Arsenic levels and speciation from ingestion exposures to biomarkers in Shanxi, China: implications for human health

Assessment of internal exposure risk from metals pollution of occupational and non-occupational populations around a non-ferrous metal smelting plant

Non-ferrous metal smelting poses significant risks to public health. Specifically, the copper smelting process releases arsenic, a semi-volatile metalloid, which poses an emerging exposure risk to both workers and nearby residents. To comprehensively understand the internal exposure risks of metal(loid)s from copper smelting, we explored eighteen metal(loid)s and arsenic metabolites in the urine of both occupational and non-occupational populations using inductively coupled plasma mass spectrometry with high-performance liquid chromatography and compared their health risks. Results showed that zinc and copper (485.38 and 14.00 µg/L), and arsenic, lead, cadmium, vanadium, tin and antimony (46.80, 6.82, 2.17, 0.40, 0.44 and 0.23 µg/L, respectively) in workers (n=179) were significantly higher compared to controls (n=168), while Zinc, tin and antimony (412.10, 0.51 and 0.15 µg/L, respectively) of residents were significantly higher than controls. Additionally, workers had a higher monomethyl arsenic percentage (MMA%), showing lower arsenic methylation capacity. Source appointment analysis identified arsenic, lead, cadmium, antimony, tin and thallium as co-exposure metal(loid)s from copper smelting, positively relating to the age of workers. The hazard index (HI) of workers exceeded 1.0, while residents and control were approximately at 1.0. Besides, all three populations had accumulated cancer risks exceeding 1.0 × 10-4, and arsenite (AsIII) was the main contributor to the variation of workers and residents. Furthermore, residents living closer to the smelting plant had higher health risks. This study reveals arsenic exposure metabolites and multiple metals as emerging contaminants for copper smelting exposure populations, providing valuable insights for pollution control in non-ferrous metal smelting.

Trace Element Distribution and Arsenic Speciation in Toenails as Affected by External Contamination and Evaluation of a Cleaning Protocol

Trace element concentrations in toenail clippings have increasingly been used to measure trace element exposure in epidemeological research. Conventional methods such as inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography ICP-MS (HPLC-ICP-MS) are commonly used to measure trace elements and their speciation in toenails. However, the impact of the removal of external contamination on trace element quantification has not been thoroughly studied. In this work, the microdistribution of trace elements (As, Ca, Co, Cu, Fe, K, Mn, Ni, Rb, S, Sr, Ti, and Zn) in dirty and washed toenails and the speciation of As in situ in toenails were investigated using synchrotron X-ray fluorescence microscopy (XFM) and laterally resolved X-ray absorption near edge spectroscopy (XANES). XFM showed different distribution patterns for each trace element, consistent with their binding properties and nail structure. External (terrestrial) contamination was identified and distinguished from the endogenous accumulation of trace elements in toenails─contaminated areas were characterized by the co-occurrence of Co, Fe, and Mn with elements such as Ti and Rb (i.e., indicators of terrestrial contamination). The XANES spectra showed the presence of one As species in washed toenails, corresponding to As bound to sulfhydryl groups. In dirty specimens, a mixed speciation was found in localized areas, containing AsIII-S species and AsV species. ArsenicV is thought to be associated with surface contamination and exogenous As. These findings provide new insights into the speciation of arsenic in toenails, the microdistribution of trace elements, and the effectiveness of a cleaning protocol in removing external contamination.

Micro-distribution of arsenic in toenail clippings using laser ablation inductively coupled plasma mass spectrometry: implications for biomonitoring

Toenails are a common monitoring tool for arsenic exposure, but the risk of external contamination of toenails has cast doubt on its usefulness. The main objective of this study is to investigate the micro-distribution of arsenic through the dorsoventral plane of nail clippings to understand endogenous vs exogenous sources. We used laser-ablation inductively coupled plasma mass spectrometry to measure arsenic through a dorsoventral cross-section of the nail plate collected from reference (N = 17) and exposed individuals (N = 35). Our main results showed (1) bulk toenail concentrations measured using ICP-MS in this study ranged from 0.54 to 4.35 µg/g; (2) there was a double-hump pattern in arsenic concentrations, i.e., dorsal and ventral layers had higher arsenic than the inner layer; (3) the double-hump was more pronounced in the exposed group (ventral: 6.25 μg/g; inner: 0.75 μg/g; dorsal: 0.95 μg/g) than the reference group (ventral: 0.58 μg/g; inner: 0.15 μg/g; dorsal: 0.29 μg/g) on average; (4) the distribution was, in part, associated with different binding affinity of nail layers (i.e., ventral > dorsal > inner); (5) most individuals in the higher exposure group showed > 25% contamination in ventral and dorsal nail layers; and (6) there were no statistically significant correlations between LA-ICP-MS arsenic with either bulk toenail arsenic or urine arsenic from the same individuals. Our results on micro-distribution and binding affinity provide insight into the impact of external contamination on arsenic concentrations and show how LA-ICP-MS can access the protected inner nail layer to provide a more accurate result.

Assessing the health risks of coal-burning arsenic-induced skin damage: A 22-year follow-up study in Guizhou, China

Risk assessment of arsenic-induced skin damage has always received significant global attention. Theories derived from arsenic exposure in drinking water may not be applicable to the coal-burning type to arsenic-exposed area. Furthermore, very few studies have successfully determined the reference value of cumulative arsenic (CA) exposure that leads to specific skin lesions. In this study, we conducted a 22-year follow-up investigation to assess the risk of skin lesions and cancer resulting from long-term, multi-channel arsenic exposure from hazard identification, dose-response assessment, exposure assessment, and risk characterization. The results show that the arsenic exposure can significantly increase the prevalence of skin lesions. For each interquartile range increase of hair arsenic (HA) and CA, the risk of skin damage increased by 1.91 and 3.90 times, respectively. The lower confidence limit of the benchmark dose of HA of arsenic-induced various skin lesions ranged from 0.07 to 0.12 μg·g-1, and 932.57 to 1368.92 mg for CA. The chronic daily intake, lifetime average daily dose in the arsenic-exposed area after the comprehensive prevention and control measures have decreased significantly, but remained higher than the daily baseline level of 3.0 μg·kg-1·d-1. Even as recently as 2020, the hazard quotients and hazard index still exceeded 1, measuring 155.33 and 55.20, and the lifetime excess risk of skin cancer (2.80 × 10-3) remains significantly higher than the acceptable level of 10-6. Our study underscores the effectiveness of comprehensive prevention and control measures in managing high arsenic exposure in coal-burning arsenic poisoning areas. However, it is crucial to acknowledge that the risk of both non-carcinogenic and carcinogenic effects on the skin remains substantially higher than the acceptable level. We recommend setting reference limits for monitoring skin damage among individuals exposed to arsenic, with a recommended upper limit of 0.07 μg·g-1 for HA and a maximum acceptable level of 935.57 mg for CA.

Trace Metal(loid) Migration from Road Dust to Local Vegetables and Tree Tissues and the Bioaccessibility-Based Health Risk: Impacts of Vehicle Operation-Associated Emissions

Traffic activities release large amounts of trace metal(loid)s in urban environments. However, the impact of vehicle operation-associated emissions on trace metal(loid) enrichment in road dust and the potential migration of these trace metal(loid)s to the surrounding environment remain unclear. We evaluated the contamination, sequential fraction, and bioaccessibility of trace metal(loid)s in urban environments by assessing their presence in road dust, garden vegetables, and tree tissues, including bark and aerial roots, at a traffic-training venue impacted by vehicle operation emissions and, finally, calculated the bioaccessibility-based health risk. The results indicated a significant accumulation of trace metal(loid)s in road dust, with the highest lead (Pb), cadmium (Cd), and antimony (Sb) concentrations in the garage entrance area due to higher vehicle volumes, frequent vehicle starts and stops, and lower speeds. Aerial roots exposed to hill start conditions exhibited the highest Pb, Zn, and Sb levels, potentially caused by high road dust resuspension, confirming that this tree tissue is an appropriate bioindicator. Sequential extraction revealed high percentages of carbonate-, Fe/Mn oxide-, and organic/sulphide-associated fractions of Pb, copper (Cu), and zinc (Zn) in road dust, while most Cd, Cr, Ni, and Sb occurred as residual fractions. According to the potential mobilizable fractions in sequential extraction, the in vitro gastrointestinal method could be more suitable than the physiologically based extraction test to evaluate the bioaccessibility-related risk of traffic-impacted road dust. The bioaccessibility-based health risk assessment of the road dust or soil confirmed no concern about noncarcinogenic risk, while the major risk originated from Pb although leaded gasoline was prohibited before the venue establishment. Furthermore, the cancer risks (CRs) analysis showed the probable occurrence of carcinogenic health effects from Cd and Ni to adults and from Cd, Cr, and Ni to children. Furthermore, the Cd and Pb concentrations in the edible leaves of cabbage and radish growing in gardens were higher than the recommended maximum value. This study focused on the health risks of road dust directly impacted by vehicle emissions and provides accurate predictions of trace metal(loid) contamination sources in the urban environment.

