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Thallium (Tl) is an extremely toxic element, whose toxicity is even higher than mercury, arsenic, and cadmium. It is of great significance to hinder the migration and transfer of Tl from soils to the plants. A synthetic mineral amendment (SMA), mainly composed of different silicates, was evaluated for its effects on the transformation and retention of Tl in two typical highly Tl-contaminated soils from Southwest China. The results indicated that the addition of mineral amendment increased the soil of the pH by 0.46–2.13 units and distinctly reduced the content of active thallium in the soils. The extent of Tl reduction was related to the morphological characteristics of the original soil In particular, the application of the mineral amendment transformed 25.8–52.5% of the active Tl fractions in the soils to the residual fraction at 60 d. Adding mineral amendment to the soils can provide conditions to facilitate Tl to enter the silicate crystal lattice. The results of XPS evidenced that the proportion of Tl(I) in the soil was greatly reduced after adding the mineral amendment. • A synthetic mineral amendment (SMA) was applied to restore thallium (Tl) polluted soil. • SMA transformed 25.8–52.5% of the active Tl fractions to the residual fraction. • The proportion of Tl(I) in soil was greatly decreased after SMA was applied. • SMA immobilization method provides practical significance in Tl hazard mitigation. [ABSTRACT FROM AUTHOR]

• Tl isotopic fractionation was firstly observed in industrial pyrite smelting process. • Large Tl isotopic variations were detected during the smelting process. • Tl isotope fractionation may be due to Rayleigh fractionation and adsorption process. • Tl isotopic compositions provide a new way to trace Tl pollution process. Thallium (Tl) is typical rare element with severe toxicity comparable to Hg and Pb. To track Tl pollution, isotopic fractionation of Tl was evaluated during pyrite smelting for sulfuric acid production. Large variations in Tl isotope compositions were observed among the pyrite ore (PO) and its four different smelting wastes. The starting raw PO had an ε 205Tl value of +1.28. The fluidized-bed furnace slag generated by high-temperature smelting had the heaviest ε 205Tl (+16.24) in the system. Meanwhile, the boiler fly ash (ε 205Tl = +8.34), cyclone fly ash (ε 205Tl = +2.17), and electrostatic precipitation fly ash (ε 205Tl = –1.10), with decreasing grain sizes during the treatment processes, were characterized by elevated levels of Tl contents and substantial enrichment in the light Tl isotopes relative to the furnace slag. Further calculation and high-resolution transmission electron microscopy indicated that Tl isotope fractionation could be governed by both Rayleigh-type fractionation and adsorption of volatilized Tl by particles of various grain sizes. According to the substantial differences in the PO from its smelting wastes and the measurement precision of isotopic fractionation, it is suggested that Tl isotopes can serve as a new tool for tracing pollution of Tl. [ABSTRACT FROM AUTHOR]

Inorganic pollution induced by smelting waste has threatened the safety of environment, whereas the impacts on farmlands with regards to potentially toxic elements (PTEs) receive insufficient attention. Herein, the contents, transfer pathways and potential risks of the PTEs in common crops were examined from different farmlands distributed around an indigenous Zn-smelting area in Guizhou, China. The results showed that Tl in cabbage (Brassica oleracea L.) (up to 3.74 mg/kg) and radish (Raphanus sativus L.) (up to 1.16 mg/kg) at some sites exceeded the maximum permissible level (MPL) (0.5 mg/kg) for food, and, under the same pollution condition, cabbage and radish were more likely to enrich PTEs, and the edible portion of maize was not prone to Tl risk. Hazard quotient calculations of Tl, Ba, and U were greater than 1, indicating the edible risk of crops for these PTEs. Further characterization of selected soils revealed that MnFe 2 O 4 and Fe 2 O 3 controlled the phase transformation of Tl(III) in rhizospheric soils. Furthermore, distinctive mullite was detected in the soil which confirmed the contribution of high temperature smelting to PTEs pollution. The findings indicate an emergent need for soil remediation around historical indigenous metal smelting areas for the sake of food security. [Display omitted] • Visibly elevated thallium (Tl) contents were observed in some crops at site CS-5. • Iron oxides may affect the phase transformation of Tl(I)–Tl(III) in rhizospheric soils. • Some species of the studied crops may exert a non-negligible health risk for consumers. [ABSTRACT FROM AUTHOR]

