High Concentrations Of Arsenic Research Articles

Machine learning prediction of health risk and spatial dependence of geogenic contaminated groundwater from the Hetao Basin, China

Geogenic contaminated groundwater (GCG), characterized by elevated arsenic, fluoride, and iodine levels, present a significant challenge to public health and government management. Conventional survey-based approaches of collecting groundwater samples, conducting physicochemical tests, and performing spatial interpolation to obtain regional groundwater chemical component maps are inefficient and costly. More importantly, it does not take into account the actual hydrogeological conditions or the characteristics of pollutant transport and enrichment. To address this issue, we utilized Support Vector Machine (SVM), Random Forest (RF), Adaptive Boosting (AdaBoost), and Extreme Gradient Boosting (XGBoost) to analyze the likelihood of occurrence of arsenic, fluoride, and iodine as well as their spatial distribution in shallow groundwater from the Hetao Basin. Our study incorporated 20 indicators related to meteorology, soil physicochemical properties, and groundwater conditions, along with 1505 labeled samples consisting of groundwater arsenic, fluoride, and iodine concentrations and their corresponding coordinates. Subsequently, the study automatically analyzed the meteorological, soil physicochemical properties and groundwater conditions by constructing a machine learning model using the available data. In order to optimise and select the best prediction model, this paper presents a quantitative evaluation of the prediction performance of various machine learning models. The accuracy (AC), area under curve (AUC) and mean squared error (MSE) were calculated to predict the spatial distribution of CGC. Subsequently, the optimized model for predicting the spatial distribution of GCG was selected. The results showed that the XGBoost algorithm provided optimal predictions for groundwater with arsenic concentrations above 10 μg/L and fluoride concentrations exceeding 1.5 mg/L, whereas the RF model provided the best predictions for groundwater with arsenic concentrations surpassing 50 μg/L and iodine concentrations exceeding 100 μg/L. Subsequently, groundwater health risk zones were delineated based on an optimal prediction model, and demographic analysis was conducted in both the direct and potential groundwater risk zones. Model predictions indicated that hundreds of thousands of people in the Hetao Basin were facing a public health crisis caused by high concentrations of arsenic, fluoride and iodine in groundwater. These findings underscore the significant health challenge in the study area. Considering the agricultural development and increasing groundwater use in the area, our findings can guide local governments in managing the extent of groundwater development, establishing control zones, and enhancing protection measures for populations at risk from groundwater contamination.

Amphibian tolerance to arsenic: microbiome-mediated insights

Amphibians are often recognized as bioindicators of healthy ecosystems. The persistence of amphibian populations in heavily contaminated environments provides an excellent opportunity to investigate rapid vertebrate adaptations to harmful contaminants. Using a combination of culture-based challenge assays and a skin permeability assay, we tested whether the skin-associated microbiota may confer adaptive tolerance to tropical amphibians in regions heavily contaminated with arsenic, thus supporting the adaptive microbiome principle and immune interactions of the amphibian mucus. At lower arsenic concentrations (1 and 5 mM As3+), we found a significantly higher number of bacterial isolates tolerant to arsenic from amphibians sampled at an arsenic contaminated region (TES) than from amphibians sampled at an arsenic free region (JN). Strikingly, none of the bacterial isolates from our arsenic free region tolerated high concentrations of arsenic. In our skin permeability experiment, where we tested whether a subset of arsenic-tolerant bacterial isolates could reduce skin permeability to arsenic, we found that isolates known to tolerate high concentrations of arsenic significantly reduced amphibian skin permeability to this metalloid. This pattern did not hold true for bacterial isolates with low arsenic tolerance. Our results describe a pattern of environmental selection of arsenic-tolerant skin bacteria capable of protecting amphibians from intoxication, which helps explain the persistence of amphibian populations in water bodies heavily contaminated with arsenic.

