Removal of thallium in water/wastewater: A review

Synthesis of porous carbon derived from coal tar residue via bimetallic salt activation for effective and selective adsorption of thallium(I)

As a highly toxic rare metal, the removal of thallium (Tl) from wastewater has been widely investigated, and adsorption is considered one of the most promising treatment technologies for Tl-containing contaminated water because of its cost-effectiveness, convenience, and high efficacy. In this work, coal tar residue (CTR)-based porous carbon was synthesized through K2FeO4 activation, and applied in adsorbing Tl(I). K2FeO4 could synergistically produce porosity and load iron oxide on the produced porous carbon surface because of the catalytic cracking and oxidative etching during the activation of CTR. The adsorbent was synthesized at 800 ℃ with a mass ratio of K2FeO4/CTR being 3 (PC3-800) showed optimal Tl(I) adsorption performance. The removal efficiency and distribution coefficient of PC3-800 were above 95 % and 104 mL/g, respectively, in a wide pH range (4-10). Furthermore, the selection and reusability of PC3-800 were favorable. The adsorption was a spontaneous, exothermic, and entropy increase process. The adsorption process was dominated by electrostatic attraction, surface complexation, and surface oxidation. The results suggested that removing Tl(I) from contaminated water via CTR-based porous carbon was feasible.

Amphichdiral enhancement on singlet oxygen generation and stable thallium immobilization using iron-driven copper oxide

Thallium (Tl) as a prominent priority contaminant in aquatic environment necessitates rigorous regulation. However, limited horizon devotes the impact of selective oxidation on the process of thallium purification. In this study, selective active radical of singlet oxygen (1O2) was continually generated for Tl(Ⅰ) oxidation accomplished with efficient Tl(Ⅲ) immobilization using iron-driven copper oxide (CuFe)/peroxymonosulfate (PMS). Fe-doping changed the active center of electronic structure for enhancing the catalytic and adsorptive reactivities, and installed magnetism for solid-liquid separation. Rapid reaction rate (0.253 min-1) coupled with vigorous elimination efficiency (98.32%) relied on electrostatic attraction, surface complexation, and H-bond interaction. EPR and XPS analyses demonstrated that the synergistic effects of ≡ Cu(Ⅰ)/≡Cu(Ⅱ) and ≡ Fe(Ⅲ)/≡Fe(Ⅱ) redounded to the sustained generation of 1O2 through the pathway of PMS → •O2- → 1O2, and 1O2 exploited an advantage to selectively oxidize Tl(Ⅰ) to Tl(Ⅲ). 3D isosurface cubic charts revealed that the immobilizing ability of Tl(Ⅲ) hydrate for CuFe was notably superior to that of Tl(Ⅲ) hydrate for CuO and Tl(Ⅰ) hydrate for CuO/CuFe, which further attested surface reactivity promoted stable immobilization form. This work develops the continuous generation of 1O2 and stable immobilization with the goal of efficiently cleansing Tl-containing wastewater.

Exploring the relationship between heavy metals and diabetic retinopathy: a machine learning modeling approach

Diabetic retinopathy (DR) is one of the leading causes of adult blindness in the United States. Although studies applying traditional statistical methods have revealed that heavy metals may be essential environmental risk factors for diabetic retinopathy, there is a lack of analyses based on machine learning (ML) methods to adequately explain the complex relationship between heavy metals and DR and the interactions between variables. Based on characteristic variables of participants with and without DR and heavy metal exposure data obtained from the NHANES database (2003-2010), a ML model was developed for effective prediction of DR. The best predictive model for DR was selected from 11 models by receiver operating characteristic curve (ROC) analysis. Further permutation feature importance (PFI) analysis, partial dependence plots (PDP) analysis, and SHapley Additive exPlanations (SHAP) analysis were used to assess the model capability and key influencing factors. A total of 1042 eligible individuals were randomly assigned to two groups for training and testing set of the prediction model. ROC analysis showed that the k-nearest neighbour (KNN) model had the highest prediction performance, achieving close to 100% accuracy in the testing set. Urinary Sb level was identified as the critical heavy metal affecting the predicted risk of DR, with a contribution weight of 1.730632 ± 1.791722, which was much higher than that of other heavy metals and baseline variables. The results of the PDP analysis and the SHAP analysis also indicated that antimony (Sb) had a more significant effect on DR. The interaction between age and Sb was more significant compared to other variables and metal pairs. We found that Sb could serve as a potential predictor of DR and that Sb may influence the development of DR by mediating cellular and systemic senescence. The study revealed that monitoring urinary Sb levels can be useful for early non-invasive screening and intervention in DR development, and also highlighted the important role of constructed ML models in explaining the effects of heavy metal exposure on DR.

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.

Hydrochemical characterization and assessment of health risks of trace elements in the Huai River Basin of China

Basin water pollution is a global problem, especially in the densely populated areas. The Huai River Basin (abbreviated as HRB), including the Huai River system and the Yishu River system, is the sixth-largest and most densely populated watershed in China. However, there is a lack of comprehensive studies of river and well water throughout the Huai River basin, including hydrochemistry characterization and assessment of health risks. This study investigated water quality and pollution sources of river and well water in the HRB based on the hydrochemistry analysis and different water quality indices. The water body in the HRB showed weak alkalinity (pH = 8.4 ± 0.7) and had high TDS values (TDS = 339 ± 186 mg/L) with water types of HCO3-Ca-Mg and SO4-Cl-Ca-Mg in the Huai River system, and SO4-Cl-Ca-Mg in the Yishu River system. Atmospheric input and evaporation had less impact on hydrochemistry. Evaporite dissolution and carbonate weathering had a greater impact on hydrochemistry. Carbonate precipitation and cation exchange also influenced the dissolved solutes, especially Ca2+ and Na+. Samples had low to medium salinity hazards and sodium absorption ratios and were suitable for irrigation. For drinking purposes, samples were fresh water and have good or excellent according to the Water Quality Index (WQI). Land use types influenced water quality with the worst river water quality from cropland. Combining different assessment indices, the water quality of the Yishu River system performed better than the Huai River system. Absolute principal component analysis-multiple linear regression and the positive matrix factorization models identified the main pollutants as As, Ba, Cr, Ni, and Mn, with natural sources of As, Ba, and Ni and anthropogenic inputs of Cr, and Mn. Although the water quality of the HRB has improved in recent years, high potential risk from As, Cr, Mn, Ba, and Ni should be noted. This study provided vital information for basin hydrochemistry analysis and water quality assessment.

