Evaluation of Monochromatic Excitation X-ray Fluorescence Spectrometry for Rapid Thallium Detection in Biological Samples Using Animal Models

Monochromatic excitation X-ray fluorescence (ME-XRF) spectrometry is a novel technique for trace element analysis, characterized by its simplicity, rapidity, and low cost. The objective of this study was to evaluate the applicability of ME-XRF technique for the measurement of thallium in biological samples. Acute and subacute thallium poisoning experiments were conducted to simulate various scenarios, with blood, urine, and 10 distinct organs collected. Detection was initially performed using ME-XRF technique, followed by validation with inductively coupled plasma mass spectrometry (ICP-MS). Excellent agreement between ME-XRF and ICP-MS values was demonstrated by means of paired sample t-tests and intraclass correlation coefficients. Subsequently, the practical implementation of the proposed technique was demonstrated through an actual case study. In conclusion, this study validates ME-XRF as a suitable alternative to ICP-MS for the measurement of trace heavy metals in biological samples. These efforts promote the development of simpler and faster techniques for heavy metal detection, thereby presenting novel avenues for the prevention and diagnosis of heavy metal poisoning.

[Determination of 24 elements migration in Yixing clay pottery by inductively coupled plasma mass spectrometry]

OBJECTIVE

To establish an analytical method for determining the migration of 24 elements in Yixing clay pottery in 4% acetic acid simulated solution by inductively coupled plasma mass spectrometry.

METHODS

Four types of Yixing clay pottery, including Yixing clay teapot, Yixing clay kettle, Yixing clay pot, and Yixing clay electric stew pot, were immersed in 4% acetic acid as a food simulant for testing. The migration amount of 24 elements in the migration solution was determined using inductively coupled plasma mass spectrometry.

RESULTS

Lithium, magnesium, aluminum, iron, and barium elements with a mass concentration of 1000 μg/L; Lead, cadmium, total arsenic, chromium, nickel, copper, vanadium, manganese, antimony, tin, zinc, cobalt, molybdenum, silver, beryllium, thallium, titanium, and strontium elements within 100 μg/L there was a linear relationship within, the r value was between 0.998 739 and 0.999 989. Total mercury at 5.0 μg/L, there was a linear relationship within, the r value of 0.995 056. The detection limit of the elements measured by this method was between 0.5 and 45.0 μg/L, the recovery rate was 80.6%-108.9%, and the relative standard deviation was 1.0%-4.8%(n=6). A total of 32 samples of four types of Yixing clay pottery sold on the market, including teapots, boiling kettles, casseroles, and electric stewing pots, were tested. It was found that the migration of 16 elements, including beryllium, titanium, chromium, nickel, cobalt, zinc, silver, cadmium, antimony, total mercury, thallium, tin, copper, total arsenic, molybdenum, and lead, were lower than the quantitative limit. The element with the highest migration volume teapot was aluminum, magnesium, and barium; The kettle was aluminum and magnesium; Casserole was aluminum, magnesium, and lithium; The electric stew pot was aluminum.

CONCLUSION

This method is easy to operate and has high accuracy, providing an effective and feasible detection method for the determination and evaluation of element migration in Yixing clay pottery.

Thallium content in vegetables and derivation of threshold for safe food production in soil: A meta-analysis

Soil thallium (Tl) pollution is a serious environmental problem, and vegetables are the primary pathway for human exposure to Tl. Therefore, it is important to investigate the characteristics of soil Tl uptake by vegetables. In this study, the meta-analysis approach was first applied to explore the relationship between Tl content in vegetables and soil environment, as well as key factors influencing soil physical-chemical properties, and to derive soil thresholds for Tl. The results indicated that various types of vegetables have different capabilities for Tl accumulation. Vegetables from contaminated areas showed high Tl accumulation, and the geomean Tl content in different types of vegetables was in the following order: leafy > root-stalk > solanaceous vegetables. Taro and kale had significantly higher capability to accumulate soil Tl among the 35 species studied, with Tl bioconcentration factor values of 0.060 and 0.133, respectively. Pearson correlation analysis and meta-analysis revealed that the Tl content in vegetables was significantly correlated with soil pH and Tl content in soil. The linear predictive model for Tl accumulation in vegetables based on soil Tl content described the data well, and the fitting coefficient R2 increased with soil pH value. According to potential dietary toxicity, the derived soil Tl thresholds for all, leafy and root-stalk vegetables increased with an increase in soil pH, and were in the range of 1.46-6.72, 1.74-5.26 and 0.92-6.06 mg/kg, respectively. The soil Tl thresholds for kale, lettuce and carrot were in the range of 0.24-4.89, 2.94-3.32 and 3.77-14.43 mg/kg, respectively. Ingestion of kale, beet, sweet potato, potato, taro, pepper, turnip, Chinese cabbage, eggplant and carrot poses potential health risks. The study provides scientific guidance for vegetable production in Tl-contaminated areas and can help with the selection of vegetable species suitable for avoiding the absorption of Tl from contaminated soil.

Mechanisms of Uptake and Translocation of Thallium in Brassica Vegetables: An X-ray Fluorescence Microspectroscopic Investigation

Most nonoccupational human exposure to thallium (Tl) occurs via consumption of contaminated food crops. Brassica cultivars are common crops that can accumulate more than 500 μg Tl g-1. Knowledge of Tl uptake and translocation mechanisms in Brassica cultivars is fundamental to developing methods to inhibit Tl uptake or conversely for potential use in phytoremediation of polluted soils. Brassica cultivars (25 in total) were subjected to Tl dosing to screen for Tl accumulation. Seven high Tl-accumulating varieties were selected for follow-up Tl dosing experiments. The highest Tl accumulating Brassica cultivars were analyzed by synchrotron-based micro-X-ray fluorescence to investigate the Tl distribution and synchrotron-based X-ray absorption near-edge structure spectroscopy (XANES) to unravel Tl chemical speciation. The cultivars exhibited different Tl tolerance and accumulation patterns with some reaching up to 8300 μg Tl g-1. The translocation factors for all the cultivars were >1 with Brassica oleracea var. acephala (kale) having the highest translocation factor of 167. In this cultivar, Tl is preferentially localized in the venules toward the apex and along the foliar margins and in minute hot spots in the leaf blade. This study revealed through scanning electron microscopy and X-ray fluorescence analysis that highly Tl-enriched crystals occur in the stoma openings of the leaves. The finding is further validated by XANES spectra that show that Tl(I) dominates in the aqueous as well as in the solid form. The high accumulation of Tl in these Brassica crops has important implications for food safety and results of this study help to understand the mechanisms of Tl uptake and translocation in these crops.

High geogenic soil thallium shows limited impact on bacterial community

Thallium (Tl) is a highly toxic trace metal, included in the US EPA list of priority pollutants. Even though its toxicity is potentially higher or comparable to Cd or Hg, its environmental impact is largely unknown. Despite its toxicity, only a few recent studies are mapping the impact of recently introduced Tl on soil microbial communities, namely in agricultural systems but no studies focus on its long term effect. To complement the understanding of the impact of Tl on soil, this study aims to describe the influence of extremely high naturally occurring Tl concentration (50 mg/kg of potentially bioavailable Tl) on soil microbial communities. Our investigation concentrated on samples collected at Buus (Erzmatt, Swiss Jura, Switzerland), encompassing forest and meadow soil profiles of the local soil formed on hydrothermally mineralized dolomite rock, which is naturally rich in Tl. The soil profiles showed a significant proportion of potentially bioavailable Tl. Yet, even this high concentration of Tl has a limited impact on the richness of the soil bacterial community. Only the meadow soil samples show a reduced richness compared to control samples. Furthermore, our analysis of geogenic Tl contamination in the region unveiled a surprising finding: compared to other soils of Switzerland and in stark contrast to soils affected by recent mining activities, the structure of the bacterial community in Buus remained relatively unaffected. This observation highlights the unique ability of soil microbial communities to withstand extreme Tl contamination. Our study advances the understanding of Tl's environmental impact and underscores the resilience of soil microbes in the face of severe long-term contamination.

Production of pharmaceutical grade [201Tl]Thallous chloride using 30 MeV cyclotron

Multiple patient doses of [201Tl]TlCl has been produced using electrodeposited enriched 203Tl in 30 MeV cyclotron (Cyclone-30) with 28 MeV proton energy at 50 μA beam current for 8 h. Ion Exchange Column Chromatography (IECC) and liquid-liquid extraction has been employed for semi-automated radiochemical separation and purification of produced [201Tl]TlCl. The produced [201Tl]TlCl was used in coronary artery disease (CAD) patients.

New insights into the key role of node I in thallium accumulation in seed of coix (Coix lacryma-jobi L.)

