl concentrations in a karst spring at the rural site and a karst spring at an urban site to evaluate the role of land use in conveying these contaminants to groundwater. We found that certain trace elements (e.g., As, Ba, Fe, Sr) peaked concomitantly with Na and Cl in soil porewater at the rural site after road deicing events, suggesting their release due to excess salt inputs to the soil. We did not observe increases in trace element concentrations at the rural karst spring following individual road salt applications, likely due to low deicer inputs and trace element levels across its recharge basin. However, at the urban site, we observed that other assemblages of trace elements (e.g., As, Cu, Li) in the karst spring peaked with deicing-related Na and Cl pulses. We also found positive and significant correlations between salt applications to the recharge basin and exports of some trace elements (e.g., As, Cu, Li, Se) at the urban karst spring, indicating deicing events triggered trace element releases to groundwater. Overall, we detected road salt-driven trace element release from soil material to soil porewater and groundwater that was exacerbated by urbanization.

An introduction to the Bowland Shale Formation, UK: processes and resources

Abstract This volume showcases recent geological, geophysical and geochemical research on the Carboniferous Bowland Shale Formation. The Bowland Shale is a relatively thick and extensive Palaeozoic black shale unit with a long history of debate and controversy in the UK. The Bowland Shale is proven in many of the key Carboniferous basins in the Midlands, northern England and North Wales, and represents a significant, near-continuous temporal record spanning 16 Myr including the important mid-Carboniferous boundary (Mississippian–Pennsylvanian). Since the first geological surveys in the late nineteenth century, the Bowland Shale has been of interest for a variety of reasons, including the search for Irish-type Pb–Zn base metal mineral deposits, and as a source rock in conventional hydrocarbon systems. In the mid-2000s, attention turned to the Bowland Shale as a target for unconventional hydrocarbon extraction, shale gas, following success in the USA. This placed the Bowland Shale at the centre of a series of interconnected controversies and debates from the local to national scale. The geological credibility of the purported shale gas resource in the UK was – and continues to be – highly contentious. This volume contributes to a more updated view of the Bowland Shale, covering topics such as sedimentary, geochemical and physical properties and processes, basin-forming events, hydrocarbon prospectivity, mineralization and heat and fluid flow in the subsurface. The volume also includes a field guide to some of the key localities in the UK. With the benefit of hindsight offered by the latest generation of research, the early regional shale gas assessments failed to attach sufficient weight to the compositional heterogeneity, structural complexity, compartmentalization and highly variable exhumation, erosion and palaeo-heat flow history of the Bowland Shale. The following topics are identified as promising avenues for future research beyond shale gas: (1) the role of the Bowland Shale in the context of mineral systems; (2) the role of the Bowland Shale as a cap rock in the Lower Carboniferous limestone geothermal play and potentially as an analogue of CO 2 or radioactive waste storage in the UK; and (3) pathways and mechanisms for weathering, alteration and trace element release from the Bowland Shale into the surface and/or subsurface environment.

Trajectories of trace element accumulation in seagrass (Posidonia oceanica) over a decade reveal the footprint of fish farming

To evaluate the effect of trace element (TE) release from fish farms on seagrass Posidonia oceanica, we compared TE concentrations (As, Cd, Co, Cu, Mn, Mo, Ni, Pb, V, Zn) in shoots near fish cages (Station ‘Cage’) with those away from them (Station ‘Control’) in two fish farm facilities (Site 1 and Site 2, North Aegean Sea, Greece). We assessed the present (i.e., 2021, year of sampling) and past (reconstructed period 2012–2020) accumulation of TEs using the living compartments (leaf blades, sheaths, rhizomes, roots, epiphytes) and the dead sheaths, respectively. We also assessed possible seagrass degradation by reconstructing past rhizome production. P. oceanica rhizome production at the ‘Cage’ stations was up to 50% lower than at the ‘Control’ stations. Most TE concentrations were higher at ‘Cage’ stations, but the differences often depended on the seagrass living compartment. Significant differentiation between ‘Cage’ and ‘Control’ stations was observed based on the TE concentrations of the dead sheaths during 2012–2020. The contamination level at the ‘Cage’ stations was mostly moderate in Site 1 and low in Site 2, during the reconstructed period, while an increasing contamination trend was found for certain potential phytotoxic TEs (As, Cu, Cd, Mo, V). Our results emphasize the need for the aquaculture industry to work towards a more ecologically aware approach.