Selective removal of thallium from water by MnO2-doped magnetic beads: Performance and mechanism study

Aqueous thallium has posed an increasing threat to environment as human's intensified activities in mining, refining, process and discharge. Remediation on thallium pollution has been of up-most importance to water treatment. In present work, MnO2 and magnetic Fe3O4 have been implanted to sodium alginate (SA) in presence of carboxyl methyl cellulose (CMC), and the resultant beads consisted of SA/CMC/MnO2/Fe3O4 were characterized. The materials were applied to treatment of Tl-contaminated water as adsorbent in lab. The removal results revealed that the adsorption capacity reached 38.8 mg (Tl)·g (beads)-1 and almost 100 % removal efficiency was achieved. The residual Tl was below 0.1 μg·L-1, meeting the discharge standard regulated in China. The kinetic adsorption was better described as a pseudo-second-order and three-step intra-particle diffusion model. Freundlich isotherm was well fitted the experimental data. The absorbent shown an excellent competitive specificity (KTl/M: ∼104!) over common hazardous ions Cu2+, Cd2+, Co2+, Pb2+ and Cr3+, as well as naturally abundant K+ and Na+ (KTl/M: 10-102) in mimic environmental conditions. Regeneration and reusability of the absorbent was also verified by five absorption-desorpotion cycles. XPS results revealed that a redox reaction between Mn4+ with Tl+, and an ion exchange of H+ (-O-Fe) and Tl+ were assumed to be main process for the specific capturing. This study provided an efficient SA/CMC/MnO2/Fe3O4 composite beads that could be a promising adsorbent for Tl-polluted water treatment.

Application of dirty-acid wastewater treatment technology in non-ferrous metal smelting industry: Retrospect and prospect

Dirty-acid wastewater (DW) originating from the non-ferrous metal smelting industry is characterized by a high concentration of H2SO4 and As. During the chemical precipitation treatment, a significant volume of arsenic-containing slag is generated, leading to elevated treatment expenses. The imperative to address DW with methods that are cost-effective, highly efficient, and safe is underscored. This paper conducts a comprehensive analysis of three typical methods to DW treatment, encompassing technical principles, industrial application flow charts, research advancements, arsenic residual treatment, and economic considerations. Notably, the sulfide method emerges as a focal point due to its minimal production of arsenic residue and the associated lowest overall treatment costs. Moreover, in response to increasingly stringent environmental protection policies targeting new pollutants and carbon emissions reduction, the paper explores the evolving trends in DW treatment. These trends encompass rare metal and sulfuric acid recycling, cost-effective H2S production methods, and strategies for reducing, safely disposing of, and harnessing resources from arsenic residue.

Treatment of wastewater containing thallium(I) by long-term operated manganese sand filter: Synergistic action of MnOx and MnOM

The long-term and stable removal of thallium (Tl) from industrial wastewater generated by mining and smelting operations remains challenging. While sand filters are commonly applied for the simultaneous removal of Mn(II) and other heavy metals, they have limited efficacy in treating Tl-contaminated wastewater. To address this gap, we operated a lab-scale Mn sand filter (MF) without added microorganisms to investigate the efficiency and mechanisms of Mn(II) and Tl(I) removal. Trends in effluent Mn(II) and Tl(I) concentrations indicated three operational stages: start-up, developing and maturation. Over time, the removal efficiency of Tl(I) gradually improved, plateauing at approximately 80 % eventually. Throughout operation, Tl(I) was sequestrated via surface complexation and ion exchange. Besides, enrichment of Sphingobium and other typical manganese oxidizing microorganisms (MnOM) during operation facilitated Mn(II) and Tl(I) oxidation and sequestration by generating biogenic manganese oxides (BioMnOx). Additionally, the accurate control of water quality and operating conditions during operation could also enhance removal efficiency. In summary, physicochemical actions of Mn oxides and biochemical actions of microorganisms synergistically contributed to the sequestration of Mn(II) and Tl(I). These findings provided a novel and sustainable method for the long-term and stable treatment of industrial wastewater containing thallium.

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.

Development and evaluation of diffusive gradients in thin-films technique with a novel titanium peroxide binding gel for in situ measurement of Tl in natural waters and sediments

Speciation of thallium (Tl) controls its fate and biogeochemical behaviors. Thus, a sensitive and accurately approach for Tl monitoring is of great demand due to its ultra-low concentration and sensitivity to redox change. In this study, diffusive gradients in thin-films technique (DGT) assembled with novel titanium peroxide (TP) binding gels (TP-DGT) was developed for in situ measurement of dissolved Tl(I) and Tl(III) in waters and sediments. Laboratory test showed a linear mass accumulation of Tl(I) and Tl(III) on the TP binding gels with the deployment time from 4 to 72 h. A fascinating performance of this novel DGT was achieved in a pH range of 4-9, ionic strength range of 0.1-200 mmol L-1, and humic acid concentration of 0-30 mg L-1 with a low detection limit of 0.3 ng L-1 for Tl(I) and 0.6 ng L-1 for Tl(III). The TP binding gels own excellent stability (1-365 d) and high capacity (73.5 μg Tl disc-1) which are suitable for long-term monitoring. Field application in a river indicated that TP-DGT could work effectively, comparable to the grab sampling in waters. For the first time, the TP-DGT coupled with oxygen optode was successfully applied to map 2D distribution patterns of Tl and oxygen simultaneously in the rhizosphere of M. verticillatum L. This study confirms TP-DGT is a promising tool for routine monitoring of Tl in waters and for investigating biogeochemical processes of Tl in sediments.