The mechanisms underlying the distribution of many toxic metal(loid)s in shoots and metal(loid) transport to grains have been well documented in the quest for food safety but there remains a lack of knowledge on thallium (Tl) accumulation in food crops. Here, field investigations combined with a glasshouse pot experiment were conducted to investigate the characteristics of Tl distribution and accumulation in coix, a major food crop in south Guizhou province, China, and the role of node I in restricting Tl transport to the seed. Fourteen percent of coix seed samples collected from the Lanmuchang Tl-As-Hg mine contained higher Tl concentrations than the recommended limit for foods and feedstuffs in Germany (0.5 mg kg-1), with the highest exceedance rate of the metal(loid)s determined, when grown in soils surrounding the mine with a very high Tl concentration of 0.07-89.5 mg kg-1 and a general low pH of 4.19-6.48. Thallium concentrations were higher in coix nodes than in internodes, followed by roots and grains. The Tl translocation factors from node I to grains were 0.01-0.21 and were the lowest of any translocation factors between different tissues. Node I is therefore the key tissue restricting Tl transport to coix grains. Thallium was localized mainly in the diffuse vascular bundles (DVBs) in node I. The co-localization of Tl and sulfur in the DVBs and Tl contamination-induced phytochelatin (PC) accumulation indicate that Tl storage in the DVBs involving complexation with PCs in node I is an important process in Tl accumulation in coix grains. Moreover, the area of DVBs in node I increased with increasing soil Tl pollution level, providing more channels for Tl transport to the panicles and grains and thereby acting as a key factor restricting Tl transport to the grains. These results provide new insights into the key role of node I in Tl accumulation in coix grains and indicate key points to minimize Tl accumulation in grains for food safety.

MnFe2O4-biochar decreases bioavailable fractions of thallium in highly acidic soils from pyrite mining area

The prevalence of toxic element thallium (Tl) in soils is of increasing concern as a hidden hazard in agricultural systems and food chains. In the present work, pure biochar (as a comparison) and jacobsite (MnFe2O4)-biochar composite (MFBC) were evaluated for their immobilization effects in Tl-polluted agricultural soils (Tl: ∼10 mg/kg). Overall, MFBC exhibited an efficient effect on Tl immobilization, and the effect was strengthened with the increase of amendment ratio. After being amended by MFBC for 15 and 30 days, the labile fraction of Tl in soil decreased from 1.55 to 0.97 mg/kg, and from 1.51 to 0.88 mg/kg, respectively. In addition, pH (3.05) of the highly acidic soil increased to a maximum of 3.97 after the immobilization process. Since the weak acid extractable and oxidizable Tl were the preponderantly mitigated fractions and displayed a negative correlation with pH, it can be inferred that pH may serve as one of the most critical factors in regulating the Tl immobilization process in MFBC-amended acidic soils. This study indicated a great potential of jacobsite-biochar amendment in stabilization and immobilization of Tl in highly acidic and Tl-polluted agricultural soils; and it would bring considerable environmental benefit to these Tl-contaminated sites whose occurrence has significantly increased in recent decades near the pyrite or other sulfide ore mining and smelting area elsewhere.

Thallium uptake and risk in vegetables grown in pyrite past-mining contaminated soil amended with organic fertilizer (compost): A potential method for Tl contamination remediation

Thallium (Tl) is a highly toxic trace metal that can cause severe pollution and damage to the ecological system. In this study, a field trial was conducted in a Tl-rich pyrite-barite past-mining area to unveil the fate of Tl in agricultural practice. Tuscany kale and red chicory cultivated in soil impacted by the dismissed mine of Valdicastello Carducci (Northern Tuscany, Italy) displayed significantly different uptake behaviors of Tl. Hyper-accumulation of Tl was observed in kale leaves and its content reached up to 17.1 mg kg-1 whereas only <0.70 mg kg-1 of Tl was found in leaves of red chicory. Due to the regionally polymetallic pollution, Tuscany kale grown in this area possessed a great Tl intake risk for the residents. As for the fertilization treatment, Tl in Tuscany kale leaves fertilized with mineral fertilizer (NPK) and compost were 21.4 and 12.8 mg kg-1. The results suggested a potential remediation ability of compost in diminishing Tl in the vegetable leaves and thus may reduce its risk in the soil-crop system. Since Tl poisoning emergency may occur in agricultural fields near past-mining zones, it is critical to establish possible remediation measures to ensure food safety surrounding former mining areas likewise.

Thallium hyperaccumulation status of the violets of the Allchar arsenic-thallium deposit (North Macedonia) confirmed through synchrotron µXRF imaging

The abandoned Allchar Mine in the Republic of North Macedonia is a globally unique deposit with the highest known grades of thallium (Tl) and arsenic (As) mineralization. We aimed to determine the distribution of As and Tl in whole dehydrated shoots of the three Viola taxa using synchrotron micro-X-ray fluorescence analysis. Additionally, soil and plant organ samples were collected from all three Viola taxa at the Allchar site and analysed using inductively coupled plasma-atomic emission spectrometry. Concentrations of Tl were extremely high in all three Viola taxa (up to 58 900 mg kg-1), but concentrations of As were highly variable with V. tricolor subsp. macedonica and V. allchariensis having low As (up to 20.2 and 26.3 mg kg-1, respectively) and V. arsenica having the highest concentrations (up to 381 mg kg-1). The extremely high Tl in all three species is endogenous and not a result of contamination. Arsenic in V. tricolor subsp. macedonica and V. allcharensis is strongly affected by contamination, but not in V. arsenica where it appears to be endogenous. The pattern of As enrichment in V. arsenica is very unusual and coincides with Ca-oxalate deposits and Br hotspots. The results of this study could form the basis for more detailed investigations under controlled conditions, including plant dosing experiments.

Correlation of heavy metals' exposure with the prevalence of coronary heart disease among US adults: findings of the US NHANES from 2003 to 2018

We sought to explore the association between heavy metal exposure and coronary heart disease (CHD) based on data from the US National Health and Nutrition Examination Survey (NHANES, 2003-2018). In the analyses, participants were all aged > 20 and had participated in heavy metal sub-tests with valid CHD status. The Mann-Kendall test was employed to assess the trends in heavy metals' exposure and the trends in CHD prevalence over 16 years. Spearman's rank correlation coefficient and a logistics regression (LR) model were used to estimate the association between heavy metals and CHD prevalence. 42,749 participants were included in our analyses, 1802 of whom had a CHD diagnosis. Total arsenic, dimethylarsonic acid, monomethylarsonic acid, barium, cadmium, lead, and antimony in urine, and cadmium, lead, and total mercury in blood all showed a substantial decreasing exposure level tendency over the 16 years (all Pfor trend < 0.05). CHD prevalence varied from 3.53 to 5.23% between 2003 and 2018. The correlation between 15 heavy metals and CHD ranges from - 0.238 to 0.910. There was also a significant positive correlation between total arsenic, monomethylarsonic acid, and thallium in urine and CHD by data release cycles (all P < 0.05). The cesium in urine showed a negative correlation with CHD (P < 0.05). We found that exposure trends of total arsenic, dimethylarsonic acid, monomethylarsonic acid, barium, cadmium, lead, and antimony in urine and blood decreased. CHD prevalence fluctuated, however. Moreover, total arsenic, monomethylarsonic acid, and thallium in urine all showed positive relationships with CHD, while cesium in urine showed a negative relationship with CHD.

Highly inhibited transport of dissolved thallium(I) in manganese oxide-coated sand: Chemical condition effects and retention mechanisms

Thallium contamination in water can cause great danger to the environment. In this study, we synthesized manganese oxide-coated sand (MOCS) and investigated the transport and retention behaviors of Tl(I) in MOCS under different conditions. Characterization methods combined with a two-site nonequilibrium transport model were applied to explore the retention mechanisms. The results showed that Tl(I) mobility was strongly inhibited in MOCS media, and the retention capacity calculated from the fitted model was 510.41 mg/g under neutral conditions. The retention process included adsorption and oxidative precipitation by the manganese oxides coated on the sand surface. Cotransport with the same concentration of Mn(II) led to halving Tl(I) retention due to competition for reactive sites. Enhanced Tl(I) retention was observed under alkaline conditions, as increasing pH promoted electronegativity on the media surface. Moreover, the competitive cation Ca²⁺ significantly weakened Tl(I) retention by occupying adsorption sites. These findings provide new insights into understanding Tl(I) transport behavior in water-saturated porous media and suggest that manganese oxide-coated sand can be a cost-effective filter media for treating Tl-contaminated water.

