Historical roasting of thallium- and arsenic-bearing pyrite: Current Tl pollution in the Riotinto mine area

Biochemical transformation and bioremediation of thallium in the environment

Thallium (Tl) is a toxic element associated with minerals, and its redistribution is facilitated by both geological and anthropogenic activities. In the natural environment, the transformation and migration of Tl mediated by (micro)organisms have attracted increasing attention. This review presents an overview of the biochemical transformation of Tl and the bioremediation strategies for Tl contamination. In the environment, Tl exists in various forms and originates from diverse sources. The global distribution characteristics of Tl in various media are summarized here, while its speciation and toxicity mechanism to organisms are elucidated. Interactions between (micro)organisms and Tl are commonly observed in the environment. Microbial response mechanisms to typical Tl exposure are analyzed at both species and gene levels, and the possibility of microorganisms as bio-indicators for monitoring Tl contamination is also highlighted. The processes and mechanisms involved in the microbial and benthic mediated transformation of Tl, as well as its enrichment by plants, are discussed. Additionally, in situ bioremediation strategies for Tl contamination and bio-treatment techniques for Tl-containing wastewater are summarized. Finally, the existing knowledge gaps and future research challenges are emphasized, including Tl distribution characteristics in the atmosphere and ocean, the key molecular mechanisms underlying Tl transformation by organisms, the screening of potential Tl oxidizing microorganisms and hyperaccumulators, as well as the revelation of global biogeochemical cycling pathways of Tl.

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.

Mitigation of thallium threat in paddy soil and rice plant by application of functional biochar

Thallium (Tl) is a highly toxic metal, and its contamination in soils entails high risks to human health via food chain. It remains largely unknown of the effects of applying biochar on Tl uptake in paddy systems despite that few studies have shown that biochar exhibits great potential for decreasing Tl bioavailability in soils. Herein, we examined the mitigating effects of the application of biochar (5 and 20 g/kg pristine biochar; 5 and 20 g/kg Fe/Mn-modified biochar) on Tl uptake in paddy soil and rice plant after an entire rice growth period. The results suggested that the application of Fe/Mn-modified biochar (FMBC) considerably mitigated the accumulation of Tl in different tissues of rice plants. Specifically, total Tl content in rice plants treated with FMBC-20 decreased by over 75% compared with control experiment. In addition, the amendment of FMBC in Tl-rich paddy soils can enhance the communities of microorganisms (Actinobacteria and Proteobacteria). Further analysis of the soil microbial symbiosis network revealed that FMBC promotes the living microorganisms to play modular synergistic interactions, which is crucial for FMBC-induced Tl stabilization in soils. All these findings indicated that FMBC is an efficient and environmentally friendly Tl-immobilization alternative material and can be potentially used in the remediation of Tl-contaminated paddy soils and/or cropland.

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.

Efficient incorporation of highly migratory thallium into struvite structure: Unraveling the stabilization mechanisms from a mineralogical perspective

The remediation of high-concentration thallium (Tl+) contaminated wastewater is a critical environmental concern. Current research emphasizes the effectiveness of adsorption and oxidation methods for Tl+ treatment, yet challenges persist in enhancing their performance. This study explores the feasibility of emergency Tl+ wastewater treatment and elucidates the mechanisms of Tl+ incorporation into mineral structures, with a focus on the struvite mineral as a framework for Tl+ integration via NH4+ ion exchange. To assess the efficacy and mechanisms of Tl+ immobilization, we utilized comprehensive analytical techniques, including X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDS), Thermogravimetric Analysis (TG), and Density Functional Theory (DFT) calculations. The findings reveal that struvite adsorbs Tl+ onto its surface, followed by an ion exchange process between monovalent cations (NH4+/K+) within the structure and Tl+. Ultimately, Tl+ is incorporated in the form of a (NH4,Tl)MgPO4 solid solution within the structure, achieving a remarkable maximum incorporation capacity of 320.56 mg/g, which significantly surpasses the capacity of typical adsorbents. The findings demonstrate significant Tl+ incorporation, validating the approach for emergency wastewater treatment and suggesting the potential of mineralogy in environmental remediation. This research contributes to advancing heavy metal wastewater treatment strategies, offering a foundation for further investigation.

Potential high-risk release sources of thallium and arsenic from surrounding rocks of a typical thallium and arsenic mining area in southwest China

Abundant naturally and anthropogenically exposed surrounding rocks (NESRs and AESRs) in mining areas may pose persistent threats as sources of potentially toxic elements (PTEs), but this has been historically overlooked, especially for thallium (Tl) and arsenic (As). Here, the release risks of Tl and As from both NESRs and AESRs in a typical TlAs sulfide mining area were investigated. In a single leaching process, AESRs released 10.4 % of total Tl (157 μg L-1) and 32.5 % of total As (4089 μg L-1), 2-3 orders of magnitude higher than NESRs. Prolonged multiple leaching tests revealed notable and long-term risks of release of Tl and As from AESRs, associated with oxidation and dissolution of iron/sulfur-bearing minerals. Substantial release of PTEs was linked to the transformation/degradation of the -OH functional group and extensive dissolution of secondary sulfate minerals in AESRs. Ultrafiltration and STEM-EDS indicate that 18.4 % of water-extracted As released from AESRs existed as natural nanoparticles consisting of iron/sulfur-bearing minerals. This study highlights the high risks of Tl and As release from anthropogenically exposed surrounding rocks and the importance of nanoparticles in PTE transport, and provides insights into the control of PTEs in mining areas.

