Origin of tungsten and geochemical controls on its occurrence and mobilization in shallow sediments from Fallon, Nevada, USA

In vitro tungsten bioaccessibility in Chinese residential soils: Implications for human health risk assessments and soil screening level derivation

Tungsten (W) contamination presents emerging environmental challenges, necessitating the need to establish soil screening levels (SSLs), especially for residential soils. This study assessed the health exposure risk and derived national and regional residential SSLs for W in Chinese residential soils, incorporating machine-learning prediction of in-vitro soil W bioaccessibility. We analyzed 204 residential soil samples collected across 24 provinces, recording a wide range of W concentrations (0.01-3063.2 mg/kg). Synchrotron-based X-ray fluorescence spectroscopy, chemical extractions, and random forest modeling indicated that the key determinants of soil W bioaccessibility were soil pH, cation exchange capacity, organic matter, and clay contents. Monte Carlo simulations demonstrated that soil W contamination predominantly results in noncarcinogenic health risks to residents via oral exposure, especially in mining-affected regions. A national residential SSL (NRSSL) of 35.5 mg/kg and regional residential SSLs (RRSSLs) of 34.5-49.2 mg/kg were established. Incorporating predicted bioaccessibility increased the NRSSL to 73.8 mg/kg and the RRSSLs to 69.8-112.5 mg/kg. Southern China, which is rich in W ore, exhibited lower RRSSLs, underscoring a need for enhanced safety management. Our framework and findings provide a robust scientific foundation for future soil contamination risk assessment studies, and we present customized SSLs that can guide targeted W risk control strategies.

Comparison of multiple preservation and digestion methods for determination of tungsten concentrations in environmental media using ICP-MS

Tungsten is an emerging environmental pollutant. However, a proved robust method for preserving and determining the concentrations of tungsten in environmental media is still lacking. This study examined and compared the suitability of classic methods and previously reported tungsten-oriented methods on preserving dissolved tungsten and recovering tungsten from soil/sediment matrix. Tungsten concentrations in the water samples and digestates were then determined by inductively coupled plasma mass spectrometry. Our data showed that the tungsten-oriented HF and alkaline preservatives indeed successfully maintained the stability of dissolved tungsten. Even when preserved using HNO3 or HCl, dissolved tungsten concentrations did not notably change in most of our water samples over the course of ∼4 months. Using glass containers for storing water samples also did not produce much difference from using high-density polyethylene containers. Our data further suggested that the addition of HF in digestion was important for tungsten solubilization from soil/sediment matrix. The digestion methods with HNO3/HCl/HF and HNO3/HF/NH4OH/EDTA both yielded quantitative recoveries of tungsten from certified reference materials and known synthetic samples, while the other tested methods had limited recoveries. The methods validated by this study could be used to accurately determine tungsten concentrations in environmental media and thereby to assess the fate and potential risks of tungsten.

Fe/Mn (oxyhydr)oxides reductive dissolution promoted by cyanobacterial algal bloom-derived dissolved organic matter caused sediment W release during an algal bloom in Taihu Lake

