Arsenic and antimony: comparative approach on mechanistic toxicology

Biotransformation of arsenic and toxicological implication of arsenic metabolites

Arsenic is a well-known environmental carcinogen and chronic exposure to arsenic through drinking water has been reported to cause skin, bladder and lung cancers, with arsenic metabolites being implicated in the pathogenesis. In contrast, arsenic trioxide (As₂O₃) is an effective therapeutic agent for the treatment of acute promyelocytic leukemia, in which the binding of arsenite (iAs^III) to promyelocytic leukemia (PML) protein is the proposed initial step. These findings on the two-edged sword characteristics of arsenic suggest that after entry into cells, arsenic reaches the nucleus and triggers various nuclear events. Arsenic is reduced, conjugated with glutathione, and methylated in the cytosol. These biotransformations, including the production of reactive metabolic intermediates, appear to determine the intracellular dynamics, target organs, and biological functions of arsenic.

Comparative characterization of microbial communities that inhabit arsenic-rich and antimony-rich contaminated sites: Responses to two different contamination conditions

Due to extensive mining and industrial activities, arsenic (As) and antimony (Sb) contaminations are becoming a global environmental concern. Both As and Sb are toxic and carcinogenic metalloids from the group 15 in the periodic table. Since As and Sb share many similar geochemical properties, it is often assumed that they exert similar environmental pressure on the native microbial communities. This hypothesis, however, still requires further confirmation. In the current study, a systematic comparison of microbial responses to As and Sb contamination were conducted. The results suggested that regular geochemical parameters, such as pH, nitrate, and TOC, were the driving forces for shaping the microbial community. In correspondence, two heavily contaminated groups showed similar microbial community compositions and the same microbial populations were enriched. The interactions between the contaminant fractions (As and Sb related fractions) and the individual OTUs, however, suggested the different and more diverse impacts of As comparing to Sb fractions, with more taxa significantly impacted by As species comparing to Sb species. The identification of the keystone taxa in the heavily contaminated samples revealed a group of microbial populations that could survive in both As and Sb heavily contaminated conditions and may providing critical environmental services to the community. Further investigation of these key microbial populations may provide valuable insights on employing these microorganisms for remediation applications.

Antimony and arsenic speciation, redox-cycling and contrasting mobility in a mining-impacted river system

The Macleay River in eastern Australia is severely impacted by historic stibnite- and arsenopyrite-rich mine-tailings. We explore the partitioning, speciation, redox-cycling, mineral associations and mobility of antimony and arsenic along >70 km reach of the upper Macleay River. Elevated Sb/As occur throughout the active channel-zone and in floodplain pockets up to the regolith margin, indicating broad dispersal during floods. Sb concentrations in bulk-sediments decay exponentially downstream more efficiently than As, likely reflecting sediment dilution, hydraulic sorting and comparatively greater leaching of (more mobile) Sb(V) species. However, Sb in bulk-sediments becomes proportionally more bio-available downstream. Sb(V) and As(V) species dominate stream fine-grained (<180 μm) bulk-sediments, reflecting oxidative weathering downstream. Increasing poorly-crystalline Fe(III) [Fe(III)_HCl] in bulk-sediments also indicates progressive oxidative weathering of Fe(II)-bearing minerals downstream and significant (P < .05) correlations exist between PO₄^-3-exchangeable As and Sb fractions and Fe(III)_HCl. Accumulations of poorly-crystalline Fe(III) precipitates (mainly ferrihydrite/feroxyhyte) occur intermittently in hyporheic-zone seeps and are enriched in As relative to Sb and contain some As(III) and Sb(III) (~30-40%). There is dynamic in-stream redox-cycling of both Sb and As, with localised S-coordinated As and Sb species re-forming in organic-rich, hyporheic sediments subject to contemporary sulfidogenesis. Sb [mainly Sb(V)] is comparatively more mobile in hyporheic and surface waters under oxic conditions, whereas As [mainly As(III)] is more mobile in hyporheic porewaters subject to reducing/sulfidogenic conditions. Repeat water-leaching of bulk-sediments confirms that Sb is proportionally more mobile than As. Mean concentrations of Sb in river water 168 km downstream from the mine are significantly (P < .05) higher than As, while K_d data indicate Sb is more strongly partitioned to the aqueous phase than As. Although the (mainly) oxic flow path of this river favours aqueous Sb mobility compared to As, localised redox-driven shifts in speciation of both elements strongly influence their respective mobility and partitioning.

Antimony sensing whole-cell bioreporters derived from ArsR genetic engineering

Despite the known hazardous effects of antimony (Sb) on human health, Sb monitoring biosensors have not been as actively investigated as arsenic (As) biosensors. Whole-cell bioreporters (WCBs) employing an arsenic-responsive operon and a regulatory protein (ArsR) are reportedly capable of monitoring arsenite, arsenate, and antimonite. However, the potential of WCBs as Sb biosensors has been largely ignored. Here, the metal-binding site of ArsR (sequenced as ELCVCDLCTA from amino acid number 30 to 39) was modified via genetic engineering to enhance Sb specificity. By relocating cysteine residues and introducing point mutations, nine ArsR mutants were generated and tested for metal(loid) ion specificity. The Sb specificity of WCBs was enhanced by the C37S/A39C and L36C/C37S mutations on the As binding site of ArsR. Additionally, WCBs with other ArsR mutants exhibited new target sensing capabilities toward Cd and Pb. Although further research is required to enhance the specificity and sensitivity of WCBs and to broaden their practical applications, our proposed strategy based on genetic engineering of regulatory proteins provides a valuable basis to generate WCBs to monitor novel targets.

Fate and removal of antimony in response to stringent control activities after a mine tailing spill

When tailing spill accidents occur, the risk of contamination by antimony (Sb) tailings into adjacent rivers, sediments, aquifers and soil environments is high. The Sb concentrations in water and sediment under different stringent control activities were investigated for 60 days in the Jialing River basin after a tailing spill accident. Both reservoir regulation and the construction of a temporary dam with coagulation dosing remarkably reduced the Sb levels in the river water. The increase in dissolved Sb caused by the spill was reduced from ~400 μg/L in the inflow to ~200 μg/L in the outflow by reservoir regulation. Moreover, reservoir regulation led to a high concentration of Sb in the reservoir sediment, which was difficult to remove and may cause subsequent unpredictable long-term ecological and health risks. In contrast, the Sb-enriched deposition inside the temporary dam was convenient to remove. Notably, temperature alternations between day and night in winter resulted in a large fluctuation in coagulation efficiency, which may cause the failure of stringent control projects. The results of this study suggest potential improvements to stringent control activities after mine tailing accidents to mitigate environmental impacts and prevent secondary risks.

Risk of Cancer for Workers Exposed to Antimony Compounds: A Systematic Review

BACKGROUND

Antimony (Sb) trioxide and antimony trisulfide are "2B: Possibly carcinogenic to humans" and "3: Unclassifiable" according to the International Agency for Research on Cancer (IARC). The U.S. National Toxicology Program (NTP) concluded that antimony trioxide "is reasonably anticipated to be a human carcinogen based on studies in rats and mice". We investigated the cancer hazard of antimony compounds for workers, a population with high exposure to antimony substances.

METHODS

Using the "Guidelines for performing systematic reviews in the development of toxicity factors" (Texas Commission on Environmental Quality (TCEQ) 2017) as a guidance, we established a human and an animal toxicology data stream in Medline and ToxLine. Data from this review were applied in a human health risk assessment.

RESULTS

A final pool of 10 occupational and 13 animal toxicology articles resulted after application of TCEQ guidelines.

CONCLUSIONS

Antimony carcinogenicity evidence involving workers is inadequate, based on confounding, small sample sizes, incomparability across studies, and inadequate reference populations. An increased lung cancer risk cannot be excluded. Evidence for lung neoplasms caused by antimony trioxide inhalation in experimental animals is sufficient. Overall, carcinogenicity in workers is probable (International Agency for Research on Cancer (IARC) 2A). It remains unclear from what occupational exposure duration and dose this effect arises and whether exposure threshold values should be reconsidered.