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.

Photochemical transformation and immobilization of thallium in the presence of iron and arsenic: Mechanistic insights from the coupled formation of arsenate complexes

Despite the occurrence of thallium (Tl) in the acidic mining-affected areas being highly positively correlated with iron (Fe) and arsenic (As), the effects of the two accompanying elements on Tl redox transformation and immobilization remain largely unknown. Here, we investigated the photochemical redox kinetics and immobilization efficiency of Tl for a wide range of As/Fe and As/Tl ratios under acidic conditions. We provided the first experimental confirmation of the complexation of Tl(III) with As(V) by the spectrophotometric method and revealed the role of Tl(III)-As(V) complexes in decreasing the photoreduction rate of Tl(III) under sunlight. Additionally, the negative impact of colloidal Fe(III)-As(V) and Fe(III)-As(III) complexes formation on decreasing photoactive Fe(III) speciation and thus the apparent quantum yield of •OH was highlighted, which consequently hindered the oxidative conversion of Tl(I) to Tl(III). We rationalize the kinetics results by developing the model which quantitatively describes the photochemistry of Tl. Furthermore, we demonstrated the colloid-facilitated immobilization of Tl(III) through the formation of Tl(III)-As(V) clusters and surface adsorption onto the complexes. This study broadens the mechanistic understanding of redox transformation and immobilization potential of Tl and aids in assessing Tl speciation as well as its coupled transformation with Fe and As species in the sunlit water environment.

Potential mobilization of water-dispersible colloidal thallium and arsenic in contaminated soils and sediments in mining areas of southwest China

Water-dispersible colloids (WDCs) are vital for trace element migration, but there is limited information about the abundance, size distribution and elemental composition of WDC-bound thallium (Tl) and arsenic (As) in mining-contaminated soils and sediments solutions. Here, we investigated the potential mobilization of WDC-bound Tl and As in soils and sediments in a typical Tl/As-contaminated area. Ultrafiltration results revealed on average > 60% of Tl and As in soil solution (< 220 nm) coexisted in colloidal form whereas Tl and As in sediment solution primarily existed in the truly dissolved state (< 10 kDa) due to increased acidity. Using AF4-UV-ICP-MS and STEM-EDS, we identified Fe-bearing WDCs in association with aluminosilicate minerals and organic matter were main carriers of Tl and As. SAED further verified jarosite nanoparticles were important components of soil WDC, directly participating in the migration of Tl and As. Notably, high pollution levels and solution pH promoted the release of Tl/As-containing WDCs. This study provides quantitative and visual insights into the distribution of Tl and As in WDC, highlighting the important roles of Fe-bearing WDC, soil solution pH and pollution level in the potential mobilization of Tl and As in contaminated soils and sediments.

Removal of arsenic from jarosite waste using hydrometallurgical treatment

The jarosite waste used during this study consists of minute amount of arsenic that has a potential to be leached into environment when kept in open area. This study tried to recover arsenic from jarosite waste using hydrometallurgical treatment. The comprehensive characterization of jarosite samples was performed using various analytical techniques, including X-ray diffraction (XRD), Fourier transform Infrared (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX), and it was characterized as natrojarosite. For optimal removal of arsenic, the response surface methodology (RSM) was applied with the key factors, including dosage (A), time (B), temperature (C), and acid concentration (D) on the recovery of arsenic. The results indicated that the dosage (A) and acid concentration (D) demonstrated significant positive effects on arsenic recovery. As expected, the higher dosage and acid concentration was associated with increased recovery percentages for the arsenic from jarosite. Whereas time (B) and temperature (C) did not exhibit statistically significant recovery of arsenic within the specified experimental range. The contour plots showed the optimal operating conditions for the highest recovery percentage was approximately 52.61% when 2.5 g of jarosite was treated with 10 mol/L acid for 150 min at operating temperature of 80°. Although our study showed very moderate recovery of arsenic, it is first report where arsenic has been removed from jarosite waste. Readjustment of range of operating parameters would provide more insight into the further optimization of the yield.

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.

Persistent thallium enrichment and its high ecological risks developed from historical carbonaceous Hg-Tl mining waste

Thallium (Tl) is a priority pollutant with high biotoxicity and has been of great concern worldwide in recent years. The former Lanmuchang Hg-Tl mining site in southwest China is a hotspot of multiple metal(loid)s pollution that previously caused large-scale chronic Tl poisoning, mainly resulting from carbonaceous Tl-bearing mining waste. However, arable land destroyed by historical mining wastes persists at high ecological risks decades after reclamation, but little is known about the solid phase partitioning and species of Tl during soil formation of underlying mining wastes as potential Tl sources. In this study, a representative reclaimed soil profile (100 cm depth) was selected in the lowlands to explore the geochemical cycling and environmental fate of Tl in mining waste-derived subsoil. The Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) analysis revealed an unexpected enrichment of Mn (2920-7250 mg/kg) and Tl (205-769 mg/kg) in the mining waste-derived subsoil. Results from BCR sequential extraction, X-ray Photoelectron Spectroscopy (XPS), and Electron Probe Microanalyses (EPMA) indicate that high Tl loading Mn oxide particulates (up to 15,712 ppm Tl) dominate the sequestration of Tl in the subsoil via oxidation-complexation and have a high potential for migration to both topsoil and groundwater. In addition, insights from microbial fossils and Fe-metabolizing bacteria closely related to Tl indicated that Fe (hydr)oxide particulates showing high Tl levels (up to 3865 mg/kg) point to biomineralization. Detailed mineralogical investigations revealed that hematite-siderite syngenetic particulates could serve as a promising mineralogical proxy for redox oscillations under periodic flooding and recorded the frequent groundwater level fluctuations experienced in the probed profile. Despite the potential for long-term preservation of high Tl loading Fe/Mn (hydr)oxides under HCO3-rich groundwater conditions in karst areas, the reductive release of Tl will be inevitable during flooding, implying that underlying carbonaceous mining waste will pose persistent and severe hazards to the ecosystem.