Efficient utilization of biogenic manganese oxides in bioaugmentation columns for remediation of thallium(I) contaminated groundwater

Little attention has been paid to the in situ-generated biogenic manganese oxides (BMnOx) for practical implementation in continuous groundwater remediation systems. The enrichment effects of manganese oxidizing bacteria (MOB) in bioaugmentation columns and the in situ-generated BMnOx for continuous thallium(I) (Tl(I)) removal from groundwater were investigated. Results indicated that Pseudomonas Putida MnB1 (strain MnB1) attached on the groundwater sediments (GS) can achieve a maximum of 97.37 % Mn(II) oxidation and generate 29.6 mg/L BMnOx, which was superior than that of traditional quartz sand (QS). The in situ-generated BMnOx in MOB_GS column effectively removed 10-100 μg/L Tl(I) under the interference of high concentrations of Fe(II) and Mn(II) in groundwater. Distinctive microbial enrichment effects occurred in the bioaugmentation columns under the competition of indigenous microbes in groundwater. The release of Mn(II) from the BMnOx inhibited with the decrease in Tl(I) removal efficiency. XAFS analysis revealed Tl(I) was effectively adsorbed by BMnOx and Mn-O octahedra with Tl-O tetrahedral coordination existed in BMnOx. This study provides an in-depth understanding of the in situ-generated BMnOx for the Tl(I) removal and contributes to the application of BMnOx in groundwater remediation.

Evaluating potential ecological risks of emerging toxic elements in lacustrine sediments: A case study in Lake Fuxian, China

The fragile ecosystems of plateau lakes are in face of ecological risks from emerging toxic elements. Beryllium (Be) and thallium (Tl) have been considered priority control metals in recent years owing to their persistence, toxicity, and bioaccumulation. However, the toxic factors of Be and Tl are scarce and ecological risks of them in the aquatic environment were seldom investigated. Hence, this study developed a framework for calculating the potential ecological risk index (PERI) of Be and Tl in aquatic systems and used it to assess the ecological risks of Be and Tl in Lake Fuxian, a plateau lake in China. The toxicity factors of Be and Tl were calculated to be 40 and 5, respectively. In sediments of Lake Fuxian, the concentrations of Be and Tl were between 2.18 and 4.04 mg/kg and 0.72-0.94 mg/kg, respectively. The spatial distribution indicated that Be was more abundant in the eastern and southern regions, and Tl had higher concentrations near the northern and southern banks, consistent with the distribution of anthropogenic activities. The background values were calculated as 3.38 mg/kg and 0.89 mg/kg for Be and Tl, respectively. In comparison with Be, Tl was more enriched in Lake Fuxian. The increasing Tl enrichment has been attributed to anthropogenic activities (e.g., coal burning and non-ferrous metal production), especially since the 1980s. Generally, Be and Tl contamination has decreased over the past several decades, from moderate to low, since the 1980s. The ecological risk of Tl was low, whereas Be might have caused low to moderate ecological risks. In the future, the obtained toxic factors of Be and Tl in this study can be adopted in assessing the ecological risks of them in sediments. Moreover, the framework can be employed for the ecological risk assessment of other newly emerging toxic elements in the aquatic environment.

Thallium removal from wastewater using sulfidized zero-valent manganese: Effects of sulfidation method and liquid nitrogen pretreatment

Zero-valent manganese (ZVMn) possesses high reducibility in theory, while sulfide exhibits strong affinity towards a variety of heavy metals owing to the low solubility of metal sulfides. Yet the performance and mechanisms on using sulfidized zero-valent manganese (SZVMn) to remove thallium (Tl) from wastewater still remain unclear. In this study, the performance of Tl(I) removal using SZVMn synthesized by borohydrides reduction followed by sulfides modification, with and without liquid nitrogen treatment, was compared and the mechanism behind was investigated. The results show that at a S/Mn molar ratio of 1.0, liquid nitrogen modified SZVMn (LSZVMn) possessed more interior channels and pores than SZVMn, with 65.3% higher specific surface area and 73.7% higher porosity, leading to 6.4-8.1% improvement in adsorption of Tl(I) at pH 4-10. LSZVMn showed effectiveness and robustness in Tl(I) removal in the presence of co-existing ions up to 0.1 M. The adsorption of Tl(I) conformed to the pseudo-1st-order kinetic model, and followed the Langmuir isothermal model, with the maximum Tl adsorption capacity of 264.9 mg·g^-1 at 288 K. The mechanism of Tl(I) removal with SZVMn was found to include sulfidation-induced precipitation, manganese reduction, surface complexation, and electrostatic attraction. The liquid nitrogen pretreatment embrittled and cracked the outer shell of S/Mn compounds, resulted in a highly hierarchical structure, enhancing the manganese reduction and improving the Tl(I) removal. Based on the above results, the SZVMn and its liquid nitrogen-modified derivatives are novel and effective environmental materials for Tl(I) removal from wastewater, and the application of SZVMn to the removal of other pollutants merits investigation in future study.

Associations between trace level thallium and multiple health effects in rural areas: Chinese Exposure and Response Mapping Program (CERMP)

Thallium (Tl) is a cumulative high toxicant in the environment, but few studies have investigated the comprehensive health effects underlying chronic Tl exposure at trace levels. This study aims to evaluate the liver, kidney, lung and other potential health effects associated with chronic Tl exposure at trace levels in rural areas of China. Urinary Tl concentrations of 2883 adults from rural areas of 12 provinces in China were measured and 2363 participants were involved in the final analysis. Indicators of liver and kidney functions in the serum, as well as the lung function indicators, were determined in the participants. General linear regression and restricted cubic spline regression were combined to study the associations between urinary Tl and health indicators or outcomes. In this study, the detected rate of Tl in the urine of the participants was 97.28 %. When the urinary Tl concentration was ranged at the fourth quintile, the risk of having liver function disorder was 70 % higher [Odds ratio (OR) = 1.70 (95 % confidence intervals (CI): 1.30, 2.22)] in all the participants, whereas the farmers were more likely to have the disorder [OR = 2.08 (95 % CI: 1.49, 2.92)] than the non-farmers [OR = 1.20 (95 % CI: 0.77, 1.88)]. Nonlinear associations between most of the liver health indicators and urinary Tl were identified, of which serum bilirubin was strongly associated with the elevation of urinary Tl when its concentration was >0.40 μg/g creatinine. Besides, urinary Tl was negatively associated with lung health indicators. Our study proposes the safety re-assessment of the current exposure level of Tl in the environment, especially in rural areas of China.

Levels and determinants of urinary and blood metals in the geothermal area of Mt. Amiata in Tuscany (Italy)

Natural sources and anthropogenic activities are responsible for the widespread presence of heavy metals in the environment in the volcanic and geothermal area of Mt. Amiata (Tuscany, Italy). This study evaluates the extent of the population exposure to metals and describes the major individual and environmental determinants. A human biomonitoring survey was carried out to determine the concentrations of arsenic (As), mercury (Hg), thallium (Tl), antimony (Sb), cadmium (Cd), nickel (Ni), chromium (Cr), cobalt (Co), vanadium (V), and manganese (Mn). The associations between socio-demographics, lifestyle, diet, environmental exposure, and metal concentrations were evaluated using multiple log-linear regression models, adjusted for urinary creatinine. A total of 2034 urine and blood samples were collected. Adjusted geometric averages were higher in women (except for blood Hg) and younger subjects (except for Tl and Cd). Smoking was associated with Cd, As, and V. Some dietary habits (rice, fish, and wine consumption) were associated with As, Hg, Co, and Ni. Amalgam dental fillings and contact lenses were associated with Hg levels, piercing with As, Co, and Ni. Among environmental determinants, urinary As levels were higher in subjects using the aqueduct water for drinking/cooking. The consumption of locally grown fruits and vegetables was associated with Hg, Tl, and Co. Exposure to geothermal plant emissions was associated only with Tl.

Microbial diversity in paddy rhizospheric soils around a large industrial thallium-containing sulfide utilization zone

Thallium (Tl) is a rare and extremely toxic metal whose toxicity is significantly higher than cadmium (Cd), lead (Pb) and antimony (Sb). The extensive utilization of Tl-bearing minerals, such as mining activities, has led to severe Tl pollution in a variety of natural settings, while little is known to date about its effect on the microbial diversity in paddy soils. Also, the geochemical behavior of Tl in the periodical alterations between dry and wet conditions of paddy soils remains largely unknown. Herein, the sequential extraction method and 16S rRNA gene sequence analysis were adopted to analyze Tl's migration and transformation behavior and the microbial diversity in the paddy soils with different pollution levels. The results indicated that Tl was mainly concentrated in reducible fraction, which is different from other types of soils, and may be closely attributed to the abundance of Fe-Mn (hydr)oxides in the paddy rhizospheric soils. Further analysis revealed that pH, total S, Pb, Sb, Tl and Cd were the dominant environmental factors, and the enrichment level of these potentially toxic metal(loid)s (PTMs) exerted obvious impacts on the diversity and abundance of microorganism in the rhizospheric soils, and regulating microbial community. The geochemical fractionation of Tl was closely correlated to soil microorganisms such as Fe reducing bacteria (Geothrix) and sulfate reducing bacteria (Anaerolinea), playing a critical role in Tl geochemical cycle through redox reaction. Hence, further study on microorganisms of paddy rhizospheric soils is of great significance to the countermeasures for remediating Tl-polluted paddy fields and protect the health of residents.