Impacts of Arsenic and Antimony Co-Contamination on Sedimentary Microbial Communities in Rivers with Different Pollution Gradients

Arsenic (As) and antimony (Sb) are both toxic metalloids that are of primary concern for human health. Mining activity has introduced elevated levels of arsenic and antimony into the rivers and has increased the risks of drinking water contamination in China. Due to their mobility, the majority of the metalloids originating from mining activities are deposited in the river sediments. Thus, depending on various geochemical conditions, sediment could either be a sink or source for As and Sb in the water column. Microbes are key mediators for biogeochemical transformation and can both mobilize or precipitate As and Sb. To further understand the microbial community responses to As and Sb contamination, sediment samples with different contamination levels were collected from three rivers. The result of the study suggested that the major portions of As and Sb were in strong association with the sediment matrix and considered nonbioavailable. These fractions, however, were also suggested to have profound influences on the microbial community composition. As and Sb contamination caused strong reductions in microbial diversity in the heavily contaminated river sediments. Microorganisms were more sensitive to As comparing to Sb, as revealed by the co-occurrence network and random forest predictions. Operational taxonomic units (OTUs) that were potentially involved in As and Sb metabolism, such as Anaerolinea, Sphingomonas, and Opitutus, were enriched in the heavily contaminated samples. In contrast, many keystone taxa, including members of the Hyphomicrobiaceae and Bradyrhizobiaceae families, were inhibited by metalloid contamination, which could further impair crucial environmental services provided by these members.

Vegetation type impacts microbial interaction with antimony contaminants in a mining-contaminated soil environment

Antimony (Sb) contamination is a growing environmental concern due to the increasing use of this metalloid in mining and industrial activities. The remediation of Sb-contaminated soil is a lengthy and costly process. Phytoremediation has been suggested as a cost-effective method for the long-term management of Sb-contaminated sites. Various plant types have been found to thrive in contaminated sites and have the potential to remediate Sb contamination; however, their impacts on Sb speciation and the indigenous microbial community remain unclear. In the current study, soils from three types of vegetation environment (i.e., grass, forest, and agricultural) were collected from two Sb mining areas in Guizhou, China. Comparisons of geochemical and microbiological properties among the three vegetation types revealed that vegetation was a major driver of soil biogeochemical characteristics. Contaminant fractions (i.e., extractable fractions of Sb and As) had a greater influence on microbial communities in grass and forest soil, whereas pH had a greater impact in agricultural soil. This difference may indicate distinct microbe-environment interactions in agricultural soil affected by anthropogenic activity. The dominant taxa, including Flavobacterium, Geobacter, Janthinobacterium, Clostridium, and Mycobacterium responded positively to various contaminant fractions, indicating that the community had adapted to the chronically contaminated environment. However, the regulation of these dominant genera by geochemical properties appears to be taxon-specific. Our results demonstrate that vegetation type has a substantial impact on Sb and As biogeochemical cycles, and should be considered in future remediation efforts.

Biological, biochemical and genotoxic effects of Sb in the midge Chironomus sancticaroli Strixino and Strixino, 1981 (Diptera: Chironomidae)

In aquatic systems, antimony (Sb) is found in the water column and associated with sediment particles being bioavailable to organisms. Consequently, toxic effects have been detected in benthic invertebrates, but the toxicity after Sb exposure in Chironomidae have not been investigated. Were investigated DNA damage, activities of cholinesterase (ChE), alpha and beta esterase (EST-α, EST-β), glutathione S-transferase (GST), catalase (CAT), and superoxide dismutase (SOD) and lipid peroxidation after acute (48 h) and subchronic exposure (8 d). We also investigated the effects of subchronic (8 d) on development of larvae and chronic (25 d) Sb exposure on emergence and size of adults of Chironomus sancticaroli. Were analyze Sb nominal concentrations ranged from 0.5 to 800 μg.L^-1. Genotoxic effects occurred at higher concentrations upon acute (50, 800 μg.L^-1) and subchronic exposure (50 μg.L^-1). Acute exposure increased ChE, EST-α, EST-β, and GST activities. Subchronic Sb exposure increased EST-α activity at 0.2 μg.L^-1 and GST activity at 5 μg.L^-1. CAT activity increased at all concentrations while increasing lipid peroxidation levels were observed (1 μg.L^-1, 5 μg.L^-1 and 50 μg.L^-1), indicating oxidative stress. All concentrations of Sb delayed larval development and decreased the number of emerging adults. At high concentrations (50, 500, 800 μg.L^-1), the emerging adults were smaller. In conclusion, these varying genotoxic, biochemical and biological effects of Sb make a notable impact on the reproduction and population dynamics of C. sancticaroli.

Bacterial response to antimony and arsenic contamination in rice paddies during different flooding conditions

Rice is more vulnerable to arsenic (As) and antimony (Sb) contamination than other cereals due to the special cultivation methods, during which irrigation conditions are adjusted depending upon the growth stages. The changes in irrigation conditions may alter the oxidation states of Sb and As, which influences their mobility and bioavailability and hence uptake by rice. In this study, bacterial responses to As and Sb contamination in rice fields were investigated during two different stages of rice growth: the vegetative stage (flooded conditions), and the ripening stage (drained conditions). The substantial changes in the irrigation conditions caused a variation in geochemical parameters including the As- and Sb-extractable fractions. As and Sb were more mobile and bioaccessible during the flooded than under drained conditions. The microbial communities varied during two irrigation conditions, suggesting that the geochemical conditions may have different effects on the innate paddy microbiota. Therefore, various statistical tools including co-occurrence network and random forest (RF) were performed to reveal the environment-microbe interactions in two different irrigation conditions. One of the notable findings is that Sb- and As-related parameters exerted more influences during the flooded than under drained conditions. Furthermore, a detailed RF analysis indicated that the individual bacterial taxa may also respond differently to contaminant fractions during the two irrigation conditions. Notably, RF indicated that individual taxa such as Clostridiaceae and Geobacter may be responsible for biotransformation of As and Sb (e.g., As and Sb reduction). The results provided knowledge for As and Sb transformation during contrasting irrigation conditions and the potential mitigation strategy for contaminant removal.

Pharmacometabolomics of Meglumine Antimoniate in Patients With Cutaneous Leishmaniasis

Control of cutaneous leishmaniasis (CL) in the Americas is dependent on chemotherapy with parenteral pentavalent antimonials. High rates of treatment failure urge the search for predictive and prognostic markers of therapeutic responsiveness. In this study, we aimed to identify biomarkers of therapeutic response during treatment with meglumine antimoniate (MA). We conducted untargeted metabolomic profiling of plasma samples from CL patients (n = 39; 25 who cured and 14 who did not cure), obtained before and at the end of treatment. Exposure to MA induced metabolic perturbations primarily reflecting alteration in long-chain fatty acid β-oxidation and energy production. Allantoin, N-acetylglutamine, taurine, and pyruvate were significantly more abundant in samples from patients who responded to treatment, and were predictive and prognostic of treatment outcome in this patient cohort (AUC > 0.7). In an ex vivo model of infection, allantoin but not taurine enhanced the MA-dependent killing of intracellular Leishmania (Viannia) panamensis. Our results support the participation of metabolites mediating antioxidant and wound healing responses in clinical cure of CL, revealing relationships between metabolism and immune responses in the outcome of antileishmanial treatment.

Effect of Water Chemistry on Antimony Removal by Chemical Coagulation: Implications of ζ-Potential and Size of Precipitates

The process of coagulation and precipitation affect the fate and mobility of antimony (Sb) species in drinking water. Moreover, the solubility and physico-chemical properties of the precipitates may be affected by the media chemistry. Accordingly, the present study aimed to investigate the removal of Sb(III, V) species by ferric chloride coagulation under various water chemistry influences with a particular focus on the role of the properties of the precipitates. The results indicated that the amount of Sb(III) removed increased with increasing solution pH, showing the insignificant effects of the hydrodynamic diameter (HDD) and ζ-potential of the precipitates. However, no Sb(V) removal occurred at alkaline pH values, while a highly negative ζ-potential and the complete dissolution of precipitates were observed in the aqueous solution. The solution pH was also useful in determining the dominant coagulation mechanisms, such as co-precipitation and adsorption. The Fe solubility substantially affects the Sb removal at a certain pH range, while the HDD of the precipitates plays an insignificant role in Sb removal. The presence of divalent cations brings the ζ-potential of the precipitates close to point of zero charge (pzc), thus enhancing the Sb(V) removal at alkaline pH conditions. Pronounced adverse effects of humic acid were observed on Sb removal, ζ-potential and HDD of the precipitates. In general, this study may provide critical information to a wide group of researchers dealing with environmental protection from heavy metal pollution.

