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

Reductive Transformation of MnO2 Controls Thallium Remobilization: Differential Effects of Layered and Tunneled Structures

Mn oxides play a critical role in Tl scavenging and accumulation in the epibiotic environment. However, the effect of Mn oxide reduction in the Mn/Fe cycle on Tl mobilization is not clear. Herein, the influence of Mn oxide configuration, oxygen environment, and degree of reduction on MnO2 transformation and associated Tl species distribution is investigated. In oxic environments, both typical δ-MnO2 and α-MnO2 structures (i.e., layered and tunneled, respectively) can immobilize Tl(I) for a long time. In mild-to-moderate reducing anoxic environments, the drastic reductive transformation of δ-MnO2 results in Tl binding, mainly in an exchangeable form. In highly reducing environments, δ-MnO2 or α-MnO2 is converted to Manganite, resulting in the release of more Tl. Tl-LIII edge X-ray absorption spectroscopy indicates that oxidized Tl(III) (54-62%) is converted to structural Tl(I) (67-80%) and bound to interlayer/tunnel centers during the reductive transformation of MnO2, which enhances Tl exchange in δ-MnO2 and leads to Tl immobilization in α-MnO2. Our results show that anoxic Tl(I)-/Mn(II)-/Fe(II)-induced MnO2 transformation can enhance Tl mobilization, and tunneled MnO2 may have a more sustainable Tl immobilization potential than layered MnO2, which improves the general understanding of the geochemical behavior of Tl in different Mn-related reducing environments.

New insights into thallium(I) behaviors at birnessite surfaces: Effects of an organic buffer and goethite

Understanding the environmental behavior of thallium (Tl) is crucial due to its high toxicity and increasing anthropogenic presence. This study investigated the adsorption and redox behaviors of Tl(I) with acid birnessite (AcBi) in the presence of 1,4-piperazine-diethanesulfonic acid (PIPES) and goethite under diffusion-limited conditions using Donnan reactors in aerobic and anaerobic environments. Our findings indicate that Tl(I) preferentially adsorbs onto AcBi, with capacities 20 to 100 times higher than onto goethite, even when AcBi is partial reduced by PIPES. No net Tl(I) oxidation occurred in the Donnan reactors, likely due to complex electron transfer processes between Tl(I), birnessite, and PIPES. Any Tl(III) generated from Tl(I) oxidation by birnessite was rapidly reduced back to Tl(I) by PIPES. This was confirmed in batch experiments where reduced Tl(III) on birnessite surfaces and in Tl(III) salts. These findings highlight the need to assess the impact of Good's buffers on redox reactions involving manganese oxides and Tl, while also providing insights into the competitive retention of Tl on manganese and iron (hydr)oxides, with implications for Tl mobility and bioavailability in natural environments.

Increased atmospheric thallium threats to populated areas: A mini review

Air pollutants combined with Hg, Cd, Cr, Pb, etc. in many global populated areas were studied comprehensively, while our understanding towards thallium (Tl), an extremely toxic heavy metal, remains very limited. Further, the knowledge on atmospheric emissions, distribution, and the hidden risks associated with Tl is of great scarcity. Hence, this work aims to review recent data on significant sources of ambient Tl resulting from industrial activities, including Pb/Zn/Cu/Fe sulfide ore smelting, steel-making, coal burning, and cement production that involves the use of Tl-bearing wastes. Through the examination of Tl emissions and transfer pathways in the atmosphere, it is found that Tl is present at lower than ng/m3 in aerosols and air particulates but can increase to much higher levels even at 1000 μg/m3 in atmospheric fine particulate matters near the mining and smelting industrialized zones located near populated areas. This study highlights the importance of creating a comprehensive emission inventory for Tl, particularly in developing countries where this data is currently lacking. The time has come to develop a precise national emission inventory for Tl in order to prevent and mitigate the risks associated with ambient exposure to this element. This review offers novel insights for the scientific community and policy-makers in establishing effective control and management strategies to curb hidden Tl hazards derived from industrial activities.

Thallium isotopic fractionation in soils from a historic HgTl mining area: New insights on thallium geochemistry

Thallium (Tl), a highly toxic heavy metal, which may pose significant environmental threats due to extensive discharge from anthropogenic activities. It is crucial to understand geochemical behavior of Tl in soils for initiating proper measures for Tl pollution control. For this purpose, transport behavior of Tl and its dominant factors in soils collected from a typically Tl-enriched depth profile, surrounding a historical tailing dump near an independent HgTl mine area in China, were investigated by using Tl isotope compositions. Results showed that an overall enrichment of Tl (48.68-375.21 mg/kg) was accompanied with As elevation (135.00-619.00 mg/kg) in the whole depth profile, and Tl and As exhibited co-migration behavior with Fe, S, K, and Rb. Geochemical fractionation of Tl unveiled by sequential extraction further indicated that Mn-/Fe-bearing minerals and clay minerals act as main hosts of Tl in the studied soils. Thallium isotopic composition and its fractionation pattern further revealed that the major contributors to high Tl levels in the depth profile were tailing and lorandite minerals, with mean contribution rate of 51.99% and 42.47%, respectively. These findings facilitate the understanding of Tl transport behavior in highly contaminated environment, providing valuable insights for developing new technologies in mining waste treatment and historical mine reclamation.