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.

Terrestrial nanoparticle contaminants and geospatial optics using the Sentinel-3B OLCI satellite in the Tinto River estuary region of the Iberian Peninsula

The Tinto River is known globally for having a reddish color due to the high concentration of dissolved metals in its waters. The general objective of this study is to analyze the dispersion of nanoparticles (NPs) and ultra-fine particles in terrestrial and geospatial suspended sediments (SSs) using Sentinel-3B OLCI (Ocean Land Color Instrument) satellite images; by examining water turbidity levels (TSM_NN), suspended pollution potential (ADG_443_NN) and presence of chlorophyll-a (CHL_NN). The images were collected in the estuary of the Tinto River, in the city of Nerva, Spanish province of Huelva, between 2019 and 2021. The following hazardous elements were identified in nanoparticles and ultra-fine particles by FE-SEM/EDS: As, Cd, Ni, V, Se, Mo, Pb, Sb and Sn. Sentinel-3B OLCI satellite images detected a 2019 TSM_NN of 23.47 g^-3, and a 2021 reading of 16.38 g^-3.

Metagenomic insights into the influence of thallium spill on sediment microbial community

Thallium (Tl) is an extremely toxic metal. The release of Tl into the natural environment can pose a potential threat to organisms. So far, information about the impact of Tl on indigenous microorganisms is still very limited. In addition, there has been no report on how sudden Tl spill influences the structure and function of the microbial community. Therefore, this study explored the response of river sediment microbiome to a Tl spill. Residual T1 in the sediment significantly decreased bacterial community diversity. The increase in the abundance of Bacteroidetes in all Tl- impacted sediments suggested the advantage of Bacteroidetes to resist Tl pressure. Under T1 stress, microbial genes related to carbon fixation and gene cysH participating in assimilatory sulfate reduction were down-regulated, while genes related to nitrogen cycling were up-regulated. After T1 spill, increase in both metal resistance genes (MRGs) and antibiotic resistance genes (ARGs) was observed in Tl-impacted sediments. Moreover, the abundance of MRGs and ARGs was significantly correlated with sediment Tl concentration, implying the positive effect of Tl contamination on the proliferation of these resistance genes. Procrustes analysis suggested a significant congruence between profiles of MRGs and bacterial communities. Through LEfSe and co-occurrence network analysis, Trichococcus, Polaromonas, and Arenimonas were identified to be tolerant and resistant to Tl pollution. The colocalization analysis of contigs indicated the co-effects of selection and transfer for MRGs/ARGs were important reasons for the increase in the microbial resistance in Tl-impacted sediments. This study added new insights into the effect of Tl spill on microbial community and highlighted the role of heavy metal spill in the increase of both heavy metal and antibiotic resistance genes.

Environmental thallium exposure and the risk of early embryonic arrest among women undergoing in vitro fertilization: thallium exposure and polymorphisms of mtDNA gene interaction and potential cause exploring

Early embryonic arrest (EEA) leads to cancelation of fresh cycles among infertile women undergoing in vitro fertilization (IVF), bringing a great challenge for IVF. Whether exposure to thallium (Tl) is associated with an increased risk of EEA, especially its interaction with polymorphisms of mitochondria DNA (mtDNA) gene, is worthy of study. A case-control design was performed, including 74 EEA cases with 123 IVF cycles and 157 age and BMI-matched controls with 180 IVF cycles. Levels of Tl and other toxic metals (lead (Pb), (mercury) Hg, and (arsenci) As) were assessed by measuring them in blood samples collected on the day of oocyte retrieval; PCR amplification and sequencing were performed to screen the polymorphic sites of mtDNA gene in D-loop region. Bayesian kernel machine regression (BKMR) was used to confirm that Tl played a leading role in the situation of combined exposure; generalized estimating equation (GEE) models were used to evaluate the associations of Tl concentrations, polymorphisms of mtDNA gene, and their interactions with the risk of EEA. The impact of Tl exposure or polymorphisms of mtDNA gene on the oogenesis and embryonic development was also evaluated. BKMR analysis revealed that PIP (posterior inclusion probability) value of T1 was 0.9096, indicating that it played a leading role in the situation of combined exposure. Compared to the first quartile of Tl, the adjusted ORs (95% CIs) of EEA risk were 0.66 (0.26, 1.70), 1.18 (0.52, 2.64), and 4.53 (2.11, 9.69) for the second, third, and fourth quartile, respectively (p trend < 0.001). Compared to the wild type of mtDNA 16,519 gene (T 16,519 T), the adjusted OR (95% CI) of EEA risk for the variant type (T 16,519 C) was 3.11 (1.70, 5.72), and the variant types of the other sites with a minor allele frequency > 10% were not significantly related with the risk of EEA after FDR (False Discovery Rate) correction. With respect to interaction, compared to women at low Tl exposure level & wild type of mtDNA 16,519 gene group, the adjusted OR (95% CI) of EEA risk for women at high Tl exposure level & variant type of mtDNA 16,519 gene group was 9.28 (3.33, 25.81). Additionally, Tl exposure and polymorphisms of mtDNA 16,519 gene are inversely associated with the outcomes of oogenesis and embryonic development significantly. Our study indicated that high Tl exposure level was associated with the increased risk of EEA and Tl played a leading role in the situation of combined exposure; the strength of association was much higher when Tl exposure interacted with polymorphism of 16,519 mtDNA gene. These relationships might originate from the impact of Tl exposure or polymorphism of 16,519 mtDNA gene on the oogenesis and early embryonic development in vitro. Infertile women should keep high vigilant against Tl exposure especially those with variant type of mtDNA 16,519 gene.