Corrosion Behavior of Different Brass Alloys for Drinking Water Distribution Systems

Some α + β’ brass components of drinking water distribution systems in Morocco underwent early failures and were investigated to assess the nature and extent of the corrosion attacks. They exhibited different corrosion forms, often accompanied by extensive β’ dezincification. In order to offer viable alternatives to these traditional low cost materials, the corrosion behavior of two representative α + β’ brass components was compared to that of brass alloys with nominal compositions CuZn36Pb2As and CuZn21Si3P, marketed as dezincification resistant. CuZn21Si3P is a recently developed eco-friendly brass produced without any arsenic or lead. Electrochemical tests in simulated drinking water showed that after 10 days of immersion CuZn21Si3P exhibited the highest polarization resistance (Rp) values but after longer immersion periods its Rp values became comparable or lower than those of the other alloys. After 150 days, scanning electron microscope coupled to energy dispersive spectroscopy (SEM-EDS) analyses evidenced that the highest dezincification resistance was afforded by CuZn36Pb2As (longitudinal section of extruded bar), exhibiting dealloying and subsequent oxidation of β’ only at a small depth. Limited surface dealloying was also found on CuZn21Si3P, which underwent selective silicon and zinc dissolution and negligible inner oxidation of both α and κ constituent phases, likely due to peculiar galvanic effects.

Antimony oxidation and sorption behavior on birnessites with different properties (δ-MnO2 and triclinic birnessite)

Birnessites are abundant naturally occurring minerals with high sorption and oxidation capacity that could therefore play an important role in antimony (Sb) migration and transformation. There are various types of birnessites in the environment. However, little is known about the similarities and differences in Sb oxidation and sorption on birnessites with different properties. In this study, the behavior of Sb oxidation and sorption on two contrasting birnessites (δ-MnO₂ and triclinic birnessite (TrBir)) were investigated via batch and kinetic experiments and various spectroscopic techniques. Our results showed that the reaction mechanisms between Sb and the two birnessites were similar. The edge sites of birnessites were responsible for Sb(III) oxidation. Mn(IV) was reduced to Mn(III) and Mn(II), bound with birnessites and released to the solution, respectively. Because of the rapid rate of electron transfer of adsorbed Sb(III) to birnessites, the only Sb species on δ-MnO₂ after the oxidation reaction was Sb(V). Sb(V) was adsorbed at the edge sites of birnessites by replacing the OH group of birnessites, forming corner-sharing complexes with birnessites. However, the Sb sorption and oxidation capacities of the two birnessites were significantly different. Poorly-crystallized δ-MnO₂ exhibited a much higher oxidation and sorption capacity than well-crystallized TrBir because the former had many more edge sites than the latter. This study reveals the general mechanism of the reaction between Sb and birnessite and indicates that birnessite with a high number of edge sites would exhibit a huge capacity in Sb oxidation and sorption.

Changes in rhizosphere bacterial communities during remediation of heavy metal-accumulating plants around the Xikuangshan mine in southern China

Mining and smelting activities are the major sources of antimony (Sb) contamination. The soil around Xikuangshan (XKS), one of the largest Sb mines in the world, has been contaminated with high concentrations of Sb and other associated metals, and has attracted extensive scholarly attention. Phytoremediation is considered a promising method for removing heavy metals, and the diversity and structure of rhizosphere microorganisms may change during the phytoremediation process. The rhizosphere microbiome is involved in soil energy transfer, nutrient cycling, and resistance and detoxification of metal elements. Thus, changes in this microbiome are worthy of investigation using high-throughput sequencing techniques. Our study in Changlongjie and Lianmeng around XKS revealed that microbial diversity indices in the rhizospheres of Broussonetia papyrifera and Ligustrum lucidum were significantly higher than in bulk soil, indicating that plants affect microbial communities. Additionally, most of the bacteria that were enriched in the rhizosphere belonged to the Proteobacteria, Acidobacteria, Actinobacteria, and Bacteroidetes. In Changlongjie and Lianmeng, the diversity and abundance of the microbial community in the B. papyrifera rhizosphere were higher than in L. lucidum. In parallel, the soil pH of the B. papyrifera rhizosphere increased significantly in acidic soil and decreased significantly in near-neutral soil. Redundancy analyses indicated that pH was likely the main factor affecting the overall bacterial community compositions, followed by moisture content, Sb, arsenic (As), and chromium (Cr).

Toxicity of exogenous antimony to the soil-dwelling springtail Folsomia candida

Antimony (Sb) is a toxic pollutant, but data for Sb toxicity to springtails in soil are limited, and the effects of Sb speciation, soil physiochemical properties, and aging time on Sb toxicity have not been investigated. To address this, the effects of Sb on Folsomia candida were evaluated in laboratory studies. The results demonstrated that compared with Sb(III), no significant change in mortality was observed in Sb(V)-treated soil, but the EC₅₀ value for the reproduction was 28-fold higher than that of Sb(III). Sb(III) toxicity was very different in four soils. The LC₅₀ values for the survival were 2325-5107 mg kg^-1 in the acute test and 605-2682 mg kg^-1 in the chronic test, and the EC₅₀ values for the reproduction were 293-2317 mg kg^-1. The toxicity discrepancies were associated with the variations in oxidation potential and sorption capacity among corresponding soils. Toxicity significantly positively correlated with the clay and amorphous iron content but significantly negatively correlated with pH. Long-term aging markedly decreased Sb(III) toxicity, and the EC₅₀ and LC₅₀ values were unexpectedly higher than the highest test concentration in soil aged for 180 days. Sb(III) toxicity was probably modified more by oxidation than by changes in the available Sb fraction during aging.

Antimony speciation in the environment: Recent advances in understanding the biogeochemical processes and ecological effects

Antimony (Sb) is a toxic metalloid, and its pollution has become a global environmental problem as a result of its extensive use and corresponding Sb-mining activities. The toxicity and mobility of Sb strongly depend on its chemical speciation. In this review, we summarize the current knowledge on the biogeochemical processes (including emission, distribution, speciation, redox, metabolism and toxicity) that trigger the mobilization and transformation of Sb from pollution sources to the surrounding environment. Natural phenomena such as weathering, biological activity and volcanic activity, together with anthropogenic inputs, are responsible for the emission of Sb into the environment. Sb emitted in the environment can adsorb and undergo redox reactions on organic or inorganic environmental media, thus changing its existing form and exerting toxic effects on the ecosystem. This review is based on a careful and systematic collection of the latest papers during 2010-2017 and our research results, and it illustrates the fate and ecological effects of Sb in the environment.

Antimony enhances c-Myc stability in prostate cancer via activating CtBP2-ROCK1 signaling pathway

Antimony, one of the heavier pnictogens, is widely used in industry, and its toxicity has become a major concern. Although previous studies suggested that antimony might be a tumorigenic risk factor in several cancers, the molecular basis underlying antimony-mediated transformation remains unclear. Our results showed that the serum concentration of antimony was higher in prostate cancer specimens relative to that of benign prostate tissues, and this high serum concentration of antimony was closely associated with poorer outcome in prostate cancer patients. Additionally, we demonstrated that antimony could promote prostate cancer cell growth in vitro and in vivo. In order to gain insight into the potential mechanisms, we examined the effects of antimony exposure on downstream signaling that could contribute to tumor development. We found that low-dose antimony could regulate the expression of Ctbp2 by binding and regulating the activity of its MRE domain. Meanwhile, CtBP2 could transcriptionally regulate the expression of RhoC, which is a member of the RhoGTPase family. Subsequently, the kinase activity of ROCK1 is increased, which promotes the stability of oncogene c-Myc. Overall, our study demonstrated that antimony could enhance c-Myc protein stability and promote prostate cancer cell proliferation through activating CtBP2-ROCK1 signaling pathway. These findings also substantially highlighted the potential of targeting molecules within antimony induced CtBP2-c-Myc signaling pathway as a promising therapeutic approach for the treatment of prostate cancer.