Estimation of redox-sensitive metals in Lafarge cement company’s area in Akamkpa Nigeria: Assessment of ecological health risk

Toxic compounds such as redox-sensitive metals usually contaminate the soil. They are implicated in the causation of oxidative stress, a precursor of human diseases and ecological extinction. Having uncontaminated soil serves as the link between plant and animal health quality, and a sustainable ecosystem. Geological accumulation and spatial distribution of redox-sensitive metals in agricultural land can significantly hinder soil fertility, ecological health, food safety, and food security. This study used the soil samples from farmlands near the Lafarge industrial area at Mfamosing, Akamkpa local government area of Cross River State, Nigeria, to assess eight redox-sensitive metals (Cadmium, Chromium, Copper, Nickel, Lead, Arsenic, Cobalt, and Zinc), their spatial distribution, and geo-accumulation. The redox-sensitive metals were screened with an atomic absorption spectrophotometer connected with mass spectroscopy. A geographic information system (GIS) and ArcMap version 10:8:2 was used to infer the risk of the industrial area regarding geo-accumulation, and spatial distribution of redox-sensitive metals in the farmlands. The result shows Cd, Cr, Cu, Ni, Pb, As, Co and Zn have different concentrations among the samples. Three samples - MS2, MS3, and MS8, had the highest arsenic concentration, while samples Ms1, Ms2, Ms5, and Ms8, had the second-highest concentrations of Cadmium, Lead, and Chromium, respectively. The polluted area was moderately contaminated and distributed with other metals - Cu, Ni, and Co, respectively. Comparing these results with those of non-industrial areas, one can infer that the Lafarge industrial area is more contaminated with redox-sensitive metal. To advance this investigation, some microorganisms within the area can be used to verify a metal-hazard impact on the ecosystem and monitor the rise in redox-sensitive metals to predict the risk.

An updated ecotoxicological evaluation and health risk assessment of metal contaminants in Perna viridis mussel harvested on March to August 2018 from Pasir Gudang Coastal Area, Malaysia

Perna viridis (P. viridis) is a significant protein source globally but is often contaminated by metals due to its filter-feeding behavior. Given that Kampung Pasir Puteh, Pasir Gudang (Johor) is Malaysia's primary P. viridis harvesting site and the last health risk assessment (2015) was incomplete, the metal contamination status remains uncertain. Graphite furnace-atomic absorption spectroscopy was employed to analyze metal contaminant concentrations in P. viridis samples collected from March to August 2018, as per Malaysian legal requirements. The R2 values varied between 0.9976 and 0.9980 for P. viridis mussels and between 0.9976 and 0.9999 for seawater. The recovery for P. viridis mussels and seawater ranged from 93.95% to 106.80% and 92.73–108.84%, respectively. Precision and accuracy for both intra and inter-day measurements ranged from 0.15% to 5.49% for P. viridis and 0.05–5.58% for seawater. The concentrations of metal contaminants in P. viridis varied significantly among the different months of sampling (p < 0.05). All P. viridis samples had higher concentration of arsenic (3.16–75.80 μg g−1) than that prescribed by the Malaysian law. Higher cadmium concentration was observed during July (2.12 μg g−1) and August (2.05 μg g−1) alone. With target hazard quotients and hazard indices > 1.0, the likelihood of negative health impacts from consuming these mussels cannot be ignored. TCR values for As and Cd exceeded USEPA standards, indicating a potential lifetime carcinogenic risk from continuous P. viridis consumption. Pb (21.20–49.28 µg L−1) in all surface seawater samples was invariably higher than the allowable limit for Class 2 water areas. Metal contaminant concentrations varied significantly between P. viridis and surface seawater (p < 0.05), implying inconsistent bioaccumulation due to pollution differences. Given the significance of P. viridis mussels, concerted scientific efforts are essential to devise effective metal contaminant removal methods.

Hydrogeochemical arsenic simulation of V-Ti-Fe tailings pond ecosystem: A case study from Panxi region, China

The V-Ti-Fe mine tailings waste releases high concentrations of aquatic arsenic (As) ions to downstream ecosystems. The hydrogeochemical As simulation facilitates the prediction of toxicity (or redox state) and devising control strategies to mitigate the negative impacts. Therefore, this study utilizes the Wanniangou tailings pond (a V-Ti-Fe mine tailings reservoir) in the Panxi region, Sichuan province, China, as a case study to elucidate the As hydrogeochemical behaviour under varying pH and redox potential (Eh) conditions. Our study reveals that (1) the water-oxygen exchange and Mn are important to regulating the redox conditions in the filtrates. The Eh determines the valence states of As, which vary from reduced states to oxidized states during the runoff from the tailings pond to downstream (Rehe River). The flow of wastewater in Rehe River minimizes both the As toxicity and concentration, eventually improving water safety. (2) In a reducing environment, hematite exhibits a limited capacity for As(III) adsorption. In the case of oxidation conditions, goethite mainly adsorbed As(V), with an elevated adsorption capacity. Meanwhile, Fe-minerals remain relatively stable under varying redox and weakly acidic conditions. Consequently, targeted engineering interventions can achieve two crucial outcomes: (1) Minimize the acidity of the mine environment to retard the release of heavy metals from the tailings waste. (2) Prolonging the residence time of wastewater in Rehe River to promote the transition from a reducing state to an oxidizing state, thereby synergistically mitigating As toxicity.