Geochemical Contamination, Speciation, and Bioaccessibility of Trace Metals in Road Dust of a Megacity (Guangzhou) in Southern China: Implications for Human Health

Road dust has been severely contaminated by trace metals and has become a major health risk to urban residents. However, there is a lack of information on bioaccessible trace metals in road dust, which is necessary for an accurate health risk assessment. In this study, we collected road dust samples from industrial areas, traffic intersections, and agricultural fields from a megacity (Guangzhou), China, and conducted a geochemical enrichment, speciation, and bioaccessibility-based health risk assessment of trace metals. In comparison with local soil background values, the results revealed a significant accumulation of trace metals, including Zn, Cd, Cu, and Pb in the road dust, which is considered moderate to heavy pollution. Sequential extraction indicated that most trace metals in the road dust were primarily composed of a Fe/Mn oxide-bound fraction, carbonate-bound fraction, and residual fraction, while the dominant fraction was the organic matter-bound fraction of Cu, and the residual fractions of As, Cr, and Ni. The in vitro gastrointestinal (IVG) method revealed that high percentages of Zn, Cd, Cu, and As were bioaccessible, suggesting the possible dissolution of trace metals from adsorbed and carbonate-associated fractions in road dust exposed to the biological fluid matrix. The IVG bioaccessibility-based concentration largely decreased the noncarcinogenic health risk to a negligible level. Nevertheless, the entire population is still exposed to the cumulative probability of a carcinogenic risk, which is primarily contributed to by As, Cd, Cr, and Pb. Future identification of the exact sources of these toxic metals would be helpful for the appropriate management of urban road dust contamination.

Arsenic biotransformation in industrial wastewater treatment residue: Effect of co-existing Shewanella sp. ANA-3 and MR-1

Shewanella sp. ANA-3 with the respiratory arsenate reductase (ArrAB) and MR-1 with ferric reduction ability always coexist in the presence of high arsenic (As)-containing waste residue. However, their synergistic impacts on As transformation and mobility remain unclear. To identify which bacterium, ANA-3 or MR-1, dominates As mobility in the coexisting environment, we explored the As biotransformation in the industrial waste residue in the presence of Shewanella sp. ANA-3 and MR-1. The incubation results show that As(III) was the main soluble species, and strain ANA-3 dominated As mobilization. The impact of ANA-3 was weakened by MR-1, probably due to the survival competition between these two bacteria. The results of micro X-ray fluorescence and X-ray photoelectron spectroscopy analyses further reveal the pathway for ANA-3 to enhance As mobility. Strain ANA-3 almost reduced 100% surface-bound Fe(III), and consequently led to As(V) release. The dissolved As(V) was then reduced to As(III) by ANA-3. The results of this study help to understand the fate of arsenic in the subsurface and highlight the importance of the safe disposal of high As-containing industrial waste.

Arsenic Speciation and Metallomics Profiling of Human Toenails as a Biomarker to Assess Prostate Cancer Cases: Atlantic PATH Cohort Study

Chronic exposure to inorganic arsenic and trace metals has been linked to prostate cancer, and altered arsenic methylation capacity may have an important role in arsenic carcinogenesis. Biomarkers may be able to elucidate this role. Our objectives were to characterize profiles of arsenic species and metallome in toenails and urine samples, compare profiles between prostate cancer cases and controls, and determine the discriminant ability of toenail and urine biomarkers. Toenail samples (n = 576), urine samples (n = 152), and questionnaire data were sourced from the Atlantic Partnership for Tomorrow's Health (PATH) cohort study. Healthy controls were matched to prostate cancer cases (3:1 ratio) on sex, age, smoking status, and the province of residence. Metallome profiles and proportions of arsenic species were measured in toenail and urine samples. Analysis of covariance (ANCOVA) was used to compare the mean percent monomethylarsonic acid (%MMA), dimethylarsonic acid (%DMA), inorganic arsenic (%iAs), primary methylation index (PMI, MMA/iAs), and secondary methylation index (SMI, DMA/MMA). Multivariate analysis of covariance (MANCOVA) was used to compare selected metal concentrations. Mean %MMA was significantly lower and SMI was significantly higher in toenails from prostate cancer cases compared to controls in unadjusted and adjusted models. Proportions of arsenic species were correlated with total arsenic in toenails. Arsenic speciation in urine was not different between cases and controls, nor were metallome profiles in toenails and urine. Our results indicate that toenails are a viable biomarker for altered arsenic speciation in prostate cancer cases and may have greater utility than urine in this context.

Exposure Levels and Contributing Factors of Various Arsenic Species and Their Health Effects on Korean Adults

Arsenic is a human carcinogen. Data on urinary arsenic species analyses of Koreans are limited. This study evaluated the arsenic exposure level, contributing factors, and health effects in Korean adults. Dietary intake information and urine samples were obtained from 2044 participants. Arsenic exposure was assessed based on urinary concentrations of arsenic species, such as inorganic arsenic, As(III) and As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and arsenobetaine (AsB), using high-performance liquid chromatography with inductively coupled plasma mass spectrometry, followed by determination of biomarkers, malondialdehyde and c-peptide. The geometric mean concentrations were 30.9 μg/L for the sum of inorganic arsenic and their metabolites, and 84.7 μg/L for the total sum of arsenic measured. Urinary concentrations of arsenic species were influenced by age, inhabitant area (inland or coastal), and seafood intake, which was positively correlated with inorganic arsenic, DMA, and AsB. Rice intake was positively correlated with inorganic arsenic and its metabolites but not with AsB. Additionally, malondialdehyde and c-peptide levels were significantly associated with urinary concentrations of various arsenic species. Seafood and rice are major sources of organic/inorganic arsenic exposure in Korean adults; however, it is necessary to evaluate whether their overconsumption could have a potentially detrimental effect on human health.

Toenail speciation biomarkers in arsenic-related disease: a feasibility study for investigating the association between arsenic exposure and chronic disease

Long-term exposure to environmental arsenic has been associated with many chronic diseases, including several cancers, and diabetes. Urinary studies have implicated arsenic speciation as an important risk factor, however, such associations have not been replicated using toenail samples: a relatively new biosample for estimating long-term internal dose-exposure to arsenic. Despite having several advantages over conventional biosamples such as ease of collection and storage, standard methods for arsenic speciation analysis in toenails have not yet been established. The primary objectives of this study were to 1) establish an analytical method for arsenic speciation analysis in toenails, 2) describe preliminary arsenic speciation profiles of toenail samples from individuals with skin, lung, bladder, and kidney cancer, type II diabetes, and no known disease, and 3) determine if these speciation patterns differ between disease groups to inform the feasibility of subsequent research. A small cross-sectional feasibility study was carried out using 60 toenail samples and baseline questionnaire data from the Atlantic Partnership for Tomorrow's Health (Atlantic PATH) study. Arsenic speciation profiles were determined using high performance liquid chromatography (HPLC) paired with inductively coupled plasma-mass spectrometry (ICP-MS). While no differences in total arsenic were found, arsenic speciation profiles were significantly different between certain cancer groups and the reference group with no known disease. Specifically, the percentage of monomethylarsonic acid (%MMA) was found to be significantly higher in the toenails of individuals with lung cancer and kidney cancer, compared to healthy individuals with similar total arsenic exposure. To the best of our knowledge, this is the first study to describe arsenic speciation patterns in individuals with several arsenic-related diseases using toenails: a convenient, non-invasive, biobankable sample capable of longer-term exposure estimation than conventional biosamples. These preliminary data provide evidence that toenail arsenic speciation patterns differ between groups with arsenic-related disease, and those with no known disease. Toenail arsenic speciation analysis is feasible and could potentially have important implications for research on arsenic-related diseases. Further investigation is warranted and would benefit from including detailed arsenic exposure data to explore the observed heterogeneity in arsenic speciation profiles.

