Mobility Of Metals Research Articles

Mobilization of As, Fe, and Mn from Contaminated Sediment in Aerobic and Anaerobic Conditions: Chemical or Microbiological Triggers?

We integrated aqueous chemistry, spectroscopy, and microbiology techniques to identify chemical and microbial processes affecting the release of arsenic (As), iron (Fe), and manganese (Mn) from contaminated sediments exposed to aerobic and anaerobic conditions. The sediments were collected from Cheyenne River Sioux Tribal lands in South Dakota, which has dealt with mining legacy for several decades. The range of concentrations of total As measured from contaminated sediments was 96 to 259 mg kg-1, which co-occurs with Fe (21 000-22 005 mg kg-1) and Mn (682-703 mg kg-1). The transition from aerobic to anaerobic redox conditions yielded the highest microbial diversity, and the release of the highest concentrations of As, Fe, and Mn in batch experiments reacted with an exogenous electron donor (glucose). The reduction of As was confirmed by XANES analyses when transitioning from aerobic to anaerobic conditions. In contrast, the releases of As, Fe and Mn after a reaction with phosphate was at least 1 order of magnitude lower compared with experiments amended with glucose. Our results indicate that mine waste sediments amended with an exogenous electron donor trigger microbial reductive dissolution caused by anaerobic respiration. These dissolution processes can affect metal mobilization in systems transitioning from aerobic to anaerobic conditions in redox gradients. Our results are relevant for natural systems, for surface and groundwater exchange, or other systems in which metal cycling is influenced by chemical and biological processes.

Saltwater intrusion weakens Fe-(oxyhydr)oxide-mediated (im)mobilization of Ni and Zn in redox-fluctuating soil–groundwater system

Iron in the form of (oxyhydr)oxides plays a profound role in the (im)mobilization of heavy metals in environmental geochemical processes occurring in the soil–groundwater system. Here, the influence of saltwater intrusion on Fe-(oxyhydr)oxide-mediated (im)mobilization of Ni(II) and Zn(II) in redox-fluctuating shallow aquifers was evaluated by chemical extraction, μ-XRF-XANES analysis, and 16S rRNA high-throughput sequencing. In phreatic water, the ferrihydrite-bound Ni/Zn (Fh-Ni/Zn) in soils contributed to a 12%–17% increase in carbonate-bound Ni/Zn (Cb-Ni/Zn) due to its own reductive dissolution, whereas the illite-adsorbed Ni/Zn (illite-Ni/Zn) only contributed 6%, 7%. The relative abundance of non-salt tolerant anaerobic Herbaspirillum and iron-reducing associated Ralstonia in soils accounted for nearly 50%. During the oxidation stage, the dissolved ferrihydrite reprecipitated to bind free Ni/Zn. However, saltwater invasion strongly weakened the dissolution–precipitation of ferrihydrite by inhibiting the growth of non-salt tolerant anaerobes and iron-reducing bacteria, and highlighted the contribution of illite-Ni/Zn. Under brackish water intrusion, illite-Zn contributed to a 12% increase in Cb-Zn, thereby surpassing the contribution of Fh-Zn (8%). Under seawater invasion, the dissolution–precipitation of ferrihydrite hardly occurred and the anaerobic salt-tolerant Bacillus (> 95%) prevailed. Therefore, the increase of Cb-Ni/Zn (7%–15%) in the reduction stages was contributed by illite-Ni/Zn. However, in the oxidation stages, the carbonate replaced the original role of reprecipitated ferrihydrite to bind the free Ni/Zn in solutions. These newly recognized mechanisms may be the key to predicting the mobility of toxic elements and developing appropriate remediation techniques of permeable reactive barriers under salinity stress.