Response of Plant Endophyte Communities to Heavy Metal Stress and Plant Growth Promotion by the Endophyte Serratia marcescens (Strain JG1)

Effects of heavy metals on soil microbial communities have been extensively studied due to their persistence in the environment and imposed threats to living organisms; however, there is a lack of in-depth studies of the impacts of heavy metals on plant endophyte communities. Therefore, the responses of plant endophyte communities to different concentrations of heavy metals were investigated in this study. The endophyte communities of plants existing in severely (W1, Pb, 110.49 mg/kg, Cd, 1.11 mg/kg), moderately (W2, Pb, 55.06 mg/kg, Cd, 0.48 mg/kg), and mildly (W3, Pb, 39.06 mg/kg, Cd, 0.20 mg/kg) contaminated soils were analyzed by 16s rRNA high-throughput Illumina sequencing. Furthermore, networks were constructed to illustrate the relationships between microorganisms and environmental factors. High-quality sequences were clustered at a 97% similarity level. Results revealed that the diversity of the community and relative abundance of Cyanobacteria phylum increased with decreasing levels of pollution. Cyanobacteria and Proteobacteria were found to be the dominant phylum, while Methylobacterium and Sphingomonas were observed as the dominant genus. Tukey's HSD test showed that the relative abundances of Cyanobacteria and Proteobacteria phyla and Methylobacterium and Sphingomonas genera differed significantly (p < 0.01) among the plants of the three sample sites. Environmental factor analysis revealed a significant negative correlation (p < 0.01) of Cyanobacteria and a significant positive correlation (p < 0.01) of Methylobacterium with the heavy metal content in the environment. These findings suggest that Cyanobacteria and Methylobacterium may be phylum and genus indicators, respectively, of heavy metal toxicity. Tax4Fun analysis showed the effect of heavy metal toxicity on the abundance of genes involved in plant metabolism. In addition, culturable endophytic strains were isolated to study their resistance to heavy metal stress and their ability to promote plant growth. The potting tests showed that the JG1 strain was tolerant to heavy metals, and it could significantly promote the growth of the host plant under stress caused by multiple heavy metals. Compared to the control, the JG1-treated plants showed a 23.14% increase in height and a 12.84% increase in biomass. Moreover, AP, AK, and HN contents in JG1-treated plants were 20.87%, 12.55%, and 9.03% higher, respectively, under heavy metal stress. The results of this study provide a scientific basis for the construction of an efficient plant endophyte restoration system.

The determination of thallium in the environment: A review of conventional and advanced techniques and applications

Thallium (Tl) is a potential toxicity element that poses significant ecological and environmental risks. Recently, a substantial amount of Tl has been released into the environment through natural and human activities, which attracts increasing attention. The determination of this hazardous and trace element is crucial for controlling its pollution. This article summarizes the advancement and progress in optimizing Tl detection techniques, including atomic absorption spectroscopy (AAS), voltammetry, inductively coupled plasma (ICP)-based methods, spectrophotometry, and X-ray-based methods. Additionally, it introduces sampling and pretreatment methods such as diffusive gradients in thin films (DGT), liquid-liquid extraction, solid phase extraction, and cloud point extraction. Among these techniques, ICP-mass spectrometry (MS) is the preferred choice for Tl detection due to its high precision in determining Tl as well as its species and isotopic composition. Meanwhile, some new materials and agents are employed in detection. The application of novel work electrode materials and chromogenic agents is discussed. Emphasis is placed on reducing solvent consumption and utilizing pretreatment techniques such as ultrasound-assisted processes and functionalized magnetic particles. Most detection is performed in aqueous matrices, while X-ray-based methods applied to solid phases are summarized which provide non-destructive analysis. This work improves the understanding of Tl determination technology while serving as a valuable resource for researchers seeking appropriate analytical techniques.