Tungsten (W) can be toxic to aquatic organisms. However, the spatiotemporal characteristics and controlling factors of W mobility during harmful algal blooms (HABs) have rarely been investigated. In this study, simultaneous changes in soluble W, iron (Fe), manganese (Mn), and ultraviolet absorbance (UV254) in the sediment-water interface (SWI) were measured monthly using high-resolution peeper (HR-Peeper) devices. Laboratory experiments were conducted to verify the effects of environmental factors on W release. From May 2021 to October 2021, the concentration and flux of soluble W were higher than in other months. In addition, from May to October, DMAX (the depth at which the maximum concentration occurs on each profile) was 30-50 mm below the SWI, rather than the maximum depth. Principal component analysis (PCA) also divided the year into two periods, designated W-stable (December 2020, January, March, April and November 2021 with low soluble W concentration) and W-active periods (from May 2021 to October 2021 with high soluble W concentration). Laboratory experiments showed that both warming and anoxic conditions caused simultaneous release of soluble W, Fe(II), Mn, and dissolved organic matter (DOM), with strong correlations among soluble W, Fe(II), Mn. Partial least squares path modeling (PLS-PM) and random forest model showed that DOM directly affected W release or indirectly affected W release through promoting ferromanganese (oxyhydr)oxides reduction under warming and anaerobic conditions. The results of the field investigation showed that, in the W-stable period with low T, high DO, and an oxic SWI, the concentrations of soluble W, Fe, Mn, and DOM were low. The redundancy analysis (RDA) showed that these months were mainly affected by water DO. The significant and strong positive correlation among soluble W, Fe and Mn indicated that soluble W was probably scavenged by Fe/Mn (oxyhydr)oxides in the oxic water during the W-stable period. The W-active period corresponded to the cyanobacterial HABs (cyanoHABs) outbreak, with higher T, lower DO, and a more anoxic SWI. During this period, the concentrations of soluble W, Fe, Mn, and DOM were high and their correlations were stronger. RDA showed that these months were mainly affected by T, UV254, soluble Fe and Mn. These results indicated that reductive dissolution of Fe/Mn (oxyhydr)oxides driven by DOM generated in W-active period, especially cyanoHAB-derived DOM, mainly caused soluble W release. These results reveal the coupling relationship between cyanoHABs and W release and emphasize the need for prevention and control of heavy metal release in eutrophic lakes.

Emerging activated tungsten dust: Source, environmental behaviors, and health effects

Fusion energy investigation has stepped to a new stage adopting deuterium and tritium as fuels from the previous stage concentrating hydrogen plasma physics. Special radiation safety issues would be introduced during this stage. In addition to industrial and military uses, tungsten is also regarded as the most promising plasma facing material for fusion reactors. During the operation of fusion reactors, tungsten-based plasma facing materials can be activated via neutron nuclear reaction. Meanwhile, activated tungsten dust can be produced when high-energy plasma interacts with the tungsten-based plasma facing materials, namely plasma wall interaction. Activated tungsten dust would be an emerging environmental pollutant with radiation toxicity containing various radionuclides in addition to the chemical toxicity of tungsten itself. Nonetheless, the historical underestimation of its environmental availability has led to limited research on tungsten compared to other environmental contaminants. This paper presents the first systematic review on the safety issue of emerging activated tungsten dust, encompassing source terms, environmental behaviors, and health effects. The key contents are as follows: 1) to detail the source terms of activated tungsten dust from aspects of tungsten basic properties, generation mechanism, physical morphology and chemical component, radioactivity, as well as potential release pathways, 2) to illustrate the environmental behaviors from aspects of atmospheric dispersion and deposition, transformation and migration in soil, as well as plant absorption and distribution, 3) to identify the toxicity and health effects from aspects of toxicity to plants, distribution in human body, as well as health effects by radiation and chemical toxicity, 4) based on the research progress, research and development issues needed are also pointed out to better knowledge of safety issue of activated tungsten dust, which would be beneficial to the area of fusion energy and ecological impact caused by the routine tungsten related industrial and military applications.

Accelerating bioleaching of tungsten mining wastes using indigenous acidophilic bacteria

The growing amount of W mining waste produced globally is of concern for its proven hazard to the environment and to human health. While uncontrolled biooxidation can result in environmental harm, bioleaching, where pregnant leach solutions are controlled, has been widely used in the mining industry for valuable metals recovery, often from low-grade materials. This bioleaching study was developed to evaluate whether the biogeochemical reprocessing of W tailings could be employed for the decontamination of W-bearing mine waste, combined with valuable metals recovery, i.e., turning a waste into a resource. Using an in-vitro laboratory model, the susceptibility of wolframite [(Fe,Mn)WO₄] to acid dissolution during the concomitant oxidation of co-localized sulfidic minerals represented the basic strategy for enhanced W recovery. Encouragingly, geochemistry and synchrotron-based X-ray absorption near edge structure of weathered W tailings demonstrated that early-stage wolframite dissolution occurred. However, W dissolution was limited by the formation of secondary W minerals; weathering produced two secondary W minerals i.e., gallium-rich tungstate and minor sanmartinite [(Zn,Fe)WO₄]. The dissolution and re-precipitation of W minerals may provide a strategy for W waste reprocessing if the two processes can be separated by initially putting W into solution, and allowing for its extraction from tailings, followed by its' recovery by secondary W mineral formation.