Bioavailability of Colloidal Iron to Heterotrophic Bacteria in Sediments, and Effects on the Mobility of Colloid-Associated Metal(loid)s

The submicrometric fraction of surface sediments that accumulate in the bottom of dam reservoirs represent important sources of nutrients and contaminants in freshwater systems. However, assessing their stability in the presence of sediment bacteria as well as their bioavailability in the sediment remains poorly understood. We hypothesized that sediment’s bacteria are able to extract nutrients from sedimentary colloids (<1 µm fraction) and thus contribute to the release of other colloid-associated elements to water. Experiments were performed under laboratory conditions, using the submicrometric fractions of sediments recovered from two dam reservoirs (in calcareous and crystalline granitic contexts) and two heterotrophic bacteria (Gram-negative Pseudomonas sp. and Gram-positive Mycolicibacterium sp.). The results demonstrated that bacteria were able to maintain their metabolic activity (the acidification of the growth medium and the production of organic ligands) in the presence of colloids as the sole source of iron (Fe) and regardless of their chemical composition. This demonstrates that bioavailable Fe, aside from ionic forms, can also occur in colloidal forms. However, the bacteria also catalyzed the release of potentially toxic metallic elements (such as Pb) associated with colloids. These results help improve our understanding of the processes that influence contaminants’ mobility in the ecosystems as well as provide an important insight into current research evaluating the bioavailability of different forms of nutrients.

Comparative studies on the effects of biochar and cow dung amendments on the mobility, bioavailability and toxicity of heavy metals in lead-acid contaminated soil

This study compared the heavy metals remediation potency of biochar and cow dung in soils contaminated by lead-acid batteries. Soil samples were gathered from three different battery charging shops in Benin City at the depth of 0-15cm using systematic grid sampling method. Hardwood was pyrolyzed at 350°C for 80minutes and cow dung was air dried and pound into powder. The soil was characterized using standard methods, and was fractionated using modified European Community Bureau of Reference (BCR) three-step sequential extraction procedure while the concentration of heavy metals was determined using Atomic Absorption Spectrophotometer (AAS). The total metal concentration in the lead-acid contaminated soil was 127.50mg/kg Pb, 0.32mg/kg Cr, 0.03mg/kg Cd, 0.18mg/kg Ni and 135.00mg/kg Fe. The contaminated soil was remediated with biochar and as well with cow dung at 5%, 10%, 15% and 20%. The soil was also amended using biochar-cow dung mixture (1:1, 2:1 and 1:2). The outcome revealed that the metal content in lead-acid contaminated soil remediated with biochar and cow dung were found to generally decrease as the percentage of amenders increases, with biochar being further efficient in lowering the levels of heavy metals in the contaminated soil. However, biochar when mixed with cow dung at 2:1 ratio at 20% amendment gives a better result than when used separately. Pot experiment was designed and the amounts of heavy metals bioavailable to plant were determined. The mobility factors and bioavailability indices of the metals reduced as the percentage of amenders’ increases. The result obtained from this study revealed that although biochar and cow dung were effective amenders, biochar was more potent in lowering the mobility, bioavailability and toxicity of heavy metals in lead-acid contaminated soil. Biochar when mixed with cow dung at 2:1 ratio gave the best result in remediation of lead-acid contaminated soil.

Acid generation potential and kinetics of metal(loid) release from resuspended sulfidic mine waste

Sulfidic mine waste exposed to oxidizing conditions can generate acidity and leach metal(loid)s into the environment, posing a risk to surrounding ecosystems. In the present study, four sulfidic mine waste samples were investigated using both kinetic and static experiments to determine the acid generation potential and mobilization of metal(loid)s. A long-term resuspension experiment of 821 days was performed to study the effect of oxidation on the acid generation and the release of metal(loid)s from the mine waste samples. The mineralogy of the mine waste after 821 days of oxidation was determined and compared with the original sample. A kinetic study of a pH-dependent leaching test was also performed to study the influence of time on metal(loid) release. Additionally, a static acid-base accounting test was used to gain more insight into the acid generation and neutralization potentials. The mineralogical study revealed the presence of sulfide minerals (e.g., pyrite, and sphalerite) both as free particles and embedded within other minerals (e.g., quartz). The mine waste samples exhibited a high acid generation potential, where the pH of all samples decreased to pH< 3 after 272 days. The resuspension of the mine wastes also resulted in a considerable release of As, Cd, Cu, and Zn (up to 4500, 100, 4000, and 11,500 mg/kg, respectively). However, Pb exhibited low leaching levels, due to the formation of secondary Pb-bearing minerals (i.e., beudantite and/or plumbojarosite). Overall, the samples pose an environmental risk based on the high acid generation potential and high release of metal(loid)s.