Arsenic exposure analysis for children living in central China: From ingestion exposure to biomarkers

Emerging evidence indicates that chronic low-dose arsenic (As) exposure can pose adverse health effects to children. This study aimed to systematically study the exposure risk induced by As ingestion in children living in Hubei Province, central China. The feasibility of first morning spot urine instead of 24-h urine as an environmental exposure biomarker was also explored. A total of 120 children aged 2-17 years were recruited from an urban area for the collection of biomarker samples (first morning and 24-h urine samples), environmental exposure samples (duplicate diets, drinking water, and soil), and related child-specific exposure factors. The external exposure risk, internal exposure level, and source of exposure to As in children were analyzed. The results indicated that As concentration in duplicated diets, water, and soil were 29.2 μg kg^-1, 1.3 μg L^-1, and 9.3 mg kg^-1, respectively; these were all below the corresponding maximum allowable levels in China (the threshold value of As in most food, drinking water and soil are 0.5 mg⸱kg^-1, 0.01 mg L^-1, and 20 mg⸱kg^-1, respectively). Dietary intake was the predominant exposure route, accounting for 90% of the total daily dose. The combined oral non-carcinogenic and carcinogenic risks all exceeded the corresponding maximum acceptable risk level. Therefore, As bioavailability should be investigated and used in health risk assessment. Multiple linear regression analysis indicated that urinary As was positively associated with dietary As, with a one-unit increase in daily As intake from the diet associating with 4.82 and 5.21 μg g^-1 increases in 24-h urine and first morning urine, respectively. Furthermore, significant correlations with 24-h urine and external exposure metrics suggested that creatine-adjusted As concentrations in first morning urine could be an appropriate substitute of 24-h urine as exposure biomarkers.

Environmental geochemistry of thioantimony: formation, structure and transformation as compared with thioarsenic

Antimony (Sb), a redox-sensitive toxic element, has received global attention due to the increased awareness of its rich geochemistry. The past two decades have witnessed the explosive development in geochemistry of oxyanionic Sb(OH)₃ and Sb(OH)₆^-. Emerging thioantimony species (Sb-S) have recently been detected, which actually dominate the Sb mobility in sulfate-reducing environments. However, the instability and complexity of Sb-S present the most pressing challenges. To overcome these barriers, it is urgent to summarize the existing research on the environmental geochemistry of Sb-S. Since Sb-S is an analogous species to thioarsenic (As-S), a comparison between Sb-S and As-S will provide insightful information. Therefore, this review presents a way of comparing environmental geochemistry between Sb-S and As-S. Here, we summarize the formation and transformation of Sb-S and As-S, their chemical structures and analytical methods. Then, the challenges and perspectives are discussed. Finally, the important scientific questions that need to be addressed are also proposed.

Usage of Si, P, Se, and Ca Decrease Arsenic Concentration/Toxicity in Rice, a Review

Rice is one of the most important routes for arsenic to enter the human food chain and threatens more than half of the world’s population. In addition, arsenic-contaminated soils and waters increase the concentration of this element in various tissues of rice plants. Thus, direct or indirect—infecting livestock and poultry—increase diseases such as respiratory diseases, gastrointestinal tract, liver, and cardiovascular diseases, cancer, and ultimately death in the long term. Therefore, finding different ways to reduce the uptake and transfer of arsenic by rice would reduce the contamination of rice plants with this dangerous element and improve animal and human nutrition and ultimately disease and mortality. In this article, we aim to take a small step in improving sustainable life on earth by referring to the various methods that researchers have taken to reduce rice contamination by arsenic in recent years. Adding micronutrients and macronutrients as fertilizer for rice is one way to improve this plant’s growth and health. In this study, by examining two types of macronutrients and two types of micronutrients, their role in reducing arsenic toxicity and absorption was investigated. Therefore, both calcium and phosphorus were selected from the macronutrients, and selenium and silicon were selected from the micronutrients, whose roles in previous studies had been investigated.

Current applications and future perspectives on elemental analysis of non-invasive samples for human biomonitoring

Humans are continuously exposed to numerous environmental pollutants including potentially toxic elements. Essential elements play an important role in human health. Abnormal elemental levels in the body, in different forms that existed, have been reported to be correlated with different diseases and environmental exposure. Blood is the conventional biological sample used in human biomonitoring. However, blood samples can only reflect short-term exposure and require invasive sampling, which poses infection risk to individuals. In recent years, the number of research evaluating the effectiveness of non-invasive samples (hair, nails, urine, meconium, breast milk, placenta, cord blood, saliva and teeth) for human biomonitoring is increasing. These samples can be collected easily and provide extra information in addition to blood analysis. Yet, the correlation between the elemental concentration in non-invasive samples and in blood is not well established, which hinders the application of those samples in routine human biomonitoring. This review aims at providing a fundamental overview of analytical methods of non-invasive samples in human biomonitoring. The content covers the sample collection and pretreatment, sample preparation and instrumental analysis. The technical discussions are separated into solution analysis and solid analysis. In the last section, the authors highlight some of the perspectives on the future of elemental analysis in human biomonitoring.

Exposure characteristics of antimony and coexisting arsenic from multi-path exposure in typical antimony mine area

In this study, samples of daily foods, drinking waters, surface waters, and soils were collected and screened to investigate the external exposure of Sb and As from various intake pathways in typical Sb mining area. Biomarker samples of residents were analyzed to monitor internal exposure characteristic of Sb and As in human body. Exposure dosages of As and Sb and transfer of Sb and As from environment to human body were estimated based on the external and internal exposure. The following results were obtained: daily intakes of food accounted for major intakes of both Sb and As, and highlighted the significance of foods intakes from rice and vegetable. The results of Monte Carlo simulations showed that total daily intake of Sb(n = 1444)and As(n = 1131) approximately reached 1.08 × 10^-2 mg/kg/d and 1.19 × 10^-3 mg/kg/d, in which 98.82% and 63.07% of residents have exceeded the threshold dosages of Sb and As. The contaminants contents in biomarkers indicated that Sb exhibited the similar internal exposure as As, while the total transfer rate of Sb from environment to human were estimated as approximately 2.04-2.40 times lower than As. This study also suggested that drinking water is another important pathway with high bioavailability and male resident may present higher priority than female in uptake of Sb and As. The paper suggested the similarity and difference on bioavailability existed in Sb and its group V elements, As, that would provide the essential information on exposure of Sb and As in the typical Sb mine area.

Root microbiome assembly of As-hyperaccumulator Pteris vittata and its efficacy in arsenic requisition

The assemblage of root-associated microorganisms plays important roles in improving their capability to adapt to environmental stress. Metal(loid) hyperaccumulators exhibit disparate adaptive capability compared to that of non-hyperaccumulators when faced with elevated contents of metal(loid)s. However, knowledge of the assemblage of root microbes of hyperaccumulators and their ecological roles in plant growth is still scarce. The present study used Pteris vittata as a model plant to study the microbial assemblage and its beneficial role in plant growth. We demonstrated that the assemblage of microbes from the associated bulk soil to the root compartment was based on their lifestyles. We used metagenomic analysis and identified that the assembled microbes were primarily involved in root-microbe interactions in P. vittata root. Notably, we identified that the assembled root microbiome played an important role in As requisition, which promoted the fitness and growth of P. vittata. This study provides new insights into the root microbiome and potential valuable knowledge to understand how the root microbiome contributes to the fitness of its host.

Enhanced arsenic removal from water by mass re-equilibrium: kinetics and performance evaluation in a binary-adsorbent system

Because arsenic (As) is highly toxic and carcinogenic, its efficient removal from drinking water is essential. Considering some adsorption media may adsorb As fast but are too expensive to be applied in a household, while others could be abundantly available at low cost but with slow uptake kinetics, we explored a novel mass re-equilibrium (MRE) process between two media with different adsorption characteristics to enhance the overall As removal. We employed an adsorbent with fast adsorption kinetics to grab As from water, and then allow it to transfer to a second adsorbent with large capacity for As retention. In the system containing two adsorbents separated by a dialysis membrane, the results showed that As associated with a fast-adsorbing iron-based ordered mesoporous carbon could diffuse to a slow-adsorbing but high-capacity iron-based activated carbon. Column tests were further conducted, showing that the mixed medium, composed of the two adsorbents, could be used to adsorb As at a very short empty bed contact time (≤ 1 min) and the removal was improved by the MRE that potentially redistributed solid-phase As during pump-off periods. This study points to a new direction that by the MRE process, novel binary-adsorbent approaches may be developed for contaminant removal, if suitable media and process configuration could be identified.