Characteristics, sources, and risk assessment of thallium and associated with metal(loid)s in the Yarlung Tsangpo River Basin, southern Tibetan Plateau

The Tibetan Plateau (TP) is known as the water tower of Asia, and the water quality has long been a focus of public concern, especially in the Yarlung Tsangpo River Basin (YTRB), a unique area that is climate-sensitive, geologically complex, eco-fragile, and densely populated. Thallium (Tl) is a typical metal that is more toxic than Pb, Cd, and As and often occurs in sulfide minerals. Although large-scale polymetallic sulfide mineralization developed in the YTRB, the geochemical dispersion and potential risk of Tl in aquatic environments of the YTRB remain poorly understood. In this study, the concentration, distribution, source, and health risk of Tl and associated metal(loid)s in the hot springs and surface water in the YTRB were systematically analyzed. The results showed that the trace elements (Cd, Cr, Zn, Cu, Al, Sr, Ni, Co, Mn, Pb) in water environments are within the recommended limits, except for Tl and As. Principal component analysis (PCA) and correlation analysis (CA) showed that the elements of Tl and As were positively related to each other in either both hot spring water and surface water, indicating their common origin. Spatial variations suggested that high levels of Tl and As observed in the north YTRB, which may be relevant to the reduction-dissolution of Tl (As)-bearing minerals and the magmatic hydrothermal system formed in the shallow part of the northern YTRB. Furthermore, source apportionment identified natural sources of Cu, Ni, Cr, Co, Mn, Zn, and Cd and anthropogenic inputs of Al and Pb. Exposure assessment studies have found that ingestion is the primary route of As and Tl exposure to local population, and balneological and bathing purposes do not constitute a human health concern. This study offers valuable insights into the risk of naturally occurring Tl enrichment being hidden in As-rich hydrosphere in the YTRB and other regions with similar geoenvironmental contexts.

Calcium Enhances Thallium Uptake in Green Cabbage (Brassica oleracea var. capitata L.)

Thallium (Tl) is a nonessential and toxic trace metal that is detrimental to plants, but it can be highly up-taken in green cabbage (Brassica oleracea L. var. capitata L.). It has been proven that there is a significant positive correlation between Tl and Calcium (Ca) contents in plants. However, whether Ca presents a similar role for alleviating Tl toxicity in plants remains unclear, and little is known in terms of evidence for both Ca-enhanced uptake of Tl from soils to green cabbage and associated geochemical processes. In this study, we investigated the influence of Ca in soils on Tl uptake in green cabbage and the associated geochemical process. The pot experiments were conducted in 12 mg/kg Tl(I) and 8 mg/kg Tl(III) treatments with various Ca dosages. The results showed that Ca in soils could significantly enhance Tl uptake in green cabbage, increasing 210% in content over the control group. The soluble concentrations of Tl were largely increased by 210% and 150%, respectively, in 3.0 g/kg Ca treatment, compared with the corresponding treatment without Ca addition. This was attributed to the geochemical process in which the enhanced soluble Ca probably replaces Tl held on the soil particles, releasing more soluble Tl into the soil solution. More interestingly, the bioconcentration factor of the leaves and whole plant for the 2.0, 2.5, 3.0 g/kg Ca dosage group were greatly higher than for the non-Ca treatment, which could reach 207%, implying the addition of Ca can improve the ability of green cabbage to transfer Tl from the stems to the leaves. Furthermore, the pH values dropped with the increasing Ca concentration treatment, and the lower pH in soils also increased Tl mobilization, which resulted in Tl accumulation in green cabbage. Therefore, this work not only informs the improvement of agricultural safety management practices for the farming of crops in Tl-polluted and high-Ca-content areas, but also provides technical support for the exploitation of Ca-assisted phytoextraction technology.

Pollution levels and risk assessment of thallium in Chinese surface water and sediments

Thallium (Tl) is one of the most toxic metals and can cause chronic and acute damage to humans. Due to occurrences of incidents involving Tl pollution in China, its potential environmental impacts are receiving increased attention. However, there is still limited information on Tl concentrations in the environment and their risks to human health and wildlife. This paper provides an overview of the contamination of surface water and sediments by Tl across China and assesses the potential risks using several methods. The acute and chronic aquatic life criteria for Tl were determined to be 13.25 and 1.65 μg/L, respectively. The acute and chronic risk quotients (RQs) of Tl in surface water near mining areas were 0.01-41.51 and 0.20-666.67, respectively, indicating medium to high ecological risks to aquatic organisms. Tl in sediments of Pearl and Gaofeng rivers pose a high risk based on the higher geo-accumulation index (Igeo) and potential ecological risk index (EI) values. Exposure parameters for the Chinese population were used to derive health criteria and assess non-carcinogenic risk posed by Tl in centralized drinking water sources. Tl criteria for protection of human health were calculated to be 0.18 μg/L for water+organisms and 0.30 μg/L for organisms only. The non-carcinogenic risk posed by Tl was acceptable. The human health criteria of Tl for children were the lowest among all age groups. The risks posed by Tl to health of children are greater than those for adults. Therefore, emphasis should be placed on protecting children from exposure to Tl. For the Chinese population, the drinking water guidance value to ensure protection of human health was determined to be 0.44 μg/L. The availability of multiple Tl guidance values for designated water uses will improve the environmental regulation and surveillance of Tl pollution in China and other countries.

Bioaccumulation of 35 metal(loid)s in organs of a freshwater mussel (Hyriopsis cumingii) and environmental implications in Poyang Lake, China

Benthic bioaccumulation of hazardous materials has been a great challenge to the health of lake ecosystems. As representative benthic macroinvertebrates, freshwater mussels and their accumulation characteristics have been regarded as effective indicators for assessing potential risks induced by sedimentary metal(loid)s in lakes. Here we profile organ-specific accumulation of 35 metal(loid)s in a freshwater mussel (Hyriopsis cumingii) and their correlations to metal speciation in sediments of Poyang Lake, the largest lake of China. Significant organ-specific characteristics of metal accumulation were found in gills, though higher thallium (Tl) and selenium (Se) were found in the hepatopancreas, and greater arsenic (As) mostly accumulated in gonads. Pearson correlation analysis revealed that the bioaccumulation of silver (Ag), cobalt (Co), and rare earth elements (ΣREE) in gills and As in gonads were closely associated with those in bioavailable fraction of sediments. Based on the biochemical analysis in the major organs, gills exhibited the highest enzymatic activity compared with hepatopancreas and gonads. Sedimentary metals, particularly for available Ag, Co, and ΣREE, play key roles in causing lipid peroxidation in gills and significantly promote the activities of superoxide dismutase (SOD)/glutathione reductase (GR), while many metals (e.g., cadmium, manganese, Se) inhibit the glutathione (GSH) content in gonads and hepatopancreas. Our study indicates a high physiological sensitivity of mussels to these target metals, which highlights the significance of organ-specific accumulation of metal(loid)s in understanding the potential ecological risks of sedimentary metal(loid)s in lake ecosystems.

Thallium adsorption onto phyllosilicate minerals

The adsorption of thallium (Tl) onto phyllosilicate minerals plays a critical role in the retention of Tl in soils and sediments and the potential transfer of Tl into plants and groundwater. Especially micaceous minerals are thought to strongly bind monovalent Tl(I), in analogy to their strong binding of Cs. To advance the understanding of Tl(I) adsorption onto phyllosilicate minerals, we studied the adsorption of Tl(I) onto Na- and K-saturated illite and Na-saturated smectite, two muscovites, two vermiculites and a naturally Tl-enriched soil clay mineral fraction. Macroscopic adsorption isotherms were combined with the characterization of the adsorbed Tl by X-ray absorption spectroscopy (XAS). In combination, the results suggest that the adsorption of Tl(I) onto phyllosilicate minerals can be interpreted in terms of three major uptake paths: (i) highest-affinity inner-sphere adsorption of dehydrated Tl⁺ on a very low number of adsorption sites at the wedge of frayed particle edges of illite and around collapsed zones in vermiculite interlayers through complexation between two siloxane cavities, (ii) intermediate-affinity inner-sphere adsorption of partially dehydrated Tl⁺ on the planar surfaces of illite and muscovite through complexation onto siloxane cavities, (iii) low-affinity adsorption of hydrated Tl⁺, especially in the hydrated interlayers of smectite and expanded vermiculite. At the frayed edges of illite particles and in the vermiculite interlayer, Tl uptake can lead to the formation of new wedge sites that enable further adsorption of dehydrated Tl⁺. On the soil clay fraction, a shift in Tl(I) uptake from frayed edge sites (on illite) to planar sites (on illite and muscovite) was observed with increasing Tl(I) loading. The results from this study show that the adsorption of Tl(I) onto phyllosilicate minerals follows the same trends as reported for Cs and Rb and thus suggests that concepts to describe the retention of (radio)cesium by different types of phyllosilicate minerals in soils, sediments and rocks are also applicable to Tl(I).