Oxidation of antimony (III) in soil by manganese (IV) oxide using X-ray absorption fine structure

The oxidation of antimony (III) in soils was studied using X-ray absorption fine structure (XAFS) spectra. An andosol soil sample and artificial soil samples (SiO₂ blended with iron (III) hydroxide and manganese (IV) oxide) were used herein. After adding antimony (III) oxide to all soil samples, the oxidation process was observed by recording the XAFS spectra of Sb K-edge, Fe K-edge, and Mn K-edge. The results indicated that manganese (IV) oxide played an important role in the oxidation of Sb(III); however iron (III) hydroxide was not directly related to the reaction. During a 2-hr continuous Sb K-edge X-ray absorption near edge structure (XANES) measurement with an interval of 1min of one of the artificial soil samples (SiO₂+MnO₂+Sb₂O₃), a pseudo-first-order reaction was determined with an average estimated rate of 0.52±0.04hr^-1. Compared to the lower oxidation rate of andosol, it is suggested that because of the low concentration of Mn(IV) in natural soils, the oxidation process of Sb(III) might be relatively slow and require more time to convert Sb(III) to Sb(V).

Antimony-Induced Neurobehavioral and Biochemical Perturbations in Mice

Groundwater used for drinking has been contaminated with naturally occurring inorganic arsenic and other metals, and metal-contaminated drinking water is the biggest threat to public health in Bangladesh. Toxic metals present in the drinking water have a strong relationship with chronic diseases in humans. Antimony (Sb), a naturally occurring metal, has been reported to be present in the drinking water along with other heavy metals in Bangladesh. Although Sb is present in the environment, very little attention has been given to the toxic effects of Sb. The present study was designed to investigate the in vivo effects of Sb on neurobehavioral changes like anxiety, learning and memory impairment, and blood indices related to organ dysfunction. Mice exposed to antimony potassium-tartrate hydrate (Sb) (10 mg/kg body weight) significantly (p < 0.05) decreased the time spent in open arms while increased the time spent in closed arms compared to the control mice in elevated plus maze. The mean latency time of control group to find the platform decreased (p < 0.05) significantly during 7 days learning as compared to Sb-treated group in Morris water maze test, and Sb-exposed group spent significantly (p < 0.05) less time in the desired quadrant as compared to the control group in probe trial. Sb treatment also significantly altered blood indices related to liver and kidney dysfunction. Additionally, Sb-induced biochemical alterations were associated with significant perturbations in histological architecture of liver and kidney of Sb-exposed mice. These data suggest that Sb has a toxic effect on neurobehavioral and biochemical changes in mice.

Black plastics: Linear and circular economies, hazardous additives and marine pollution

Black products constitute about 15% of the domestic plastic waste stream, of which the majority is single-use packaging and trays for food. This material is not, however, readily recycled owing to the low sensitivity of black pigments to near infrared radiation used in conventional plastic sorting facilities. Accordingly, there is mounting evidence that the demand for black plastics in consumer products is partly met by sourcing material from the plastic housings of end-of-life waste electronic and electrical equipment (WEEE). Inefficiently sorted WEEE plastic has the potential to introduce restricted and hazardous substances into the recyclate, including brominated flame retardants (BFRs), Sb, a flame retardant synergist, and the heavy metals, Cd, Cr, Hg and Pb. The current paper examines the life cycles of single-use black food packaging and black plastic WEEE in the context of current international regulations and directives and best practices for sorting, disposal and recycling. The discussion is supported by published and unpublished measurements of restricted substances (including Br as a proxy for BFRs) in food packaging, EEE plastic goods and non-EEE plastic products. Specifically, measurements confirm the linear economy of plastic food packaging and demonstrate a complex quasi-circular economy for WEEE plastic that results in significant and widespread contamination of black consumer goods ranging from thermos cups and cutlery to tool handles and grips, and from toys and games to spectacle frames and jewellery. The environmental impacts and human exposure routes arising from WEEE plastic recycling and contamination of consumer goods are described, including those associated with marine pollution. Regarding the latter, a compilation of elemental data on black plastic litter collected from beaches of southwest England reveals a similar chemical signature to that of contaminated consumer goods and blended plastic WEEE recyclate, exemplifying the pervasiveness of the problem.

Influence of the Chemical Form of Antimony on Soil Microbial Community Structure and Arsenite Oxidation Activity

In the present study, the influence of the co-contamination with various chemical forms of antimony (Sb) with arsenite (As[III]) on soil microbial communities was investigated. The oxidation of As(III) to As(V) was monitored in soil columns amended with As(III) and three different chemical forms of Sb: antimony potassium tartrate (Sb[III]-tar), antimony(III) oxide (Sb₂O₃), and potassium antimonate (Sb[V]). Soil microbial communities were examined qualitatively and quantitatively using 16S rDNA- and arsenite oxidase gene (aioA)-targeted analyses. Microbial As(III) oxidation was detected in all soil columns and 90–100% of added As(III) (200 μmol L⁻¹) was oxidized to As(V) in 9 d, except in the Sb(III)-tar co-amendments that only oxidized 30%. 16S rDNA- and aioA-targeted analyses showed that the presence of different Sb chemical forms significantly affected the selection of distinct As(III)-oxidizing bacterial populations. Most of the 16S rRNA genes detected in soil columns belonged to Betaproteobacteria and Gammaproteobacteria, and some sequences were closely related to those of known As(III) oxidizers. Co-amendments with Sb(III)-tar and high concentrations of Sb₂O₃ significantly increased the ratios of aioA-possessing bacterial populations, indicating the enrichment of As(III) oxidizers resistant to As and Sb toxicity. Under Sb co-amendment conditions, there was no correlation between aioA gene abundance and the rates of As(III) oxidation. Collectively, these results demonstrated that the presence of different Sb chemical forms imposed a strong selective pressure on the soil bacterial community and, thus, the co-existing metalloid is an important factor affecting the redox transformation of arsenic in natural environments.

Traffic-related distribution of antimony in roadside soils

Vehicular emissions have become one of the main source of pollution of urban soils; this highlights the need for more detailed research on various traffic-related emissions and related distribution patterns. Since the banning of asbestos in the European Union, its substitution with antimony (Sb) in brake linings has led to increased inputs of this toxic metalloid to environmental compartments. The objective of this study was to provide detailed information about the spatial distribution patterns of Sb and to assess its mobility and bioavailability. Roadside soils along an arterial road (approx. 9000 vehicles per day) in Cologne (Germany) were studied along five transects, at four soil depths and at seven sampling points set at varying distances from the road (n = 140). For all samples, comprehensive soil characterization was performed and inverse aqua regia-extractable trace metal content was determined being pseudo-total contents. Furthermore, for one transect, also total Sb and a chemical sequential extraction procedure was applied (n = 28). Pseudo-total Sb for all transects decreased significantly with soil depth and distance from the road, reflecting a distribution pattern similar to that of other trace metals associated with brake lining emissions. Conversely, metals associated with exhaust emissions showed a convex distribution. The geochemical fractionation of Sb revealed the following trends: i) non-specifically sorbed Sb was <5%; ii) specifically sorbed Sb was only detected within 1 m distance from the road and decreased with depth; iii) Sb associated with poorly-crystalline Fe oxides decreased with distance from the road; and iv) content of Sb bounded to well-crystalline Fe oxides, and Sb present in the residual fraction remained relatively constant at each depth. Consequently, roadside soils appear to inhibit brake lining-related Sb contamination, with significant but rather low ecotoxicological potential for input into surface and groundwater.