Distance impacts toxic metals pollution in mining affected river sediments

The study of metals mobility derived from mining activities in an ultramafic lithology is limited. This study investigates the effects of distance on potentially toxic metals such as Co, Cu, Fe, Mn, Ni, Pb, and Zn pollution, and the geochemical processes of fluvial system downstream of an ex-copper mine (Mamut River). The toxicity level of the river was evaluated using various sediment quality guidelines, ecotoxicological risks (ecological risk and risk index) and pollution indices. The geochemical behavior and stability of these toxic metals in the solid-phase samples were also examined. The results show that elevated concentrations of Ni, Cu, and Fe in the sediments can be linked to the adsorption and precipitation of metals from the aqueous-phase samples. We found that the metal scavenging rate as a function of distance is more evident in tropical environments than it was previously thought (10 km downstream). Such an inference could be explained by the greater amount of rainfall (pH 5.5–6.5) received in the tropics and higher weathering products that could react and form stable complexes. Geochemical analysis of the river sediment indicates that Ni, Cu, and Fe in the river sediment have increased 44-, 81-, and 90-fold compared to the background values, respectively. A significant decrease in the concentration of the potentially toxic metals was found at 5.5 km downstream. The scavenging rate of Fe is the highest (1485.82 μg g−1 km−1) followed by Cu (141.48 μg g−1 km−1), Ni (10.23 μg g−1 km−1), Pb (8.12 μg g−1 km−1) and Zn (5.01 μg g−1 km−1) in the tropical river system. In contrast, the concentration of Co and Mn in the river sediments doubled as the river flows approximately 5 km downstream due to the higher mineral solubility and weaker metal partition coefficient. This study also discusses the possibility of asbestos (mainly as chrysotile in the X-ray diffraction) as a potential hidden risk present within the ultramafic setting. This case study can be extrapolated to explain the dispersion of inorganic pollutants in an ultramafic environment in a global context.

INFLUENCE OF FERTILIZERS APPLICATION ON MOBILITY OF METALS

Metals play an important role in the life of plants and animals, and in small quantities, most of them are necessary for the normal functioning of living organism. However, increased concentrations can also harm the same functions of a living organism. In the soil cover, metals can be contained in various species, which determine their mobility and toxicity. Metals are transferred from soil to plants and then to animal and human organisms only if they are mobile. The mobile fractions include the water-soluble, exchangeable, carbonate, reducible and oxidizable forms and they can migrate from one environment to another and cause a negative cumulative effect. An increase in anthropogenic load leads to an increase in the mobility of metals. A special place is occupied by agricultural activity, which, using various fertilizers, increases the proportion of geochemically mobile species of metals. This work is aimed at studying the effect of fertilization on the mobility of some metals. As part of the work, the soils of the Almaty region (Baiterek village) of the Republic of Kazakhstan were studied by applying various fertilizers (ammonium nitrate and monopotassium phosphate), followed by studying the species of metals and the most toxic radionuclides (polonium-210 and lead-210) according to the method of A. Tessier. Using the fertilizers under investigation insignificantly affects the species of alkali metals, polonium-210, and lead-210. While application of monopotassium phosphate increases the geochemical mobility of sodium and alkaline earth elements due to the transition to the water-soluble and exchangeable fractions, and heavy metals due to the transition to the exchangeable fraction. The obtained data are useful as the basis for the development of recommendations for the application of certain types of fertilizers to reduce the risk of impact on the life and health of the local population without reducing the productivity of agricultural crops.