Revealing the toxicity of monovalent and trivalent thallium to medaka fish in controlled exposure conditions

Thallium (Tl) is a rare earth element increasingly being used in high-technology manufacturing. It is also an emerging pollutant with high exposure and toxicity risks to aquatic ecosystems. Tl exists in the environment in a monovalent [thallous, Tl(I)] or trivalent [thallic, Tl(III)] state. Currently, the stability of the two Tl species in natural water is uncertain and the toxicity in algae and daphnia are inconsistent due to lack of robust characterization of Tl species and matrix effects, while studies with fish are sparse. In this study, larvae of medaka fish (Oryzias latipes) were dosed with environmentally relevant concentrations of Tl(I) or Tl(III) spiked into synthetic and natural river water for 7 days to observe the toxic effects of two Tl species on fish. The transformation of Tl(I) and Tl(III) in water was analyzed by high performance liquid chromatography coupled with inductively coupled plasma and mass spectrometry. Analytical and toxicity results showed that Tl(I) is more stable presenting higher mortality and bioconcentration in medaka than Tl(III) in different water matrices. Tl(I)-induced LC₅₀ and body burden in treated fish were highly correlated with its competitive ion, potassium (K), especially in waters containing medium K levels. This study provides reliable evidence regarding the stability and toxicity of Tl(I) and Tl(III) as well as the interaction of aqueous K versus Tl(I) in fish. Such information is useful for justifying water-quality guidelines and ecological risks of Tl pollution in natural water ecosystems.

Association between trace metals exposure and hearing loss

Background

Trace metals have side-effect on human health. The association between trace metals exposure and hearing loss remains unclear.

Methods

A total of 8,128 participants were exacted for analysis of association between trace metals and hearing loss from the database of the National Health and Nutrition Examination Survey (NHANES) (2013-2018). Multivariable logistic regression and restricted cubic spline models were used to examine the association between trace metals and hearing loss.

Results

Participants with hearing loss had a higher level of lead, cadmium, molybdenum, tin, thallium, and tungsten (all p < 0.05). After adjusting for confounders, compared with the reference of the lowest quartile, the ORs with 95%CIs for hearing loss across quartiles were 1.14 (0.86, 1.51), 1.49 (1.12, 1.98), 1.32 (0.97, 1.80) for cobalt, and 1.35 (0.98, 1.87), 1.58 (1.15, 2.16), 1.75 (1.28, 2.40) for tin. Individuals with the level of cobalt at third quartile had 49% higher risks of hearing loss than those at lowest quartile. And participants with highest quartile of tin had 1.75-folds risks of hearing loss than those with lowest quartile of tin. There were increasing trends in risks of hearing loss with a raised level of thallium (p for trend <0.05). Restricted cubic spline regression analysis indicated that there was a nonlinear association between hearing loss and the levels of tin (p for nonlinearity = 0.021). Subgroup analysis showed that individuals of female, without hypertension and diabetes, and with a higher level of low-density lipoprotein cholesterol had modified effects on the associations between hearing loss and exposure to tin.

Conclusions

Our study indicated that exposure to cobalt and tin were significantly associated with hearing loss.

Exposure to mixture of heavy metals and muscle strength in children and adolescents: a population-based study

Human beings are exposed to heavy metals through various ways in daily life. However, the effect of heavy metal mixtures on muscle strength in children and adolescents remains unclear. We aimed to investigate the relationship of exposure to heavy metal mixtures (barium, cadmium, cobalt, manganese, molybdenum, lead, antimony, strontium, tin, thallium, tungsten, uranium, and cesium) with muscle strength in children and adolescents. A total of 1357 (boys, 50.8%) participants aged between 8 and 17 were extracted from the National Health and Nutrition Examination Surveys 2011-2014. Urine metals were measured by inductively coupled plasma-mass spectrometry. Muscle strength was measured through a grip test using a handgrip dynamometer. Weighted quantile sum regression was performed to estimate the mixture effect of urinary metals on muscle strength. After adjusting for potential confounders, comparing participants in the highest versus lowest quartiles of cobalt, molybdenum, lead, antimony, strontium, thallium, and cesium, the handgrip strength decreased by - 4.48 kg (95% CI: - 6.93, - 2.03), - 6.13 kg (- 8.76, - 3.51), - 2.26 kg (- 4.22, - 0.30), - 2.38 kg (- 4.68, - 0.08), - 2.29 kg (- 4.45, - 0.13), - 4.78 kg (- 7.13, - 2.44), and - 5.68 kg (- 9.20, - 2.17), respectively. Furthermore, exposure to a mixture of metals were also significantly associated with decreased muscle strength (β: - 2.62 kg; 95% CI: - 3.71, - 1.54). Findings from the present study suggest that higher heavy metal exposure and the exposure levels of a mixture of metals in urine are inversely related to handgrip strength, implying that children's grip strength is not entirely explained by energy intake or lack of exercise, but may be related to environmental pollutants.

Effect of peat organic matter on sulfide weathering and thallium reactivity: Implications for organic environments

Weathering of Tl-containing sulfides in a model (12-week) peat pot trial was studied to better understand their geochemical stability, dissolution kinetics, alteration products and the associated release and mobility of anthropogenic Tl in organic environments. We also present the effect of industrial acid rainwater on sulfide degradation and Tl migration in naturally acidic peat. Sphalerite (ZnS) was much less stable in peat than other Tl-containing sulfides (galena and pyrite), and thus acted as a major phase responsible for Tl mobilization. Furthermore, Tl incongruently leached out over Zn from ZnS, and accumulated considerably more in the peat solutions (≤5 μg Tl/L) and the peat samples (≤0.4 mg Tl/kg) that were subjected to acid rain watering compared to a deionized H₂O regime. This finding was in good agreement with the absence of secondary Tl-containing phases, which could potentially control the Tl flux into the peat. The behavior of Tl was not as conservative as Pb throughout the trial, since a higher peat mobility and migration potential of Tl was observed compared to Pb. In conclusion, industrial acid precipitations can significantly affect the stability of ZnS even in acidic peat/organic environments, making it susceptible to enhanced weathering and Tl release in the long term.

Thallium and potentially toxic elements distribution in pine needles, tree rings and soils around a pyrite mine and indication for environmental pollution

In this study, the distributions of thallium (Tl), and other potential toxic elements, such as Cd, Co, Cu, Pb, Sr, As, Cr, Ni, Zn, and Mn in needles, tree rings and soils of pine trees in one of the largest pyrite mining areas in the world, i.e., Yunfu, China were investigated. The results showed that pseudo-total Tl concentration of the tree rings ranged from 0.41 to 2.03 mg/kg (average: 1.12 mg/kg) during the year of 1998 to 2011. This indicates an overall obvious enrichment of Tl. Further investigation of element level variations in the pine needles showed a negative correlation between Tl content and the distance from the mining area. The results of Principal Component Analysis additionally demonstrated that Tl in the tree rings was most likely derived from the pine needles. Notably, Tl contents in the tree rings exhibited generally similar distribution pattern to the annual production intensity of Yunfu pyrite mining activities. The findings suggest that metal(loid)s in particular of Tl in pine tree rings can be used as alternative proxies to approximatively reconstruct the chronological change of atmospheric environmental pollution induced by pyrite associated mining/smelting activities.

Synergetic removal of thallium and antimony from wastewater with jacobsite-biochar-persulfate system

Both of thallium (Tl) and antimony (Sb) are toxic elements in the natural environment. Emerging Tl and Sb pollution in water has gradually gained public concerns globally. However, limited technologies are available for co-removal of Tl and Sb from wastewater. Herein, an novel system was successfully fabricated to enhance the synergetic removal of both Tl and Sb in wastewater. In this study, MnFe₂O₄-biochar composite (MFBC) facilely synthesized by a one-pot hydrothermal method was used as adsorbent and persulfate (PS) activator for simultaneously removing Tl and Sb from wastewater. The optimal reaction conditions for best removal efficiency of Tl and Sb simultaneously were obtained by using the response surface design combined with Box-Behnken Design (BBD) model. Results unveiled that the average removal rates of Tl and Sb can achieve 98.33% and 89.14%, respectively under the optimal reaction conditions. Electron Spin Resonance (ESR), and radical quenching experiments showed that OH^• and SO₄^•- play a critical role in the removal of Tl-Sb compound pollution. Via using different characterization, it is revealed that the mechanism of removing Tl-Sb containing wastewater by MFBC-1.4/PS system is oxidation, adsorption, complexation and ion exchange. All these results indicate that MFBC-1.4/PS technology is prospective in highly effective removal of Tl and Sb from wastewater simultaneously.