Development of a process for the manufacturing of SU-8 100 for the use in cell culture

SU-8 100 is a negative-tone photoresist which is used for the manufacturing of structures with high thickness and aspect ratio. The use of SU-8 100 systems in cell culture is difficult due to its cytotoxicity resulting from leachables. In this article, the production process of non-cytotoxic SU-8 100 foils is described. The aim is to create a polymer scaffold with integrated sensors in order to enable online measurements of cell growth and viability within a three-dimensional cell culture. This scaffold could be a useful tool for testing biological effects of pharmaceutical substances. Therefore, the scaffold material must not have a negative influence on the cell growth and viability. Among the biocompatibility tests described in DIN EN ISO 10993-5, the neutral red uptake method was chosen to evaluate the cytotoxicity of polymer foils. The production process of SU-8 100 was altered in such a way that non-cytotoxic SU-8 100 foils can be manufactured.

Interaction of Sb(III) with iron sulfide under anoxic conditions: Similarities and differences compared to As(III) interactions

This study examined the reaction mechanism of arsenite, As(III), and antimonite, Sb(III), with iron sulfide and compared their pH-dependent reaction behaviors under strictly anoxic environments. The comparison of Sb(III) with As(III), based on their chemical similarity, may provide useful insight into understanding the geochemical behavior of the less studied Sb(III). The pH-dependent batch sorption studies revealed that As(III) and Sb(III) displayed similar removal trends with pH in terms of the removal efficiency. However, the aqueous As(III) species transformed to thioarsenite species, while aqueous Sb(III) species remained inert under the highly sulfidic anoxic system. An X-ray absorption spectroscopy study demonstrated the reaction of As(III) and Sb(III) at acidic pH was closely related to the precipitation of sulfide minerals As₂S₃ and Sb₂S₃, respectively, as a consequence of the reaction with sulfide produced through mackinawite dissolution. Meanwhile, the removal at basic pH was inferred as a surface reaction, possibly through surface complexation, surface-precipitation, or both. In this study, the pH-dependent Sb(III) uptake mechanisms proved to be similar to the corresponding mechanisms for As(III) uptake, with mackinawite demonstrating a superior capacity to scavenge Sb(III) in ferrous and sulfide-rich reducing environments.

Environmental Metals and Cardiovascular Disease in Adults: A Systematic Review Beyond Lead and Cadmium

Published systematic reviews concluded that there is moderate to strong evidence to infer a potential role of lead and cadmium, widespread environmental metals, as cardiovascular risk factors. For other non-essential metals, the evidence has not been appraised systematically. Our objective was to systematically review epidemiologic studies on the association between cardiovascular disease in adults and the environmental metals antimony, barium, chromium, nickel, tungsten, uranium, and vanadium. We identified a total of 4 articles on antimony, 1 on barium, 5 on chromium, 1 on nickel, 4 on tungsten, 1 on uranium, and 0 on vanadium. We concluded that the current evidence is not sufficient to inform on the cardiovascular role of these metals because of the small number of studies. Few experimental studies have also evaluated the role of these metals in cardiovascular outcomes. Additional epidemiologic and experimental studies, including prospective cohort studies, are needed to understand the role of metals, including exposure to metal mixtures, in cardiovascular disease development.

Sorption-desorption of antimony species onto calcined hydrotalcite: Surface structure and control of competitive anions

Calcined hydrotalcite can be applied to remove anionic contaminants from aqueous systems such as antimony species due to its great anion exchange capacity and high surface area. Hence, this study evaluated antimonite and antimonate sorption-desorption processes onto calcined hydrotalcite in the presence of nitrate, sulfate and phosphate. Sorption and desorption experiments of antimonite and antimonate were carried out in batch equilibrium and the post-sorption solids were analyzed by X-ray fluorescence (EDXRF). Sorption data were better fitted by dual-mode Langmuir-Freundlich model (R²>0.99) and desorption data by Langmuir model. High maximum sorption capacities were found for the calcined hydrotalcite, ranging from 617 to 790meqkg^-1. The competing anions strongly affected the antimony sorption. EDXRF analysis and mathematical modelling showed that sulfate and phosphate presented higher effect on antimonite and antimonate sorption, respectively. High values for sorption efficiency (SE=99%) and sorption capacity were attributed to the sorbent small particles and the large surface area. Positive hysteresis indexes and low mobilization factors (MF>3%) suggest very low desorption capacity to antimony species from LDH. These calcined hydrotalcite characteristics are desirable for sorption of antimony species from aqueous solutions.

Influence of weak magnetic field and tartrate on the oxidation and sequestration of Sb(III) by zerovalent iron: Batch and semi-continuous flow study

The influence of weak magnetic field (WMF) and tartrate on the oxidation and sequestration of Sb(III) by zerovalent iron (ZVI) was investigated with batch and semi-continuous reactors. The species analysis of antinomy in aqueous solution and solid precipitates implied that both Sb(III) adsorption preceding its conversion to Sb(V) in solid phase and Sb(III) oxidation to Sb(V) preceding its adsorption in aqueous phase occurred in the process of Sb(III) sequestration by ZVI. The application of WMF greatly increased the rate constants of Sb_tot (total Sb) and Sb(III) disappearance during Sb(III)-tartrate and uncomplexed-Sb(III) sequestration by ZVI. The enhancing effect of WMF was primarily due to the accelerated ZVI corrosion in the presence of WMF, as evidenced by the influence of WMF on the change of solution and solid properties with reaction. However, tartrate greatly retarded Sb removal by ZVI. It was because tartrate inhibited ZVI corrosion, competed with Sb(III) and Sb(V) for the active surface sites, increased the negative surface charge of the generated iron (hydr)oxides due to its adsorption, and formed soluble complexes with Fe(III). The positive effect of WMF on Sb(III)-tartrate and uncomplexed-Sb(III) removal by ZVI was also verified with a magnetic semi-continuous reactor.

Potentially harmful elements in house dust from Estarreja, Portugal: characterization and genotoxicity of the bioaccessible fraction

Due to their behavioral characteristics, young children are vulnerable to the ingestion of indoor dust, often contaminated with chemicals that are potentially harmful. Exposure to potentially harmful elements (PHEs) is currently exacerbated by their widespread use in several industrial, agricultural, domestic and technological applications. PHEs cause adverse health effects on immune and nervous systems and can lead to cancer development via genotoxic mechanisms. The present study is an integrated approach that aims at assessing the genotoxicity of bioaccessible PHEs following ingestion of contaminated house dust. A multidisciplinary methodology associating chemical characterization of five house dust samples, extraction of the bioaccessible PHEs in gastric extracts by the unified BARGE method, determination of the bioaccessible fraction and in vitro genotoxicity of gastric extracts in adenocarcinoma gastric human (AGS) cells was developed. The five gastric extracts induced dose-dependent genotoxicity in AGS cells. Copper (bioaccessible concentration up to 111 mg/kg) was probably the prevalent PHE inducing primary DNA damage (up to 5.1-fold increase in tail DNA at 0.53 g/l of gastric extract). Lead (bioaccessible concentration up to 245 mg/kg) was the most prevalent PHE inducing chromosome-damaging effects (r = 0.55; p < 0.001 for micronucleated cells induction). The association of principal component analysis and Spearman's correlations was decisive to understand the chromosome-damaging properties of the bioaccessible PHEs in AGS cells. This methodology could be used on a larger-scale study to provide useful information for science-based decision-making in regulatory policies, and a better estimation of human exposure and associated health risks.

Removal of antimonate from wastewater by dissimilatory bacterial reduction: Role of the coexisting sulfate

The priority pollutant antimony (Sb) exists primarily as Sb(V) and Sb(III) in natural waters, and Sb(III) is generally with greater mobility and toxicity than Sb(V). The bio-reduction of Sb(V) would not become a meaningful Sb-removal process unless the accumulation of produced dissolved Sb(III) could be controlled. Here, we examined the dissimilatory antimonate bio-reduction with or without the coexistence of sulfate using Sb-acclimated biomass. Results demonstrated that 0.8mM Sb(V) was almost completely bio-reduced within 20h along with 48.6% Sb(III) recovery. Kinetic parameters q_max and K_s calculated were 0.54mg-Sb mg-DW^-1h^-1 and 41.96mgL^-1, respectively. When the concentrations of coexisting sulfate were 0.8mM, 1.6mM, and 4mM, the reduction of 0.8mM Sb(V) was accomplished within 17, 9, and 5h, respectively, along with no final Sb(III) recovery. Also, the bio-reduction of sulfate occurred synchronously. The precipitated Sb₂O₃ and Sb₂S₃ were characterized by scanning electron microscopy coupled with energy dispersive spectrometer, X-ray diffraction, and X-ray photoelectron spectroscopy. Compared with bacterial compositions of the seed sludge obtained from anaerobic digestion tank in a wastewater treatment plant, new genera of Pseudomonas and Geobacter emerged with large proportions in both Sb-fed and Sb-sulfate-fed sludge, and a small portion of sulfate reduction bacteria emerged only in Sb-sulfate-fed culture.