The rhizosphere microbiome reduces the uptake of arsenic and tungsten by Blechnum orientale by increasing nutrient cycling in historical tungsten mining area soils

The growth of pioneer plants in metal mining area soil is closely related to their minimal uptake of toxic elements. Pioneer plants can inhibit the uptake of toxic elements by increasing nutrient uptake. However, few studies have focused on the mechanisms by which the rhizosphere microbiome affect nutrient cycling and their impact on the uptake of toxic elements by pioneer plants. In this study, we selected Blechnum orientale to investigate the potential roles of the rhizosphere microbiome in nutrient cycling and plant growth in a historical tungsten (W) mining area. Our results showed that while the arsenic (As) and W contents in the soil were relatively high, the enrichment levels of As and W in the B. orientale were relatively low. Furthermore, we found that the As and W contents in plants were significantly negatively correlated with soil nutrients (S, P and Mo), suggesting that elevated levels of these soil nutrients could inhibit As and W uptake by B. orientale. Importantly, we found that these nutrients were also identified as the most important factors shaping rhizosphere microbial attributes, including microbial diversity, ecological clusters, and keystone OTUs. Moreover, the genera, keystone taxa and microbial functional genes enriched in the rhizosphere soils from mining areas played a key role in nutrient (S, P and Mo) bioavailability, which could further increase the nutrient uptake by B. orientale. Taken together, our results suggest that rhizosphere microorganisms can improve pioneer plant growth by inhibiting toxic element accumulation via the increase in nutrient cycling in former W mining areas.

Physiology and molecular basis of thallium toxicity and accumulation in Arabidopsis thaliana

Thallium (Tl) is a non-essential metal mobilized through industrial processes which can lead to it entering the environment and exerting toxic effects. Plants are fundamental components of all ecosystems. Therefore, understanding the impact of Tl on plant growth and development is of great importance for assessing the potential environmental risks of Tl. Here, the responses of Arabidopsis thaliana to Tl were elucidated using physiological, genetic, and transcriptome analyses. Thallium can be absorbed by plant roots and translocated to the aerial parts, accumulating at comparable concentrations throughout plant parts. Genetic evidence supported the regulation of Tl uptake and movement by different molecular compartments within plants. Thallium primarily caused growth inhibition, oxidative stress, leaf chlorosis, and the impairment of K homeostasis. The disturbance of redox balance toward oxidative stress was supported by significant differences in the expression of genes involved in oxidative stress and antioxidant defense under Tl exposure. Reduced GSH levels in cad2-1 mutant rendered plants highly sensitive to Tl, suggesting that GSH has a prominent role in alleviating Tl-triggered oxidative responses. Thallium down-regulation of the expression of LCHII-related genes is believed to be responsible for leaf chlorosis. These findings illuminate some of the mechanisms underlying Tl toxicity at the physiological and molecular levels in plants with an eye toward the future environment management of this heavy metal.

Distribution and migration of uranium, chromium, and accompanying metal(loid)s in soil-plants system around a uranium hydrometallurgical area

The extraction and utilization of uranium (U) ores have led to the release of significant amounts of potentially toxic metal(loid)s (PTMs) into the environment, constituting a grave threat to the ecosystem. However, research on the distribution and migration mechanism of U, chromium (Cr), and their accompanying PTMs in soil-plant system around U hydrometallurgical area remains insufficient and poorly understood. Herein, the distribution, migration, and risk level of PTMs were evaluated in soil and plant samples around U hydrometallurgical area, Northern Guangdong, China. The results demonstrated that the maximum content of U and Cr found in the analyzed soils were up to 84.2 and 238.9 mg/kg, respectively. These values far exceed the soil background values in China and other countries. The highest content of U (53.6 mg/kg) was detected in Colocasia antiquorum Schott, and the highest content of Cr (349.5 mg/kg) was observed in Pteridium aquilinum, both of which were enriched in their roots. The risk assessment of PTMs demonstrated that the study area suffered from severe pollution (PN > 3), especially from U, Cr, Th, and As, suggesting the non-negligible anthropogenic impacts. Hence, in light of the significant ecological hazard posed by the U hydrometallurgical area, it is imperative to implement appropriate restoration measures to ensure the human health and maintain the stability of the ecosystem.

Applying thallium isotopic compositions as novel and sensitive proxy for Tl(I)/Tl(III) transformation and source apportionment