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

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

Effects of heavy metal exposure on hypertension: A machine learning modeling approach

Heavy metal exposure is a common risk factor for hypertension. To develop an interpretable predictive machine learning (ML) model for hypertension based on levels of heavy metal exposure, data from the NHANES (2003-2016) were employed. Random forest (RF), support vector machine (SVM), decision tree (DT), multilayer perceptron (MLP), ridge regression (RR), AdaBoost (AB), gradient boosting decision tree (GBDT), voting classifier (VC), and K-nearest neighbour (KNN) algorithms were utilized to generate an optimal predictive model for hypertension. Three interpretable methods, the permutation feature importance analysis, partial dependence plot (PDP), and Shapley additive explanations (SHAP) methods, were integrated into a pipeline and embedded in ML for model interpretation. A total of 9005 eligible individuals were randomly allocated into two distinct sets for predictive model training and validation. The results showed that among the predictive models, the RF model demonstrated the highest performance, achieving an accuracy rate of 77.40% in the validation set. The AUC and F1 score for the model were 0.84 and 0.76, respectively. Blood Pb, urinary Cd, urinary Tl, and urinary Co levels were identified as the main influencers of hypertension, and their contribution weights were 0.0504 ± 0.0482, 0.0389 ± 0.0256, 0.0307 ± 0.0179, and 0.0296 ± 0.0162, respectively. Blood Pb (0.55-2.93 μg/dL) and urinary Cd (0.06-0.15 μg/L) levels exhibited the most pronounced upwards trend with the risk of hypertension within a specific value range, while urinary Tl (0.06-0.26 μg/L) and urinary Co (0.02-0.32 μg/L) levels demonstrated a declining trend with hypertension. The findings on the synergistic effects indicated that Pb and Cd were the primary determinants of hypertension. Our findings underscore the predictive value of heavy metals for hypertension. By utilizing interpretable methods, we discerned that Pb, Cd, Tl, and Co emerged as noteworthy contributors within the predictive model.

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

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

Dynamic retention of thallium(I) on humic acid: Novel insights into the heterogeneous complexation ability and responsiveness

Widely distributed soil humic acid (HA) would significantly affect the environmental migration behavior of Tl(I), but a quantitative and mechanistic understanding of the dynamic Tl(I) retention process on HA is limited. A unified kinetic model was established by coupling the humic ion-binding model with a stirred-flow kinetic model, which quantified the complexation constants and responsiveness coefficients during dynamic Tl(I)-HA complexation. Furthermore, the heterogeneous complexation mechanism of HA and Tl(I) was revealed by batch adsorption experiments, stirred-flow migration experiments, and 2D-FTIR-COS analysis. An increase in pH significantly improved the responsiveness of HA organic binding sites, promoting Tl(I) dynamic retention. Monodentate carboxyl groups induced rapid Tl(I) complexation (k_d = 1.9 min^-1) in strongly acidic environments. Under weakly acidic conditions, Tl(I) retention on HA was mainly attributed to the synergistic complexation effect of carboxyl and amide groups. Among the groups, multidentate carboxyl-phenolic hydroxyl sites could achieve sustained Tl(I) retention due to their stable complexing properties (logK = 4.48∼7.46) and slow response (k_d = 1.1 × 10^-3 min^-1). These findings are crucial for a comprehensive understanding of the environmental interactions of Tl(I) with humic substances in swamp environments.

Thallium-mediated NO signaling induced lipid accumulation in microalgae and its role in heavy metal bioremediation

Thallium (Tl⁺) is a trace metal with extreme toxicity and is highly soluble in water, posing a great risk to ecological and human safety. This work aimed to investigate the role played by Tl⁺ in regulating lipid accumulation in microalgae and the removal efficiency of Tl⁺. The effect of Tl⁺ on the cell growth, lipid production and Tl⁺ removal efficiency of Parachlorella kessleri R-3 was studied. Low concentrations of Tl⁺ had no significant effect on the biomass of microalgae. When the Tl⁺ concentration exceeded 5 μg L^-1, the biomass of microalgae showed significant decrease. The highest lipid content of 63.65% and lipid productivity of 334.55 mg L^-1 d^-1 were obtained in microalgae treated with 10 and 5 μg L^-1 Tl⁺, respectively. Microalgae can efficiently remove Tl⁺ and the Tl⁺ removal efficiency can reach 100% at Tl⁺ concentrations of 0-25 μg L^-1. The maximum nitric oxide (NO) level of 470.48 fluorescence intensity (1 × 10⁶ cells)^-1 and glutathione (GSH) content of 343.51 nmol g^-1 (fresh alga) were obtained under 5 μg L^-1 Tl⁺ stress conditions. Furthermore, the exogenous donor sodium nitroprusside (SNP) supplemented with NO was induced in microalgae to obtain a high lipid content (59.99%), lipid productivity (397.99 mg L^-1 d^-1) and GSH content (430.22 nmol g^-1 (fresh alga)). The corresponding analysis results indicated that NO could participate in the signal transduction pathway through modulation of reactive oxygen species (ROS) signaling to activate the antioxidant system by increasing the GSH content to eliminate oxidative damage induced by Tl⁺ stress. In addition, NO regulation of ROS signaling may enhance transcription factors associated with lipid synthesis, which stimulates the expression of genes related to lipid synthesis, leading to increased lipid biosynthesis in microalgae. Moreover, it was found that the change in Tl⁺ had little effect on the fatty acid components and biodiesel properties. This study showed that Tl⁺ stress can promote lipid accumulation in microalgae for biodiesel production and simultaneously effectively remove Tl⁺, which provided evidence that NO was involved in signal transduction and antioxidant defense, and improved the understanding of the interrelation between NO and ROS to regulate lipid accumulation in microalgae.

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.

Versatile Magnetic Mesoporous Carbon Derived Nano-Adsorbent for Synchronized Toxic Metal Removal and Bacterial Disinfection from Water Matrices

Contamination of water resources by toxic metals and opportunistic pathogens remains a serious challenge. The development of nano-adsorbents with desired features to tackle this problem is a continuously evolving field. Here, magnetic mesoporous carbon nanospheres grafted by antimicrobial polyhexamethylene biguanidine (PHMB) are reported. Detailed mechanistic investigations reveal that the electrostatic stabilizer modified magnetic nanocore interfaced mesoporous shell can be programmatically regulated to tune the size and related morphological properties. The core-shell nano-adsorbent shows tailorable shell thickness (≈20-55 nm), high surface area (363.47 m² g^-1 ), pore volume (0.426 cm³ g^-1 ), radially gradient pores (11.26 nm), and abundant biguanidine functionality. Importantly, the nano-adsorbent has high adsorption capacity for toxic thallium (Tl(I) ions (≈559 mg g^-1 ), excellent disinfection against Staphylococcus aureus and Escherichia coli (>99.99% at 2 and 2.5 µg mL^-1 ), ultrafast disinfection kinetics rate (>99.99% within ≈4 min), and remarkable regeneration capability when exposed to polluted water matrices. The Tl(I) removal is attributed to surface complexation and physical adsorption owing to open ended mesopores, while disinfection relies on contact of terminal biguanidines with phospholipid head groups of membrane. The significance of this work lies in bringing up effective synchronic water purification technology to combat pathogenic microorganisms and toxic metal.