Unexpected enrichment of thallium and its geochemical behaviors in soils impacted by historically industrial activities using lead‑zinc carbonate minerals

Thallium is a trace metal with severe toxicity. Contamination of thallium (Tl) generated by steel and non-ferrous metals industry is gaining growing concern worldwide. However, little is known on Tl contamination owing to industrial activities using carbonate minerals. This study revealed abundant geochemical mobile/bioavailable Tl (> 65.7%, in average; mostly in oxidizable fraction) in soils from a carbonate-hosted PbZn ore utilizing area in China for the first time. Unexpected Tl enrichment was observed in soil accompanying with 3655, 7820, 100.1, 27.3 and 29.9 mg/kg (in average) of Pb, Zn, As, Cd and Sb, respectively. Characterization using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis further confirmed that historical industrial activities impose anthropogenic catastrophic effects on the local agricultural soil system. The ecological and health risk assessment of heavy metal(loid)s in soils proclaimed serious potential non-carcinogenic risks of Pb and V to adults, and Pb, Tl and As to children. Sequential extraction analysis showed that Tl, as well as Pb, Zn, Mn, Co, and Cd, mainly existed in the mobile fractions (exchangeable/acid-extractable, reducible and oxidizable), indicating an ecological risk of biological accumulation of multiple metal(loid)s in this area. These findings provide a theoretical basis for taking appropriate remediation measures in order to ensure safety of soils in such industrial areas likewise.

Association between urinary thallium exposure and cardiovascular disease in U.S. adult population

Exposure to environmental metals, especially heavy metals, can damage human health. However, the association between metals and the prevalence of cardiovascular disease (CVD) remains controversial. The objective of this study was to determine the relationship of urinary metals to CVD in a general population of U.S. adults. We analyzed the cross-sectional data from 6867 adult (age ≥20 years) participants with 12 urinary metals in the National Health and Nutrition Examination Survey (NHANES) (2011-2016). Multivariate logistic regression and restricted cubic spline (RCS) regression were conducted to explore the association between urinary metals and CVD outcomes. Sensitivity analyses were performed to test the robustness of the results. Compared to the lowest quartile, the odds ratios with 95% confidence intervals for CVD across the quartiles were 0.73 (0.38, 1.42), 0.58 (0.42, 0.81), and 0.71 (0.59, 0.84) for urinary thallium (U-Tl) (P for trend <0.001). RCS plot showed the nonlinear association between log₂-transformed U-Tl levels and CVD (P for nonlinearity = 0.001). Sensitivity analyses confirmed the robustness. Higher concentrations of urinary cobalt, manganese and tungsten were associated with an increased risk of CVD. In summary, the large sample data suggests U-Tl is nonlinearly and negatively associated with the prevalence of CVD in the U.S. general adults with low exposure levels. Considering the shortcomings of cross-sectional study design, further studies are warranted to verify our results and to clarify the potential mechanisms.

Evaluation of thallium isotopic fractionation during the metallurgical processing of sulfides: An update

In this study, we report combined Tl isotopic and Tl mineralogical and speciation data from a set of Tl-rich sulfide concentrates and technological wastes from hydrometallurgical Zn extraction. We also present the first evaluation of Tl isotopic ratios over a cycle of sulfide processing, from the ore flotation to pyro- and hydrometallurgical stages. The results demonstrate that the prevailing Tl form in all samples is Tl(I), without any preferential incorporation into sulfides or Tl-containing secondary phases, indicating an absence of Tl redox reactions. Although the Tl concentrations varied significantly in the studied samples (~9-280 mg/kg), the overall Tl isotopic variability was small, in the range of -3.1 to -4.4 ± 0.7 (2σ) ε²⁰⁵Tl units. By combining present ε²⁰⁵Tl results with the trends first found for a local roasting plant, it is possible to infer minimum Tl isotopic effects throughout the studied industrial process. As a result, the use of Tl isotopic ratios as a source proxy may be complicated or even impossible in areas with naturally high/extreme Tl background contents. On the other hand, areas with two or more isotopically contrasting Tl sources allow for relatively easy tracing, i.e., in compartments which do not suffer from post-depositional isotopic redistributions.

Monitoring of ion release, bioavailability and ecotoxicity of thallium in contaminated paddy soils under rice cultivation conditions

Paddy soils contaminated by thallium (Tl) have been frequently reported; however, their ecotoxicological impact in the paddy field is less known. We used a novel soil-fish exposure system with larvae of rice fish medaka (Oryzias latipes) to assess the bioavailability of Tl from soils to fish and causal toxicity under simulated conditions of rice cultivation. Two acidic soils [Pingzhen (Pc) and Sankengtzu (Sk)] spiked with monovalent Tl [Tl(I), 75-250 mg/kg] released higher Tl⁺ into pore or overlying waters than neutral soils [Sangkang (Su)], which resulted in higher mortality to exposed fish. The addition of K fertilizers into the system did not significantly reduce Tl release and fish mortality, but a drainage/re-flooding treatment worked effectively. The acidic Pc soil contaminated with low Tl(I) (2.5 and 15 mg/kg) caused higher sublethal toxicity in medaka than the neutral Su soil, including altered growth and swimming behavior with increased Tl body burden. These Tl-induced effects by low-Tl soils were significantly alleviated by K addition. The Tl/K ratios in aqueous phases were correlated with the mortality or Tl body burden in exposed fish. This study provides useful bio-analytical evidence that can help assess the ecological risks of Tl pollution in paddy field-related ecosystems.

Quantification of smelter-derived contributions to thallium contamination in river sediments: Novel insights from thallium isotope evidence

Thallium(Tl), an extremely toxic metal, is posing great hazards to water safety through anthropogenic activities (e.g., Pb-Zn smelter) and natural weathering in riverine systems. However, the relative contribution from each source remains obscure. This study investigated enrichment pattern of Tl and its isotopic compositions in sediment profiles from a recipient river, which was continuously collecting various Tl-bearing wastes discharged from a large Pb-Zn smelter in South China. Results show that high Tl content and ultra-fine particles (~ μm) of Tl-bearing mineral assemblages, probably derived from Pb-Zn smelting wastes, were ubiquitously observed in both of the depth profiles. In addition, the sediments generally yielded intermediate ε²⁰⁵Tl values of -3.76 to 1.01, which resembled those found in smelting wastes. A ternary mixing model was for the first time proposed for quantifying relative Tl contributions from each possible source. The calculation suggests that the smelter wastes are the major contributors, contributing approximately 80% of Tl contamination. All these results indicate that Tl isotope can be used as powerful proxies for quantitatively identifying potential different contributors in the environment. This is of critical importance to further implementation of pollution control and remediation strategy for the riverine systems in the near future.

One-pot synthesis of magnetic Prussian blue for the highly selective removal of thallium(I) from wastewater: Mechanism and implications

Thallium (Tl) often enters the environment via mineral exploitation and utilization. The main restriction of Tl removal is the interference of high concentrations of coexisting ions in wastewater, therefore, enhancing the selectivity for Tl is essential to its treatment. Magnetic Prussian blue particles (Fe₃O₄@PB), an ion-sieving material with an open structure, were synthesized through a "one-pot" method at room temperature for the highly selective removal of Tl⁺. The removal percentage of Tl⁺ was over 92% even when the concentration of coexisting ions (e.g. Zn²⁺, Cd²⁺, Cu²⁺, and Pb²⁺) were 10,000 times higher than the initial concentration of Tl⁺. The maximal experimental removal capacity was 528 mg Tl/g Fe₃O₄@PB, and the removal percentage remained steady at pH 3-10. The high selectivity of Fe₃O₄@PB for Tl⁺ is attributed to the fact that hydrated Tl⁺ has a smaller hydrated diameter and a lower hydration free energy than other coexisting ions, while the rapid adsorption kinetics of Tl⁺ results from the negative surface charge and the network of nanocapillaries of the Fe₃O₄@PB. Overall, a new low-cost material that is easy to synthesize and has superior Tl⁺ removal capacity with extremely high selectivity for Tl⁺ was obtained for effective magnetic removal of thallium from wastewater.