Thallium is a rare metal known for its highly toxic nature. Recent research has indicated that the precise determination of Tl isotopic compositions using Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP MS) provides new opportunities for understanding Tl geochemical behavior. While isotopic fractionation of Tl derived from anthropogenic activities (e.g., mining, smelting) have been reported, there is limited information regarding Tl influenced by both natural weathering processes and anthropogenic origins. Herein, we investigated, for the first time, the Tl isotopic compositions in soils across a representative Tl-rich depth profile from the Lanmuchang (LMC) quicksilver mine (southwest China) in the low-temperature metallogenesis zone. The results showed significant variations in Tl isotope signatures (ε205Tl) among different soil layers, ranging from -0.23 to 3.79, with heavier isotope-205Tl enrichment observed in the bottom layers of the profile (ε205Tl = 2.18-3.79). This enrichment of 205Tl was not solely correlated with the degree of soil weathering but was also partially associated with oxidation of Tl(I) by Fe (hydr)oxide minerals. Quantitative calculation using ε205Tl vs. 1/Tl data further indicated that the Tl enrichment across the soil depth profile was predominantly derived from anthropogenic origins. All these findings highlight that the robustness and reliability of Tl isotopes as a proxy for identifying both anthropogenic and geogenic sources, as well as tracing chemical alterations and redox-controlled mineralogical processes of Tl in soils. The nascent application of Tl isotopes herein not only offers valuable insights into the behavior of Tl in surface environments, but also establishes a framework for source apportionment in soils under similar circumstances.

Exploring the accumulation capacity of dominant plants based on soil heavy metals forms and assessing heavy metals contamination characteristics near gold tailings ponds

Heavy metal contamination of soil commonly accompanies problems around gold mine tailings ponds. Fully investigating the distribution characteristics of heavy metals and the survival strategies of dominant plants in contaminated soils is crucial for effective pollution management and remediation. This study aims to investigate the contamination characteristics, sources of heavy metals (As, Cd, Pb, Hg, Cu, Zn, Cr, and Ni) in soils around gold mine tailings ponds areas (JHH and WZ) and to clarify the form distribution of heavy metals (As, Cd, Pb, Hg) in contaminated plots as well as their accumulation and translocation in native dominant plants. The results of the study showed that the concentrations of As, Pb, Cd, Cu, and Zn in soil exceeded the national limits at parts of the sampling sites in both study areas. The Nemerow pollution index showed that both study areas reached extreme high pollution levels. Spatial analysis showed that the main areas of contamination were concentrated around metallurgical plants and tailings ponds, with Cd exhibiting the most extensive area of contamination. In the JHH, As (74%), Cd (66%), Pb (77%), Zn (47%) were mainly from tailings releases, and Cu (52%) and Hg (51%) were mainly from gold ore smelting. In the WZ, As (42%), Cd (41%), Pb (73%), Cu (47%), and Zn (41%) were mainly from tailings releases. As, Cd, Pb, and Hg were mostly present in the residue state, and the proportion of water-soluble, ion-exchangeable, and carbonate-bound forms of Cd (19.93%) was significantly higher than that of other heavy metals. Artemisia L. and Amaranthus L. are the primary dominating plants, which exhibited superior accumulation of Cd compared to As, Pb, and Hg, and Artemisia L. demonstrated a robust translocation capacity for As, Pb, and Hg. Compared to the concentrations of other forms of soil heavy metals, the heavy metal content in Artemisia L correlates significantly better with the total soil heavy metal concentration. These results offer additional systematic data support and a deeper theoretical foundation to bolster pollution-control and ecological remediation efforts in mining areas.

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.

Source identification and health risk assessment of heavy metals with mineralogy: the case of soils from a Chinese industrial and mining city

Understanding the precise sources of heavy metals (HMs) in soil and the contribution of these sources to health risks has positive effects in terms of risk management. This study focused on the HMs in the soil of five land uses in an industrial and mining city. The sources of HMs in soils were identified, and the soil mineralogical characteristics and health risks of HMs were discussed. The results showed that the HMs (Cu, Zn, Ni, Cd, Pb) found in the soil of the five land uses were affected by human activities. For example, the Cu in grassland, gobi beach, woodland, green belt, and farmland is 22.3, 3.5, 22.5, 16.7, and 21.3 times higher than the soil background values in Gansu Province, respectively. The Positive Matrix Factorization model (PMF) results revealed that traffic emissions and industrial and agricultural activities were the primary sources of HMs in the soil, with industrial sources accounting for the largest share at 55.79%. Furthermore, various characteristics proved that the studied HMs were closely related to smelting products. Concentration-oriented health risk assessments showed that HMs in the different soil types held non-carcinogenic and carcinogenic risks for children and adults. Contamination source-oriented health risk assessments of children and adults found that industrial activities controlled non-carcinogenic and carcinogenic risks. This study highlighted the critical effects of smelting on urban soil and the contribution of pollution sources to health risks. Furthermore, this work is significant in respect of the risk control of HMs in urban soils.