Sediment Spatial Distribution and Quality Assessment of Metals in Chinook Salmon and Resident Killer Whale Marine Habitat in British Columbia, Canada

At-risk resident killer whale (Orcinus orca) populations of the northeastern Pacific, Canada, and their main prey, Chinook Salmon (Oncorhynchus tshawytscha), are exposed to a variety of contaminants including chemical elements from both natural and anthropogenic sources, which may be constraining their recovery. Concentrations of 36 chemical elements in subtidal surface sediments (1-435 m depth) collected from 98 sites along the British Columbia coast were used to characterize coast-wide patterns, and a subset of metals (mercury (Hg), cadmium (Cd), arsenic (As), nickel (Ni), copper (Cu), and lead (Pb)) were selected to assess Chinook Salmon and resident killer whale marine habitat quality. Principal component analysis (PCA) showed a dominance of Hg, antimony (Sb), Pb, Cu, and zinc (Zn) for Prince Rupert Harbour, Victoria Harbour, and Burrard Inlet, suggesting local sources. Based on the PCA, geochemical properties such as total organic carbon (TOC), acid volatile sulfide (AVS), and pH explained the spatial distribution of all elements in sediment (p < 0.001). Mercury, Cd, As, Ni, Cu, and Pb hotspots were identified along the coast of Vancouver Island, the central and north coast, in the Strait of Georgia, and Haida Gwaii. Bischof Island of Haida Gwaii and Ardmillan Bay on the central coast were most contaminated and enriched by Cd, determined by geoaccumulation index (Igeo) and enrichment factor (EF), respectively. Marine habitat quality was assessed by comparing metal concentrations to Canadian Sediment Quality Guidelines (SQGs). Chinook Salmon populations may be indirectly affected by metal toxicity (As > Cd and Cu > Ni > Hg > Pb) to lower trophic level prey species. Toxicity related impacts to benthic organisms as a result of exposure to elevated Cd and As concentrations in Northern Resident Killer Whale critical habitat and to Hg, Cd, As, Ni, Cu, and Pb concentrations in Southern Resident Killer Whale critical habitat may indirectly pose a threat to resident killer whale populations, highlighting a need for management actions to reduce risks associated with these metals.

Soil ridging combined with biochar or calcium-magnesium-phosphorus fertilizer application: Enhanced interaction with Ca, Fe and Mn in new soil habitat reduces uptake of as and Cd in rice