Microbial response and adaption to thallium contamination in soil profiles

Thallium (Tl) is a trace metal with high toxicity. Comprehensive investigation of spatial distribution of Tl and microorganism is still limited in soils from mining area. In this study, 16S rRNA sequencing and network analysis were used for deciphering the co-occurrence patterns of bacterial communities in two different types of soil profiles around a typical Tl-bearing pyrite mine. The results showed that geochemical parameters (such as pH, S, Tl, Fe and TOM) were the driving forces for shaping the vertical distribution of microbial community. According to network analysis, a wide diversity of microbial modules were present in both soil profiles and affected by depth, significantly associated with variations in Tl geochemical fractionation. Phylogenetic information further unveiled that the microbial modules were mainly dominated by Fe reducing bacteria (FeRB), Fe oxidizing bacteria (FeOB), S oxidizing bacteria and Mn reducing bacteria. The results of metagenome indicated that Fe, Mn and S cycle in soil are closely involved in the biogeochemical cycle of Tl. The findings of co-occurrence patterns in the bacterial network and correlation between microorganisms and different geochemical fractions of Tl may benefit the strategy of bioremediation of Tl-contaminated soils with indigenous microbes.

Transformation and fate of thallium and accompanying metal(loid)s in paddy soils and rice: A case study from a large-scale industrial area in China

Thallium (Tl) is an extremely toxic metal, while its occurrence and fate in paddy soil environment remain understudied. Herein, the enrichment and migration mechanisms and potential health risks of Tl and metal(loid)s were evaluated in paddy soils surrounding an industrial park utilizing Tl-bearing minerals. The results showed that Tl contamination was evident (0.63-3.16 mg/kg) in the paddy soils and Tl was generally enriched in root of rice (Oryza sativa L.) with a mean content of 1.27 mg/kg. A remarkably high level of Tl(III) (30-50%) was observed in the paddy soils. Further analyses by STEM-EDS and XPS indicated that Tl(I) in the paddy soils was jointly controlled by adsorption, oxidation, and precipitation of Fe/Mn(hydr)oxide (e.g. hematite and birnessite), which might act as important stabilization mechanisms for inhibiting potential Tl uptake by rice grains. The health quotient (HQ) values indicated a potentially high Tl risk for inhabitants via consumption of the rice grains. Therefore, it is critical to establish effective measures for controlling the discharge of Tl-containing waste and wastewater from different industrial activities to ensure food safety in the rice paddy soils.

Stable isotope fractionation of thallium as novel evidence for its geochemical transfer during lead‑zinc smelting activities

Thallium (Tl) is a highly toxic trace metal. Lead (Pb)‑zinc (Zn) smelting, which is a pillar industry in various countries, is regarded as one of the dominant anthropogenic sources of Tl contamination in the environment. In this study, thallium isotope data have been evaluated for raw material and a set of industrial wastes produced at different stages of Pb-Zn smelting in a representative large facility located by the North River, South China, in order to capture Tl isotope signatures of such typical anthropogenic origin for laying the foundation of tracking Tl pollution. Large variations in Tl isotopic compositions of raw Pb-Zn ores and solid smelting wastes produced along the process chain were observed. The ε²⁰⁵Tl values of raw Pb-Zn ores and return fines are -0.87 ± 0.26 and -1.0 ± 0.17, respectively, contrasted by increasingly more negative values for electrostatic precipitator dust (ε²⁰⁵Tl = -2.03 ± 0.14), lime neutralizing slag (ε²⁰⁵Tl = -2.36 ± 0.18), and acid sludge (ε²⁰⁵Tl = -4.62 ± 0.76). The heaviest ε²⁰⁵Tl (1.12 ± 0.51) was found in clinker. These results show that isotopic fractionation occurs during the smelting processes. Obviously, the lighter Tl isotope is enriched in the vapor phase (-3.75 ε²⁰⁵Tl units). Further XPS and STEM-EDS analyses show that Tl isotope fractionation conforms to the Rayleigh fractionation model, and adsorption of ²⁰⁵Tl onto hematite (Fe₂O₃) may play an important role in the enrichment of the heavier Tl isotope. The findings demonstrate that Tl isotope analysis is a robust tool to aid our understanding of Tl behavior in smelting processes and to provide a basis for source apportionment of Tl contaminations.

Releasing Characteristics and Biological Toxicity of the Heavy Metals from Waste of Mercury-Thalliummine in Southwest Guizhou of China

In this paper, the releasing characteristics and biological toxicity of Tl, Hg, As and Sb in waste of Lanmuchang mercury-thallium mine were studied. The results indicated that strong acidity can significantly promote the release of Tl from waste. With the increase of pH, the release of Sb grew steadily, while Hg and As showed a trend of first increasing and then decreasing. Fe₂(SO₄)₃ contributed less to the release of As and Sb than to that of Hg and Tl. FeCl₃ significantly inhibited the release of As, Sb and Tl. In the leaching experiments of litter and root exudates, the lixiviums appeared neutral, and the litter and root exudates solution significantly reduced the release of Tl, and showed less toxicity to luminescent bacteria. However, they promoted the release of Hg, As and Sb at different levels.

Thallium and lead variations in a contaminated peatland: A combined isotopic study from a mining/smelting area

Vertical profiles of Tl, Pb and Zn concentrations and Tl and Pb isotopic ratios in a contaminated peatland/fen (Wolbrom, Poland) were studied to address questions regarding (i) potential long-term immobility of Tl in a peat profile, and (ii) a possible link in Tl isotopic signatures between a Tl source and a peat sample. Both prerequisites are required for using peatlands as archives of atmospheric Tl deposition and Tl isotopic ratios as a source proxy. We demonstrate that Tl is an immobile element in peat with a conservative pattern synonymous to that of Pb, and in contrast to Zn. However, the peat Tl record was more affected by geogenic source(s), as inferred from the calculated element enrichments. The finding further implies that Tl was largely absent from the pre-industrial emissions (>~250 years BP). The measured variations in Tl isotopic ratios in respective peat samples suggest a consistency with anthropogenic Tl (ε²⁰⁵Tl between ~ -3 and -4), as well as with background Tl isotopic values in the study area (ε²⁰⁵Tl between ~0 and -1), in line with detected ²⁰⁶Pb/²⁰⁷Pb ratios (1.16-1.19). Therefore, we propose that peatlands can be used for monitoring trends in Tl deposition and that Tl isotopic ratios can serve to distinguish its origin(s). However, given that the studied fen has a particularly complicated geochemistry (attributed to significant environmental changes in its history), it seems that ombrotrophic peatlands could be better suited for this type of Tl research.

Secondary Sulfate Minerals from Pyrite Oxidation in Lanmuchang Hg-Tl Deposit, Southwest Guizhou Province, China: Geochemistry and Environmental Significance

Thallium (Tl) is a highly toxic trace metal posing a significant threat to human health. Tl pollution in soils and chronic Tl poisoning related to Tl-rich sulfides weathering in the Lanmuchang mine of southwest Guizhou province, China, have been intensively studied in recent years. And yet, there are few studies on the role of secondary sulfate minerals associated with Tl mobility in this area. The sulfate minerals were characterized by XRD and SEM-EDS. The concentrations of Tl and other elements were determined by ICP-MS. The results show that sulfate minerals are predominantly melanterite, halotrichite, and fibroferrite. The average contents of Tl in rock, sulfate minerals, and soil samples were 156.4, 0.11, and 72.1 µg g^-1, respectively. This study suggests that Tl in the mineralized rocks entered soils by pyrite oxidation with less scavenged of the sulfate minerals. The dissolution of the ferric sulfate minerals accelerates pyrite oxidation and maintains soil acidity, and this likely enhances Tl mobility from soil to crops.

Method Validation for Determination of Thallium by Inductively Coupled Plasma Mass Spectrometry and Monitoring of Various Foods in South Korea

Thallium (Tl) is a rare element and one of the most harmful metals. This study validated an analytical method for determining Tl in foods by inductively coupled plasma mass spectrometry (ICP-MS) based on food matrices and calories. For six representative foods, the method's correlation coefficient (R2) was above 0.999, and the method limit of detection (MLOD) was 0.0070-0.0498 μg kg-1, with accuracy ranging from 82.06% to 119.81% and precision within 10%. We investigated 304 various foods in the South Korean market, including agricultural, fishery, livestock, and processed foods. Tl above the MLOD level was detected in 148 samples and was less than 10 μg kg-1 in 98% of the samples. Comparing the Tl concentrations among food groups revealed that fisheries and animal products had higher Tl contents than cereals and vegetables. Tl exposure via food intake did not exceed the health guidance level.