Arsenic Exposure and Incident Hypertension of Adult Residents Living in Rural Areas Along the Yangtze River, Anhui, China

OBJECTIVE

As a widespread toxic metal, arsenic had potential effect for hypertensive. We evaluated the association between urinary arsenic and the incidence of hypertension in adult residents along the Yangtze River of China.

METHODS

We conducted the study of 1358 adults 18 to 74 years of age from Chizhou, Maanshan, and Tongling of Anhui province, who participated in the baseline study in 2014 to 2015. Inductively coupled plasma optical emission spectrometry was used to measure urinary as of residents, and follow-up extended through 2016 to 2017.

RESULTS

We identified 275 hypertension events. The hazard ratios (HRs) of highest quartile arsenic compared with lowest quartile was 1.49 for hypertension events (95% confidence interval [CI] = 1.05 to 2.12), and HRs (≥P20 vs <P20) was 1.37 (95% CI = 1.02 to 1.84).

CONCLUSIONS

Higher level of arsenic exposure might play a role in increasing the incidence of hypertension.

Dietary exposure to arsenic and human health risks in western Tibet

The health effects of drinking water exposure to inorganic arsenic are well known but are less well defined for dietary exposure. The rising concerns of arsenic risks from diet motivated this study of arsenic concentrations in highland barley, vegetables, meat, and dairy products to evaluate arsenic exposure source and to assess health risks among rural residents of Ngari area, western Tibet. Total arsenic and arsenic speciation were measured by inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography combined with ICP-MS (HPLC-ICP-MS) respectively. Average total arsenic concentrations of 0.18 ± 0.21 (n = 45, median: 0.07 mg·kg^-1), 0.40 ± 0.57 (n = 17, median: 0.15 mg·kg^-1), 0.21 ± 0.16 (n = 12, median: 0.17 mg·kg^-1), and 0.18 ± 0.08 (n = 11, median: 0.22 mg·kg^-1) were observed in highland barley, vegetables, meat, and dairy products, respectively. Inorganic arsenic was determined to be the main species of arsenic in highland barley, accounting for about 64.4 to 99.3% (average 83.3%) of total arsenic. Nearly half (44.4%) of the local residents had ingested >3.0 × 10^-4 mg·kg^-1·d^-1 daily dose of arsenic from highland barley alone, above the maximum oral reference dose recommended by the United States Environmental Protection Agency (USEPA). The inorganic arsenic daily intake from highland barley was 3.6 × 10^-4 mg·kg^-1·d^-1. Dietary exposure to inorganic arsenic alone increased the cancer risk probability to 5.4 in 10,000, assuming that the inorganic arsenic in highland barley has the same carcinogenic effects as that in water.

Health risk-oriented source apportionment of PM2.5-associated trace metals

In health-oriented air pollution control, it is vital to rank the contributions of different emission sources to the health risks posed by hazardous components in airborne fine particulate matters (PM_2.5), such as trace metals. Towards this end, we investigated the PM_2.5-associated metals in two densely populated regions of China, the Yangtze River Delta (YRD) and Pearl River Delta (PRD) regions, across land-use gradients. Using the positive matrix factorization (PMF) model, we performed an integrated source apportionment to quantify the contributions of the major source categories underlying metal-induced health risks with information on the bioaccessibility (using simulated lung fluid) and speciation (using synchrotron-based techniques) of metals. The results showed that the particulate trace metal profiles reflected the land-use gradient within each region, with the highest concentrations of anthropogenically enriched metals at the industrial sites in the study regions. The resulting carcinogenic risk that these elements posed was higher in the YRD than in the PRD. Chromium was the dominant contributor to the total excessive cancer risks posed by metals while manganese accounted for a large proportion of non-carcinogenic risks. An elevated contribution from industrial emissions was found in the YRD, while traffic emissions and non-traffic combustion (the burning of coal/waste/biomass) were the common dominant sources of cancer and non-cancer risks posed by metals in both regions. Moreover, the risk-oriented source apportionment of metals did not mirror the mass concentration-based one, suggesting the insufficiency of the latter to inform emission mitigation in favor of public health. While providing region-specific insights into the quantitative contribution of major source categories to the health risks of PM_2.5-associated trace metals, our study highlighted the need to consider the health protection goal-based source apportionment and emission mitigation in supplement to the current mass concentration-based framework.

Simultaneous analysis of typical halogenated endocrine disrupting chemicals and metal(loid)s in human hair

Hair analysis has been an important approach in evaluating population exposure to various environmental factors. To meet the requirements of human environmental epidemiology studies, we aimed to develop an efficient method for simultaneous analysis of various metal(loid)s and some typical environmental halogenated endocrine disrupting chemicals (hEDCs) (i.e., polychlorinated biphenyls, polybrominated diphenyl ethers, and organochlorine pesticides, as well as some of their hydroxyl substituted metabolites) in a single hair sample. The hair was washed successively with surfactant solutions, methanol solvent, and deionized water to remove impurities attached to the hair surface. Efficiency was comprehensively compared among various washing strategies. The hair sample was further pulverized into fine powder with a median diameter (25th-75th percentile) of 8.6 (5.9-13.5) μm. The hair organic components were extracted by acetonitrile solvent and compared with the microwave-assisted extraction method. The hEDCs in the supernatant acetonitrile phase were quantified by gas chromatography-mass spectrometry, and the metal(loid)s in the precipitate hair were further analyzed by inductively coupled plasma mass spectrometry. Our developed method was further applied to analyze the hair samples of 165 pregnant women. The results showed that particles attached to the surface of the hair could not be washed off completely. However, we proposed a protocol framework to wash hair with relatively high efficience, which includes warm water incubation, and use of surfactant and organic solvent. The recoveries of the concerned hEDCs and metal(loid)s were overall in the range of 80% to 120%. For the women population, the method can efficiently recognize the typical exposure characteristics of the concerned hEDCs and metal(loid)s. Our study significantly ameliorated the deficiencies of the traditional hair washing strategy and developed an efficient method for simultaneous analysis of various metal(loid)s and hEDCs in a single hair sample. This method will provide important support for population complex exposure analysis and facilitate environmental exposome studies.

Metagenomic insights into microbial arsenic metabolism in shallow groundwater of Datong basin, China

Elevated arsenic (As) in groundwater is an urgent environmental problem that has caused serious endemic diseases in Datong basin, China. The fate and toxicity of As are generally regulated by microbial As metabolic processes. However, little is known about the microbial community and As metabolism in Datong basin. Herein, the microbial community structure and As metabolism genes in four wells with different levels of As concentration in Shanyin county were investigated using metagenomics approach. The results showed that the presence of As influenced the microbial communities, and Rhodococcus genus was significantly enriched in elevated As wells. As resistance genes were dominant from low to high As containing wells, and As efflux genes such as arsB and acr3 were positively correlated with As concentrations, suggesting that microbes tend to pump As out of the cell as a strategy for As detoxification. Other environmental factors including oxidation-reduction potential (ORP), total organic carbon (TOC), sulfate, and temperature also played a role in shaping the microbial community structure and As metabolic processes.

Spraying silicon to decrease inorganic arsenic accumulation in rice grain from arsenic-contaminated paddy soil

Addition of Si to soil can reduce As uptake and accumulation in rice, while also enhancing As release from soil particles via competing sorption sites in soil minerals with As. Foliar application of Si might be an alternative pathway to reduce As accumulation in rice. It is not clear which growing stage would be better for spraying different types of Si solution to reduce inorganic As in edible parts of rice. Soil pot experiments were conducted to investigate whether total As and inorganic As accumulation in rice grains was alleviated via spraying Si in As-contaminated paddy soil. The results showed that foliar Si application at the tillering or jointing stage significantly reduced As concentrations in rice husks and grain via inhibiting the translocation of As from straw to husk or grain compared with other growing stages. Spraying of Si at the tillering stage markedly decreased the concentrations of inorganic As in rice bran and polished rice, accounting for 27.3% and 61.4% respectively. Furthermore, spraying Si solution mixed with surfactant-Tween 80 not only dramatically reduced the total As in rice tissues by 48.8%, but also significantly alleviated the accumulation of inorganic As in rice grain by 49.2%. Spraying Si restricted inorganic As in rice grain through the mechanism by which foliar Si application at tillering stage increased the Si concentrations in shoot and root, which downregulated Si transporters of Lsi1 and Lsi2 in the root and Lsi6 in the blade and sheath significantly, and finally decreased As uptake and transport. Therefore, spraying Si is an alternative and efficient pathway to reduce inorganic As accumulation of rice grain in As-contaminated soil.