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.

Prenatal serum thallium exposure and cognitive development among preschool-aged children: A prospective cohort study in China

Thallium, a highly toxic heavy metal and priority pollutant, has been widely reported to cause neurodevelopmental toxicity in animals. However, accessible epidemiological studies concerning the neurodevelopmental toxicity of early-life thallium exposure in humans are limited. In a prospective birth cohort including 2164 mother-child pairs, we explored the effect of prenatal serum thallium exposure on cognitive development among preschool-aged children born in Ma'anshan, Anhui, China. Serum thallium concentrations were measured in the first trimester, second trimester, third trimester, and cord blood by inductively coupled plasma mass spectrometry (ICP-MS). Child cognitive development was appraised by the Chinese version of the Wechsler Preschool and Primary Scale of Intelligence-Fourth Edition (WPPSI-IV) at 4.5 years old. Multiple informants generalized estimating equations (GEEs) were fit to jointly estimate the association between the four repeated measurements of thallium concentrations and the preschool-aged children's cognitive test scores. After adjusting for potential confounders, the visual spatial index (VSI) was 1.45 points lower in the highest tertile of serum thallium during the first trimester than in the lowest tertile (p for trend = 0.04). Moreover, children in the highest tertile of serum thallium during the third trimester had a significantly lower full-scale intelligence quotient (FSIQ) (β = -1.51, 95% CI: -2.68, -0.35), VSI (β = -1.79, 95% CI: -3.16, -0.42), fluid reasoning index (FRI) (β = -1.41, 95% CI: -2.73, -0.10), and processing speed index (PSI) (β = -1.47, 95% CI: -2.71, -0.24) scores than the children in the lowest tertile. When performing stratified analysis by child sex, the associations of first- and third-trimester thallium concentrations with cognitive test scores were more prominent in boys than in girls. Our findings revealed that maternal serum thallium exposure during the first and third trimesters, but not other periods, had detrimental effects on preschoolers' cognitive development, and these effects showed sex differences.

Thallium geochemical fractionation and migration in Tl-As rich soils: The key controls

Thallium (Tl) pollution caused by mining and processing of Tl-enriched ores has become an increasing concern. This study explored the geochemical fractionation and vertical transfer of Tl in a soil profile (200 cm) from a representative Tl-As mineralized area, Southwest China. The results showed that the soils were heavily enriched by Tl and As, with concentration ranging from 3.91-17.3 and 1830-8840 mg/kg (6.79 and 2973 mg/kg in average), respectively. Approximately 50% of Tl occurred in geochemically mobile fractions in the topsoil, wherein the reducible fraction was the most enriched fraction. Further characterization using LA-ICP-MS and TEM revealed that enriched Tl and As in soils were mainly inherited from the weathering of mine tailing piles upstream. XPS characterization indicated that Fe oxides herein may play a critical role in the oxidation of Tl(I) to Tl(III) which provoked further adsorption of Tl onto Fe oxides, thereby facilitating Tl enrichment in the reducible fraction. The findings highlight that the pivotal role of Fe oxides from mineralized area in the co-mobility and migration of Tl and As in the depth profile.

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.

Retention of thallium by natural minerals: A review

Though thallium (Tl) is usually present in trace amounts in natural environments, its biotoxicity is extremely high. With the development of mining, the metallurgy industry, and the growing application of Tl in high-tech fields, the threat of Tl to ecological environments and human health is increasing. Natural minerals, such as clay minerals, iron oxides, and manganese oxides, are natural Tl adsorbents due to their mineralogy and crystal structures. In this review, we discuss the mechanisms of Tl adsorption by various natural minerals, compare the adsorption capacities of common soil minerals for Tl, and describe the limitations of traditional sequential extraction methods for identifying the chemical states of Tl on minerals and source of Tl. We also provide suggestions on future directions needed in Tl research including a) additional in-depth studies on the competitive adsorption of Tl by minerals; b) more direct comparison of Tl adsorption behavior from lab-based experiments with field observations to clarify the mechanisms of Tl adsorption by minerals under environmental conditions; c) more research data are needed to support the establishment and improvement of relevant research methods based on modern leading-edge technologies such as synchrotron radiation. Further, we suggest further research is needed in adsorption technologies used for Tl treatment. This is the first review on the research progress of Tl adsorption by natural minerals with the purpose of helping understanding the mechanisms of Tl migration and transformation controlled by natural minerals, and providing theoretical supports for the development of Tl adsorbents and the treatments of Tl pollution.