Reducing the bioavailability of both cadmium (Cd) and arsenic (As) in paddy fields is a worldwide challenge. The authors investigated whether ridge cultivation combined with biochar or calcium-magnesium-phosphorus (CMP) fertilizer effectively reduces the accumulation of Cd and As in rice grains. Field trial showed that applying biochar or CMP on the ridges was similar to the continuous flooding, which maintained grain Cd at a low level, but grain As was reduced by 55.6%, 46.8% (IIyou28) and 61.9%, 59.3% (Ruiyou 399). Compared with ridging alone, the application of biochar or CMP decreased grain Cd by 38.7%, 37.8% (IIyou28) and 67.58%, 60.98% (Ruiyou399), and reduced grain As by 38.9%, 26.9% (IIyou28) and 39.7%, 35.5% (Ruiyou 399). Microcosm experiment showed that applying biochar and CMP on the ridges decreased As in soil solution by 75.6% and 82.5%, respectively, and kept Cd at a comparably low level at 0.13-0.15 μg L^-1. Aggregated boosted tree (ABT) analysis revealed that ridge cultivation combined with soil amendments altered soil pH, redox state (Eh) and enhanced the interaction of Ca, Fe, Mn with As and Cd, which promoted the concerted reduction of As and Cd bioavailability. Application of biochar on the ridges enhanced the effects of Ca and Mn to maintain a low level of Cd, and enhanced the effects of pH to reduce As in soil solution. Similar to ridging alone, applying CMP on the ridges enhanced the effects of Mn to reduce As in soil solution, and enhanced the effects of pH and Mn to maintain Cd at a low level. Ridging also promoted the association of As with poorly/well-crystalline Fe/Al and the association of Cd on Mn-oxides. This study provides an effective and environmentally friendly method to decrease Cd and As bioavailability in paddy fields and mitigate Cd and As accumulation in rice grain.

Multiple mechanisms collectively mediate tungsten homeostasis and resistance in Citrobacter sp. Lzp2

Tungsten (W) is an emerging contaminant, and current knowledge on W resistance profiles of microorganisms remains scarce and fragmentary. This study aimed to explore the physiological responses of bacteria under W stress and to resolve genes and metabolic pathways involved in W resistance using a transcriptome expression profiling assay. The results showed that the bacterium Citrobacter sp. Lzp2, screened from W-contaminated soil, could tolerate hundreds of mM W(VI) with a 50% inhibiting concentration of ∼110 mM. To cope with W stress, Citrobacter sp. Lzp2 secreted large amounts of proteins through the type VI secretory system (T6SS) to chelate W oxoanions via carboxylic groups in extracellular polymeric substances (EPS), and could transport cytosolic W outside via the multidrug efflux pumps (mdtABC and acrD). Intracellular W is probably bound by chaperone proteins and metal-binding pterin (tungstopterin) through the sulfur relay system. We propose that tetrathionate respiration is a new metabolic pathway for cellular W detoxification likely producing thio-tungstate. We conclude that multiple mechanisms collectively mediate W homeostasis and resistance in Citrobacter sp. Lzp2. Our results have important implications not only for understanding the intricate regulatory network of W homeostasis in microbes but also for bio-recovery and bioremediation of W in contaminated environments.

Microbially influenced tungsten mobilization and formation of secondary minerals in wolframite tailings

Wolframite [(Fe,Mn)WO₄] tailings represent a hazardous waste that can pose a threat to the environment, humans, animals and plants. The present study aims to conduct a high-resolution depth profile characterization of wolframite tailings from Wolfram Camp, North Queensland, Australia, to understand the biogeochemical influences on W mobilization. Several indigenous Fe- and S-oxidizing bacteria (e.g., Streptococcus pneumoniae and Thiomonas delicata) in wolframite tailings were found highly associated with W, As, and rare earth elements. Biooxidation of metal sulfides, i.e., pyrite, molybdenite and bismuthinite, produced sulfuric acid, which accelerated the weathering of wolframite, mobilizing tungstate (WO₄^2-). Using synchrotron-based X-ray fluorescence microscopy (XFM) and W L-edge X-ray absorption near-edge spectroscopy (µ-XANES) analysis, wolframite was initially transformed into Na- and Bi- tungstate as well as tungstic acid (partial weathering) followed by the formation of Ga- and Zn- tungstate after extensive weathering, i.e., the wolframite had disappeared. While W (VI) was the major W species in wolframite tailings, minor W(0) and W(II), and trace W(IV) were also detected. The major contaminant in the Wolfram Camp tailings was As. Though wolframite tailings are hazardous waste, the toxicity of W was unclear. Tungsten waste still has industrial value; apart from using them as substitution material for cement and glass production, there is interest in reprocessing W waste for valuable metal recovery. If the environmental benefits are taken into consideration, i.e., preventing the release of toxic metals into surrounding waterways, reprocessing may be economic.