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

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

Recent Advances in Thallium Removal from Water Environment by Metal Oxide Material

Thallium is widely used in industrial and agricultural development. However, there is still a lack of systematic understanding of its environmental hazards and related treatment methods or technologies. Here, we critically assess the environmental behavior of thallium in aqueous systems. In addition, we first discuss the benefits and limitations of the synthetic methods of metal oxide materials that may affect the practicality and scalability of TI removal from water. We then assess the feasibility of different metal oxide materials for TI removal from water by estimating the material properties and contaminant removal mechanisms of four metal oxides (Mn, Fe, Al, and Ti). Next, we discuss the environmental factors that may inhibit the practicality and scalability of Tl removal from water. We conclude by highlighting the materials and processes that could serve as more sustainable alternatives to TI removal with further research and development.

Integrated physiological, biochemical, and transcriptomic analysis of thallium toxicity in zebrafish (Danio rerio) larvae

Although several studies have evaluated the effects of Thallium (Tl) in adult species of fish, the developmental toxicity of Tl has not been previously explored. In this study, zebrafish embryos (<4 h post fertilization (hpf)) were exposed to Tl at concentrations from 0.8 to 400 μg L^-1 for 7 d. The results showed that the decreased hatching rate and increased malformation rate were observed in the larvae. The swimming velocity of larvae from 200 and 400 μg L^-1 treatments was respectively reduced by ~26 % and 15 %. Histopathological analysis of liver indicated the number of cells of karyolysis (143 % and 202 %) and pyknosis (170 % and 131 %) were respectively increased in 200 and 400 μg L^-1 Tl treatments. Meanwhile, the Tl body burden and metallothionein (MT) levels in the larvae were increased with elevated Tl concentrations. The level of malondialdehyde (MDA) was increased by ~20 to 51 % in all Tl treatments and total antioxidant capacity (TAC) was decreased by ~12 % at 200 μg L^-1. The activities of Na⁺/K⁺-ATPase and protease were inhibited in 200 and 400 μg L^-1 Tl treatments. Moreover, the transcripts of genes (Nrf2, HO-1, TNF-α, IL-1β, IL-8, IL-10, TGF) were significantly altered. In addition, a total of 930 differentially expressed genes (DEGs) and 1549 DEGs were found in the 200 and 400 μg L^-1 treatments with 458 overlapped DEGs by transcriptomic analysis. The protein digestion and absorption, ECM-receptor interaction, and complement and coagulation cascades pathways were shown to be the most significantly enriched pathways. This study helps better understand the molecular mechanisms of Tl toxicity in fish.

Zwitterionic ammonium-sulfonato grafted cellulose for efficient thallium removal and adsorption mechanism study

Thallium (Tl) has posed serious impacts on human being concerning increasingly serious pollution in aqueous environments. However, little information on removal method than conventional heavy metals have been available. In the present work, zwitterionic N-(3-sulfonato-1-propyl)-N,N-dimethylammonium grafted cellulose fibre (DMAE-PS) has been fabricated. The chemical component, thermal stability and surface properties of as-prepared materials are identified by FT-IR, elemental analysis, TGA, XRD, BET and SEM. DMAE-PS is shown to be very efficient for removing Tl(I) from water samples with a loading capacity of 274.7 mg (Tl(I))·g^-1 (DMAE-PS)_, representing one of the best performances among bio-mass derived materials. The adsorption is consistent with the Freundlich model following a pseudo-second order (K₂ = 4.36 × 10^-4 g·mg^-1·min^-1, R² = 0.999) and two-step intra-particle diffusion kinetics. The selectivity towards Tl(I) is also remarkably, 1-2 orders (distribution ratio K_Tl/M = 14.85-289.29) of magnitude larger than competing metals (Zn²⁺, Cr³⁺, Mn²⁺, Cu²⁺ and Cd²⁺). The SEM, XPS and UV-visible spectrum collectively reveal that -SO₃^--Tl(I) ionic interaction is probably the main driving force for specific adsorption, which shows a high stability against pH variation. The fabricated DMAE-PS is a sustainable bio-adsorbent with synthetic availability, high removing capacity and strong selectivity, therefore, potentially feasible in treatment of Tl(I) polluted environmental samples.

Efficient Adsorption of Tl(I) from Aqueous Solutions Using Al and Fe-Based Water Treatment Residuals

Iron and aluminum water treatment residuals from a water supply plant were used as adsorbents for Tl(I) to treat thallium-containing Tl(I) wastewater and realize the resource utilization of water treatment residuals. The feasibility study results showed that Fe-WTR and Al-WTR reached adsorption equilibria within 120 min. The Langmuir model showed maximum adsorption capacities of Tl(I) on Fe-WTR and Al-WTR as 3.751 and 0.690 mg g−1 separately at an initial concentration of 5 mg L−1. The adsorption capacities of Fe-WTR and Al-WTR positively correlated with pH. The removal of Tl(I) using Fe-WTR exceeded Al-WTR; the adsorbed Tl(I) in Fe-WTR occurred primarily in the reduced state, while the Tl(I) adsorbed in Al-WTR was mainly in acid-extractable and reduced states. FTIR and XPS data showed that Tl(I) and Fe/Al-OH-functional groups formed stable surface complexes (Fe/Al-O-Tl) during adsorption, and there was no redox reaction. This confirmed that WTR is a highly efficient adsorbent for the stable removal of Tl(I), which provides a practical foundation for industrial application in Tl(I)-containing wastewater treatment.

Perspective on Fe0-PS synergetic effect and reaction mechanism in the thallium(I) contaminated water treatment

Due to extreme toxicity of the element of thallium (Tl), increasing aqueous Tl pollution incidents have aroused growing concerns. As the prevalent and stable form, i.e., monovalent Tl, the highly efficient removal methodologies of Tl(I) from (waste)water remains limited and challenging. In this study, an advanced oxidation method, the feasibility of using zero valent iron (Fe⁰) coupled with persulfate (PS) to treat Tl(I)-containing synthetic wastewater was investigated. Its influence parameters, including reaction time, initial Tl concentration, dosages of PS and Fe⁰, initial and coagulation pH, temperature, coexisting ions and organic matter (NO₃^-, SO₄^2-, Cl^- and HA) were examined. The results revealed that the system can be applied to a wide range of pH and temperature and the reaction equilibrium can be reached in about 30 min. Favorable Tl(I) removal rate (>98%) was observed in the synthetic wastewater with medium and relatively high Tl(I) concentration (≤0.250 mM). The analyses of characterization results including electron spin resonance spectrometer and X-ray photoelectron spectroscopy indicated that ·OH played a vital role in the removal of Tl(I), which was oxidized and removed by co-precipitation. Fe⁰ can be served as a stable source of Fe²⁺ to efficiently catalyze PS. The remaining Fe⁰ can be easily separated because of its magnetism, assuring the promising reusability of the reactant. The study aims to provide references for treatment of real Tl polluted wastewater.