Cadmium isotopic fractionation in lead-zinc smelting process and signatures in fluvial sediments

Cadmium (Cd) is a toxic heavy metal pollutant. Various industrial activities, especially metal smelting, are the main sources of Cd pollution. Cd isotopes have exhibited the ability to be excellent source tracers and can be used to assess the pollution contributions from different sources. Herein, in a typical lead-zinc smelter, Shaoguan, China, significant Cd isotopic fractionation was found during the high temperature smelting process and followed a Rayleigh distillation model. The heavier Cd isotopes were concentrated in the slag, while the lighter Cd isotopes were concentrated in the dust. In the downstream sediment profile of the smelter, sediments have extremely high Cd concentrations that far exceed the Chinese background sediment, indicating severe pollution levels. The ε^114/110Cd of the sediment core, ranged from - 0.62 ± 0.5-1.73 ± 0.5, are found between slag (ε^114/110Cd=10.42) and dust (ε^114/110Cd=-5.68). The binary mixture model suggests that 88-93% of the Cd in sediment profile was derived from the slag, and 7-12% from the deposition of dust. The findings demonstrate the great potential to apply Cd isotopes as a new geochemical tool to distinguish anthropogenic sources and quantify the contribution from various sources in the environment.

Geochemical behaviour and transport of technology critical metals (TCMs) by the Tinto River (SW Spain) to the Atlantic Ocean

This paper addresses the behaviour of several technology critical metals (TCMs), i.e., rare earth elements (REEs), Y, Sc, Ga and Tl, in the Tinto River (SW Spain), quantifying their fluxes to the Atlantic Ocean and unravelling the governing geochemical processes controlling their solubility. To accomplish this goal, a high-resolution (2-24 h) sampling was performed during the hydrological year 2017/18. Mean dissolved concentrations of 380 μg/L of REE, 99 μg/L of Y, 15 μg/L of Sc, 9.2 μg/L of Ga and 4.8 μg/L of Tl were found. Most TCMs followed a behaviour similar to that of sulphate and base metals throughout the year, exhibiting a quasi-conservative behaviour due to acidic conditions. However, dissolved Tl concentrations seem to be strongly controlled by Tl incorporation onto secondary minerals and diatoms deposited on the riverbed, especially during the dry season. The remobilization of riverbed sediments led to the transport of significant amounts of TCMs associated with particulate matter, especially Al oxy-hydroxy-sulphates or Al-silicates rather than Fe precipitates (except for Tl and Ga). Around 5.8 t of REE, 1.3 t of Y, 248 kg of Sc, 139 kg of Ga and 138 kg of Tl were delivered annually in their dissolved forms by the Tinto River to the Atlantic Ocean, which constitutes around 0.09% of the dissolved global flux into the oceans of Y, 0.02% of the REE flux, 0.01% of the Ga flux and 0.001% of the Sc flux.

Quantitative isotopic fingerprinting of thallium associated with potentially toxic elements (PTEs) in fluvial sediment cores with multiple anthropogenic sources

Thallium (Tl) is a dispersed trace metal showing remarkable toxicity. Various anthropogenic activities may generate Tl contamination in river sediments, posing tremendous risks to aquatic life and human health. This paper aimed to provide insight into the vertical distribution, risk assessment and source tracing of Tl and other potentially toxic elements (PTEs) (lead, cadmium, zinc and copper) in three representative sediment cores from a riverine catchment impacted by multiple anthropogenic activities (such as steel-making and Pb-Zn smelting). The results showed high accumulations of Tl combined with associated PTEs in the depth profiles. Calculations according to three risk assessment methods by enrichment factor (EF), geoaccumulation index (I_geo) and the potential ecological risk index (PERI) all indicated a significant contamination by Tl in all the sediments. Furthermore, lead isotopes were analyzed to fingerprint the contamination sources and to calculate their quantitative contributions to the sediments using the IsoSource software. The results indicated that a steel-making plant was the most important contamination source (∼56%), followed by a Pb-Zn smelter (∼20%). The natural parental bedrock was found to contribute ∼24%. The findings highlight the importance of including multiple anthropogenic sources for quantitative fingerprinting of Tl and related metals by the lead isotopic approach in complicated environmental systems.