A novel application of thallium isotopes in tracing metal(loid)s migration and related sources in contaminated paddy soils

Thallium (Tl) is a highly toxic heavy metal, which is harmful to plants and animals even in trace amounts. Migration behaviors of Tl in paddy soils system remain largely unknown. Herein, Tl isotopic compositions have been employed for the first time to explore Tl transfer and pathway in paddy soil system. The results showed considerably large Tl isotopic variations (ε²⁰⁵Tl = -0.99 ± 0.45 ~ 24.57 ± 0.27), which may result from interconversion between Tl(I) and Tl(III) under alternative redox conditions in the paddy system. Overall higher ε²⁰⁵Tl values of paddy soils in the deeper layers were probably attributed to abundant presence of Fe/Mn (hydr)oxides and occasionally extreme redox conditions during alternative dry-wet process which oxidized Tl(I) to Tl(III). A ternary mixing model using Tl isotopic compositions further disclosed that industrial waste contributed predominantly to Tl contamination in the studied soil, with an average contribution rate of 73.23%. All these findings indicate that Tl isotopes can be used as an efficient tracer for fingerprinting Tl pathway in complicated scenarios even under varied redox conditions, providing significant prospect in diverse environmental applications.

Release and mobility characteristics of thallium from polluted farmland in varying fertilization: Role of cation exchange

Batch and column leaching tests were used to study thallium's release and migration behaviour and evaluate its potential toxicity risks in soil. The results indicated that leaching concentrations of Tl using TCLP and SWLP were much higher than the threshold, indicating a high risk of thallium pollution in the soil. Furthermore, the intermittent leaching rate of Tl by Ca²⁺ and HCl reached its maximum value, demonstrating the easy release of Tl. After HCl leaching, the form of Tl in the soil has changed, and ammonium sulfate has increased its extractability. Additionally, the extensive application of calcium promoted the release of Tl, increasing its potential ecological risk. Spectral analysis showed that Tl was mainly present in minerals such as Kaolinite and Jarosite, and exhibited significant adsorption capacity for Tl. HCl and Ca²⁺ damaged the crystal structure of the soil, greatly enhancing the migration and mobility of Tl in the environment. More importantly, XPS analysis confirmed that the release of Tl (I) in the soil was the leading cause of increased mobility and bioavailability. Therefore, the results revealed the risk of Tl release in the soil, providing theoretical guidance for its pollution prevention and control.

Stable thallium (Tl) isotopic signature as a reliable source tracer in river sediments impacted by mining activities

Thallium (Tl) is an extremely toxic metal, whose geochemical behavior remains poorly understood. This study aims to clarify the migration pathway and source apportionment of Tl in sediments from a watershed downstream of an open and large-scale pyrite mine area in south China, using high-precised Tl isotopic compositions. Results showed that Tl isotopic fractionations were mainly influenced by the anthropogenic Tl sources in all the sediments as a whole from the studied watershed, while in situ mineral adsorption and biological activity were limited. Moreover, plot of ε²⁰⁵Tl vs. 1/Tl further illustrated that three possible end-members, viz. background sediments, pyrite tailings, and sewage treatment wastes were ascribed to predominant sources of Tl enrichment in the sediments. A ternary mixing model unveiled that waste from pyrite mining activities (i.e., both pyrite tailings and sewage treatment wastes) affected the downstream sediments up to 10 km. All these findings suggest that Tl isotopic signature is a reliable tool to trace Tl sources in the sediments impacted by mining activities. It is highly critical for further target-oriented and precise remediation of Tl contamination.

Metal Exposure Promotes Colorectal Tumorigenesis via the Aberrant N6-Methyladenosine Modification of ATP13A3

Element contamination, including that from heavy metals, is associated with gastrointestinal tumorigenesis, but the effects and mechanisms of crucial element exposure associated with colorectal cancer remain unclear. We profiled 56 elements by ICP-MS and used logistic regression, LASSO, BKMR, and GAM to identify colorectal cancer-relevant elements. A series of biochemical experiments were performed to demonstrate the cytotoxicity and the mechanisms of malignant transformation after metal exposure. Using an elementomics approach, we first found that the metal thallium (Tl) was positively correlated with many toxic metals and was associated with a significantly increased risk of colorectal cancer. Acute exposure to Tl induced cytotoxicity and cell death by accelerating the generation of reactive oxygen species and DNA damage. Chronic exposure to Tl led to the inhibition of cell death and thereby induced the malignant transformation of normal colon cells and xenograft tumor formation in nude mice. Furthermore, we describe the first identification of a significant metal quantitative trait locus for the novel colorectal cancer susceptibility locus rs1511625 near ATP13A3. Mechanistically, Tl increased the level of aberrant N⁶-methyladenosine (m⁶A) modification of ATP13A3 via the METLL3/METTL14/ALKBH5-ATP13A3 axis to promote colorectal tumorigenesis. This study provides a basis for the development of public health strategies for reducing metal exposure among populations at high risk for colorectal cancer.