Removal of Thallium from Aqueous Solutions by Adsorption onto Alumina Nanoparticles

Thallium (I) was removed from aqueous solution by using gamma-alumina nanoparticles (γANPs) materials as nano adsorbents. Varied experimental conditions such as adsorbent dose, agitation time, initial concentration, pH, and temperature effects were carried out in batch conditions in view of the optimization of thallium (I) adsorption and the identification of the adsorption mechanisms in the system γANPs-Tl. The pH effect indicated a remarkable increase in the quantity of Tl(I) removed for pH values ranging from 4 to 8, an almost constant magnitude for pH values between 8 and 10, and a decrease for pH values above 10. Considering an initial Tl(I) concentration of 20 µg/L and an adsorbent dose of 1 g/L at a pH value of 8.5, the removal was achieved at 95.12 ± 0.02% efficiency. The pseudo-second-order kinetics and the Freundlich isotherm perfectly described the adsorption mechanism. The process of thallium (I) adsorption reaction, as highlighted by thermodynamic investigations, was found to be spontaneous and exothermic with coexistence of physisorption and chemisorption with a dominance of physisorption. The diffusion model predicted multi-linearity, suggesting an involvement of surface spread and intraparticle diffusion in the sorption process. Thallium removal was effective by using γANPs as nano adsorbents.

Light- and H2O2-Mediated Redox Transformation of Thallium in Acidic Solutions Containing Iron: Kinetics and Mechanistic Insights

The redox transformation between the oxidation states of thallium (Tl(I) and Tl(III)) is the key to influencing its toxicity, reactivity, and mobility. Dissolved iron (Fe) is widely distributed in the environment and coexists at a high level with Tl in acidic mine drainages (AMDs). While ultraviolet (UV) light and H₂O₂ can directly (by inducing Tl(III) reduction) and indirectly (by inducing Fe(III) to form reactive intermediates) impact the redox cycles of Tl in Fe(III)-containing solutions, the kinetics and mechanism remain largely unclear. This study is the first to investigate the UV light- and H₂O₂-mediated Tl redox kinetics in acidic Fe(III) solutions. The results demonstrate that UV light and H₂O₂ could directly reduce Tl(III) to Tl(I), with the extent of reduction dependent on the presence of Fe(III) and the solution pH. At pH 3.0, Tl(I) was completely oxidized to Tl(III), which can be ascribed to the generation of hydroxyl radicals (^•OH) from the Fe(III) photoreduction or Fe(III) reaction with H₂O₂. The kinetics of Tl(I) oxidation were strongly affected by the Fe(III) concentration, pH, light source, and water matrix. Kinetic models incorporating Tl redox kinetics with Fe redox kinetics were developed and satisfactorily interpreted Tl(III) reduction and Tl(I) oxidation under the examined conditions. These findings emphasize the roles of the UV light- and H₂O₂-driven Fe cycles in influencing the redox state of Tl, with implications for determining its mobility and fate in the environment.

Sustainable and efficient technologies for removal and recovery of toxic and valuable metals from wastewater: Recent progress, challenges, and future perspectives

Due to their numerous effects on human health and the natural environment, water contamination with heavy metals and metalloids, caused by their extensive use in various technologies and industrial applications, continues to be a huge ecological issue that needs to be urgently tackled. Additionally, within the circular economy management framework, the recovery and recycling of metals-based waste as high value-added products (VAPs) is of great interest, owing to their high cost and the continuous depletion of their reserves and natural sources. This paper reviews the state-of-the-art technologies developed for the removal and recovery of metal pollutants from wastewater by providing an in-depth understanding of their remediation mechanisms, while analyzing and critically discussing the recent key advances regarding these treatment methods, their practical implementation and integration, as well as evaluating their advantages and remaining limitations. Herein, various treatment techniques are covered, including adsorption, reduction/oxidation, ion exchange, membrane separation technologies, solvents extraction, chemical precipitation/co-precipitation, coagulation-flocculation, flotation, and bioremediation. A particular emphasis is placed on full recovery of the captured metal pollutants in various reusable forms as metal-based VAPs, mainly as solid precipitates, which is a powerful tool that offers substantial enhancement of the remediation processes' sustainability and cost-effectiveness. At the end, we have identified some prospective research directions for future work on this topic, while presenting some recommendations that can promote sustainability and economic feasibility of the existing treatment technologies.

Kinetics and mechanism of Thallium(I) oxidation by Permanganate: Role of bromide

The oxidation of thallium(I) (Tl (I)) to Tl (III) is referred to as an efficient means for Tl removal. Bromide (Br‾) inevitably occurs in nearly all water sources at concentrations of 0.01-67 mg/L (0.14-960 μM). The effect of Br‾ remains largely unclear but likely of critical importance on the redox fate and thus the removal potential of Tl (I) during typical oxidation treatment processes. Here, we investigate the kinetics and tackle the mechanism of Tl (I) oxidation by permanganate (KMnO₄) under the influence of Br‾. The results demonstrated that Br‾ at environmental levels exhibited significant catalytic effect on Tl (I) oxidation kinetics by KMnO₄ at acidic pH of 4.0-7.0, while no significant effect of Br‾ was observed for Tl(I) oxidation under alkaline conditions of pH 8.0 and 9.0. It was found that the enhanced oxidation kinetics under acidic conditions was driven by the combined effect of and autocatalysis mediated by MnO₂ and a fast oxidation kinetics served by in-situ formed bromine species. Through quantifying the relative contributions of those bromine species to the homogenous oxidation of Tl(I), HOBr, Br₂ and Br₂O were found to play roles in catalyzing the oxidation of Tl(I) by KMnO₄. The results discussed herein highlight the critical role of Br‾ on the Tl(I) complex oxidation process by KMnO₄ and may have implications for evaluating the redox cycle and removal potential of Tl in bromide-containing water treatment.