Comprehensive Analysis of Biomass, Nutrient, and Heavy Metal Contributions of Pelagic Sargassum Species (Phaeophyceae) Inundations in South Florida

Pelagic Sargassum landings (hereby referred to as sargasso) increased dramatically in 2011 throughout the equatorial tropical Atlantic due to the formation of the Great Atlantic Sargassum Belt (GASB). Despite increasing reports, understanding of local abundances and vegetative characteristics, especially in South Florida, remains limited. From 2018 to 2021, sargasso was collected at two South Florida beaches, with additional sampling at a third beach to assess nutrient and heavy metal concentrations. Biomass landings varied greatly, with S. fluitans III predominant during the “peak season” (May to July) and S. natans I predominant in the “off season”, while S. natans VIII was consistently least abundant. This suggests that South Florida may receive sargasso from the Sargasso Sea during the low season and from the GASB during the peak sargasso season. Across all three morphotypes, mean nitrogen (N) and phosphorus (P) contents were 0.97% and 0.04% (dry weight), respectively. Out of the 16 heavy metals detected, our values were similar to those reported across the Caribbean. Arsenic was the most prevalent heavy metal, with sargasso containing epibionts having higher arsenic concentrations. These results provide comprehensive information to better understand the characteristics and potential origin of sargasso landings in South Florida.

Lead and Arsenic Content in Everyday Drinkware

This research explores the issue of lead and arsenic contamination in everyday drinkware which highlights the profound implications for consumer safety. The ubiquity of glassware in everyday life underscores the urgency of investigating the sources and levels that pose health risks associated with these toxic elements within drinkware products. Through a systematic examination and use of flame atomic absorption spectroscopy (FAAS), identifying the levels of lead and arsenic contamination has been achieved. This research rigorously quantifies the levels of contamination in commonly used drinkware, revealing possible correlations with concentration, condition, and price points. These correlations furthermore emphasize the need for regulatory measures and heightened consumer awareness. This comprehensive exploration serves as a vital contribution to safeguarding consumer safety in the context of drinkware usage, paving the way for informed decisions and targeted interventions in the pursuit of a healthier living environment. This research found that 20% of all tested samples leached an average of 0.84 ppm lead with a standard deviation of 0.32 ppm. 30% of all samples that tested positive for arsenic had an average of 4.10 ppm leached and a standard deviation of 0.88 ppm. No correlation was found between prices and concentration and a highly negative correlation was found between both metals. Low concentrations of arsenic had high concentrations of lead. Likewise, high concentrations of arsenic had low concentrations of lead. Damaged, or internally exposed ceramics tested higher for both lead and arsenic.

Effect of Pretreatment on a Copper Concentrate with High Arsenic Content

Effect of Pretreatment on a Copper Concentrate with High Arsenic Content

Microalgae for freshwater arsenic bioremediation: examining cellular toxicity, bioconcentration factor and eluding an alternative arsenic detoxification pathway