Speciation, leachability and bioaccessibility of tungsten in tungsten ore processing residue

Tungsten ore processing residue (TOPR) poses a potential risk due to tungsten (W) leaching. However, the leachability of W in TOPR is not well understood. Herein, the mechanism of W leachability from TOPR was investigated using complementary characterization techniques and leaching experiments. Our X-ray absorption near edge structure (XANES) analysis resolved wolframite in TOPR with a distorted octahedral coordination. The sequential extraction procedure showed that 78% of mobile fraction W in TOPR were bound to Fe oxides, and consequently W leachability was positively correlated with dissolved Fe concentration as evidenced by the general acid neutralizing capacity (GANC) test. The GANC results showed that the W release was negatively correlated with Ca concentration due to CaWO₄ precipitation. The in vitro gastrointestinal procedure (IVG) results indicated that organic acids, abundant in fruits and vegetables, significantly improved the bioaccessibility of W from 10% to 20% of total W in TOPR. As a consequence, accidental ingestion of TOPR with a chemical daily intake at 0.8 mg kg^-1 day^-1 evidenced its emerging concern in the environment and human health.

Tungsten distribution and vertical migration in soils near a typical abandoned tungsten smelter

As an emerging contaminant, tungsten's distribution and speciation in soils are far from understood. In this study, two soil profiles near a typical abandoned tungsten smelter in Hunan Province, China were collected and investigated, to ascertain the binding and association of tungsten with different soil components and subsequently to understand its mobility. The data showed that past tungsten smelting activities resulted in elevated concentrations of both tungsten and arsenic in the soil profiles, both of which ranged from dozens of to a few hundred mg/kg. Nano-scale secondary ion mass spectrometry (NanoSIMS) was employed to quantify the distribution and association of tungsten with various other elements. Combined with sequential extraction and mineralogical analysis, the data from NanoSIMS showed that aluminosilicates including kaolinite and illite were the most important mineral hosts for tungsten, whereas arsenic was predominantly bound to iron (oxyhydr)oxides. Additional data from ¹³C nuclear magnetic resonance and X-ray photoelectron spectroscopy revealed that soil organic matter retained tungsten in deep soils (>70 cm) by binding tungsten through carboxyls on aromatic rings. Compared to arsenic, tungsten migrated deeper in the soil profiles, suggesting its higher mobility and potential risk to groundwater quality.

Natural dissolved organic matter (DOM) affects W(VI) adsorption onto Al (hydr)oxide: Mechanisms and influencing factors

Tungsten (W) is a contaminant with health implications whose environmental behaviors are not understood well. Sorption to mineral surfaces is one of the primary processes controlling the mobility and fate of W in soils, sediments, and aquifers. However, few papers published hitherto have not yet figured out the influences of dissolved organic matter (DOM) on this process. Here, we examine W(VI) adsorption behaviors onto Al (hydr)oxide (AAH) in the presence or absence of DOM derived from plant rhizosphere, using batch experiments coupled with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The morphology and functional group analyses results show that DOM can facilitate the aggregation of AAH and block surface Al-OH groups. Coexisting DOM inhibits W(VI) adsorption onto AAH at acidic to neutral pH (4-7), and the presence of either Na ⁺ or PO₄^3- can exert a completely different impact on W(VI) adsorption. XPS and FTIR characterizations further demonstrate surface W complexes with the Al-OH groups of AAH and carboxyl groups of DOM. There is no reduction of W(VI) during the adsorption processes, and poly-tungstate species are formed on the surface of both AAH and AAH-DOM coprecipitates. This study provides the first evidence of the roles of natural DOM on W sequestration at the mineral-water surface, which has an important implication for the prediction of the migration and bioavailability of W in natural environments.