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

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

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

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

Kinetics of Thallium(I) Oxidation by Free Chlorine in Bromide-Containing Waters: Insights into the Reactivity with Bromine Species

The oxidation of thallium [Tl(I)] to Tl(III) by chlorine (HOCl) is an important process changing its removal performance in water treatment. However, the role of bromide (Br^-), a common constituent in natural water, in the oxidation behavior of Tl(I) during chlorination remains unknown. Our results demonstrated that Br^- was cycled and acted as a catalyst to enhance the kinetics of Tl(I) oxidation by HOCl over the pH range of 5.0-9.5. Different Tl(I) species (i.e., Tl⁺ and TlOH(aq)) and reactive bromine species (i.e., HOBr/BrO^-, BrCl, Br₂O, and BrOCl) were kinetically relevant to the enhanced oxidation of Tl(I). The oxidation by free bromine species became the dominant pathway even at a low Br^- level of 50 μg/L for a chlorine dose of 2 mg of Cl₂/L. It was found that the reactions of Tl⁺/BrCl, Tl⁺/BrOCl, and TlOH(aq)/HOBr dominated the kinetics of Tl(I) oxidation at pH < 6.0, pH 6.0-8.0, and pH > 8.0, respectively. The species-specific rate constants for Tl⁺ reacting with individual bromine species were determined and decreased in the order: BrCl > Br₂ > BrOCl > Br₂O > HOBr. Overall, the presented results refine our knowledge regarding the species-specific reactivity of TI(I) with bromine species and will be useful for further prediction of thallium mobility in chlorinated waters containing bromide.

Cotransport of thallium(I) with polystyrene plastic particles in water-saturated porous media

Exploring the transport behaviors of thallium (Tl) in porous media is crucial for predicting Tl pollution in natural soils and groundwater. In recent years, the misuse of plastics has led to plastic becoming an emerging pollutant in soil. In this work, the effects of plastic particles on Tl(I) transport in water-saturated sand columns were investigated under different ionic strengths (ISs), pH values, and plastic particle sizes. The two-site nonequilibrium model was selected to fit the breakthrough curves (BTCs) of Tl(I). The results demonstrated that nanoplastics (NPs) accelerated Tl(I) transport at pH 7, which might be attributed to the competitive adsorption of NPs and Tl(I) on sand surfaces. However, at pH 5, the deposited NPs might provide more adsorption sites for Tl(I), and thus enhance its retention in the columns. In addition, the "straining" process could intercept microplastics (MPs) with Tl(I) that was attached under unfavorable attachment conditions, which would result in the inhibited mobility of Tl(I). On the other hand, the migration of plastics was restrained to some extent when Tl(I) was present. Overall, the findings from this work provided a new perspective for understanding the transport of Tl(I) and plastics in subsurface environments.

Highly efficient removal of thallium(I) by facilely fabricated amorphous titanium dioxide from water and wastewater

In this study, amorphous hydrous titanium dioxide was synthesized by a facile precipitation method at room temperature, aiming to effectively remove thallium(I) from water. The titanium dioxide prepared using ammonia as precipitant (TiO2I) is more effective for thallium(I) uptake than the one synthesized with sodium hydroxide (TiO2II). The TiO2 obtained particles are amorphous, aggregates of many nanoparticles and irregular in shape. The thallium(I) uptake increases with the rise of solution pH value. Under neutral pH conditions, the maximal thallium(I) adsorption capacities of TiO2I and TiO2II are 302.6 and 230.3 mg/g, respectively, outperforming most of the reported adsorbents. The amorphous TiO2 has high selectivity towards thallium(I) in the presence of multiple cations such as K+, Ca2+, Mg2+, Zn2+ and Ni2+. Moreover, the TiO2I is efficient in removing thallium(I) from real river water and mining wastewater. Additionally, the spent TiO2I can be regenerated using hydrochloric acid solution and reused. The Tl(I) adsorption is achieved via replacing the H+ in hydroxyl group on the surface of TiO2 and forming inner-sphere surface complexes. Owing to its high efficiency, facile synthesis and environmental friendliness, the TiO2I has the potential to be used as an alternative adsorbent to remove Tl(I) from water.

Yeasts isolated from a lotic continental environment in Brazil show potential to produce amylase, cellulase and protease

Yeasts have wide applicability in the industrial field, as in the production of enzymes used in biocatalysts. Biocatalysts are more efficient when compared to chemical catalysts, with emphasis on hydrolytic enzymes, such as amylase, cellulase and protease. Here we focused on prospecting yeasts, with a high capacity to synthesize hydrolytic enzymes, from a continental lotic ecosystem environment in Brazil. 75 yeasts were grown in Yeast Extract-Peptone-Dextrose (YPD) medium supplemented with antibacterial and their capacity for enzymatic production was tested in specific media. Accordingly, 64 yeasts showed enzyme production capacity. From those, six showed good enzyme indexes, 3 for amylase, 2 for cellulase and 1 for protease. All showed at least one hydrolytic enzyme activity for the tested enzymes (amylase, cellulase and protease), which suggested that the yeasts are metabolically active. By sequencing the 26S gene, we identified Naganishia diffluens and Apiotrichum mycotoxinivorans as the species with highest enzyme production activities. Those species showed potential for application as biological catalysts in the biotechnological scope, collaborating in a sustainable way for the development of industrial products.

Thallium(I) Salts: New Partners for Calix[4]pyrroles

Calix[4]pyrrole 1 can form host-guest complexes with certain thallium salts, for example, TlF, not only in the gas phase but also in solution and in the solid state. The complexation of TlF by calix[4]pyrrole 1 was found to promote self-assembly and the formation of well-defined and highly ordered fibrous supramolecular morphologies, as revealed by polarizing microscopy and scanning electron microscopy. The findings reported here serve to broaden the scope of cationic substrates that may be complexed as ion pairs by calix[4]pyrrole receptors while setting the stage for the development of new hosts for thallium(I) salts.

Distributed treatment systems

This section presents a review of the scientific literature published in 2019 on topics relating to distributed treatment systems. This review is divided into the following sections: constituent removal, treatment technologies, planning and treatment management, and other topics. PRACTITIONER POINTS: Highlights changes and innovation in removal techniques and technologies in water treatment. Reviews management systems of distributed treatment systems. Discusses point-of-use treatment systems.