Microalgae are photoautotrophic organisms in freshwater systems known to uptake and bioremediate arsenic, a heavy metal. In this study, we compared the growth and arsenic uptake of two microalgae strains, Nostoc and Chlorella, to determine their suitability for arsenic bioremediation. As compared to the control, our results showed that treatment with As (III) enhanced the Nostoc growth by approximately 15% when grown in the absence of phosphate. The highest bioconcentration factor of Nostoc at this treatment was 1463.6, whereas 0.10 mg L−1 As (V) treatment improved the Chlorella growth by 25%, in the presence of phosphate. However, arsenic uptake reduced from 175.7 to 32.3 throughout the cultivation period for Chlorella. This suggests that Nostoc has an upper advantage in the bioremediation of arsenic as compared to the Chlorella strain. To gain insights into the potential of Nostoc in arsenic bioremediation, we further conducted SEM analysis on the vegetative cell surface. The SEM results showed that As (III) disrupted the Nostoc vegetative cell surface and structure. Further to this, pathway analysis and polymerase chain reaction (PCR) were conducted to identify the potential arsenic pathway regulated by Nostoc. The primary As (III)-related pathways elucidated include the arsA transporter and arsD complex that require ATP and As (III) methylation to S-adenosylmethionine. The phosphate deficiency condition resulting in the inability to generate ATP caused As (III) could not be excreted from the Nostoc cells, potentially contributing to the high arsenic concentration accumulated under phosphate-depleted conditions. These insights contribute to understanding the efficacy of microalgae strains in freshwater arsenic bioremediation.

The Dynamics of the Concentration and Speciation of Arsenic in Private Drinking Water Wells in Eastern Wisconsin, USA

About 2.5 billion people rely on groundwater as their main drinking water source, and arsenic pollution within the groundwater system can cause serious short- and long-term health issues. Within the natural environment, arsenic generally exists as oxyanions which have two oxidation states, As(III) and As(V). Under ambient pH conditions, As(V) is primarily present as an anion (i.e., H2AsO4−) while As(III) tends to be uncharged (i.e., H3AsO3), making it much more difficult to remove As(III) through existing treatment techniques such as adsorption and reverse osmosis (RO). In Eastern Wisconsin, the dolomite and dolomite/sandstone aquifers represent a major drinking water source and high arsenic concentrations have been observed. Previous studies showed that arsenic can be released into private drinking water wells due to the oxidation of sulfide-bearing minerals with arsenic impurities that are usually dispersed within the dolomite and sandstone bedrock. However, there is a lack of information on the concentrations of each arsenic species as well as arsenic dynamics during water pumping/usage. The primary goals of this research were (1) to quantify the baseline concentrations of each arsenic species within selected Eastern Wisconsin private drinking water wells, and (2) to determine how the arsenic concentrations and species could be affected by continuous water usage. Our results showed that As(III) was the dominant species of arsenic, and during continuous water usage, there could be an upward trend in arsenic concentration (there was minimal change in arsenic speciation). Upon the completion of water pumping, arsenic concentrations decreased over time and returned to pre-pumping levels. Our findings highlighted the importance of quantifying the speciation and dynamics of arsenic during water use to the assessment of public health risks and the design of appropriate water treatment techniques.

Systematic review and meta-analysis of arsenic concentration in drinking water sources of Iran.

Recent studies have found arsenic contamination of drinking water in some parts of Iran, as in many other countries. Thus, a comprehensive systematic review is necessary to assess the distribution and concentration of arsenic in drinking water sources. For this purpose, articles published from the first identification until December 2023, were retrieved from various national and international databases. Of all the studies examined (11,726), 137 articles were selected for review based on their conceptual relationship to this survey. A review of the extracted studies presented that ICP methods (ICP-MS, ICP-OES, 56%) and atomic absorption spectrophotometry (AAS, 34.1%) were the two most commonly used techniques for the analysis of arsenic in water samples. The order of arsenic content in the defined study areas is descending, as follows: northwest ˃ southeast ˃ southwest ˃ northeast. A review of studies performed in Iran depicted that provinces such as Kurdistan, Azerbaijan, and Kerman have the highest arsenic concentrations in water resources. Accordingly, the maximum concentration of arsenic was reported in Rayen, Kerman, and ranged from < 0.5-25,000µg/L. The primary cause of elevated arsenic levels in water resources appears to be geologic structure, including volcanic activity, biogeochemical processes, sulfur-bearing volcanic rocks, Jurassic shale, the spatial coincidence of arsenic anomalies in tube wells and springs, and, to some extent, mining activities. The findings of the presented survey indicate that it is essential to take serious measures at the national level to minimize the health risks of arsenic contamination from drinking water consumption.