Calculation and application of Sb toxicity coefficient for potential ecological risk assessment

The potential ecological risk index (RI) is a diagnostic tool for pollution control which integrate the concentration of heavy metals with ecological effect, environmental effect and toxicity. However, the lack of toxicity coefficients for specific heavy metals limits its widespread use. In this study, we calculated the toxicity coefficient (=7) for antimony (Sb) based on Hakanson's principles, thus broadening the range of potential applications of this risk assessment tool. Taking the case of Xikuangshan (XKS), the largest Sb mine in the world, we predicted the potential ecological risk factor (E_rⁱ) of Sb for sediment and soil. This was then compared with the enrichment factor (EF) and index of geoaccumulation (I_geo). Results showed that Sb shared the similar pollution categories regardless of E_rⁱ, EF or I_geo indexes was used indicating the appropriateness of the determined toxicity coefficient. Regression analysis results further demonstrated that E_rⁱ was in agreement with bioavailable concentrations (Diffusive Gradient in Thin Films and Community Bureau of Reference extraction concentrations), particularly in sediments. This means that E_rⁱ is a reliable and logical index for evaluating Sb pollution in sediments within aquatic environments and in soils within terrestrial environments.

Fate and chemical speciation of antimony (Sb) during uptake, translocation and storage by rye grass using XANES spectroscopy

Antimony (Sb) is a contaminant of increased prevalence in the environment, but there is little knowledge about the mechanisms of its uptake and translocation within plants. Here, we applied for the synchrotron based X-ray absorption near-edge structure (XANES) spectroscopy to analyze the speciation of Sb in roots and shoots of rye grass (Lolium perenne L. Calibra). Seedlings were grown in nutrient solutions to which either antimonite (Sb(III)), antimonate (Sb(V)) or trimethyl-Sb(V) (TMSb) were added. While exposure to Sb(III) led to around 100 times higher Sb accumulation in the roots than the other two treatments, there was no difference in total Sb in the shoots. Antimony taken up in the Sb(III) treatment was mainly found as Sb-thiol complexes (roots: >76% and shoots: 60%), suggesting detoxification reactions with compounds such as glutathione and phytochelatins. No reduction of accumulated Sb(V) was found in the roots, but half of the translocated Sb was reduced to Sb(III) in the Sb(V) treatment. Antimony accumulated in the TMSb treatment remained in the methylated form in the roots. By synchrotron based XANES spectroscopy, we were able to distinguish the major Sb compounds in plant tissue under different Sb treatments. The results help to understand the translocation and transformation of different Sb species in plants after uptake and provide information for risk assessment of plant growth in Sb contaminated soils.

Health and ecological risk assessment of heavy metals pollution in an antimony mining region: a case study from South China

In recent years, international research on the toxicity of the heavy metal, antimony, has gradually changed focus from early medical and pharmacological toxicology to environmental toxicology and ecotoxicology. However, little research has been conducted for sources identification and risk management of heavy metals pollution by long-term antimony mining activities. In this study, a large number of investigations were conducted on the temporal and spatial distribution of antimony and related heavy metal contaminants (lead, zinc, and arsenic), as well as on the exposure risks for the population for the Yuxi river basin in the Hunan province, China. The scope of the investigations included mine water, waste rock, tailings, agricultural soil, surface water, river sediments, and groundwater sources of drinking water. Health and ecological risks from exposure to heavy metal pollution were evaluated. The main pollution sources of heavy metals in the Yuxi River basin were analyzed. Remediation programs and risk management strategies for heavy metal pollution were consequently proposed. This article provides a scientific basis for the risk assessment and management of heavy metal pollution caused by antimony basin ore mining.

Synthesis, Characterization, and Adsorptive Properties of Fe3O4/GO Nanocomposites for Antimony Removal

A magnetic Fe₃O₄/GO composite with potential for rapid solid-liquid separation through a magnetic field was synthesized using GO (graphene oxide) and Fe₃O₄ (ferriferous oxide). Characterization of Fe₃O₄/GO used scanning electron microscope (SEM), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), and Vibrating Sample Magnetometer (VSM). A number of factors such as pH and coexisting ions on adsorbent dose were tested in a series of batch experiments. The results showed that GO and Fe₃O₄ are strongly integrated. For pH values in the range of 3.0~9.0, the removal efficiency of Sb(III) using the synthesized Fe₃O₄/GO remained high (95%). The adsorption showed good fit to a pseudo-second-order and Langmiur model, with the maximum adsorption capacity of 9.59 mg/g maintained across pH 3.0-9.0. Thermodynamic parameters revealed that the adsorption process was spontaneous and endothermic. Analysis by X-ray photoelectron spectroscopy (XPS) showed that the adsorption process is accompanied by a redox reaction.

Antimony and sleep-related disorders: NHANES 2005-2008

BACKGROUND

Antimony is used as a flame-retardant in textiles and plastics, in semiconductors, pewter, and as pigments in paints, lacquers, glass and pottery. Subacute or chronic antimony poisoning has been reported to cause sleeplessness. The prevalence of short sleep duration (<7h/night) has been reported to be 37.1% in the general US population, and obstructive sleep apnea (OSA) affects 12-28 million US adults. Insufficient sleep and OSA have been linked to the development of several chronic conditions including diabetes, cardiovascular disease, obesity and depression, conditions that pose serious public health threats.

OBJECTIVE

To investigate whether there is an association between antimony exposure and sleep-related disorders in the US adult population using the National Health and Nutrition Examination Survey (NHANES) 2005-2008.

METHODS

We performed multivariate logistic regression to analyze the association of urinary antimony with several sleep disorders, including insufficient sleep and OSA, in adult (ages 20 years and older) participants of NHANES 2005-2008 (n=2654).

RESULT

We found that participants with higher urinary antimony levels had higher odds to experience insufficient sleep (≤6h/night) (OR 1.73; 95%CI; 1.04, 2.91) as well as higher odds to have increased sleep onset latency (>30min/night). Furthermore, we found that higher urinary antimony levels in participants were associated with OSA (OR 1.57; 95%CI; 1.05, 2.34), sleep problems, and day-time sleepiness.

CONCLUSION

In this study, we found that urinary antimony was associated with higher odds to have insufficient sleep and OSA. Because of the public health implications of sleep disorders, further studies, especially a prospective cohort study, are warranted to evaluate the association between antimony exposure and sleep-related disorders.

Low concentrations of antimony impair DNA damage signaling and the repair of radiation-induced DSB in HeLa S3 cells

Antimony is utilized in a large variety of industrial applications, leading to significant environmental and occupational exposure. Mainly based on animal experiments, the IARC and MAK Commission have classified antimony and its inorganic compounds as Group 2B or 2 carcinogens, respectively. However, the underlying mode(s) of action are still largely unknown. In the present study, we investigated the impact of non-cytotoxic up to cytotoxic concentrations of SbCl₃ on DNA DSB repair and cell cycle control in HeLa S3 cells. We induced DSB by γ-irradiation and analyzed inhibitory actions of antimony on potential molecular targets of the DSB repair machinery. Antimony disturbed cell cycle control, affecting phosphorylation of Chk1. Furthermore, the repair of DSB was impaired in the presence of antimony, as monitored by pulsed-field gel electrophoresis and γH2AX foci formation of cells in G1 and G2 phase. Specifically, BRCA1 and RAD51 were identified as molecular targets. Our results point towards an interference with both non-homologous end-joining (NHEJ) and homologous recombination (HR), and inhibitory effects may be explained by interactions with critical cysteine groups; this needs to be further investigated. Altogether, the results provide further evidence for the impairment of DNA repair processes as one underlying mechanism in antimony-induced carcinogenicity.