Effects of fiddler crab bioturbation on the geochemical migration and bioavailability of heavy metals in coastal wetlands

Fiddler crabs, found in coastal wetlands worldwide, function as ecosystem engineers. Their burrowing activity can significantly alter biogeochemistry at the local scale, however, the mobility of heavy metals (HMs) in burrow sediments remains unclear. Here, we used diffusive gradients in thin-film probes to obtain bioavailable Fe and HMs (Cu, Zn, Ni, Cd, Pb, Co, and Mo) in crab burrows from coastal wetlands (mudflats, salt marshes, and mangroves). The depth-profile results showed that most HMs were enriched at shallow and deep depths but deficient at middle depths. We highlighted that bioturbation improved oxic conditions, enhanced HM concentrations, and favored dissolved HM retention in burrow sediments, which served as a sink for overlying water HMs via burrow flushing but a potential source of particle HMs via enhanced resuspension. In deep anoxic layers, Fe(III) reduction drove the remobilization of HMs, except Cu and Mo, leading to the co-release of HMs with Fe. This Fe-HM coupling/decoupling was verified using enhanced two-dimensional high-resolution imaging, which revealed highly spatial heterogeneity of multiple HMs. Moreover, the hydrological conditions regulating bioturbation effects on HM behavior varied across different coastal wetlands. With coastal environmental changes, the key role of ubiquitous bioturbation in HM migration and bioavailability should be reconsidered.

Impact of Seasonal Variations and Oil Activities on the Total Concentrations, Geochemical Fractions, And Human Health Problems of Trace Metals in Soils Within the Oil-Bearing Communities of South-South Region of Nigeria

The impacts of oil activities and seasonal variations on the total concentrations, geochemical fractions, and human health problems of trace metals in soils within oil-bearing communities of Akwa Ibom State, Nigeria were examined. Top soils were obtained from Eket, Onna, Esit Eket, and Ibeno local government areas between January and December, 2017. Samples were also collected from Etinan local government area of the State and used as the Control. The samples and Control were subjected to standard analytical procedures and analysed for their physicochemical properties and total metal concentrations. The modified BCR methods were employed for the speciation of metals. The findings revealed that the pH levels were higher during the dry season while, the electrical conductivity, organic matter, and cation exchange capacity of the studied soils were higher in the rainy season. The total mean concentrations of Pb, As, Cd, Cr, Fe, and V were higher in the dry season whereas, Ni was higher in the wet season. Though, their concentrations were within the acceptable limits. Generally, the concentrations of all the parameters in the studied soils were higher than at the control site. Pb, As, Ni, and V existed predominantly in the reducible fraction, Cd and Cr in acid extractable while, Fe existed mostly in the residual fraction in the studied soils. However, at the control site all the metals except Cd existed mainly in the residual fraction. The study showed that all the studied locations were highly contaminated with these metals and substantial seasonal variations were also recorded for the pollution indices. It was also noted that, seasonal changes and oil activities were the key factors affecting the quality of the studied soils. Daily intake rates for the metals through exposure to soil for both the young and old populations were within their required oral reference doses. The non-carcinogenic risks recorded for both populations were less than one. However, both populations were exposed to high Pb and the younger ones were more susceptible. The study revealed the influence of seasonal change and oil activities on the mobility and toxicity of metals in the studied soils.

Variability of sulfur isotopes and trace metals in pyrites from the upper oceanic crust of the South China Sea basin, implications for sulfur and trace metal cycling in subsurface