Dual elemental doping activated signaling pathway of angiogenesis and defective heterojunction engineering for effective therapy of MRSA-infected wounds

Multi-drug resistant bacterial infections pose a significant threat to human health. Thus, the development of effective bactericidal strategies is a pressing concern. In this study, a ternary heterostructure (Zn–CN/P-GO/BiS) comprised of Zn-doped graphite phase carbon nitride (g-C3N4), phosphorous-doped graphene oxide (GO) and bismuth sulphide (Bi2S3) is constructed for efficiently treating methicillin-resistant Staphylococcus aureus (MRSA)-infected wound. Zn doping-induced defect sites in g-C3N4 results in a reduced band gap (ΔE) and a smaller energy gap (ΔEST) between the singlet state S1 and triplet state T1, which favours two-photon excitation and accelerates electron transfer. Furthermore, the formation of an internal electric field at the ternary heterogeneous interface optimizes the charge transfer pathway, inhibits the recombination of electron-hole pairs, improves the photodynamic effect of g-C3N4, and enhances its catalytic performance. Therefore, the Zn–CN/P-GO/BiS significantly augments the production of reactive oxygen species and heat under 808 nm NIR (0.67 W cm−2) irradiation, leading to the elimination of 99.60% ± 0.07% MRSA within 20 min. Additionally, the release of essential trace elements (Zn and P) promotes wound healing by activating hypoxia-inducible factor-1 (HIF-1) and peroxisome proliferator-activated receptors (PPAR) signaling pathways. This work provides unique insight into the rapid antibacterial applications of trace element doping and two-photon excitation.

Evaluating health risks from the release of trace elements to groundwater by rock-water interaction in a weathered gneissic aquifer.

High concentration of trace elements in groundwater poses more health risks to humans by drinking groundwater and dermal contact. This work aimed to assess the trace element concentrationin groundwater, water quality for drinking purposes, and its effect on human health upon prolonged consumption. The study was carried out in the gneissic terrain of Perambalur District, Tamil Nadu, India, where groundwater is used mainly for drinking, agricultural, and domestic purposes. Hydrochemistry, water quality, and health risk assessments of trace elements from 44 groundwater samples for pre- and post-monsoon were determined by drinking water quality, hazard quotient, hazard index, and carcinogenic risk. The dominance of trace elements in groundwater was in the order of Zn > Fe > Cu > Ni > Te > Pb > Co. Ni and Co are released more during the post-monsoon, and Zn, Fe, Cu, and Pb concentration during the pre-monsoon. The dominant type of groundwater was Ca-HCO3 and mixed Ca-Mg-Cl type. The dissolution of fissile hornblende biotite gneissic rock dissolves more trace elements to groundwater than charnockite rock. The correlation matrix indicates that major ion and trace elements were positively good in groundwater during the pre-monsoon and post-monsoon 2018. The principal component analysis suggests that the weathering of rocks, rainwater recharge, and evaporation processes controlled the hydrochemistry of trace and major ions. The concentration of Pb, Ni, and Cd elements exceeded the permissible limit of BIS and WHO; these elements are unsuitable for drinking. The trace element concentration in groundwater was good for drinking and irrigation in the study area, except in a few wells. The hazard quotient and hazard index were computed, which revealed that non-carcinogenic risk to human health by drinking groundwater was more of a problem for children than adults. This study will help prevent children from health risks of trace elements.

Spatio-temporal variations in dissolved trace elements in peat bog porewaters impacted by dust inputs from open-pit mining activities in the Athabasca Bituminous Sands (ABS) region

Considerable volumes of dust are generated from open-pit bitumen mining operations in northern Alberta, Canada. The reactive mineral phases of these dust particles can potentially dissolve in acidic (pH < 4) bog waters. Their dissolution could release trace elements (TEs), which could eventually alter these bog ecosystems. The impact of dust dissolution on the abundance of TEs in the dissolved (<0.45 μm) fraction of porewaters from excavated pits (30–40 cm deep) in the ombrogenic zone of five peatlands was evaluated. Porewaters were collected from four bogs situated within 70 km of mines and upgraders in the Athabasca Bituminous Sands (ABS) region, Alberta, Canada, and from a reference bog situated 264 km away. Over two consecutive years, the dissolved concentrations of some conservative (Al, Th, Y) and mobile lithophile elements (Fe, Li, Mn, Sr), as well as the metals enriched in bitumen (V, Ni, Mo), all increased with proximity to the mining area, in the ABS region. These trends reflect the observed increase in dust deposition with proximity to the mining area from independent studies of snow, lichens, and Sphagnum moss. Contrarily, the impact of dust dissolution on the concentration of potentially toxic TEs (As, Cd, Pb, Sb, and Tl) was negligible. Thus, the elements which are more abundant in the porewaters near industry are either ecologically benign (e.g. Li and Sr) or essential micronutrients (e.g. Fe, Mn, Ni, and Mo). Manganese was the only element which was enriched by more than 10x at all sites near the mining area, compared to its concentration at the reference site. The enrichments of all other elements were <10x, indicating that anthropogenic dust emissions from mining areas have had only a modest effect on the TEs abundance in peat porewaters.