The changes in the physicochemical properties of calcareous soils and the factors of arsenic (As) uptake by wheat were investigated after the cessation of effluent irrigation for nearly 20 years

It is not known what the buffering capacity of soils and arsenic (As) enrichment by crops is for calcareous agricultural soils after the end of long-term effluent irrigation. In this study, changes in soil physicochemical properties and factors of influencing As uptake by wheat were investigated in agricultural soils where sewage irrigation had been ceased for nearly 20 years. The results showed that the content of CaCO₃ and pH in soil increased compared to the period before the cessation of sewage irrigation, but remained below the soil background value. Furthermore, CaCO₃ is by far the main buffering substance in agricultural soils and indirectly contributes to the increase in pH. The As concentration in the soil was 36.4 ± 34.8 mg/kg, which was 0.56-10.28 times and 0.28-5.18 times higher than the soil background and risk screening values, respectively, but showed a decreasing trend. pH and Fe dissolution were the main reasons for the lower As concentration in the soil. Total As in soil was a better predictor of As in wheat, and soil electrical conductivity (EC) and soil organic matter (SOM) promoted As uptake by wheat. The competitive uptake of As by dissolved Si was an important reason for the mismatch between As concentrations in soil and wheat. This study highlighted the key issues of As transport transformation in soil-wheat systems after cessation of effluent irrigation, using agricultural soils, and provided a reference for soil risk management in agricultural soils in mining areas.

Effect of montmorillonite biochar composite amendment on thallium bioavailability in contaminated agricultural soils and its mitigated health risk

Little information is available on the effect of clay minerals and biochar composite on the remediation and bioavailability of thallium in agricultural soils. This study thus investigated the influence of montmorillonite biochar composite (Mnt-BC) amendment on the remediation of agricultural soil contaminated artificially by Tl and its potential health risks. Herein, bok choi was cultured to estimate the efficiency of soil Mnt-BC amendments through the bioavailability of Tl of the vegetable. Results showed that Tl bioavailability was significantly reduced in Mnt-BC-amended soils, mainly ascribed to the elevated soil pH and other improved soil properties of high functional groups (-OH, -COOH), negative charges, and exchangeable cations after amendment. Specifically, the highest immobilization efficiency of Tl in soils was observed in 2.5% treated soils with 79.11%, while in plant leaves the highest reduction of Tl was estimated to be 75.1% compared to the control treatment. Hence, the amendment dosage improved the immobilization of Tl in soil and subsequently reduced Tl uptake by the vegetable. Furthermore, from target hazard quotient (THQ) estimation, Mnt-BC amendment can lower the potential health risk while consuming such cultured bok choi in Tl-contaminated soils. Considering the environmental friendliness and high efficiency of Mnt-BC, it could be used as a potential soil amendment to remediate agricultural soils contaminated by Tl.

Hidden risks from potentially toxic metal(loid)s in paddy soils-rice and source apportionment using lead isotopes: A case study from China

Pyrite is a typical sulfide mineral which contains various potentially toxic metal(loid)s (PTMs). The pyrite smelting and subsequent industrial utilization activities usually release numerous amounts of PTMs into nearby ecosystem, which may be enriched in the nearby farmland soils and crops, leading to hidden but irreversible harm to human health via the food chain. Herein, the distribution pattern, source apportionment, and potential health risks of Pb, Zn, Cu, Cd and multiple seldom monitored PTMs (Ag, Bi, Sb, Sr, Th, U, W, and V) in the paddy soils and different organs of the rice plants from ten various sites in a typical industrial zone were investigated, where pyrite ores were used for the production of sulfuric acid and subsequent cement over several decades. The results showed that the contents of Cd, Pb and Zn in studied paddy soils generally exceeded the maximum permissible level (MPL) in China, and the contents of Sb and V were approaching the MPL. Moreover, the rice is easier to bioaccumulate Cd, Cu, and Zn than the other studied elements. The hazard quotient (HQ) calculations indicate that the rice containing such multiple elements may cause a high potential non-carcinogenic and carcinogenic health risk for residents, particularly for the senior group. The Pb isotope tracing method combined with PCA (principal component analysis) further uncovered that the pyrite industrial utilization contributed 18.58-55.41 % to the highly enriched PTMs in paddy soils. All these findings indicate that the paddy soil system has been contaminated by the pyrite industrial activities and certain distances or areas should be rigidly forbidden from rice cultivation in the proximity of the pyrite smelting and related industrial sites.