Microbial insights into the biogeochemical features of thallium occurrence: A case study from polluted river sediments

Thallium (Tl) is a trace element with extreme toxicity. Widespread Tl pollution in riverine systems, mainly due to escalating mining and smelting activities of Tl-bearing sulfide minerals, has attracted increasing attention. Insights into the function of the microbial communities with advanced characterization tools are critical for understanding the biogeochemical cycle of Tl. Herein, microbial communities and their adaptive evolution strategies in river sediments from a representative Tl-bearing pyrite mine area in southern China were profiled via 16S rRNA gene sequence analysis and shotgun metagenomic analysis. In total, 64 phyla and 778 genera of microorganisms were observed in the studied sediments. The results showed that pH, Tl, Pb, Zn and total organic carbon (TOC) had a significant influence on microbial community structure. Some important reductive microorganisms (such as Erysipelothrix, Geobacter, desulfatiferula, desulfatihabadium and fusibacter) were involved in the biogeochemical cycle of Tl. The ruv, rec, ars and other resistance genes enhanced the tolerance of microorganisms to Tl. The study suggested that relevant C, N and S cycle genes were the main metabolic paths of microorganisms surviving in the high Tl-polluted environment. The findings were critical for establishment, operation and regulation in the microbial treatment of Tl containing or related wastewater.

Persistent thallium contamination in river sediments, source apportionment and environmental implications

The adverse impacts of detrimental thallium (Tl) contamination are of increasing concerns to sustainable development. Herein, the contents, distributions and sources of Tl and potential toxic elements (PTEs) (Pb, As, Cr, Cu, Ni, Co, Sb, Cd and U) were investigated in sediments collected in Gaofeng River, which has been contaminated by long-term mining activities, located in Yunfu City, Southern China. Results indicated that excessive Tl levels were found in sediments (1.80-16.70 mg/kg). Sequential extraction procedure indicated that despite a large amount of Tl entrapped in residual fraction, a significant level of Tl (0.28-2.34 mg/kg) still exhibited in geochemically labile fractions, which was easy for Tl mobilization and availability. Pb isotope tracing method further confirmed that the pyrite exploitations may be the prime contaminated contributor (47-76%) to these sediments. These findings highlight that it is essential to establish more effective measures for Tl contamination control and call for engineered remediation countermeasures towards polluted river sediments.

Ecological Risk Assessment of Heavy Metals in Water Bodies around Typical Copper Mines in China

In order to understand the heavy metal pollution status and ecological effect in aquatic environment around copper mine areas, seven heavy metals (Cd, Cd, Cr, Cu, Hg, Zn, the Ni, and Pb) in aquatic environments in seven representative copper mine regions were selected from the literature in 2005–2013 for ecological risk assessment by using potential ecological risk index, geoaccumulation index, nemerow index and species sensitivity distribution method (Potential Affected Fraction (PAF) and Multi-Substance PAF (MSPAF)). The results of sediment ecological risk analysis showed that Cd, Cu and Pb were the main pollutants in sediments. The results of species sensitivity distribution analysis showed that the HC5 values (Hazardous Concentration for 5% of species) of seven heavy metals were different with order Zn > Cr > Cd > Pb > Cu > Ni > Hg. The MSPAF of seven copper mines in the following order with species sensitivity distribution method was as follows: Dabaoshan (99%) = Dahongshan (99%) = Baiyin (99%) > Dexing (97%) > Jinchuan (92%) > Tongling (39%) > Daye (24%). This study analyzes the impact of copper mining on the aquatic environment, and the results of this study will be great value for the comprehensive pollution governance of mining.

Thallium and co-genetic trace elements in hydrothermal Fe-Mn deposits of Central Spain

Thallium (Tl) is a hazardous trace metal that can harm human and environmental health. Tl pollution can result from the mining and smelting of Tl-bearing minerals, but also the natural weathering of Tl-bearing sulfide minerals may induce Tl release to the environment. In this study, hydrothermal deposits hosted in dolostone rocks sited along fossil thermal springs in the Lodares region (Soria province, central Spain) were studied. In this hydrothermal mineralization zone, Tl association with primary minerals, identified Tl-bearing secondary products resulting from natural weathering of primary minerals, as well as the dispersion from its natural source along a seasonal small streambed were explored. Samples were analyzed by chemical, microscopic and spectroscopic techniques and epithermal pyrite, sphalerite, galena and barite and secondary gypsum, jarosite, scorodite, anglesite, goethite, epsomite and elemental sulfur produced by both inorganic and bacterial processes were found. The highest Tl contents were found in hydrothermal pyrite (188 mg kg^-1), jarosite (142 mg kg^-1), Mn-oxides (27 mg kg^-1) or kerogen (13 mg kg^-1). Feldspar was identified by electron probe microanalysis as potential host phase of Tl. XANES results confirmed the association of Tl(I) with metal sulfides in pyrite-rich samples and highlighted the role of jarosite-like minerals for Tl(I) sequestration upon pyrite oxidation, even in carbonate-rich samples at near-neutral pH. In addition to micaceous minerals, jarosite-group minerals and K-feldspars may contribute to the natural attenuation of Tl in soils and sediments.

Hyperaccumulation and transport mechanism of thallium and arsenic in brake ferns (Pteris vittata L.): A case study from mining area

Both thallium (Tl) and arsenic (As) bear severe toxicity. Brake fern (Pteris vittata L.) is well-known for its hyperaccumulation capacity of As, yet its role on Tl accumulation remains unknown. Herein, brake ferns growing near an As tailing site in Yunnan, Southwestern China are for the first time discovered as a co-hyperaccumulator of both Tl and As. The results showed that the brake ferns extracted both As and Tl efficiently from the soils into the fronds. The studied ferns growing on Tl and As co-polluted soils were found to accumulate extremely high levels of both As (7215-11110 mg/kg) and Tl (6.47-111 mg/kg). Conspicuously high bio-accumulation factor (BCF) was observed for As (7.8) and even higher for Tl (28.4) among these co-hyperaccumulators, wherein the contents of As and Tl in contaminated soils were 1240 ± 12 and 3.91 ± 0.01 mg/kg, respectively. The applied advanced characterization techniques (e.g. transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS)) indicated a preferential uptake of Tl(I) while simultaneous accumulation of As (III) and As(V) from the Tl(I)/Tl(III)-As (III)/As(V) co-existent rhizospheric soils. The findings benefit the phytoremediation practice and pose implications for managing and restoring Tl-As co-contaminated soils in other countries.