Spatial distribution and molecular speciation of copper in indigenous plants from contaminated mine sites: Implication for phytostabilization

Contaminated mining sites require ecological restoration work, of which phytoremediation using appropriate plant species is an attractive option. Our present study is focused on one typical contaminated mine site with indigenous plant cover. The X-ray absorption near edge structure (XANES) analysis indicated that Cu (the major contaminant) was primarily associated with goethite (adsorbed fraction), with a small amount of Cu oxalate-like species (organic fraction) in mine affected soil. With growth of plant species like Miscanthus floridulus and Stenoloma chusanum, the Cu-oxalate like organic species in rhizosphere soil significantly increased, with corresponding decrease in Cu-goethite. In the root cross-section of Miscanthus floridulus, synchrotron-based micro-X-ray fluorescence (μ-XRF) microscopy and micro-XANES results indicated that most Cu was sequestered around the root surface/epidermis, primarily forming Cu alginate-like species as a Cu-tolerance mechanism. From the root epidermis to the cortex and vascular bundle, more Cu(I)-glutathione was observed, suggesting reductive detoxification ability of Cu(II) to Cu(I) during the transport of Cu in the root. The observation of Cu-histidine in root internal cell layers showed another Cu detoxification pathway based on coordinating amino ligands. Miscanthus floridulus showed ability to accumulate phosphorous and nitrogen nutrients in rhizosphere and may be an option for in situ phytostabilization of metals in contaminated mining area.

A review of arsenic interfacial geochemistry in groundwater and the role of organic matter

Recent discoveries on arsenic (As) biogeochemistry in aquifer-sediment system have strongly improved our understanding of As enrichment mechanisms in groundwater. We summarize here the research results since 2015 focusing on the As interfacial geochemistry including As speciation, transformation, and mobilization. We discuss the chemical extraction and speciation of As in environmental matrices, followed by As redox change and (im)mobilization in typical minerals and aquifer system. Then, the microbial-assisted reductive dissolution of Fe (hydr)oxides and As transformation and liberation are summarized from the aspects of bacterial isolates, microbial community and gene analysis by comparing As rich groundwater cases worldwide. Finally, the potential effect of organic matter on As interfacial geochemistry are addressed in the aspects of chemical interactions and microbial respiring activities for Fe and As reductive release.

Arsenic mobilization from soils in the presence of herbicides

Arsenic (As) mobilization in soils is a fundamental step controlling its transport and fate, especially in the presence of the co-existing components. In this study, the effect of two commonly used herbicides, glyphosate (PMG) and dicamba, and two competing ions including phosphate and humic acid, on As desorption and release was investigated using batch and column experiments. The batch kinetics results showed that As desorption in the presence of competing factors conformed to the pseudo-second order kinetics at pH range of 5-9. The impact of phosphate on desorption was greatest, followed by PMG. The competitive effect of dicamba and humic acid was at the same level with electrolyte solution. In situ flow cell ATR-FTIR analysis was performed to explore the mechanism of phosphate and PMG impact on As mobilization. The results showed that PMG promoted As(III) desorption by competiting for available adsorption sites with no change in As(III) complexing structure. On the other hand, phophate changed As(III) surface complexes from bidentate to monodentate structures, exhibiting the most siginficant effect on As(III) desorption. As(V) surface complexes remained unchanged in the presence of PMG and phosphate, implying that the competitive effect for As(V) desorption was primarily determined by the available adsorption sites. Long-term (10 days) soil column experiments suggested that the effect of humic acid on As mobilization became pronounced from 3 days (18 PVs). The insights of this study help us understand the transport and fate of As due to herbicides application.

Oral Bioavailability of As, Pb, and Cd in Contaminated Soils, Dust, and Foods based on Animal Bioassays: A Review

Metal contamination in soil, dust, and food matrices impacts the health of millions of people worldwide. During the past decades, various animal bioassays have been developed to determine the relative bioavailability (RBA) of As, Pb, and Cd in contaminated soils, dust, and foods, which vary in operational approaches. This review discusses the strengths and weaknesses of different animal models (swine and mice), dosing schemes (single gavage dose, repeated gavage dose, daily repeated feeding, and free access to diet), and end points (blood, urine, and tissue) in metal-RBA measurement; compares metal-RBA obtained using mouse and swine bioassays, different dosing schemes, and different end points; and summarizes key findings on As-, Pb-, and Cd-RBA values in contaminated soils, dust, and foods. Future directions related to metal-RBA research are highlighted, including (1) comparison of metal-RBA determinations between different bioassays and different laboratories to ensure robust bioavailability data, (2) enhancing the metal-RBA database for contaminated dust and foods, (3) identification of physiological and physicochemical mechanisms responsible for variability in metal-RBA values, (4) formulation of strategies to decrease metal-RBA values in contaminated soils, dust, and foods, and (5) assessing the impacts of cocontaminants on metal-RBA measurement.

Simultaneous arsenic and fluoride removal using {201}TiO2-ZrO2: Fabrication, characterization, and mechanism

The coexistence of arsenic (As) and fluoride (F) in drinking water is an urgent environmental issue that causes increasing public concerns. The need for effective simultaneous removal of As and F has motived great research efforts. Herein, a novel {201}TiO₂-ZrO₂ composite was synthesized and its application mechanism was explored. Batch adsorption experiments show that the As(III), As(V), and F adsorption followed the pseudo-second-order kinetics with the Langmuir adsorption capacity at 58.5, 21.6, and 13.1 mg/g, respectively. EXAFS and in situ ATR-FTIR results suggested that TiO₂ surface sites were occupied by As(III) and As(V) in bidentate binuclear structures, and ZrO₂ sites preferentially adsorbed As(III) and F in monodentate mononuclear configurations. This molecular structure obtained in the mono-adsorption system was integrated with the charge distribution multisite surface complexation model to accurately predict the As and F co-existing adsorption behaviors. The results in competitive adsorption, regeneration, and application evidenced that the {201}TiO₂-ZrO₂ composite is a promising adsorbent for simultaneous As and F removal.

Arbuscular mycorrhizal fungi reduce arsenic uptake and improve plant growth in Lens culinaris

Arsenic (As) is a carcinogenic and hazardous substance that poses a serious risk to human health due to its transport into the food chain. The present research is focused on the As transport in different lentil genotypes and the role of Arbuscular Mycorrhizal Fungi (AMF) in mitigation of As phyto-toxicity. Arsenic transport from soil to root, shoot and grains in different lentil genotypes was analyzed by flow injection hydride generation atomic absorption spectrophotometry. AMF were applied for the reduction of As uptake as well as the improvement of plant growth in lentil genotypes. Arsenic phyto-toxicity was dose-dependent as evidenced by relatively higher shoot length, fresh and dry weight of root and shoot in 5 and 15 mgkg-1 As-treated lentil plants than that in 100 mgkg-1 As-treated lentil. Arsenic accumulation occurred in roots and shoots of all BARI-released lentil genotypes. Arsenic accumulation in grains was found higher in BARI Mashur 1 than other lentil genotypes. AMF treatment significantly increased growth and biomass accumulation in lentil compared to that in non-AMF plants. Furthermore, AMF effectively reduced the As concentrations in roots and shoots of lentil plants grown at 8 and 45 mgkg-1 As-contaminated soils. This study revealed remarkable divergence in As accumulation among different BARI-released lentil genotypes; however, AMF could reduce As uptake and mitigate As-induced phyto-toxicity in lentil. Taken together, our results suggest a great potential of AMF in mitigating As transfer in root and shoot mass and reallocation to grains, which would expand lentil cultivation in As-affected areas throughout the world.