Simultaneous quantitative analysis of K+ and Tl+ in serum and drinking water based on UV-Vis spectra and chemometrics

The simultaneous detection of K⁺ and Tl⁺ can serve as a toxicological diagnostic tool for thallium poisoning. Colorimetric-reaction-based nanoprobes have emerged as promising sensors for the rapid and ultrasensitive detection of molecular species in simple systems. However, the development of viable screening tools for multicomponent analysis in complex systems remains challenging owing to interference from coexisting materials in the media. Herein, a simple chemical sensor array based on the peroxidase-like activity of gold nanoparticles modified with single-stranded DNA (AuNPs-ssDNA) and chemometrics was developed for the simultaneous detection of K⁺ and Tl⁺ in aqueous solutions and serum. The use of a K⁺ adapter conferred high selectivity to the developed method. Optimized AuNPs-ssDNAs were used to construct a sensor array, which together with chemometrics provided fingerprints that can facilitate the simultaneous analysis of multiple components. The developed colorimetric reaction in combination with the chemometrics assay was directly used as a biosensor array, which exhibited detection limits of 107.33 nM for K⁺ and 19.26 nM for Tl⁺. The developed method could potentially serve as a diagnostic technique for investigating thallium poisoning and toxicology.

Thallium(I) Oxidation by Permanganate and Chlorine: Kinetics and Manganese Dioxide Catalysis

The oxidation of the toxic heavy metal thallium(I) (Tl(I)) is an efficient way to enhance Tl removal from water and wastewater. However, few studies have focused on the kinetics of Tl(I) oxidation in water, especially at environmentally relevant pH values. Therefore, the kinetics and mechanisms of Tl(I) oxidation by the common agents KMnO₄ and HOCl under environmentally relevant pH condition were explored in the present study. The results indicated that the pH-dependent oxidation of Tl(I) by KMnO₄ exhibited second-order kinetics under alkaline conditions (pH 8-10) with the main active species being TlOH, while the reaction could be characterized by autocatalysis at pH 4-6, and Mn(III) might also play an essential role in the MnO₂ catalysis. Furthermore, a two-electron transfer mechanism under alkaline conditions was preliminarily proposed by using linear free energy relationships and X-ray photoelectron spectroscopy (XPS) analysis. Distinctively, the reaction rate of Tl(I) oxidation by HOCl decreased with increasing pH, and protonated chlorine might be the main active species. Moreover, the Tl(I)-HOCl reaction could be regarded as first order with respect to Tl(I), but the order with respect to HOCl was variable. Significant catalysis by MnO₂ could also be observed in the oxidation of Tl(I) by HOCl, mainly due to the vacancies on MnO₂ as active sites for sorbing Tl. This study elucidates the oxidation characteristics of thallium and establishes a theoretical foundation for the oxidation processes in thallium removal.

Insights into facile synthesized pomelo biochar adsorbing thallium: potential remediation in agricultural soils

Little information is available on thallium (Tl) adsorption onto fruit-derived biochar. In this study, pomelo peel and waste pomelo were thus chosen to prepare two kinds of biochars recorded as PPB and WPB. The two produced biochars subsequently evaluated their potential remediation of thallium (Tl) contamination in agricultural soils by their Tl adsorption capacity. Results showed that the two pomelo-derived biochars presented obvious microporous structure and rich oxygen-containing functional group, supported by the observant data of specific surface area, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Furthermore, Langmuir isothermal adsorption model can better fit the adsorption behavior of thallium onto PPB and WPB, and the subsequent maximum adsorption capacity was 4283.9 μg g^-1 and 5286.0 μg g^-1, respectively. In addition, the pseudo-second-order kinetic model could well fit the kinetic behavior of thallium adsorption onto PPB and WPB, indicating that the process is accompanied by chemical adsorption. Meanwhile, in agricultural soils, PPB and WPB can be used as environmentally friendly adsorbents to remediate Tl contamination due to their pH increase of the tested soils and their comparable adsorption ability of Tl. The obtained findings can provide insights into comprehensively developed fruit-derived biochar technology to remediate Tl contamination in agricultural soils.

Removal of thallium(I) from aqueous solutions using titanate nanomaterials: The performance and the influence of morphology

Thallium (Tl) pollution has attracted environmental attention due to its high toxicity, thus the cleanup of Tl from the environment is of significance. Titanate nanomaterials (TNMs) with different morphologies can be synthesized via a hydrothermal reaction under different conditions but the knowledge of the Tl(I) removal by them is limited. Our results indicated that TNM prepared at 130 °C exhibited a nanotubular appearance and a longer reaction time resulted in the formation of perfect nanotube, while that prepared at 180 °C exhibited a nanowire-like arrangement. The nanotubular and nanowire-like TNMs possessed approximately excellent Tl(I) adsorption capacities, wide pH, and temperature application ranges but different adsorption kinetics. Inorganic ions influenced the Tl(I) removal and the inhibiting effect of heavy metal ions followed the sequence Pb(II) > Cu(II) > Cd(II) > Zn(II). The anti-interference ability and selectivity of wire-like TNMs for Tl(I) removal were higher than those of tubular TNMs. High Tl(I) uptakes of tubular and wire-like TNMs were driven by the electrostatic attraction, ion exchange with Na⁺/H⁺, and complexation with -ONa functional groups in the interlayers and Ti-OH on the surfaces of TNMs as well as microprecipitation; while their adsorption configurations were different. TNMs are promising for potential applications in Tl(I) elimination from wastewater due to the high adsorption capacity and regenerability. This work indicates that TNMs synthesized under different conditions have the similar Tl(I) adsorption performances and the preparation of TNMs used for Tl(I) removal has an undemanding synthesis condition.

Highly efficient removal of thallium(I) from wastewater via hypochlorite catalytic oxidation coupled with adsorption by hydrochar coated nickel ferrite composite

In this study, tannery wastewater was used as carbon source to hydrothermally synthesize magnetic carbon-coated nickel ferrite composite (NiFe₂O₄@C), which was employed as a catalyst for thallium (Tl) oxidation by hypochlorite and simultaneously as an adsorbent for Tl removal from wastewater. Compared with NiFe₂O₄@C adsorption or hypochlorite oxidation alone, the combination of NiFe₂O₄@C and hypochlorite substantially enhanced the rate and efficiency of Tl(I) removal. In addition, this process was highly effective for Tl(I) removal over a wide pH range (6-12). The maximum Tl(I) removal capacity was 1699 mg/g at pH 10, which is the highest one reported so far. Electron spin resonance spectra suggested the formation of hypochlorite-based free radicals induced by the NiFe₂O₄@C composite, which enhanced the Tl(I) oxidation and removal. Oxidation-induced surface precipitation and surface complexation were found to be the main Tl(I) removal mechanisms. Consecutive cyclic regeneration tests implied robust regeneration and reuse performance of the composite. Moreover, it was effective for Tl(I) removal from real industrial wastewater. Therefore, the hypochlorite catalytic oxidation coupled with adsorption by the magnetic NiFe₂O₄@C composite is a promising technique for Tl(I) removal from wastewater. This hybrid process also has great potential for the removal of other pollutants.