Techno-economic evaluation of antimony and bismuth upcycling from pyrometallurgical copper wastes

The recovery of critical raw materials (CRMs) is important to reduce the supply risk disruption and the dependency on third-countries within the European Union (EU). The present study evaluates the techno-economic implications of antimony (Sb) and bismuth (Bi) recovery from the process stream produced in the polishing stages of the copper electrorefining circuit. The upcycling process was based on the selective precipitation of Sb and Bi from the concentrated hydrochloric acid (HCl) (up to 5–6 M) process stream containing high arsenic (As) concentrations. Four different scenarios were included in the evaluation, in which Sb and Bi were recovered as Sb4O5Cl2(s)/Sb2O3(s) and BiOCl(s)/Bi2O3(s), respectively. The results showed that implementing Bi and Sb upcycling configurations in the copper metallurgical facilities was economically feasible when recovering BiOCl(s)/Sb4O5Cl2(s) and BiOCl(s)/Sb2O3(s) from the eluate stream. Sb recovery was the most cost-intensive process in all the configurations evaluated due to the high chemical requirements needed to neutralize the free HCl excess. The consumption of chemicals represented the most important cost contributor, since high amounts of chemicals are needed for the selective Sb and Bi precipitation. The sensitivity analysis illustrated that recovering these CRMs was economically attractive for all the configurations when achieving Sb and Bi prices above 8.5 and 9.5 €/kg, respectively. Under these CRM prices, the payback period and internal rate of return for the different scenarios range from 4 to 19 years and from 6 to 28 %, respectively. This output highlights that future increase in CRM prices can be an important driver to implement Sb and Bi recovery schemes. Overall, the results of this study highlight the economic potential of implementing Sb and Bi recovery schemes in copper metallurgical plants to align with the ambitious circular economy objectives established by the EU.

Characteristics and risk assessment of arsenic contamination in a lead and zinc plant area in Yunnan Province

Taking a lead and zinc plant plot in Yunnan as the research object, the land use status and planting types of the region were investigated, the original enterprise distribution area and crop growing area of the plot were defined, and 67 surface soil samples and 14 columnar soil samples were systematically arranged in the plot for monitoring. Combined with the monitoring results and analysis, it is concluded that there is no definite basis that the high arsenic content in soil in the region is caused by the enterprise production, and the high arsenic content in the region may be caused by the background value. Based on the monitoring and investigation results, the risk assessment of the area was carried out. The results showed that the non-carcinogenic risk and carcinogenic hazard index of arsenic exceeded the prescribed acceptable level when the area was developed as the second type of construction land, and soil remediation should be carried out. At the same time, the collaborative distribution monitoring of regional crops showed that the arsenic content of crops was low, which met the requirements of food standards, possibly because the cultivated crops did not have strong adsorption and enrichment effects on the arsenic occurrence form in the regional soil.

Scorodite synthesis process using solid iron oxides

The immobilization of arsenic in the form of scorodite (FeAsO4·2H2O), which has excellent chemical stability, is attracting attention as a method for treating wastewater containing high concentrations of arsenic generated at nonferrous metal smelting plants. Scorodite, with its low solubility and high arsenic content per volume, is expected to be an environmentally friendly arsenic fixation method suitable for final disposal. Various scorodite synthesis methods have been studied. The first synthesis method proposed is the hydrothermal method using an autoclave to synthesize highly crystalline scorodite. Although the hydrothermal method is capable of synthesizing scorodite with good crystallinity, from an economic point of view, scorodite synthesis under ambient pressure and at low temperatures is more attractive. As a low-temperature scorodite synthesis method under atmospheric pressure, the oxidation of Fe(II) process by O2 bubbling was proposed. In this method, ferrous sulfate is added to an arsenic-containing solution as a Fe ion source, and in situ oxidation of Fe(II) by O2 or air bubbling to form scorodite with good crystallinity. In addition to temperature, other conditions, pH, Fe/As ratio, and reaction time have been reported to affect scorodite crystallization. Recently, scorodite synthesis using solid iron oxide as the Fe source for scorodite synthesis, instead of aqueous Fe salt solutions, has attracted much attention. In this presentation, we will report on the investigation of reaction parameters, such as the type of iron oxide and reaction temperature, for the scorodite synthesis using solid iron oxide.