The removal of heavy metal pollution from wastewaters using thermophilic B. cereus SO-16 bacteria

In this study, bioaccumulation, remediation, tolerance, and effects of manganese ions (Mn(II)) and copper ions (Cu(II)) on antioxidant enzymes of thermophilic Bacillus cereus (B. cereus) SO-16 were investigated in detail. The findings of the study showed that Mn(II) was less toxic than Cu(II) to B. cereus SO-16. Moreover, B. cereus SO-16 was exhibited less tolerance to Mn(II) and Cu(II) ions in the liquid medium compared to the solid medium. The growth of bacteria was expressively effective for Mn(II) and Cu(II) concentrations of 2.5 mg/L at 24th h. The highest Mn(II) and Cu(II) bioaccumulation values after 48 h incubation of thermophilic B. cereus SO-16 were measured as 102.04 (24th h) and 87.96 (36th h) metal/dry bacteria weight. The change in morphology and functionality of B. cereus SO-16 after interaction with Mn(II) and Cu(II) was tested using various methods. The results indicated that B. cereus SO-16, a thermophilic bacterium, can be utilized in industrial wastewaters to recover and remediation of toxic metals.

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.

Comparative study on the characteristics and environmental risk of potentially toxic elements in biochar obtained via pyrolysis of swine manure at lab and pilot scales

Pyrolysis is considered as a promising method to immobilize potentially toxic elements (PTEs) in animal manures. However, comparative study on characteristics and environmental risk of PTEs in biochar obtained by pyrolysis of animal manure at different reactors are lacking. In this study, swine manure was pyrolyzed at 300-600 °C in a lab-scale or pilot-scale reactor with the aim to investigate their effects on characteristics and environmental risk of As, Cd, Cu, Ni, Pb, and Zn in swine manure biochar. Results showed that biochars produced from pilot scale had lower pH and carbon (C) content but higher oxygen (O) content than those from lab scale. Biochars from pilot scale had higher total PTEs (except Cd) concentrations and releasable PTEs (except Pb) but lower CaCl₂-extractable PTEs and phytotoxicity germination index (GI) to radish seedings than those from lab scale. Chemical speciation analysis indicated that PTEs in biochar produced from pilot-scale fast pyrolysis at 400 °C had higher percentage of more stable fraction (F5 fraction) and lower potential ecological risk index (RI) than those from lab-scale slow pyrolysis. These findings demonstrated that bioavailability and potential ecological risk of PTE in swine manure biochar were greatly decrease in the pilot-scale pyrolysis reactor and the optimum temperature was 400 °C considering the lowest potential ecological risk index.

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.

Effective Sb(V) removal from aqueous solution using phosphogypsum-modified biochar

Antimonate is the dominant form of antimony (Sb) in Sb mine water. The treatment of high-Sb mine water essentially reduces the discharge of antimonate oxyanions ([Sb(OH)₆]^-) in it. Biochar obtained from phosphogypsum-modified anaerobic digested distillers' grain (PADC) can effectively adsorb antimonate from water. In this work, using batch adsorption experiments, mathematical models, and characterization methods, the mechanism of Sb(V) adsorption by PADC was studied. Compared with pristine biochar, PADC biochar showed abundant lamellar and vesicular structures with significant calcium ion loading on the surface. The kinetics data of the adsorption of Sb(V) on the PADC biochar followed the Elovich equation (R² = 0.992), indicating that heterogeneous adsorption had occurred. The results also showed that intraparticle diffusion played an important role in controlling Sb(V) adsorption by PADC biochar. The Redlich-Peterson model best fit the Sb(V) adsorption isotherm (R² = 0.997), indicating that the adsorption was a combination of the Langmuir and Freundlich models. The maximum adsorption capacity of PADC biochar for Sb(V) is 8123 mg/kg, which is more than twice that of the pristine biochar (3487 mg/kg) and is sufficient for Sb(V) treatment in most mine water. Fourier transform infrared (FTIR) spectra, X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), and Transmission electron microscopy with energy dispersive X-ray spectroscopy (TEM-EDS) analyses revealed that the dominant mechanism of Sb(V) removal by PADC biochar was the formation of Ca-O-Sb complexes or amorphous surface precipitation as well as electrostatic adsorption. This work demonstrated the potential of PADC biochar in the treatment of Sb-contaminated mine water.

Thermodynamic and kinetic coupling modeling for thallium(I) sorption at a heterogeneous titanium dioxide interface

The transformations of monovalent thallium (Tl) in an aqueous environment may be affected significantly by Tl(I) partitioning at the solid-water interface during sorption. Models used to quantify the kinetics of Tl(I) adsorption on heterogeneous adsorbents and formation of multiple complexes under a wide range of water chemistry conditions can accurately predict the environmental fate of thallium. In this study, Tl(I) sorption on representative titanium dioxide at different solution pH values and loading concentrations was investigated with two unified adsorption models, diffuse layer modeling and kinetics modeling. Three Tl(I) surface complexes, TiOTl, TiOHTl⁺, and TiOTlOH^-, were used in the diffuse layer model and successfully described batch adsorption and the results of spectroscopic analyses. The contribution of TiOHTl⁺ to the adsorption capacity was much higher than those of TiOTl and TiOTlOH^- under neutral and weakly alkaline conditions, while the species TiOTlOH^- predominated among Tl(I) complexes in strongly alkaline environments. The adsorption and desorption rate coefficients derived from thermodynamics and kinetics coupling modeling suggested the influence of different complex characteristics on adsorption and desorption of Tl(I). Our results provide a comprehensive model for predicting the dynamic binding behavior of Tl at heterogeneous solid-water interfaces.