The circulation of seawater within the oceanic crust promotes cycling of metals and sulfur, as well as development of the subsurface biosphere. Characterization of the full spectrum of sulfide geochemistry in the altered oceanic crust is critical for a complete understanding of global cycling of sulfur and metals, while those in off-axis hydrothermal circulation have received less attention. This study applied a combination of in-situ sulfur isotopic and trace metal analyses to study the pyrite geochemical features in altered basalts of the South China Sea basin. This contribution unravels a detailed picture of the cycling of sulfur and metals in the subsurface. Such cycling is likely to be co-controlled by the hydrothermal and microbial activities when oceanic crusts transit from on-axis to off-axis hydrothermal systems.A total of five groups of pyrites associated with distinct mineral assemblages, morphologies, trace metal enrichment and sulfur isotopic values were observed in altered basalts. Pyrite disseminated (type 1) within the background hydrothermal alteration is characterized by δ34S values close to zero, with relative enrichment of trace metals (> 500 ppm), such as Ni, Co, and Cu. This type of pyrite is most likely to precipitate from upwelling high-temperature hydrothermal fluids when they ascended towards the seafloor. Sulfur was mainly derived from magmatic sulfides. Linear regression analyses of trace metal contents in disseminated pyrite show various strong positive correlations between trace metals reflecting a series of metal mobility processes, including incorporation into pyrite and leaching directly from sulfides or silicate minerals. Additionally, a population of pyrite has δ34S values ranging from +4 to +8 ‰ and low trace element contents, which reveals precipitation conditions where the ascending high-temperature hydrothermal fluids have mixed with significant amounts of seawater-sourced fluids. This group of pyrites is either formed by the replacement of silicates as patchy texture (type 2) or are exclusively associated with epidote‑carbonate veins (type 3). Furthermore, strongly positive δ34S signatures are observed within framboidal pyrite (type 4) (δ34S up to +57 ‰) and within overgrown euhedral pyrite (type 5) (δ34S up to +24 ‰). These unprecedented isotopically-heavy framboidal pyrite in modern oceanic crust presents a well-preserved organic matter framework, which is interpreted as a consequence of microbial sulfate reduction activities based on current observations. The extremely positive values of the sulfur isotopes could be produced by Rayleigh isotopic fractionation when ~77% sulfate (assumed with an initial seawater sulfate δ34S of 21%) is consumed by microorganisms in closed systems, in this case, the cavities in the altered basalt. The microorganisms meanwhile may enhance the sequestration of trace metals into pyrite, possibly through microbial metabolisms or detoxification processes. The positive δ34S values of overgrown euhedral pyrite (type 5) are interpreted to be mainly introduced by the involvement of seawater-derived sulfur or inherited from the framboidal pyrite.The various isotopic and elemental signatures in these five types of pyrites could be linked to either the hydrothermal or microbial processes occurring within the upper oceanic crust in the South China Sea basin. Both processes are critical to the metal and sulfur cycling in subsurface and should be considered jointly in future studies. Additionally, our results exemplify the potential roles of microorganisms, not only in accumulating trace metals in sulfides in the subsurface but also as a potential biosignature to reveal microbial activities in similar environments in the early Earth.

Impact of Long-term and Intensive Rice Cultivation on Heavy Metal Accumulation in Soil: An Observation from Mae La River Basin, Central Thailand

Intensive rice cultivation relies greatly on chemical fertilizers and pesticides, some of which contain heavy metals as impurities. Application of these agrochemicals can result in heavy metal accumulation in soil. This research discusses the current concentrations and migration pathways of heavy metals (Cu, Pb and Zn) in paddy soil subjected to long-term use of chemical fertilizers and pesticides. The study of soil pH and metal concentrations in 60 surface and subsurface samples from a relatively small river basin revealed that although highly varied, pH values and metal concentrations in topsoil were significantly different from values in subsurface soil. The soil pH as low as 5.4 was observed in topsoil. Although the observed levels in topsoil were in within safe limits according to the Dutch standard, they were significantly elevated above the subsurface concentrations. Evidence on the differences between their concentrations in paddy soil and river sediments suggests that considerable amount of metals in paddy fields have been transported into the river. A detailed study of input inventory, fluxes and migration pathways of these metals in the river basin can provide a better understanding of their mobility and measures that might needed to safeguard aquatic habitats, especially the well-known striped snakehead fish in Mae La River.&#x0D; HIGHLIGHTS&#x0D; &#x0D; Agrochemicals such as chemical fertilizers and pesticides contain heavy metals as impurities&#x0D; Long-term and continuous use of agrochemicals in rice production has resulted in lower pH and higher heavy metal contents in topsoil&#x0D; Low pH in topsoil can enhance metal mobility, suggesting that some of the heavy metals from agrochemical inputs are likely to be transported from paddy fields to their surrounding environments&#x0D; This study demonstrates that the effects of agrochemical use extend beyond agricultural soil. Impact assessment of their application, thus, should cover all major compartments/systems in the basin&#x0D; &#x0D; GRAPHICAL ABSTRACT