Geochemical distribution and speciation of thallium in groundwater impacted by acid mine drainage (Southern China)

Thallium (Tl) commonly occurs in shallow groundwater affected by acid mine drainage (AMD); however, our knowledge of the occurrence of Tl in shallow groundwater is limited. This study observes that the shallow groundwater in an AMD-impacted area in Southern China contains an elevated Tl concentration (22 μg/L) under the oxidizing conditions and a low Tl concentration (<1 μg/L) in the reducing environment. The groundwater Tl concentration is positively correlated with oxidation-reduction potential (Eh) and negatively correlated with Cl content. The modelling results of the Tl species demonstrate that Tl⁺, TlSO₄^-, TlCl, and TlNO₃ are the main forms of Tl in groundwater. Tl may precipitate as Tl(OH)₃ under weakly acidic to alkaline conditions. Drill-core analysis of wells indicates that the Tl content in the vadose zone is equal to the background soil Tl content under oxidizing conditions. However, under artificial reducing conditions, the Tl content at the 3-4 m depth below the groundwater level ranges from 1.6 to 3.5 μg/g. This finding demonstrates that Tl solute in groundwater migrates into the aquifer when redox conditions change. Mn-oxides and illite in the weak permeable aquifer are the key minerals for Tl adsorption; some major sites of illite start to uptake Tl from pH 8.0. This study highlights not only the geochemical distribution of Tl in groundwater but also the influences of changes in redox conditions caused by human activities on Tl enrichment in groundwater. Enhancing our understanding of the aqueous geochemistry of Tl is of significance for the prevention and control of Tl pollution.

Escalating health risk of thallium and arsenic from farmland contamination fueled by cement-making activities: A hidden but significant source

Soil-to-vegetable migration of toxic metal(loid)s is a pivotal pathway of human exposure to chemical intoxication. Thallium (Tl) and arsenic (As) are highly toxic metal(loid)s but their co-occurrence in soils and vegetables remain poorly understood. Herein, the present study focuses on potential health risk arising from co-occurrence of TlAs in various common vegetables cultivated in different farmlands around an industrial area featured by cement production activities. The results reveal obvious co-contamination of Tl (2.28 ± 1.39 mg/kg) and As (102.0 ± 66.7 mg/kg) in soils. Fine particles bearing sulfide and other minerals associated with Tl and As are detected in fly ash from cement plant, which can be migrated by wind over a long distance with hidden but inevitable pollution. Bioaccumulation Factor (BCF) and Enrichment Factor (EF) show that taro and corn preferentially accumulate Tl especially in underground parts. Hazard Quotient (HQ) indicates that consumption of these vegetables may result in chronic poisoning and/or even carcinogenic risk. The study highlights that the pathway and high risk of co-contamination of TlAs in the nearby farmlands posed by cement-making activities should be highly concerned.

Thallium in aquatic environments and the factors controlling Tl behavior

Although thallium (Tl) usually exists in a very low level in the natural environment, it is highly toxic. With the development of mining and metallurgical industry and the wide application of Tl in the field of high technologies, Tl poses an increasing threat to the ecological environment and human health. This paper summarizes the research results of the toxicity of Tl as well as the distribution, occurrence forms, migration, and transformation mechanism of Tl in rivers, lakes, mining areas, estuaries, coastal waters, and oceans. It also discusses the influence mechanisms of pH, redox potential, suspended particulate matters, photochemical reaction, natural minerals, cation/anion, organic matters, and microorganisms on the environmental behavior of Tl. This paper points out the shortcomings of Tl research methods in water environment, and looks forward to the future development directions: First, the technology for separating Tl(III) and Tl(I) is still immature, especially it is difficult to effectively separate Tl(III) and Tl(I) in seawater. Second, the development of many advanced in situ detection technologies will bring great convenience to the studies of the dynamic mechanisms of Tl migration and transformation in the environments. Third, adsorption is the most effective mechanism to remove Tl from water, in which modified metal oxides or macrocyclic organic compounds have high application potential.

Pedogeochemical distribution of gallium, indium and thallium, their potential availability and associated risk in highly-weathered soil profiles of Taiwan

Gallium (Ga), indium (In), and thallium (Tl) are emerging soil contaminants. Profile distribution of total content and available form as well as assessing the contamination degree of these elements in highly-weathered soils have not been studied. Consequently, the aim of this study was to determine the distribution of total (HF-digestion) and available (EDTA-extracted form) content of Ga, In, and Tl in eleven soil profiles collected from aged fluvial materials on the Quaternary terraces representing highly-weathered soils (Ultisols and Oxisols) in Taiwan as affected by soil properties. We also assessed the soils contamination degree using indices including enrichment factor (EF), geo-accumulation index (I_geo), and pollution loading index (PLI). The total element content varied from 9460 to 2340 μg kg^-1 for Ga, 4.77-37.1 μg kg^-1 for In, and from 55.7 to 206 μg kg^-1 for Tl. The elements showed different profile distribution in the soils. Soil contamination degree was low in all profiles according to the I_geo and PLI values, but the contamination degree according to the EF was severe for Ga and minor or moderate for In in selected horizons of some profiles. The median content of EDTA-extracted Ga, In, and Tl accounted for 24.0, 8.70, and 5.1% of the total content, respectively. The available Ga and Tl can be predicted by a function of total element and clay using multivariate linear regression analysis. The available In was not able to be predicted by a significant fit of the regression with total In and the studied soil properties, and thus we require more assessment approaches of In availability for the soils in the future.

Thallium Contamination of Drinking Water: Health Implications in a Residential Cohort Study in Tuscany (Italy)

In 2014–2015, concentrations of thallium above the recommended reference value (EPA: 2 µg/L) were measured in some parts of the drinking water distribution system in the municipality of Pietrasanta (Tuscany, Italy). An extensive campaign of water samples and human biomonitoring surveys were implemented to quantify the exposure of population. A residential cohort epidemiological study was carried out on the population of the municipality of Pietrasanta, aimed at comparing the health status of residents in the areas affected by thallium contamination with residents living in the rest of the municipality. Cohort included people residing in the municipality of Pietrasanta from 1 January 2000 to 31 December 2015. Residence addresses were georeferenced and each subject living in one of the three contaminated areas were defined as exposed. Mortality, hospital discharge data and adverse pregnancy outcomes were taken from administrative health databases. Cox proportional hazard models and logistic models were used to test the association between thallium exposure and health outcome. This study did not show any excess of risk in terms of mortality and hospitalization in the population residing in the areas served by thallium-contaminated aqueduct branches, compared to the rest of the not contaminated area. Increased risks for low birth weight (OR = 1.43 95% CI 0.91–2.25) and pre-term birth (OR = 1.40 95% CI 0.82–2.37) were observed. In view of the paucity of epidemiological studies on thallium, this study is an important contribution to the state of knowledge of the health effects of chronic exposures to low concentrations of thallium.

Emergent thallium exposure from uranium mill tailings

Thallium (Tl) pollution caused by the exploitation of uranium (U) mines has long been neglected due to its low crustal abundance. However, Tl may be enriched in minerals of U ore because Tl has both sulfurophile and lithophile properties. Herein, a semi-dynamic leaching experiment combined with statistical analysis, geochemical speciation and multi-characterization provided novel insight into the distinct features and mechanisms of Tl release from uranium mill tailings (UMT). The results showed that particle size effects prevail over the pH on Tl release, and surface dissolution is the pivotal mechanism controlling Tl release based on Fick's diffusion model. The study revealed that long-term leaching and weathering can lead to the increased acid-extractable and oxidizable fractions of Tl in UMT, and that the exposure and dissolution of Tl-containing sulfides would largely enhance the flux of Tl release. The findings indicate that UMT containing (abundant) pyrite should be paid particular attention due to Tl exposure. Besides, critical concern over the potential Tl pollution in universal U mining and hydrometallurgical areas likewise may need to be seriously reconsidered.

Contamination, oral bioaccessibility and human health risk assessment of thallium and other metal(loid)s in farmland soils around a historic TlHg mining area

In this study, tweenty-nine soil samples were collected from a historic TlHg mining area, located in southwest Guizhou, China. Total concentrations of metal(loid)s in soils and in vitro extracts were analysed by ICP-MS, and the bioaccessibility of metal(loid)s was conducted by two often used in vitro extraction methods, Simplified bioaccessibility Extraction Test (SBET) and Physiologically Based Extraction Test (PBET). The health risk assessment based on total concentrations of metal(loid)s, bioaccessibility of SBET and PBET through soil ingestion were investigated. Results indicated that the collected cultivated soils contained elevated concentrations of Tl (44.8 ± 67.7 mg kg^-1), Hg (110 ± 193 mg kg^-1), As (84.4 ± 89.2 mg kg^-1) and Sb (14.8 ± 24.8 mg kg^-1), exceeding the regional background values of Guizhou province, China and the Chinese farmland risk screening values. However, the bioaccessibility of Tl, Hg, As and Sb were relatively low, usually less than 30% for most samples and varied greatly among metal(loid)s and sampling sites. The average bioaccessibility values of Tl, Hg, As and Sb by SBET were lower than those by PBET. The non-carsinogenic risk (HQ and HI) and Carcinogenic Risk (CR) values were significantly reduced when incorporating the bioaccessibiltiy of metal(loid)s into health risk assessment. It is worth noting that the health risk to children exceeded adults. Moreover, Tl and As contributed the most to the risk, indicating that more attention should be paid on Tl and As during the daily environmental regulation and management of contaminated soils in Lanmuchang.