Microbially-mediated aerobic oxidation of trace element-bearing pyrite in neutral-pH sandstone aquifer sediments

Disseminated pyrite grains in sandstone aquifer sediments are subject to microbially-accelerated reaction with dissolved oxygen, leading to more rapid decline in pH and release of trace elements to solution compared to abiotic reaction pathways.

Impact of a CO2 leak on the release of major and trace elements according to groundwater flow conditions in a shallow freshwater carbonate aquifer: In-situ experiments and modelling

To investigate the role of hydrogeological conditions on the release of major and trace elements during CO2 leakage occurring in shallow freshwater aquifers in a CO2 Capture and Storage context, this paper compares the results of two in-situ CO2 leakage experiments. These experiments were carried out in a shallow freshwater carbonated aquifer located in Saint-Emilion, France, during both low and high-water levels periods. In both experiments, 200 L of carbonated water were injected into a well and groundwater monitoring was carried out downstream.Due to the physical heterogeneity of the aquifer at a small scale, the CO2-rich water plume did not follow the same flow path between the two hydrogeological periods, thus highlighting preferential pathways. It was observed that geochemical changes were not of the same intensity. The concentrations of Ca2+, HCO3−, Mg2+, Fe, Mn, As, Co, Cu, Ba, Sr and V increased during the low-water level experiment while the measured concentrations only reflected the dilution of the gasified water injected during the high-water level period.

Release Characteristics of Harmful Trace Elements during Dynamic Leaching and Static Immersion of Coal Gangue in Xinjiang.

Coal gangue has dual attributes of waste residue and resources. Clarifying the release characteristics of harmful trace elements from the coal gangue can provide a theoretical basis for environmental impact and resource utilization. In this study, the characteristics of harmful trace elements released from coal gangue in Xinjiang during dynamic leaching and static immersion experiments were determined using proximate analysis, X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), and inductively coupled plasma mass spectrometry (ICP-MS). The results show that (1) the higher the content of harmful trace elements in coal gangue and the greater the concentration coefficient (CC), the greater the release of elements in dynamic leaching and static immersion experiments. The mode of occurrence of trace elements in the coal gangue determines their transport and release. Elements are associated not only with moisture but also with minerals, such as clays, sulfides, and carbonates, which are readily soluble in water. (2) The release of harmful trace elements was inversely proportional to time in the dynamic leaching experiments, and the main reason for the reduction in element release during the late leaching period was the adsorption effect of clay minerals. In the dynamic leaching experiment, harmful trace elements in the surrounding environment continued to accumulate, and static immersion experiments in water showed that harmful trace elements gradually reached dynamic equilibrium. The concentration of most elements in the late stage of the static immersion experiment was lower than that in the early stage, indicating that the environmental hazards of dynamic leaching were greater than those of the static immersion of coal gangue in Xinjiang.

РАЗРАБОТКА КИШЕЧНОРАСТВОРИМЫХ МАТРИЧНЫХ ТАБЛЕТОК С ГУМИНОВЫМИ ПРОИЗВОДНЫМИ

Medicines based on compounds of iron, copper and zinc occupy a certain place in the pharmaceutical market. A lack of iron in the body can contribute to the development of iron deficiency anemia, and in the case of copper and zinc, a deficiency in the immune response and inflammation caused by lipid peroxidation, which ultimately leads to various joint diseases such as arthritis. The basis of the treatment and prevention of diseases is the use of chelates of salts of iron, copper and zinc, the effectiveness of which largely depends on their stability and the degree of release of trace elements in various parts of the gastrointestinal tract. Therefore, there is a need to create new long-acting drugs with a certain solubility and sufficient bioavailability. This study is devoted to the development of the optimal composition of iron, copper and zinc humate matrix tablets for oral administration.

Risks of nutrients and metal(loid)s mobilization triggered by groundwater recharge containing reactive organic matter