Assessment of Trace Metals Contamination, Species Distribution and Mobility in River Sediments Using EDTA Extraction.

The impact of the ethylenediaminetetraacetic acid (EDTA) on speciation image of selected trace metals (Zn, Cd, Cu, Pb) in bottom sediments was determined. The influence on the effectiveness of metal removal of extraction multiplicity, type of metal, extraction time and concentration of EDTA were analyzed. With the increase of extraction multiplicity, the concentration of EDTA and contact time, the efficiency of trace metals leaching increased. The speciation analysis revealed that EDTA not only leached metals from bioavailable fractions, but also caused the transition of the metals between the fractions. The biggest amounts of bioavailable forms were found for Cd, less for Zn. The amount of bioavailable fraction was the lowest for Cu and Pb. The two first-order kinetic models fitted well the kinetics of metals extraction with EDTA, allowing the metals fractionation into “labile” (Q1), “moderately labile” (Q2) and “not extractable” fractions (Q3).

Thermal Transformation of Natural Schwertmannite in the Presence of Chromium

Schwertmannite is a metastable mineral playing a crucial role in the immobilization of metal(oid)s in acid mine drainage (AMD) systems. High temperatures associated with wildfires could lead to a sudden schwertmannite transformation, changing the mobility of metal(oid)s. The objective of the present study was to examine the thermal transformation from schwertmannite to hematite, and the subsequent effect on the chromium partitioning. The immobilization of arsenate after thermal transformation and its implications on chromium mobility was also evaluated. Natural schwertmannite, with increasing contents of chromium, was thermally treated between 200 to 800 °C. Transformation products were characterized by solid-phase techniques and selective chemical extractions. Results indicated a transformation to hematite at temperatures above 400 °C. The presence of chromium barely affected the temperature at which the transformation occurred, although partitioning of chromium in the mineral changed with temperature. As the temperature increased from 25 °C to 400 °C, chromium was less mobile and less outcompeted by arsenic adsorption, suggesting a larger contribution of inner-sphere complexes with increasing temperature. At temperatures above 600 °C, non-mobile forms strongly associated with neo-formed hematite were found. Finally, neo-formation of hematite led to a decrease in arsenic adsorption, implying a potentially enhanced arsenic mobility in AMD systems upon wildfires.

Enhanced cycling of nitrogen and metals during rapid infiltration: Implications for managed recharge

We present results from a series of plot-scale field experiments to quantify physical infiltration dynamics and the influence of adding a carbon-rich, permeable reactive barrier (PRB) for the cycling of nitrogen and associated trace metals during rapid infiltration for managed aquifer recharge (MAR). Recent studies suggest that adding a bio-available carbon source to soils can enhance denitrification rates and associated N load reduction during moderate-to-rapid infiltration (≤1 m/day). We examined the potential for N removal during faster infiltration (>1 m/day), through coarse and carbon-poor soils, and how adding a carbon-rich PRB (wood chips) affects subsurface redox conditions and trace metal mobilization. During rapid infiltration, plots amended with a carbon-rich PRB generally demonstrated modest increases in subsurface loads of dissolved organic carbon, nitrite, manganese and iron, decreases in loads of nitrate and ammonium, and variable changes in arsenic. These trends differed considerably from those seen during infiltration through native soil without a carbon-rich PRB. Use of a carbon-rich soil amendment increased the fraction of dissolved N species that was removed at equivalent inflowing N loads. There is evidence that N removal took place primarily via denitrification. Shifts in microbial ecology following infiltration in all of the plots included increases in the relative abundances of microbes in the families Comamonadaceae, Pseudomonadaceae, Methylophilaceae, Rhodocyclaceae and Sphingomonadaceae, all of which contain genera capable of carrying out denitrification. These results, in combination with studies that have tested other soil types, flow rates, and system scales, show how water quality can be improved during infiltration for managed recharge, even during rapid infiltration, with a carbon-rich soil amendment.