Naturally occurring potentially toxic elements in groundwater from the volcanic landscape around Mount Meru, Arusha, Tanzania and their potential health hazard

The population of the semi-arid areas of the countries in the East African Rift Valley (EARV) is faced with serious problems associated with the availability and the quality of the drinking water. In these areas, the drinking water supply largely relies on groundwater characterised by elevated fluoride concentration (> 1.5 mg/L), resulting from interactions with the surrounding alkaline volcanic rocks. This geochemical anomaly is often associated with the presence of other naturally occurring potentially toxic elements (PTEs), such as As, Mo, U, V, which are known to cause adverse effects on human health. This study reports on the occurrence of such PTEs in the groundwater on the populated flanks of Mt. Meru, an active volcano situated in the EARV. Our results show that the majority of analysed PTEs (Al, As, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Se, Sr, Pb, and Zn) are within the acceptable limits for drinking purpose in samples collected from wells, springs and tap systems, suggesting that there is no immediate health risk associated with these PTEs. However, some of the samples were found to exceed the WHO tolerance limit for U (> 30 μg/L) and Mo (> 70 μg/L). The sample analysis also revealed that in some of the collected samples, the concentrations of total dissolved solids, Na⁺ and K⁺ exceed the permissible limits. The concerning levels of major parameters and PTEs were found to be associated with areas covered with debris avalanche deposits on the northeast flank, and volcanic ash and alluvial deposits on the southwest flanks of the volcano. The study highlights the need to extend the range of elements monitored in the regional groundwater and make a more routine measurement of PTEs to ensure drinking water safety and effective water management measures.

The Dynamics of Tungsten in Soil: An Overview

The increasing use of tungsten in the production of green energy in the aerospace and military industries, and in many other hi-tech applications, may increase the content of this element in soil. This overview examines some aspects of the behavior of tungsten in soil, such as the importance of characteristics of soils in relation to bioavailability processes, the chemical approaches to evaluate tungsten mobility in the soil environment and the importance of adsorption and desorption processes. Tungsten behavior depends on soil properties of which the most important is soil pH, which determines the solubility and polymerization of tungstate ions and the characteristics of the adsorbing soil surfaces. During the adsorption and desorption of tungsten, iron, and aluminum oxides, and hydroxides play a key role as they are the most important adsorbing surfaces for tungsten. The behavior of tungsten compounds in the soil determines the transfer of this element in plants and therefore in the food chain. Despite the growing importance of tungsten in everyday life, environmental regulations concerning soil do not take this element into consideration. The purpose of this review is also to provide some basic information that could be useful when considering tungsten in environmental legislation.

A Review of Tungsten Resources and Potential Extraction from Mine Waste

Tungsten is recognized as a critical metal due to its unique properties, economic importance, and limited sources of supply. It has wide applications where hardness, high density, high wear, and high-temperature resistance are required, such as in mining, construction, energy generation, electronics, aerospace, and defense sectors. The two primary tungsten minerals, and the only minerals of economic importance, are wolframite and scheelite. Secondary tungsten minerals are rare and generated by hydrothermal or supergene alteration rather than by atmospheric weathering. There are no reported concerns for tungsten toxicity. However, tungsten tailings and other residues may represent severe risks to human health and the environment. Tungsten metal scrap is the only secondary source for this metal but reprocessing of tungsten tailings may also become important in the future. Enhanced gravity separation, wet high-intensity magnetic separation, and flotation have been reported to be successful in reprocessing tungsten tailings, while bioleaching can assist with removing some toxic elements. In 2020, the world’s tungsten mine production was estimated at 84 kt of tungsten (106 kt WO3), with known tungsten reserves of 3400 kt. In addition, old tungsten tailings deposits may have great potential for exploration. The incomplete statistics indicate about 96 kt of tungsten content in those deposits, with an average grade of 0.1% WO3 (versus typical grades of 0.3–1% in primary deposits). This paper aims to provide an overview of tungsten minerals, tungsten primary and secondary resources, and tungsten mine waste, including its environmental risks and potential for reprocessing.