Arsenic contamination of groundwater: Review on arsenic contamination of Assam

Groundwater contamination is a global problem. Although groundwater is considered as safe, high concentrations of heavy metals in groundwater like arsenic (As) can pose potential human health concerns and hazards. Arsenic is a natural chemical element of the earth’s crust and is commonly distributed all over the environment. High concentrations of arsenic (As) in drinking water have been found in several parts of the world. World Health Organization’s provisional guideline value for arsenic in drinking water - 0.01 mg/l (10 μg/l). In Assam, many districts have been reported to be most affected by arsenic contamination of groundwater which is above the permissible level. People in Assam have directly or indirectly consumed the groundwater. This paper emphasizes the overview of the present scenario of intensity of arsenic contamination in groundwater in different districts of Assam. The paper also critically reviews the sources of arsenic contamination and arsenic led human effects.

Survey of arsenic content in edible seaweeds and their health risk assessment

Since humans are especially sensitive to arsenic exposure, predominantly through diet, a strict control of the most widely consumed seaweeds is mandatory. Total arsenic contents and arsenic species in twenty-five different seaweeds from five different origins were studied. Seaweeds selected, included Phaeophyta (brown seaweed), Chlorophyta (green seaweed) and Rhodophyta (red seaweed) genera. The highest arsenic content appears in the Phaeophyta seaweed in the range from 11 to 162 mg kg−1 dried weight. Arsenosugars were found to be the predominant species of arsenic in most seaweeds, being up to 99.7% of total arsenic in some samples. The arsenic dietary intakes for seaweeds studied were assessed and the Target Hazard Quotients (THQ) and the Target Cancer Risk (TCR) were calculated, taking into account inorganic arsenic contents (iAs). iAs species in seaweeds showed low risk of arsenic intake except for Hizikia fusiforme samples.

Vetiver grass cleans up arsenic contaminated field for subsequent safe cultivation of rice with low arsenic in grains: A two year field study

The presence of high concentrations of arsenic (As) in agricultural soils and its subsequent accumulation in rice crop is a serious issue threatening sustainability of agriculture and human health. In the present work, remediation of As contaminated field in Nadia, West Bengal, India was done through the cultivation of Vetiver (Vetiveria zizanoides L. Nash) and the same field was subsequently used for rice (Oryza sativa L.) cultivation. The results showed that V. zizanoides could reduce As concentrations in the field to bring it lower than the maximum permissible limit (20 mg kg−1) in 11 months' time. The rice plants grown in remediated field showed improvement in growth and photosynthesis parameters as compared to that of contaminated field. Importantly, yield related parameters (filled seed, 1000 grain weight, number of panicles etc.) were also significantly higher in remediated field than that in contaminated field. Arsenic concentration in roots, shoot, husk and grains of rice was found to be significantly lower in remediated field than in contaminated field. Grain As decreased from 0.75 to 0.77 μg g−1 dw in contaminated field to 0.15–0.18 μg g−1 dw. In conclusion, replacing rice for single year with V. zizanoides crop can significantly remediate the field and can be a viable option.

Arsenic in the groundwater aquifers of the Venetian Plain: geochemical modelling and occurrence of As-sulfides minerals, a review of data from the medio Brenta domain (Italy)

The Venetian Plain is known for areas with high concentrations of arsenic (As) in groundwater (up to more than 400 μg/L; exceptionally 647 μg/L, in selected areas). A study area was chosen, north of Padua, which exhibits typical residential, industrial, and agricultural characteristics similar to most Western countries and lacks hydrothermal, volcanic, or anthropogenic sources of arsenic. The pilot area was the focus of several studies which are reviewed in this note. The objectives of the studies were to verify the distribution of As concentrations in groundwater and sediments (mineralogical and geochemical analysis of groundwater sediments and of filtered and unfiltered groundwater) and to model the mobility of arsenic arising from water-rock interaction. The grain size of aquifer reservoirs includes gravel, sand, silt, and clay. The amount of organic matter in the aquifer sediments of the study area seems peculiar (higher) compared to other plains in the world; it influences the redox potential and the relative concentration of As in groundwater. Arsenic contamination in groundwater and redox conditions varied greatly in the area. Groundwater under oxidizing and highly reducing conditions had much lower arsenic concentrations compared to groundwater under intermediate reducing conditions. Arsenic minerals (such as realgar-pararealgar) occur in aquifer sediments and they were documented in the studied materials by different analytical techniques for the first time in the context of the Italian plains. Since these minerals are rare throughout the world in plain sediments not affected by volcanic or hydrothermal activity, their occurrence is a distinctive feature of the Venetian Plain aquifer. These arsenic minerals were found in peat sediments of the study area, consistent with geochemical modeling results, which require highly reducing conditions for their precipitation from groundwater. Modeling suggests that under oxidizing and up to slightly reducing conditions (from 200 mV to -50 mV), arsenic is adsorbed on solid phases, but a further decrease in redox potential leads arsenic desorption from solids and consequent groundwater contamination (from -50 mV to -250 mV). If the redox potential becomes even more negative (below -250 mV), geochemical conditions are favorable to the formation of arsenic sulfides. The precipitation of the realgar-pararealgar phases, predicted by the geochemical model, proceeds by extracting arsenic from the groundwater and quantitatively accounts for the lower arsenic concentration measured in the highly reducing groundwater of the study area.