Patterns of differentiation of the old arable horizon of fallow soils according to the content of mobile forms of manganese and copper

The differentiation of the old arable horizon (Ap old) by the content of mobile manganese (Mn) and copper (Cu) under fallow vegetation aged 15-20 years was studied. The accumulation of mobile Mn in the upper layer (0-10 cm), Cu in the 5-15 cm layer was observed. Linear modeling of the dependence of the content of Mn and Cu on alkali-soluble organic matter (OMP) and pH showed the influence of only one significant predictor on each element. The content of Mn has a significant strong (R2 adj.=0.72) influence of OMP. The pH has a statistically significant, but weak (R2 adj.= 0.19) effect on the Cu content. The difference in the patterns of differentiation is associated with the accumulation of mobile Mn by newly formed organic matter (OM) in fallows and the migration of mobile Cu with soluble fractions of OM in acidic soils. The study of changes in the mobility of heavy metals (HMs) in fallows is necessary to reduce environmental risks when changing land use, as well as to provide a realistic prediction of atmospheric carbon sequestration in fallow soils, taking into account changes in the level of toxicity of HMs. The relevance of these studies is associated with the fact that the removal of lands with heavy HM contamination from arable circulation in fallows is practiced more and more often.

Bioleaching of Metals from Printed Circuit Boards

Electronic waste or E-waste refers to the discarded electrical or electronic devices which have neared their useful life. Because of the toxicity and carcinogenicity of some compounds, the proper management and safe disposal of these electronic wastes have become serious challenges in recent years. Printed Circuit Boards (PCBs) are found almost in every other electronics these days, hence the present study focuses on bioleaching of metals from Printed Circuit Boards (PCBs) using bacterial and yeast strains (Stenotrophomonas maltophilia, Bacillus sp. and Candida tropicalis) isolated from heavily contaminated soil samples. A two-step bioleaching procedure was followed for maximum mobilization of metals. The isolated strains were able to mobilize metals from PCBs with different efficiencies depending on their ability to utilize the E-waste a carbon source when cultivated in minimal media. Bioleaching potential of isolated microbes on eight heavy metals (Cu, Ni, Mn, Pb, Fe, Cr, Zn &amp; Co) in the sample were studied using AAS and SEM analysis before and after the two-step bioleaching process and found to be efficient. The study concludes that isolated bacterial and fungal species from the study can be further standardized with regard to the growth parameters and used on large scale to carry out the efficient recovery of metals that can help in recycling E-waste in the digital world.

Sulfur Biogeochemical Cycling and Redox Dynamics in a Shale‐Dominated Mountainous Watershed

AbstractSulfur (S) is an essential macronutrient and important component of the earth’s crust, and its cycling has critical impacts on trace metal mobility, water quality, and human health. Pyrite weathering is the primary pathway by which sulfur enters surface waters. However, biogeochemical cycling of sulfur in soils and the river corridor mediates sulfate exports. In this study, we identified the major forms of sulfur across multiple compartments and scales in a pristine mountainous watershed, including shale bedrock weathering profiles, hillslope soils, and alluvial floodplain sediments, in order to provide insight into biogeochemical sulfur cycling in a hydrologically variable alpine system. X‐ray absorption near‐edge spectroscopy (XANES) analysis of shale weathering profiles showed clear evidence of pyrite oxidation to sulfate, with large accumulations of intermediate S(0) (20%–53%). Micro‐scale XANES showed evidence of reprecipitation of pyrite at fracture surfaces within the permanently saturated zone. Organic sulfur dominated S speciation in shallow hillslope soil and floodplain sediment, with little evidence of reduced inorganic S. However, mackinawite formation, representing active sulfate reduction, was observed in saturated oxbow sediments and saturated weathered shale underlying floodplain sediments. Further evidence of sulfate reduction from aqueous sulfur isotopic analysis was observed in shallow groundwater transects across an Fe‐reducing meander, whereas increases in pore water sulfate concentrations implied sulfur oxidation at other locations. The data present an integrated picture of sulfur cycling in a shale‐dominated watershed, where riverine sulfate exports are mediated by biological cycling, particularly in redox‐stratified and temporally dynamic hyporheic zone sediments.