Meglumine Antimoniate (Glucantime) Causes Oxidative Stress-Derived DNA Damage in BALB/c Mice Infected by Leishmania (Leishmania) infantum

Leishmaniasis is a neglected tropical disease caused by >20 species of the protozoan parasite Leishmania Meglumine antimoniate (Glucantime) is the first-choice drug recommended by the World Health Organization for the treatment of all types of leishmaniasis. However, the mechanisms of action and toxicity of pentavalent antimonials, including genotoxic effects, remain unclear. Therefore, the mechanism by which meglumine antimoniate causes DNA damage was investigated for BALB/c mice infected by Leishmania (Leishmania) infantum and treated with meglumine antimoniate (20 mg/kg for 20 days). DNA damage was analyzed by a comet assay using mouse leukocytes. Furthermore, comet assays were followed by treatment with formamidopyrimidine-DNA glycosylase and endonuclease III, which remove oxidized DNA bases. In addition, the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) in the animals' sera were assessed. To investigate mutagenicity, we carried out a micronucleus test. Our data demonstrate that meglumine antimoniate, as well as L. infantum infection, induces DNA damage in mammalian cells by the oxidation of nitrogenous bases. Additionally, the antileishmanial increased the frequency of micronucleated cells, confirming its mutagenic potential. According to our data, both meglumine antimoniate treatment and L. infantum infection promote oxidative stress-derived DNA damage, which promotes overactivation of the SOD-CAT axis, whereas the SOD-GPx axis is inhibited as a probable consequence of glutathione (GSH) depletion. Finally, our data enable us to suggest that a meglumine antimoniate regimen, as recommended by the World Health Organization, would compromise GPx activity, leading to the saturation of antioxidant defense systems that use thiol groups, and might be harmful to patients under treatment.

Antimony oxidation and adsorption by in-situ formed biogenic Mn oxide and Fe-Mn oxides

Antimony (Sb), which can be toxic at relatively low concentrations, may co-exist with Mn(II) and/or Fe(II) in some groundwater and surface water bodies. Here we investigated the potential oxidation and adsorption pathways of Sb (III and V) species in the presence of Mn(II) and Mn-oxidizing bacteria, with or without Fe(II). Batch experiments were conducted to determine the oxidation and adsorption characteristics of Sb species in the presence of biogenic Mn oxides (BMOs), which were formed in-situ via the oxidation of Mn(II) by a Mn-oxidizing bacterium (Pseudomonas sp. QJX-1). Results indicated that Sb(III) ions could be oxidized to Sb(V) ions by BMO, but only Sb(V) originating from Sb(III) oxidation was adsorbed effectively by BMO. Introduced Fe(II) was chemically oxidized to FeOOH, the precipitates of which mixed with BMO to form a new compound, biogenic Fe-Mn oxides (BFMO). The BMO part of the BFMO mainly oxidized and the FeOOH of the BFMO mainly adsorbed the Sb species. In aquatic solutions containing both As(III) and Sb(III), the BFMO that formed in-situ preferentially oxidized Sb over As but adsorbed As more efficiently. Chemical analysis and reverse transcription real-time polymerase chain reaction revealed that the presence of Fe(II), As(III) and Sb(III) accelerated the oxidation of Mn(II) but inhibited the activity of Mn-oxidizing bacteria. These results provide significant insights into the biogeochemical pathways of Sb, Mn(II) in aquatic ecosystems, with or without Fe(II).

Antimony as a global dilemma: Geochemistry, mobility, fate and transport

Elevated concentrations of antimony (Sb) in environmental, biological and geochemical systems originating from natural, geological and anthropogenic sources are of particular global concern. This review presents a critical overview of natural geochemical processes which trigger the mobilization of Sb from its host mineral phases and related rocks to the surrounding environments. The primary source of Sb contamination in the environment is geogenic. The geochemical characteristics of Sb are determined by its oxidation states, speciation and redox transformation. Oxidative dissolution of sulfide minerals and aqueous dissolution are the most prevalent geochemical mechanisms for the release of Sb to the environment. Transformation of mobile forms of Sb is predominantly controlled by naturally occurring precipitation and adsorption processes. Oxyhydroxides of iron, manganese and aluminum minerals have been recognized as naturally occurring Sb sequestrating agents in the environment. Antimony is also immobilized in the natural environment via precipitation with alkali and heavy metals resulting extremely stable mineral phases, such as schafarzikite, tripuhyite and calcium antimonates. Many key aspects, including detection, quantification, and speciation of Sb in different environmental systems as well as its actual human exposure remain poorly understood. Identification of global distribution of most vulnerable Sb-contaminated regions/countries along with aquifer sediments is an urgent necessity for the installation of safe drinking water wells. Such approaches could provide the global population Sb-safe drinking and irrigation water and hinder the propagation of Sb in toxic levels through the food chain. Hence, raising awareness through the mobility, fate and transport of Sb as well as further transdisciplinary research on Sb from global scientific communities will be a crucial stage to establish a sustainable Sb mitigation on a global scale.

Occurrence and Distribution of Arsenic, Antimony and Selenium in Shallow Groundwater Systems of Ibadan Metropolis, Southwestern Nigerian

BACKGROUND

Arsenic, antimony and selenium contamination of groundwater is of great concern due to the potential detrimental effects to human health.

OBJECTIVES

This study investigates the occurrence and distribution of arsenic, antimony and selenium in the shallow groundwater system of Ibadan metropolis, southwestern Nigeria.

METHODS

A total of 210 groundwater samples were collected from 35 shallow wells (3.15-7.86 m) within the residential, commercial, industrial and agricultural areas of the metropolis during the dry and wet seasons. The average daily dose intake (ADD), hazard quotient (HQ) and hazard index (HI) of arsenic, antimony and selenium exposure in groundwater were calculated from these four studied areas for children and adults.

RESULTS

Average concentrations of arsenic, antimony and selenium in groundwater ranged between 2.17±3.49 to 33.8±37.2 μg/L, 13.5±15.0 to 33.2±36.8 μg/L and 7.33±6.22 to 46.3±22.4 μg/L, respectively. A corresponding analysis relay plot showed the order of occurrence of these trace metals in groundwater to be antimony>selenium>arsenic. The principal component analysis biplot showed that arsenic, antimony and selenium were fairly distributed in all of the study areas, suggesting the influence of geogenic factors. A total of 74.3% of sampling locations had antimony levels slightly above the World Health Organization (WHO) safe limit of 20 μg/L. Statistical t testing (0.05 confidence limit) showed a significant difference in seasonal levels of groundwater antimony concentration, with the dry season recording significantly higher levels with 100% of samples exceeding WHO safe limits. The chemical of highest potential human health concern is antimony, with a non-carcinogenic HQ risk factor >2 for both age groups. The overall non-carcinogenic HI was highest in the commercial area, 4.1989 for adults and 5.2487 for children.

CONCLUSIONS

Antimony in groundwater within the Ibadan metropolis raises health concerns and a concerted effort is needed to identify its sources to avoid the risk of antimony toxicity.

Antimony speciation as geochemical tracer for anthropogenic emissions of atmospheric particulate matter

The chemical composition of atmospheric particulate matter (PM) has been studied at the cities of Cordoba and Granada (South of Spain) between 2007 and 2013, considering urban background, traffic and industrial monitoring stations. The results of Principal Component Analysis (PCA) indicated that geochemical anomalies observed in the ambient air of Cordoba (mainly Cu, Zn, Pb and Cd) are closely related to the geochemical profile obtained from fugitive metallurgy emissions of brass industries. These findings have been confirmed performing an Sb speciation analysis of PM10 samples, which allowed to distinguish between Sb(III) and Sb(V). The percentage of Sb(V) in PM10 found in the traffic station of Granada was 64-69%. At Cordoba, the percentage of Sb(V) was found to be higher (73-77%) at both urban background and traffic stations, indicating a possible second source of Sb in the PM of this city. The PM10 samples from the industrial station of Cordoba showed a 85-86% of Sb(V). A similar percentage (84-88%) of Sb(V) was found for the fugitive emissions of the brass industries, confirming this industrial source of Sb. These results show that Sb speciation can be a useful geochemical tracer to identify anthropogenic sources (traffic and industrial) emissions of PM.