Distribution and speciation of copper in rice (Oryza sativa L.) from mining-impacted paddy soil: Implications for copper uptake mechanisms

Long term mining activities can cause significant metal pollution in the environment, thereby showing potential risk to the paddy field. Elucidating the interfacial processes of trace metals from contaminated paddy soil to rice within the rhizosphere can provide important information on metal biogeochemistry and food safety. The current study aims to explore the spatial distribution and molecular speciation of Cu from rhizosphere to rice plant in a mining-impacted paddy soil, and reveal the possible uptake mechanisms. X-ray absorption near edge structure (XANES) analysis indicated that Cu was primarily associated with iron oxide and sulfide in soil with a minor proportion of organic complexed species. In the rice samples, Cu showed much higher concentrations in the roots than the shoots, as most Cu was sequestered in the root surface and epidermis (primarily in the form of C/N ligands bound Cu species), rather than root xylem, as identified by micro X-ray fluorescence (μ-XRF) imaging coupling with μ-XANES. By contrast, in the root xylem, thiol-S bound Cu(I) complex was observed, representing the reduced product of Cu(II) by thiol-S ligands in rice root. The absorbed Cu was probably transported from the root to the aerial part as C/N ligand bound Cu complex such as Cu-histidine like species, which was observed in the root xylem. The large retention capacity and reduction of Cu(II) in rice root alleviated Cu toxicity to rice, which was beneficial for food safety (e.g., lower concentration of Cu in rice grains). These findings showed for the first time that the uptake mechanisms by rice from field contaminated sites, which shed light on Cu detoxification process and potential remediation strategies.

On the Use of Hair Analysis for Assessing Arsenic Intoxication

Correlations between the concentrations of arsenic in scalp hair and in drinking water as well as in blood and/or urine have been reported. These correlations clearly show exposure–absorption–excretion relationships. In addition, arsenic metabolites such as monomethylarsonic acid and dimethylarsinic acid have been identified and quantified in these tissues and fluids, leaving little doubt that elevated levels of arsenic in the hair can reflect systemic arsenic intoxication. Consequently, hair analysis has potential merit as a screening procedure for poisoning by arsenic. However, questions regarding the exogenous versus the endogenous deposition of arsenic in the hair, and uncertainties about the normal level of arsenic in the hair remain unresolved. Pending their resolution, the determination of arsenic in hair should remain a screening tool, and clinical signs and symptoms should be employed to complete the diagnosis of arsenic poisoning.

Reductive transformation of nitroaromatic compounds by Pd nanoparticles on nitrogen-doped carbon (Pd@NC) biosynthesized using Pantoea sp. IMH

Reductive transformation of nitroaromatic compounds is a central step in its remediation in wastewater, and therefore has invoked extensive catalytical research with rare metals such as palladium (Pd). Herein, we report Pantoea sp. IMH assisted biosynthesis for Pd@NC as an efficient catalyst for the reduction of nitroaromatics. Multiple complementary characterization results for Pd@NC evidenced the evenly dispersed Pd NPs on an N-doped carbon support. Pd@NC exhibited the superior catalytic activity in the reduction of nitroaromatic compounds (4-nitrophenol, 2-nitroaniline, 4-nitroaniline, and 2,6-dichloro-4-nitroaniline). The origin of the catalytic activity was explained by its unique electronic structure, as explored with X-ray absorption near-edge structure (XANES) spectroscopy and density functional theory (DFT) calculations. XANES analysis revealed an increase of 25.6% in the d-hole count in Pd@NC compared with Pd°, as the result of pd hybridization. In agreement with our experimental observations, DFT calculations suggested the formation of Pd-C bonds and charge re-distribution between Pd and the carbon layer, which contributed to the superior catalytic activity of Pd@NC.

Coupling bioavailability and stable isotope ratio to discern dietary and non-dietary contribution of metal exposure to residents in mining-impacted areas

Both dietary and non-dietary pathways contribute to metal exposure in residents living near mining-impacted areas. In this study, bioavailability-based metal intake estimation coupled with stable Pb isotope ratio fingerprinting technique were used to discern dietary (i.e., rice consumption) and non-dietary (i.e., housedust ingestion) contribution to As, Cd, and Pb exposure in residents living near mining-impacted areas. Results showed that not only rice (n = 44; 0.10-0.56, 0.01-1.77, and 0.03-0.88 mg kg^-1) but also housedust (n = 44; 2.15-2380, 2.55-329, and 87.0-56,184 mg kg^-1) were contaminated with As, Cd, and Pb. Based on in vivo mouse bioassays, bioavailability of As, Cd, and Pb in rice (n = 11; 34 ± 15, 59 ± 13, and 31 ± 15%) were greater than housedust (n = 14; 17 ± 6.7, 46 ± 10, and 25 ± 6.8%). Estimated daily intake of As, Cd, and Pb after incorporating metal bioavailability showed that As intake via rice was 5-fold higher than housedust for adults, whereas As intake via housedust was 3-fold higher than rice for children. For both adults and children, rice was the main source for Cd exposure, while housedust was the predominant Pb contributor. To ascertain the dominant Pb source from housedust ingestion, stable Pb isotope ratios (²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb) of hair samples of local residents (n = 27, 0.8481 ± 0.0049 and 2.0904 ± 0.0102) were compared to housedust (n = 27, 0.8485 ± 0.0047 and 2.0885 ± 0.0107) and rice (n = 27, 0.8369 ± 0.0057 and 2.0521 ± 0.0119), showing an overlap between hair and housedust, but not rice, confirming that incidental housedust ingestion was the main source of Pb exposure. This study coupled bioavailability and stable isotope techniques to accurately identify the source of metal exposure as well as their potential health risk.

Antimony exposure and speciation in human biomarkers near an active mining area in Hunan, China

Antimony (Sb) exposure threatens human health. To identify human biomarkers for Sb exposure, we analyzed 480 environmental samples from an active Sb mining area in Hunan, China. Elevated Sb concentrations exceeding the reference level were detected in drinking water (70% of n = 83 total samples), foods (80%, n = 188), urine (95%, n = 63), saliva (44%, n = 48), hair (80%, n = 51) and nails (83%, n = 47). Drinking water contributed 85%-100% of the average daily dose (ADD) of Sb, and the total ADD (11.7 μg/kg bodyweight/day) was up to thirty times higher than the oral reference dose (0.4 μg/kg bodyweight/day) as recommended by USEPA. A positive correlation was found between ADD and Sb content in hair (p = 0.02), but not in urine (p = 0.051), saliva (p = 0.52) or nails (p = 0.85), suggesting that hair is the best non-invasive biomarker. Micro X-ray fluorescence analysis indicated that Sb is distributed in discrete spots in hair and nails, and Sb distribution is correlated with other metals. Methylated Sb species were predominant in urine (46%-100%) and saliva (74%-100%) in collected samples, implying that the human metabolic system adopts methylation as an effective pathway to detoxify and excrete Sb.

Screening of groundwater remedial alternatives for brownfield sites: a comprehensive method integrated MCDA with numerical simulation

Brownfield sites pollution and remediation is an urgent environmental issue worldwide. The screening and assessment of remedial alternatives is especially complex owing to its multiple criteria that involves technique, economy, and policy. To help the decision-makers selecting the remedial alternatives efficiently, the criteria framework conducted by the U.S. EPA is improved and a comprehensive method that integrates multiple criteria decision analysis (MCDA) with numerical simulation is conducted in this paper. The criteria framework is modified and classified into three categories: qualitative, semi-quantitative, and quantitative criteria, MCDA method, AHP-PROMETHEE (analytical hierarchy process-preference ranking organization method for enrichment evaluation) is used to determine the priority ranking of the remedial alternatives and the solute transport simulation is conducted to assess the remedial efficiency. A case study was present to demonstrate the screening method in a brownfield site in Cangzhou, northern China. The results show that the systematic method provides a reliable way to quantify the priority of the remedial alternatives.

Rethinking anaerobic As(III) oxidation in filters: Effect of indigenous nitrate respirers

Microorganisms play a key role in the redox transformation of arsenic (As) in aquifers. In this study, the impact of indigenous bacteria, especially the prevailing nitrate respirers, on arsenite (As(III)) oxidation was explored during groundwater filtration using granular TiO₂ and subsequent spent TiO₂ anaerobic landfill. X-ray absorption near edge structure spectroscopy analysis showed As(III) oxidation (46% in 10 days) in the presence of nitrate in the simulated anaerobic landfills. Meanwhile, iron (Fe) species on the spent TiO₂ were dominated by amorphous ferric arsenate, ferrihydrite and goethite. The Fe phase showed no change during the anaerobic landfill incubation. Batch incubation experiments implied that the indigenous bacteria completely oxidized As(III) to arsenate (As(V)) in 10 days using nitrate as the terminal electron acceptor under anaerobic conditions. The bacterial community analysis indicated that various kinds of microbial species exist in groundwater matrix. Phylogenetic tree analysis revealed that Proteobacteria was the dominant phylum, with Hydrogenophaga (34%), Limnohabitans (16%), and Simplicispira (7%) as the major bacterial genera. The nitrate respirers especially from the Hydrogenophaga genus anaerobically oxidized As(III) using nitrate as an electron acceptor instead of oxygen. Our study implied that microbes can facilitate the groundwater As oxidation using nitrate on the adsorptive media.