Groundwater dependent ecosystems in coastal Mediterranean regions: Characterization, challenges and management for their protection

Coastal lagoons deliver a wide range of valuable ecosystem goods and services. These ecosystems, that are often maintained by direct or indirect groundwater supplies, are collectively known as groundwater dependent ecosystems (GDEs). The importance of groundwater supplies is greatly exacerbated in coastal Mediterranean regions where the lack of surface water and the over-development of anthropogenic activities critically threaten the sustainability of coastal GDEs and associated ecosystem services. Yet, coastal GDEs do not benefit from a legal or managerial recognition to take into account their specificity. Particular attention should be paid to the characterization of environmental and ecological water requirements. The hydrogeological knowledge about the management and behavior of coastal aquifers and GDEs must be strengthened. These investigations must be supplemented by a stronger assessment of potential contaminations to develop local land-uses and human activities according to the groundwater vulnerability. The quantitative management of water resources must also be better supervised and/or more constrained in order to ensure the water needs necessary to maintain coastal GDEs. The transdisciplinary approach between hydrogeology, hydrology, social sciences and law is essential to fully understand the socio-economic and environmental complexity of coastal GDEs. Priority must now be given to the development of an appropriate definition of coastal GDEs, based on a consensus between scientists and lawyers. It is a necessary first step to develop and implement specific protective legislation and to define an appropriate management scale. The investment and collaboration of local water users, stakeholders and decision-makers need to be strengthened through actions to favor exchanges and discussions. All water resources in the coastal areas should be managed collectively and strategically, in order to maximize use efficiency, reduce water use conflicts and avoid over-exploitation. It is important to continue to raise public awareness of coastal aquifers at the regional level and to integrate their specificities into coastal zone management strategies and plans. In the global context of unprecedented anthropogenic pressures, hydro-food crises and climate change, environmental protection and preservation of coastal GDEs represents a major challenge for the sustainable socio-economic and environmental development of Mediterranean coastal zones.

Zero-valent iron-manganese bimetallic nanocomposites catalyze hypochlorite for enhanced thallium(I) oxidation and removal from wastewater: Materials characterization, process optimization and removal mechanisms

Nano zero-valent metals adsorption coupled with advanced oxidation for environmental pollutants removal has been gaining attention recently. In this study, zero-valent iron-manganese (nZVIM) bimetallic nanocomposites were prepared via one-pot borohydride reduction and coupled with hypochlorite (ClO^-) oxidation for enhanced thallium (Tl) removal from wastewater. Amorphous nZVIM nanoparticles were successfully synthesized, with a specific surface area of 106.89 m²/g, and a saturation magnetization of 65.16 emu/g. In comparison with the nZVIM adsorption or ClO^- oxidation alone, the hybrid nZVIM/ClO^- process achieved much faster Tl(I) removal rate over a wide pH range from 6 to 10. Maximum Tl(I) removal capacity was as high as 990.0 mg/g. The oxidation-induced adsorption for Tl(I) removal well followed the pseudo-first kinetic order model. Stable and effective adsorbent regeneration was achieved during the cyclic adsorption-desorption tests. This process also had high resistance to the interference of external cations, can act as an effective pretreatment for Tl(I) removal from the actual saline industrial wastewater. The main mechanisms for Tl(I) removal were found to be oxidation, surface precipitation, pore retention, and surface complexation. The nZVIM coupled with ClO^- approach has great potential for Tl(I) removal from wastewater, and its application in other fields is highly anticipated.

Quantification of Tl (I) and Tl (III) based on microcolumn separation through ICP-MS in river sediment pore water

Thallium (Tl) is a typical toxic element, whose biological effects and geochemical behavior are closely related with its chemical speciation in the environment. In this context, the objective of the present study was to develope an effective method for separation of Tl (I) and Tl (III) based on solid-phase extraction (SPE) using anion exchange resin AG1-X8 as a sorbent and ICP-MS measurement. In this proposed method, Tl (I) and Tl (III) could be separated by selective adsorption of Tl (III)-DTPA in the resin, while Tl (III) was eluted by the solution mixed with HCl and SO₂. The validity of this method was confirmed by assays of standard solutions of Tl (I) and Tl (III), as well as with spike of contaminated samples. The present study results revealed that higher concentration of Tl (I) (245.48 μg/l) and Tl (III) (20.92 μg/l) had been found near the acid mine drainage (AMD) sample of sediment pore water. The results revealed that Tl (I) of 61.47 μg/l and Tl (III) of 9.73 μg/l were present in the river water contaminated by acid mine drainage. This thallium speciation analysis implied that the dominant Tl (I) species in the river water studied might be due to the weathering of sulfide mineral-bearing rocks, mining, and smelting activities in the studied area.

Removal of Trace Thallium from Industrial Wastewater by Fe0-Electrocoagulation

As thallium (Tl) is a highly toxic heavy metal, there are compulsory environmental regulations in many countries on minimizing its release. This research investigated the treatment of real industrial wastewater with low Tl(I) concentration by Fe0-electrocoagulation (Fe0-EC) in a batch aeration-forced pump cycle reactor. The effects of pH (7–12), current density (8.3–33.3 mA/cm2), dissolved oxygen (DO) in wastewater, and initial Tl(I) concentration (66–165 µg/L) on Tl(I) removal efficiency were investigated. The removal efficiency of Tl(I) is pH-dependent, to be exact, it increases significantly with pH rising from 8 to 11. Initial pH of influent and DO concentration were the key operation parameters which strongly affect Tl(I) removal. After the water sample with initial Tl(I) concentration of 115 µg/L was treated for 12 min by a single-step process at pH of 11 and current density of 16.7 mA/cm2, the residual Tl(I) concentration was decreased to beneath the emission limit in China (2 µg/L) with a low energy consumption of 0.82 kWh/m3. By prolonging the operation time, the concentration was further reduced to 0.5 µg/L or even lower. The main composition of the flocculent sludges is iron oxyhydroxide, yet its crystal structure varies dependent on pH value which may result in different Tl(I) removal efficiency. Feroxyhyte nanosheets generate in situ by Fe0-EC, which contributes to the rapid and effective removal of Tl(I), while the speedy oxidation under DO-enriched conditions benefits the feroxyhyte formation. The mechanism of Tl(I) removal by Fe0-EC is attributed to the combination of electrostatic attraction and the formation of inner-sphere complexes. As shown in the technical and mechanical studies, Fe0-EC technology is an effective method for low Tl concentration removal from wastewater.