A microscopic and spectroscopic study of rapid antimonite sequestration by a poorly crystalline phyllomanganate: differences from passivated arsenite oxidation

Surface passivation during the adsorption of Mn(ii) and the formation of Mn(iii) was the predominant cause for the decrease in the As(iii) oxidation rate, whereas it may not have been the limiting factor during Sb(iii) oxidation.

Treatment of groundwater containing Mn(II), Fe(II), As(III) and Sb(III) by bioaugmented quartz-sand filters

High concentrations of iron (Fe(II)) and manganese (Mn(II)) often occur simultaneously in groundwater. Previously, we demonstrated that Fe(II) and Mn(II) could be oxidized to biogenic Fe-Mn oxides (BFMO) via aeration and microbial oxidation, and the formed BFMO could further oxidize and adsorb other pollutants (e.g., arsenic (As(III)) and antimony (Sb(III))). To apply this finding to groundwater remediation, we established four quartz-sand columns for treating groundwater containing Fe(II), Mn(II), As(III), and Sb(III). A Mn-oxidizing bacterium (Pseudomonas sp. QJX-1) was inoculated into two parallel bioaugmented columns. Long-term treatment (120 d) showed that bioaugmentation accelerated the formation of Fe-Mn oxides, resulting in an increase in As and Sb removal. The bioaugmented columns also exhibited higher overall treatment effect and anti-shock load capacity than that of the non-bioaugmented columns. To clarify the causal relationship between the microbial community and treatment effect, we compared the biomass of active bacteria (reverse-transcribed real-time PCR), bacterial community composition (Miseq 16S rRNA sequencing) and community function (metagenomic sequencing) between the bioaugmented and non-bioaugmented columns. Results indicated that the QJX1 strain grew steadily and attached onto the filter material surface in the bioaugmented columns. In general, the inoculated strain did not significantly alter the composition of the indigenous bacterial community, but did improve the relative abundances of xenobiotic metabolism genes and Mn oxidation gene. Thus, bioaugmentation intensified microbial degradation/utilization for the direct removal of pollutants and increased the formation of Fe-Mn oxides for the indirect removal of pollutants. Our study provides an alternative method for the treatment of groundwater containing high Fe(II), Mn(II) and As/Sb.

Disrupting ROS-protection mechanism allows hydrogen peroxide to accumulate and oxidize Sb(III) to Sb(V) in Pseudomonas stutzeri TS44

Background

Microbial antimonite [Sb(III)] oxidation converts toxic Sb(III) into less toxic antimonate [Sb(V)] and plays an important role in the biogeochemical Sb cycle. Currently, little is known about the mechanisms underlying bacterial Sb(III) resistance and oxidation.

Results

In this study, Tn5 transposon mutagenesis was conducted in the Sb(III)-oxidizing strain Pseudomonas stutzeri TS44 to isolate the genes responsible for Sb(III) resistance and oxidation. An insertion mutation into gshA, encoding a glutamate cysteine ligase involved in glutathione biosynthesis, generated a strain called P. stutzeri TS44-gshA₅₄₀. This mutant strain was complemented with a plasmid carrying gshA to generate strain P. stutzeri TS44-gshA-C. The transcription of gshA, the two superoxide dismutase (SOD)-encoding genes sodB and sodC as well as the catalase-encoding gene katE was monitored because gshA-encoded glutamate cysteine ligase is responsible for the biosynthesis of glutathione (GSH) and involved in the cellular stress defense system as are superoxide dismutase and catalase responsible for the conversion of ROS. In addition, the cellular content of total ROS and in particular H₂O₂ was analyzed. Compared to the wild type P. stutzeri TS44 and TS44-gshA-C, the mutant P. stutzeri TS44-gshA₅₄₀ had a lower GSH content and exhibited an increased content of total ROS and H₂O₂ and increased the Sb(III) oxidation rate. Furthermore, the transcription of sodB, sodC and katE was induced by Sb(III). A positive linear correlation was found between the Sb(III) oxidation rate and the H₂O₂ content (R² = 0.97), indicating that the accumulated H₂O₂ is correlated to the increased Sb(III) oxidation rate.

Conclusions

Based on the results, we propose that a disruption of the pathway involved in ROS-protection allowed H₂O₂ to accumulate. In addition to the previously reported enzyme mediated Sb(III) oxidation, the mechanism of bacterial oxidation of Sb(III) to Sb(V) includes a non-enzymatic mediated step using H₂O₂ as the oxidant.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0902-5) contains supplementary material, which is available to authorized users.

Heavy metals in drinking water: Occurrences, implications, and future needs in developing countries

Heavy metals in drinking water pose a threat to human health. Populations are exposed to heavy metals primarily through water consumption, but few heavy metals can bioaccumulate in the human body (e.g., in lipids and the gastrointestinal system) and may induce cancer and other risks. To date, few thousand publications have reported various aspects of heavy metals in drinking water, including the types and quantities of metals in drinking water, their sources, factors affecting their concentrations at exposure points, human exposure, potential risks, and their removal from drinking water. Many developing countries are faced with the challenge of reducing human exposure to heavy metals, mainly due to their limited economic capacities to use advanced technologies for heavy metal removal. This paper aims to review the state of research on heavy metals in drinking water in developing countries; understand their types and variability, sources, exposure, possible health effects, and removal; and analyze the factors contributing to heavy metals in drinking water. This study identifies the current challenges in developing countries, and future research needs to reduce the levels of heavy metals in drinking water.

Sources, migration and transformation of antimony contamination in the water environment of Xikuangshan, China: Evidence from geochemical and stable isotope (S, Sr) signatures

The Xikuangshan (XKS) mine in central China is the largest antimony (Sb) mine in the world. The mining activity has seriously contaminated the waters in the area. To determine the sources, migration and transformation of Sb contamination, 32 samples from groundwater (aquifer water), surface water and mine water were collected for water chemistry, trace element and SSO4 and Sr stable isotope analyses. The results showed that the groundwater and surface water were in an oxidized environment. The SSO4 and Sr isotope compositions in the water indicated that dissolved Sb and SO4(2) originated from sulfide mineral (Sb2S3) oxidation, whereas radiogenic Sr may have been sourced from silicified limestone and stibnite in the Shetianqiao aquifer. Furthermore, a positive correlation between δ(34)SSO4 and δ(87)Sr values revealed that the Sr, S and Sb in the waters had a common contamination source, i.e., silicified limestone and stibnite, whereas the Sr, S and Sb in rock and ore were sourced from Proterozoic basement clastics. The analysis also indicated that the isotope composition of dissolved SO4(2-) had been influenced by slight bacterial SO4 reduction in the Magunao aquifer. Mining or rock collapse may have caused Shetianqiao aquifer water to contaminate the Magunao aquifer water via mixing. This study has demonstrated that the stable isotopes of (34)SSO4 and (87)Sr, combined with hydrochemical methods, are effective in tracking the sources, migration and transformation of Sb contamination.

Kinetic modeling of antimony(III) oxidation and sorption in soils

Kinetic batch and saturated column experiments were performed to study the oxidation, adsorption and transport of Sb(III) in two soils with contrasting properties. Kinetic and column experiment results clearly demonstrated the extensive oxidation of Sb(III) in soils, and this can in return influence the adsorption and transport of Sb. Both sorption capacity and kinetic oxidation rate were much higher in calcareous Huanjiang soil than in acid red Yingtan soil. The results indicate that soil serve as a catalyst in promoting oxidation of Sb(III) even under anaerobic conditions. A PHREEQC model with kinetic formulations was developed to simulate the oxidation, sorption and transport of Sb(III) in soils. The model successfully described Sb(III) oxidation and sorption data in kinetic batch experiment. It was less successful in simulating the reactive transport of Sb(III) in soil columns. Additional processes such as colloid facilitated transport need to be quantified and considered in the model.