Transferability of heavy metal(loid)s from karstic soils with high geochemical background to peanut seeds

Globally distributed karstic soils are characterized by the high accumulation of heavy metal(loid)s, such as Cd. Biogeochemistries and transferability of metal(loid)s in such soils are notably different from that in soils of anthropogenic pollution as evidenced by increasing studies about rice and maize. To solve the question about metal(loid) background and transferability in the system of karstic soils and crops with underground fruits, we designedly collected 246 paired soil-peanut seed samples in a world-famous karstic region in Southwestern China covering an area of 98,700 km². The concentrations of eight regulatory metal(loid)s (Cd, As, Cr, Cu, Hg, Ni, Pb, and Zn) in soil samples exceeded current standards to different degrees, demonstrating a typical high background. However, the transferability of metal(loid)s from soils to peanut seeds is quite low, resulting in a low exceedance rate of metal(loid)s (Cd, 12.2% and Pb, 1.2%) in seeds ("seed metal(loid)s"), in accordance with the results that metal(loid)s in soils mostly distributed in the inert/residual fractions. Based on the distinct response characteristics of peanut seed metal(loid)s to soil status from rice/maize grain metals, a model was further developed for effectively predicting the concentration of Cd in peanut seeds. Collectively, this study provides a basis for the assessment of soil environmental quality and safety zoning of upland field in karst areas.

Thallium isotopic compositions as tracers in environmental studies: A review

Thallium is a highly poisonous heavy metal. Since Tl pollution control has been neglected worldwide until the present, countless Tl pollutants have been discharged into the environment, endangering the safety of drinking water, farmland soil, and food chain, and eventually posing a great threat to human health. However, the source, occurrence, pathway and fate of Tl in the environment remains understudied. As Tl in non-contaminated systems and from anthropogenic origin exhibits generally different isotopic signatures, which can provide fingerprint information and a novel way for tracing the anthropogenic Tl sources and understanding the environmental processes. This review summarizes: (i) the state-of-the-art development in highly-precise determination analytical method of Tl isotopic compositions, (ii) Tl isotopic fractionation induced by the low-temperature surface biogeochemical process, (iii) Tl isotopic signature of pollutants derived from anthropogenic activities and isotopic fractionation mechanism of Tl related to the high-temperature industrial activities, and (iv) application of Tl isotopic composition as a new tracer emerging tracer for source apportionment of Tl pollution. Finally, the limitations and possible future research about Tl isotopic application in environmental contamination is also proposed: (1) Tl fractionation mechanism in different environmental geochemistry processes and industrial activities should be further probed comprehensively; (2) Tl isotopes for source apportionment should be further applied in other different high Tl-contaminated scenarios (e.g., agricultural systems, water/sediment, and atmosphere).

Uptake, organ distribution and health risk assessment of potentially toxic elements in crops in abandoned indigenous smelting region

Inorganic pollution induced by smelting waste has threatened the safety of environment, whereas the impacts on farmlands with regards to potentially toxic elements (PTEs) receive insufficient attention. Herein, the contents, transfer pathways and potential risks of the PTEs in common crops were examined from different farmlands distributed around an indigenous Zn-smelting area in Guizhou, China. The results showed that Tl in cabbage (Brassica oleracea L.) (up to 3.74 mg/kg) and radish (Raphanus sativus L.) (up to 1.16 mg/kg) at some sites exceeded the maximum permissible level (MPL) (0.5 mg/kg) for food, and, under the same pollution condition, cabbage and radish were more likely to enrich PTEs, and the edible portion of maize was not prone to Tl risk. Hazard quotient calculations of Tl, Ba, and U were greater than 1, indicating the edible risk of crops for these PTEs. Further characterization of selected soils revealed that MnFe₂O₄ and Fe₂O₃ controlled the phase transformation of Tl(III) in rhizospheric soils. Furthermore, distinctive mullite was detected in the soil which confirmed the contribution of high temperature smelting to PTEs pollution. The findings indicate an emergent need for soil remediation around historical indigenous metal smelting areas for the sake of food security.

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.

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.

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.

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.