Antimony Redox Biotransformation in the Subsurface: Effect of Indigenous Sb(V) Respiring Microbiota

Anaerobic microbiological antimonate [Sb(V)] respiration is a newly discovered process regulating the Sb redox transformation in soils. However, little is known about the role microbiological Sb(V) respiration plays in the fate of Sb in the subsurface, especially in the presence of sulfate and electron shuttles. Herein, we successfully enriched a Sb(V) reducing microbiota (SbRM) from the subsurface near an active Sb mine. SbRM was dominated by genus Alkaliphilus (18-36%), Clostridiaceae (17-18%), Tissierella (24-27%), and Lysinibacillus (16-37%). The incubation results showed that SbRM reduced 88% of dissolved Sb(V) to Sb(III), but the total Sb mobility remained the same as in the abiotic control, indicating that SbRM alone did not increase the total Sb release but regulated the Sb speciation in the subsurface. Micro X-ray fluorescence (μ-XRF) analysis suggested the association of Sb and Fe, and electron shuttles such as anthraquinone-2,6-disulfonic disodium salt (AQDS) markedly enhanced the Sb release due to its ability to facilitate Fe mineral dissolution. Sb L-edge and S K-edge X-ray absorption near edge structure (XANES) results demonstrated that indigenous SbRM immobilized Sb via Sb₂S₃ formation, especially in a sulfur-rich environment. The insights gained from this study shed new light on Sb mobilization and its risk assessment in the subsurface environment.

Biomarkers of arsenic exposure in arsenic-affected areas of the Hetao Basin, Inner Mongolia

Seventy saliva samples, seventy urine samples, seventy nail samples, seventy hair samples, eight drinking water samples and ninety-three crop samples were collected from four villages of the Hetao Basin in Inner Mongolia to determine arsenic (As) exposure biomarkers and evaluate relationship between As uptake and human health risk. Trivalent As (As(III)), pentavalent As (As(V)), dimethylarsinic acid (DMA), arsenobetaine (AsB) and monomethylarsonic acid (MMA) were found in all urine samples. Only As(III) and As(V) were detected in saliva samples. In nail and hair samples, DMA, MMA, As(III) and As(V) were observed. Based on total As contents in crops and drinking water, the local residents' daily intake of total arsenic (TDI_As), the hazard quotient (HQ), and the cancer risk (R) were assessed. Male, older and cases of skin lesion participants generally had higher As contents in saliva, urine, nail and hair samples in relative to others. Salivary, urinary, nail and hair As were not significantly affected by body mass index (BMI) and smoking. Good correlations were observed between TDI_As and salivary, urinary, nail and hair As, showing that saliva, urine, nail and hair samples can be used as biomarkers of As exposure. Individually, levels of arsenicosis were positively correlated with TDI_As. The relationship between TDI_As and prevalence of arsenicosis concluded that, although As levels in crops and drinking water did not exceed national standards, they still pose a potential threat to human health. It was suggested that the maximum permissible levels of crop As and drinking water As should be re-evaluated for protecting human health.

Human health implications, risk assessment and remediation of As-contaminated water: A critical review

Arsenic (As) is a naturally occurring metalloid and Class-A human carcinogen. Exposure to As via direct intake of As-contaminated water or ingestion of As-contaminated edible crops is considered a life threatening problem around the globe. Arsenic-laced drinking water has affected the lives of over 200 million people in 105 countries worldwide. Limited data are available on various health risk assessment models/frameworks used to predict carcinogenic and non-carcinogenic health effects caused by As-contaminated water. Therefore, this discussion highlights the need for future research focusing on human health risk assessment of individual As species (both organic and inorganic) present in As-contaminated water. Various conventional and latest technologies for remediation of As-contaminated water are also reviewed along with a discussion of the fate of As-loaded waste and sludge.

Do Si/As ratios in growth medium affect arsenic uptake, arsenite efflux and translocation of arsenite in rice (Oryza sativa)?

Silicon (Si) may decrease the uptake and accumulation of arsenic (As) in rice. However, the effects of Si/As ratios in growth medium on arsenic uptake, arsenite efflux to the external medium and translocation of arsenite in rice are currently unclear. Rice seedlings (Oryza sativa L.) were exposed to nutrient solutions with 10 μM arsenite [As(III)] or 10 μM arsenate [As(V)] to explore the influence of different silicic acid concentrations (0, 10, 100, 1000 μM) on arsenic uptake and translocation of arsenite with or without 91 μM phosphate for 24 h. Arsenic speciation was determined in nutrient solutions, roots, and shoots. In the arsenite treatments, different Si/As ratios (1:1, 10:1, 100:1) did not affect As(III) uptake by rice roots, however they did inhibit translocation of As(III) from roots to shoots significantly (P < 0.001) in the absence of P. In the arsenate treatments, a Si/As ratio of 100:1 significantly decreased As(V) uptake and As(III) efflux compared with the control (Si/As at 0:1), accounting for decreases of 27.4% and 15.1% for -P treatment and 47.8% and 61.1% for + P treatment, respectively. As(III) is the predominant species of arsenic in rice roots and shoots. A Si/As ratio of 100:1 reduced As(III) translocation from roots to shoots markedly without phosphate. When phosphate was supplied, As(III) translocation from roots to shoots was significantly inhibited by Si/As ratios of 10:1 and 100:1. The results indicated that in the presence of P, different silicic acid concentrations did not impact arsenite uptake and transport in rice when arsenite was supplied. However, a Si/As ratio of 100:1 inhibited As(V) uptake, as well as As(III) efflux and translocation from roots to shoots when arsenate was supplied.

Speciation and leaching of trace metal contaminants from e-waste contaminated soils

Primitive electrical and electronic waste (e-waste) recycling activities have caused serious environmental problems. However, little is known about the speciation and leaching behaviors of metal contaminants at e-waste contaminated sites. This study investigated trace metal speciation/mobilization from e-waste polluted soil through column leaching experiments involving irrigation with rainwater for almost 2.5 years. Over the experimental period, Cu and Zn levels in the porewater were 0.14±0.08mg/L, and 0.16±0.08mg/L, respectively, increasing to 0.33±0.16mg/L, and 0.69±0.28mg/L with plant growth. The amounts of Cu, Zn, and Pb released in surface soil (0-2cm) contributed 43.8%, 22.5%, and 13.8%, respectively, to the original levels. The released Cu and Zn were primarily caused by the mobilization of the carbonate species of metals, including Cu(OH)₂, CuCO₃, and Zn₅(CO₃)₂(OH)₆, and amorphous Fe/Mn oxides associated fractions characterized by sequential extraction coupling with X-ray absorption spectroscopy. During the experiments, trace metals were not detected in the effluent, and the re-sequestration of trace metals was mainly attributed to the adsorption on the abundant Fe/Mn oxides in the sub-layer soil. This study quantitatively elucidated the molecular speciation of Cu and Zn in e-waste contaminated soil during the column leaching process.

Associations between Diet and Toenail Arsenic Concentration among Pregnant Women in Bangladesh: A Prospective Study

This prospective study evaluated the relationship between long-term dietary habits and total arsenic (As) concentration in toenail clippings in a cohort of 1616 pregnant women in the Bangladeshi administrative regions of Sirajdikhan and Pabna Sadar. Diet was assessed at Gestation Week 28 and at Postpartum Month 1, using a locally-validated dish-based semi-quantitative food-frequency questionnaire. Toenail As concentration was analyzed by microwave-assisted acid digestion and inductively coupled plasma mass spectrometry. Associations between natural log-transformed consumption of individual food items and temporally matched natural log-transformed toenail As concentration were quantified using general linear models that accounted for As concentration in the primary drinking water source and other potential confounders. The analysis was stratified by As in drinking water (≤50 μg/L versus >50 μg/L) and the time of dietary assessment (Gestation Week 28 versus Postpartum Week 1). Interestingly, toenail As was not significantly associated with consumption of plain rice as hypothesized. However, toenail As was positively associated with consumption of several vegetable, fish and meat items and was negatively associated with consumption of rice, cereal, fruits, and milk based food items. Further studies in pregnant women are needed to compare As metabolism at different levels of As exposure and the interaction between dietary composition and As absorption.