Tracing marine conditions in the Ipubi Black Shales, Araripe Basin, NE Brazil: An approach by chemical elements contents

The aim of this study was to test the hypothesis of a marine influence during the Ipubi Formation deposition (late Barremian-early Aptian age) in the Araripe Basin northeast, Brazil. For this, it was utilized a representative section in the southernmost part of the basin. The section is composed of mudstone, shale-marl laminae, and black shale rocks. The organic matter in the samples is 3.27 and 18.28%; whereas the CaCO3 present values in order of 23.42–66.46%. The geochemical proxies, such as V/Ni, Ni/V (V/(V + Ni) Fe/Al suggest depositional condition from sub-oxic to anoxic. The Sr/Ba and Rb/Sr data range from brackisch to hypersaline waters. The ingression of a seawater in the Araripe Basin triggered the organic matter accumulation, as well as the trace metals mobility in the bottom surface. Our data suggests that the Ipubi Formation represents the boundary of transitional to marine conditions in the Araripe Basin, and the basin owned as a silled basin when the increase of relative sea level made it possible the water inlet in the basin.

Effect of F-Rich Fluids on the A-Type Magmatism and Related Metal Mobilization: New Insights from the Fogang-Nankunshan-Yajishan Igneous Rocks in Southeast China

Effect of F-Rich Fluids on the A-Type Magmatism and Related Metal Mobilization: New Insights from the Fogang-Nankunshan-Yajishan Igneous Rocks in Southeast China

Anthropogenic activities influence the mobilization of trace metals and oxyanions in coastal sediment porewaters

The biogeochemical cycle of trace metals and oxyanions in marine sediments is mainly controlled by early diagenesis of organic material, but anthropogenic activities such as dumping of dredged sludge or shipyard activities can strongly perturb these natural processes. Therefore, the impact of dumping of dredged sludge, shipyard activities such as blasting of boat hulls and the mixing of polluted Scheldt estuary water with less polluted coastal water on the mobilization of trace metals and oxyanions in the sediments was studied in the pre- and post-bloom period (March and October) in Belgian Coastal Zone (BCZ). Vertical profiles of total and labile dissolved trace element concentrations, dissolved sulfide, pH and redox potential were assessed in sediment porewaters. Generally, total and labile dissolved element profiles in the porewaters are well correlated, showing higher concentrations in March when the redox potential is lower and sulfide concentrations higher. Low pH levels were documented together with high amounts of Fe and associated elements in March at the dumping station. At the coastal station in the vicinity of the shipyards, sediment porewaters are enriched in dissolved Zn while at the mouth of the Scheldt estuary the highest dissolved Cu levels were found. Theoretical calculations with Visual MINTEQ confirm the increased Fe and associated element concentrations in March (lower pH) and the lower metal concentrations in October (lower Eh). R values, ratio of labile dissolved to total dissolved concentrations, reflect the potential of the solid sediment phase to supply labile elements to the porewater. They were lowest for Cu and highest for V. This study showed that anthropogenic activities in the BCZ such as dumping of dredged sludge and blasting of boat hulls have a serious impact on the levels, distribution and bioavailability of contaminants in the sediments, which may form a real threat to the benthic ecosystem.