The potential risk of multiple contaminants mobilization from sediment was evaluated under the infiltration of reactive organic matter (OM) during groundwater recharge. Significant NH4-N, PO43−, As, Fe, and Mn release were observed which show elevated peaks in the initial stage (0–19 d) and declines afterwards until reach quite low and stable content (20–37 d). When re-oxidize with SO42− (38–65 d), the reducing condition is stimulated to release more Fe and Mn however no As, NH4-N and PO43−. The microbial reductive Fe oxides dissolution is the main driving force for NH4-N, PO43−, As, Fe, and Mn release. The NH4-N and PO43− release was attributed by passive mobilization from Fe/Mn oxides due to its dissolution. The cation exchange also works significantly on NH4+ release while desorption works on PO43− as well. Microorganism responses to the infiltration reactive OM and further impacts the mobilization of multiple contaminants. The precipitation of secondary Fe/Mn minerals accompanied by co-precipitation and/or re-absorption lower down their aqueous levels. However, this aqueous contamination risk was hidden in solid reactive secondary minerals when oxidizer like SO42− perturbs the recurrence of Fe and Mn contamination occurs. This shows the perennial release of nutrients and trace elements should be paid attention in areas with reactive OM infiltration followed by redox/groundwater chemistry fluctuations, potentially in hyporheic zone of river/lake, managed aquifer recharge zone, etc.

Limited access to oxygen reduces the release of harmful trace elements from submerged alum shale debris

Construction and mining activities in acid-producing alum shale regions often produce large volumes of crushed rock. Disposal under groundwater level (e.g., a bog) may minimize oxygen access. In this study, the effect of varying oxygen access on the leaching potential of alum shale was investigated by submerging tunnel construction rock debris in synthetic rainwater under atmospheric (AOC) and low oxygen conditions (LOC) for 52 weeks. The sulphate increase and nitrate decrease in the leachates suggested that pyrite (FeS2) in the alum shale was oxidized, but carbonates originating from calcite dissolution provided sufficient buffering capacity (leachate pH ~7.7 over 52 weeks), resulting in neutral rock drainage. Less available oxygen led to significantly lower production of sulphate and acid from pyrite oxidation, reducing the release of harmful elements. Under LOC, the leaching of Mo, Co, Ni, Zn and Cd was 2–4 times lower than under AOC and the lower buffering requirement diminished the release of Ca as well as divalent cations (Mg, Sr, Mn) likely present as impurities in calcite. Contrastingly, limited pyrite oxidation led to less oversaturation with respect to BaSO4 and lower release of Fe in the LOC leachates. Thus, co-precipitation of 226Ra was inhibited and scavenging of leached V, As and Sb by newly formed Fe(OH)3 was not as dominant as in the AOC systems. Leaching of U was ~20 % higher under LOC likely due to enhanced complexation by dissolved carbonate. In general, element leaching rates were slower under low O2 levels. Characterization of water collected at the disposal site after ~1.2 years of discarding tunnel materials showed that the weathering of debris submerged in the open, water-filled pond occurred similarly to leaching under low oxygen conditions. Overall, these results highlight the importance of minimal oxygen access or anaerobic conditions when acid-producing rock waste is stored under water.

Soil Contaminated with Hazardous Waste Materials at Rio Tinto Mine (Spain) Is a Persistent Secondary Source of Acid and Heavy Metals to the Environment

Mineralogical analysis and laboratory-based leaching tests coupled with speciation modeling were undertaken to quantify the potential for short-term acid generation and the release of trace elements from soils heavily contaminated with mine waste at Rio Tinto. Three different waste materials were considered as case studies: roasted pyrite, copper slags, and leached sulfide ores. The results showed elevated values of net acid generation (up to 663 mmol H+/kg), the major pools being potential sulfidic acidity and acidity retained in jarosite. Remarkable contents of As and toxic heavy metals were found especially in the slag-contaminated soil. Copper, Zn, and Pb were the most abundant metals in the acid leach solutions resulting from mine soil-water interaction, with peak values of 55.6 mg L−1, 2.77 mg L−1, and 2.62 mg L−1, respectively. Despite the high total contents of trace elements occurring in soil, the mobile fraction was limited to maximum release values of 12.60% for Cd and 10.27% for Cu, according to the test leaching. Speciation calculations indicated that free metal ions (M2+) and sulfate species (MSO40) accounted for most of the dissolved load. Acid soil drainage is a secondary source of acid and heavy metals in the mine site and, therefore, an effective land reclamation program should ensure that acidity and metal mobility are reduced to environmentally sustainable levels.

Trace element release from Bowland Shale into spring water in Lancashire

Abstract A sulfurous spring emerges at an outcrop of Bowland Shale Formation on Crimpton Brook, Lancashire. The spring is marked by the precipitation of white and yellow jarosite. Comparable light sulfur isotope compositions suggest that the jarosite was derived from surface oxidation of pyritic shale. The shale contains anomalous concentrations of selenium and other trace elements, in common with other exposures of the Bowland Shale Formation in the north of England. The selenium is resident in the pyrite, and was released during oxidation and incorporated into the jarosite in Crimpton Brook. The small scale of the water flow at the site and the remote situation pose no environmental problem, but the data exemplify the potential danger of pyrite weathering into groundwater on a larger scale.