Slag-based stabilization/solidification of hazardous arsenic-bearing tailings as cemented paste backfill: Strength and arsenic immobilization assessment

The widespread occurrence of toxic arsenic in sulfidic and non-ferrous waste tailings hinders its disposal as cement paste backfill (CPB). Alkali activated slag (AAS) has recently begun to be practiced as an alternative to normal Portland cement (OPC). Nevertheless, technical information on arsenic immobilization and mechanical characteristics of arsenic-rich AAS-CPB is rather few. The impacts of activator nature, cure temperature and arsenic content on strength and arsenic immobilization of AAS-CPB explored. Despite AAS-CPB having greater strength, OPC-CPB consistently has a stronger (1.7–21.1% higher) ability to immobilize arsenic. The optimum silica modulus for maximal strength and arsenic immobilization capability depends on curing time. Strength at3 days is enhanced by higher activator doses, whereas strength at later ages (≥ 28 days) is decreased. At all curing ages, the lowest arsenic immobilization capacity is produced by medium activator concentration (0.35). Irrespective of cement type, strength increases as curing temperature rose, however OPC-CPB's strength is more responsive to temperature changes than AAS-CPB's. At room temperature (20°C), OPC-CPB has a higher (6.0–21.1% greater) arsenic immobilization efficiency (AIE) than AAS-CPB, but the opposite is true at lower (5°C) and higher (35°C) temperatures (i.e., 5.4–12.0% and 4.4–12.0% lower at 5 and 35°C respectively). Early on, the influence of arsenic content on strength is not immediately apparent, but it tends to become more obvious with longer curing times. As a role of cement type and elapsed time, high arsenic contents cause a rise or a decrease in AIE. Notably, there is no apparent connection between UCS and AIE. Electrical conductivity and moisture content can be steadily employed to portray the hydration progression of both arsenic-free and arsenic-containing CPB.

Microbiology of Big Soda Lake, a multi-extreme meromictic volcanic crater lake in the Nevada desert.

Big Soda Lake, Nevada, is a multi-extreme meromictic lake, whose hypersaline hyperalkaline bottom waters feature permanent anoxia and high concentrations of arsenic, sulphide and ammonia. These properties make Big Soda Lake-and the adjacent Little Soda Lake-a fascinating system for exploring life's boundaries, discovering novel microbial taxa and identifying biotechnologically useful strains. To date, the taxonomic diversity and metabolic capabilities of microorganisms in this system remain largely unknown. Here, we fill this gap using microbiome surveys across the Big and Little Soda Lake water columns, including 16S rRNA sequencing, fungal ITS2 sequencing and gene- and genome-resolved metagenomics. We accompany these surveys with measurements of salinity, pH, temperature, oxygen, ammonium and ammonia concentrations. Our analyses reveal rich bacterial communities, taxonomically and functionally differentiated along Big Soda Lake's oxycline and, to lesser extent, between lakes. Fungal communities were dominated by a small number of families, while nearly no archaea were detected. Pathways related to perchlorate reduction, anoxygenic phototrophy, fermentation, dissimilatory metabolism of arsenite/arsenate, sulphur compounds, nitrogen compounds and hydrogen, were particularly prevalent. A total of 129 high-quality bacterial and archaeal metagenome-assembled genomes (completeness ≥ 80%, contamination ≤ 5%) were recovered, yielding insight into the taxonomic distribution of microbial metabolic pathways.