Thallium contamination, health risk assessment and source apportionment in common vegetables

As an element with well-known toxicity, excessive thallium (Tl) in farmland soils, may threaten food security and induce extreme risks to human health. Identification of key contamination sources is prerequisite for remediation technologies. This study aims to examine the contamination level, health risks and source apportionment of Tl in common vegetables from typical farmlands distributed over a densely populated residential area in a pyrite mine city, which has been exploiting Tl-bearing pyrite minerals over 50 years. Results showed excessive Tl levels were exhibited in most of the vegetables (0.16-20.33 mg/kg) and alarming health risks may induce from the vegetables via the food chain. Source apportionment of Tl contamination in vegetables was then evaluated by using Pb isotope fingerprinting technique. Both vegetables and soils were characterized with overall low ²⁰⁶Pb/²⁰⁷Pb. This indicated that a significant contribution may be ascribed to the anthropogenic activities involving pyrite deposit exploitation, whose raw material and salgs were featured with lower ²⁰⁶Pb/²⁰⁷Pb. Further calculation by binary mixing model suggested that pyrite mining and smelting activities contributed 54-88% to the thallium contamination in vegetables. The results highlighted that Pb isotope tracing is a suitable technique for source apportionment of Tl contamination in vegetables and prime contamination from pyrite mining/smelting activities urges authorities to initiate proper practices of remediation.

Thallium(I) sequestration by jarosite and birnessite: Structural incorporation vs surface adsorption

Jarosite and birnessite secondary minerals play a pivotal role in the mobility, transport and fate of trace elements in the environment, although geochemical interactions of these compounds with extremely toxic thallium (Tl) remain poorly known. In this study, we investigated the sorption behavior of Tl(I) onto synthetic jarosite and birnessite, two minerals commonly found in soils and sediments as well as in mining-impacted areas where harsh conditions are involved. To achieve this, sorption and desorption experiments were carried out under two different acidic conditions and various Tl(I) concentrations to mimic natural scenarios. In addition, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and inductively coupled plasma (ICP) analyses were conducted to determine the performance of both minerals for Tl(I) sequestration. Our results indicate that both phases can effectively remove aqueous Tl by different sorption mechanisms. Jarosite preferentially incorporates Tl(I) into the structure to form Tl(I)-jarosite and eventually the mineral dorallcharite (TlFe₃(SO₄)₂(OH)₆) as increasing amounts of Tl are employed. Birnessite, however, favorably uptakes Tl(I) through an irreversible surface adsorption mechanism, underlining the affinity of Tl for this mineral in the entire concentration range studied (0.5-5 mmol L^-1). Lastly, the presence of Tl(I) in conditions where aqueous molar ratio Tl/Mn is ∼0.25 inhibits the formation of birnessite since oxidation of Tl(I) to Tl(III) followed by precipitation of avicennite (Tl₂O₃) take place. Thus, the present research may provide useful insights on the role of both jarosite and birnessite minerals in Tl environmental cycles.

Geochemical fractionation of thallium in contaminated soils near a large-scale Hg-Tl mineralised area

Enriched levels of thallium (Tl) in the environment are not only derived from anthropogenic sources but also have potential natural origins owing to Tl-rich sulphide mineralization. However, little is known regarding the geochemical fractionations of Tl in contaminated soils from geogenic sources. This study aims to reveal the Tl geochemical fractionations in different types of soils from a large-scale independent Tl mine in southwestern China, via a modified Institute for Reference Materials and Measurement (IRMM) sequential extraction (four-step) scheme. The results revealed that a large percentage of Tl was related to the labile portions (including reducible, weak-acid-exchangeable, and oxidizable fraction) of the soils (68.8-367 mg kg^-1). Further analyses by Scanning Transmission Electron Microscopy-Energy Dispersive X-ray Spectrometer (STEM-EDS) found that Tl mainly existed in the Fe-containing minerals (such as jarosite and hematite) with fine particles (∼1 μm). These results highlight that, apart from the anthropogenically induced Tl pollution, the naturally occurring Tl contamination in soils may also pose significant risks to human health and ecological safety. Owing to the relatively high mobility and bioavailability of Tl in the labile fractions, it is important to understand geochemical fractionations of this element for alleviating Tl pollution and effective management of naturally occurring Tl contaminated soils.