A perspective of chronic low exposure of arsenic on non-working women: Risk of hypertension

The relationship between arsenic (As) exposure and hypertension risk are extensively studied. The As content in scalp hair has been used as a reliable indicator of population for long-time exposure from different sources. Therefore, we investigated the association between hair As concentration and hypertension risk, as well as the potential modifying effects of single nucleotide polymorphisms (SNPs) related to phase II metabolism enzyme genes. We recruited 398 non-working women in Shanxi Province, northern China, from Aug 2012 to May 2013, including 163 subjects with hypertension (cases) and 235 healthy controls. Scalp hair and blood samples were collected from each subject. We analyzed the As concentrations of ~24-cm-long strands of hair representing the two most recent years of growth and SNPs of three genes (epoxide hydrolase 1, N-acetyltransferase 2, and glutathione S-transferase P1) in each subject. The results revealed that the hair As concentration of this population was significantly lower than in populations living near high As polluted sources in China and other countries. The median As concentration (inter-quartile range) of hair in the cases (i.e. 0.211 [0.114-0.395] μg/g hair) was higher than in the controls (i.e. 0.101 [0.048-0.227] μg/g hair). Higher hair As concentrations were associated with an elevated hypertension risk, with an adjusted odds ratio of 2.55 [95% confidence interval: 1.55-4.20]. No interaction effects between hair As concentration and SNPs related to phase II metabolism enzymes on hypertension risk were observed. It was concluded that chronic low exposure level of As might be associated with hypertension risk among the study subjects.

CoFe2O4@MIL-100(Fe) hybrid magnetic nanoparticles exhibit fast and selective adsorption of arsenic with high adsorption capacity

In this study, we report the synthesis and application of mesoporous CoFe₂O₄@MIL-100(Fe) hybrid magnetic nanoparticles (MNPs) for the simultaneous removal of inorganic arsenic (iAs). The hybrid adsorbent had a core-shell and mesoporous structure with an average diameter of 260 nm. The nanoscale size and mesoporous character impart a fast adsorption rate and high adsorption capacity for iAs. In total, 0.1 mg L⁻¹ As(V) and As(III) could be adsorbed within 2 min, and the maximum adsorption capacities were 114.8 mg g⁻¹ for As(V) and 143.6 mg g⁻¹ for As(III), higher than most previously reported adsorbents. The anti-interference capacity for iAs adsorption was improved by the electrostatic repulsion and size exclusion effects of the MIL-100(Fe) shell, which also decreased the zero-charge point of the hybrid absorbent for a broad pH adsorption range. The adsorption mechanisms of iAs on the MNPs are proposed. An Fe-O-As structure was formed on CoFe₂O₄@MIL-100(Fe) through hydroxyl substitution with the deprotonated iAs species. Monolayer adsorption of As(V) was observed, while hydrogen bonding led to the multi-layer adsorption of neutral As(III) for its high adsorption capacity. The high efficiency and the excellent pH- and interference-tolerance capacities of CoFe₂O₄@MIL-100(Fe) allowed effective iAs removal from natural water samples, as validated with batch magnetic separation mode and a portable filtration strategy.

Association of Arsenic Methylation Capacity with Developmental Delays and Health Status in Children: A Prospective Case-Control Trial

This case–control study identified the association between the arsenic methylation capacity and developmental delays and explored the association of this capacity with the health status of children. We recruited 120 children with developmental delays and 120 age- and sex-matched children without developmental delays. The health status of the children was assessed using the Pediatric Quality of Life Inventory (PedsQL) and Pediatric Outcomes Data Collection Instrument (PODCI). The arsenic methylation capacity was determined by the percentages of inorganic arsenic (InAs%), monomethylarsonic acid (MMA^V%), and dimethylarsinic acid (DMA^V%) through liquid chromatography and hydride generation atomic absorption spectrometry. Developmental delays were significantly positively associated with the total urinary arsenic concentration, InAs%, and MMA^V%, and was significantly negatively associated with DMA^V% in a dose-dependent manner. MMA^V% was negatively associated with the health-related quality of life (HRQOL; −1.19 to −1.46, P < 0.01) and functional performance (−0.82 to −1.14, P < 0.01), whereas DMA^V% was positively associated with HRQOL (0.33–0.35, P < 0.05) and functional performance (0.21–0.39, P < 0.01–0.05) in all children and in those with developmental delays. The arsenic methylation capacity is dose-dependently associated with developmental delays and with the health status of children, particularly those with developmental delays.

Proteomic profiling reveals candidate markers for arsenic-induced skin keratosis

Proteomics technology is an attractive biomarker candidate discovery tool that can be applied to study large sets of biological molecules. To identify novel biomarkers and molecular targets in arsenic-induced skin lesions, we have determined the protein profile of arsenic-affected human epidermal stratum corneum by shotgun proteomics. Samples of palm and foot sole from healthy subjects were analyzed, demonstrating similar protein patterns in palm and sole. Samples were collected from the palms of subjects with arsenic keratosis (lesional and adjacent non-lesional samples) and arsenic-exposed subjects without lesions (normal). Samples from non-exposed healthy individuals served as controls. We found that three proteins in arsenic-exposed lesional epidermis were consistently distinguishably expressed from the unaffected epidermis. One of these proteins, the cadherin-like transmembrane glycoprotein, desmoglein 1 (DSG1) was suppressed. Down-regulation of DSG1 may lead to reduced cell-cell adhesion, resulting in abnormal epidermal differentiation. The expression of keratin 6c (KRT6C) and fatty acid binding protein 5 (FABP5) were significantly increased. FABP5 is an intracellular lipid chaperone that plays an essential role in fatty acid metabolism in human skin. This raises a possibility that overexpression of FABP5 may affect the proliferation or differentiation of keratinocytes by altering lipid metabolism. KRT6C is a constituent of the cytoskeleton that maintains epidermal integrity and cohesion. Abnormal expression of KRT6C may affect its structural role in the epidermis. Our findings suggest an important approach for future studies of arsenic-mediated toxicity and skin cancer, where certain proteins may represent useful biomarkers of early diagnoses in high-risk populations and hopefully new treatment targets. Further studies are required to understand the biological role of these markers in skin pathogenesis from arsenic exposure.

Biological and behavioral factors modify urinary arsenic metabolic profiles in a U.S. population

BACKGROUND

Because some adverse health effects associated with chronic arsenic exposure may be mediated by methylated arsenicals, interindividual variation in capacity to convert inorganic arsenic into mono- and di-methylated metabolites may be an important determinant of risk associated with exposure to this metalloid. Hence, identifying biological and behavioral factors that modify an individual's capacity to methylate inorganic arsenic could provide insights into critical dose-response relations underlying adverse health effects.

METHODS

A total of 904 older adults (≥45 years old) in Churchill County, Nevada, who chronically used home tap water supplies containing up to 1850 μg of arsenic per liter provided urine and toenail samples for determination of total and speciated arsenic levels. Effects of biological factors (gender, age, body mass index) and behavioral factors (smoking, recent fish or shellfish consumption) on patterns of arsenicals in urine were evaluated with bivariate analyses and multivariate regression models.

RESULTS

Relative contributions of inorganic, mono-, and di-methylated arsenic to total speciated arsenic in urine were unchanged over the range of concentrations of arsenic in home tap water supplies used by study participants. Gender predicted both absolute and relative amounts of arsenicals in urine. Age predicted levels of inorganic arsenic in urine and body mass index predicted relative levels of mono- and di-methylated arsenic in urine. Smoking predicted both absolute and relative levels of arsenicals in urine. Multivariate regression models were developed for both absolute and relative levels of arsenicals in urine. Concentration of arsenic in home tap water and estimated water consumption were strongly predictive of levels of arsenicals in urine as were smoking, body mass index, and gender. Relative contributions of arsenicals to urinary arsenic were not consistently predicted by concentrations of arsenic in drinking water supplies but were more consistently predicted by gender, body mass index, age, and smoking.

CONCLUSIONS

These findings suggest that analyses of dose-response relations in arsenic-exposed populations should account for biological and behavioral factors that modify levels of inorganic and methylated arsenicals in urine. Evidence of significant effects of these factors on arsenic metabolism may also support mode of action studies in appropriate experimental models.