High contamination risks of thallium and associated metal(loid)s in fluvial sediments from a steel-making area and implications for environmental management

Thallium (Tl) is an uncommon toxic element, with an even greater toxicity than that of As, Hg and Cd. Steel-making industry has been identified as an emerging new significant source of Tl contamination in China. This paper presents a pilot investigation of the contamination and geochemical transfer of Tl and associated metal(loid)s in river sediments affected by long-term waste discharge from the steel-making industry. The results uncovered an overall Tl contamination (1.96 ± 0.42 mg/kg) across a sediment profile of approximately 1.5 m in length, even 10 km downstream the steel plant. Highly elevated contents of Pb, Cu, Cd, Zn and Sb were found in the fluvial sediments, displaying strong positive correlations with Tl contents. Elevated levels of geochemically mobile Tl as well as Cd, Zn, Cu and Pb occurred in the fluvial sediments, signifying anthropogenic imprints from steel production activities at high temperature. Levels of contamination and ecological risk were calculated to be moderate to considerable for Tl, Cu, Zn and high to very high for Cd, Pb, Sb. The results highlight that there is a great challenge in view of potentially considerable Tl pollution due to continuous massive steel production in many other parts of China. It is high time to initiate process-based management of Tl contamination control for the ambient aquifer system in the steel-making area.

The hydro-fluctuation belt of the Three Gorges Reservoir: Source or sink of microplastics in the water?

Reservoirs can be an important environmental compartment for microplastic pollution. Previous investigations have found that surface waters and sediments in the Three Gorges Reservoir (TGR) have had high microplastic abundance, and the Xiangxi River, which is one of the largest primary tributaries of the TGR, has had much higher microplastic abundance than several marine and freshwater systems in China. A strip of land on the bank of the reservoir area, which is called the hydro-fluctuation belt (HFB), is periodically exposed due to the special hydrodynamic conditions in the TGR. The HFB may be an important source and/or sink of microplastics in TGR. In this study, microplastic occurrence in sediments from the Xiangxi River HFB was investigated to reflect the local microplastic pollution status and to evaluate its potential to serve as a source/sink of microplastics in the TGR. Seven sampling sites were selected, and sediments within the HFB and above the belt were collected in summer when the water level was low. The results showed that the microplastic abundance ranged from 0.55 ± 0.12 × 10³ to 14.58 ± 5.67 × 10³ particles m^-2, which was one to two orders of magnitude higher than that in sediments from the Xiangxi River in our previous study (80-846 particles m^-2). Statistical analysis revealed that the microplastic abundance within the HFB was significantly higher than that of the area above the HFB. The results indicate that the HFB can be an important microplastic sink when the water level is low, and the belt can turn into a potential source when the water level is high. Cluster analysis was applied to reveal the characteristics of the microplastics collected at different sites, and the results suggest that the cluster analysis may be a useful tool in elucidating the source and fate of microplastics.

Thallium pollution in China and removal technologies for waters: A review

Thallium (Tl) is a typical toxic metal, which poses a great threat to human health through drinking water and the food chain (biomagnification). China has rich Tl-bearing mineral resources, which have been extensively explored and utilized, leading to release of large amounts of Tl into the environment. However, research on Tl pollution and removal techniques is relatively limited, because Tl has not been listed within the scope of environmental monitoring in China for several decades. This paper reviewed Tl pollution in wastewater arising from various industries in China, as well as the latest available methods for treating Tl-containing industrial wastewater, in order to give an outlook on effective technologies for controlling Tl pollution. Conventional physical and chemical treatment technologies are efficient at removing trace amounts of Tl, but it proved to be difficult to achieve the stringent environmental standard (≤0.1-5 μg/L) cost-effectively. Adsorption by using newly developed nanomaterials, and metal oxide modified polymer materials and microbial fuel cells are highly promising and expected to become next-generation technologies for remediation of Tl pollution. With the potential for greater Tl contamination in the environment under accelerated growth of industrialization, researches based on lab-scale implementation of such promising treatment technologies should be further expanded to pilot and industrial scale, ensuring environmental protection and the safety of drinking water for sustainable development. Comprehensive insights into experiences of Tl pollution in China and in-depth perspectives on new frontier technologies of Tl removal from wastewaters will also benefit other nations/regions worldwide, which are susceptible to high exposure to Tl likewise.

Response of microbial communities and interactions to thallium in contaminated sediments near a pyrite mining area

Thallium (Tl) is a well-recognized hazardous heavy metal with very high toxicity. It is usually concentrated in sulfide minerals, such as pyrite (FeS₂), sphalerite (ZnS), chalcopyrite (CuS) and galena (PbS). Here, this study was carried out to investigate the indigenous microbial communities via 16S rRNA gene sequence analysis in typical surface sediments with various levels of Tl pollution (1.8-16.1 mg/kg) due to acid mine drainage from an active Tl-containing pyrite mining site in South China. It was found with more than 50 phyla from the domain Bacteria and 1 phyla from the domain Archaea. Sequences assigned to the genera Ferroplasma, Leptospirillum, Ferrovum, Metallibacterium, Acidithiobacillus, and Sulfuriferula manifested high relative abundances in all sequencing libraries from the relatively high Tl contamination. Canonical correspondence analysis further uncovered that the overall microbial community in this area was dominantly structured by the geochemical fractionation of Tl and geochemical parameters such as pH and Eh. Spearman's rank correlation analysis indicated a strong positive correlation between acidophilic Fe-metabolizing species and Tl_total, Tl_oxi, and Tl_res. The findings clarify potential roles of such phylotypes in the biogeochemical cycling of Tl, which may facilitate the development of in-situ bioremediation technology for Tl-contaminated sediments.