Thallium (Tl) pollution caused by the exploitation of uranium (U) mines has long been neglected due to its low crustal abundance. However, Tl may be enriched in minerals of U ore because Tl has both sulfurophile and lithophile properties. Herein, a semi-dynamic leaching experiment combined with statistical analysis, geochemical speciation and multi-characterization provided novel insight into the distinct features and mechanisms of Tl release from uranium mill tailings (UMT). The results showed that particle size effects prevail over the pH on Tl release, and surface dissolution is the pivotal mechanism controlling Tl release based on Fick's diffusion model. The study revealed that long-term leaching and weathering can lead to the increased acid-extractable and oxidizable fractions of Tl in UMT, and that the exposure and dissolution of Tl-containing sulfides would largely enhance the flux of Tl release. The findings indicate that UMT containing (abundant) pyrite should be paid particular attention due to Tl exposure. Besides, critical concern over the potential Tl pollution in universal U mining and hydrometallurgical areas likewise may need to be seriously reconsidered. ga1 • Thallium (Tl) in uranium mill tailings (UMT) was mainly released by surface dissolution. • Particle size effect instead of leachant pH critically influenced Tl release. • Significantly increased labile Tl fraction was observed after 20 weeks' leaching. • Weathering based sulfide exposure largely facilitated Tl mobilization. • UMT containing pyrite should receive particular attention due to highly toxic Tl release. [ABSTRACT FROM AUTHOR]

• Vegetable grown soils were highly enriched with Tl, As, Pb, Cd, Cr, Cu and Mn. • Non-negligible potential health risk of toxic Tl, As, etc. in vegetables was found. • Carcinogenic risk is higher than the threshold for As, Cd and Cr. • Steel-making activities contribute 35–80% of Pb-As in vegetables via binary mixing model. Industrial activities tend to deteriorate adjacent agricultural lands due to accumulation of potentially toxic elements in soils and crops. However, better understanding of their distinctive source partitions and transfer process remains insufficient in steel-making area. The paper focuses on the pollution levels, health risks, and provenance identification of Tl, As, Pb, Cu, Ni, Co, Sb, Cd, Zn, Be, Cr, Fe, Mn, Mo, Sn, and V in common vegetables from different farmlands near a steel-making plant. The results showed that the Tl, As, Pb, Cd, Cr, Cu and Mn were of high-level contamination in soils and generally above the maximum permissible level (MPL). Calculation using hazard quotients (HQ) exhibited that consumption of the studied vegetables may entail significant health risks to residents, especially for children, resulting from the elevated contents of Tl, As and associated toxic elements. Calculation by binary mixing model using Pb isotopic compositions suggested that steel-making activities contributed to 35–80% of the contamination of Pb and As in vegetables. It is necessary to adopt appropriate remediation measures to mitigate the farmland contamination and ensure the food safety of the agricultural products. [ABSTRACT FROM AUTHOR]

Metal(loid) contamination caused by industrial activities in agricultural soils has become a universal environmental and food safety concern. This study revealed the contamination, pathway, and source contribution of metal(loid)s such as lead (Pb), zinc (Zn) and cadmium (Cd) in maize and soils in different residential areas impacted by long-term historical artisanal zinc smelting activities from Southwest China. Results revealed that the soils were contaminated heavily by metals like Pb, Zn and Cd, with contents of 40–14,280, 150–47,020 and 1.28–61.7 mg/kg, respectively. Hazard quotients of food uptake for Pb, Cd and Cr in maize grains were extremely high for residents, in particular for the children. To trace the sources of metal health risk, lead isotope fingerprinting and binary mixing modeling were applied. It indicated that the anthropogenic activities contributed over 80% to the Pb contamination in maize grains. The findings highlighted warning levels of health risks to the residents in consuming maize grains in the historical artisanal Pb Zn smelting area. Therefore, an effective strategy including pollution source control and remediation measures must be taken to improve the soil quality and guarantee food safety around the historical smelting areas likewise. Unlabelled Image • Maize and rhizospheric soils were heavily contaminated by Pb, Zn and Cd. • Local residents were under high intake risks for Pb, Zn, Cd and Cr. • Pb-Zn artisanal smelting contributed over 80% to the contamination in the maize grains. • Lead isotopic source tracing is critical to address metal contamination inventory. [ABSTRACT FROM AUTHOR]

Farmland soil contamination of heavy metal(loid)s (HM) derived from smelting activities is a global concern, owing to its potential threat for human health through food chain. This study aims to evaluate total contents and bioavailability of HMs (Pb, Zn, Tl, Cd, Cu, As, Ag, Co, Cr and Ni) in farmland soils distributed over ten different villages from a former artisanal zinc smelting area in the northwest Guizhou province, China. The results showed that most of the studied soils still exhibited exceptionally high enrichment of Pb, Zn, Cd and As. High levels of bioavailable HMs were also observed in some samples, which may enter the human food chain through agricultural activities. Further analyses by Scanning Transmission Electron Microscopy - Energy Dispersive Spectroscopy (STEM-EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) showed the presence of Zn smelting by-products such as Fe oxides, ZnO and PbSO 4 even in nanoscale particles retained by the soils. Elemental mapping by EDS confirmed a close association of the studied HMs with the smelting waste particles. All these results signify that high levels of HM-contamination from historical artisanal zinc smelting activities still persist and threaten the health of local residents, despite the fact that the major industrial-derived-contamination period ended >15 years ago. Our findings highlight pivotal concerns in similar artisanal-smelting-affected farmland soils of suspected contamination, due to less-expected toxic elements such as Tl, which may cause high ecological health risks. Unlabelled Image • The farmland soils in a historical artisanal zinc smelting area were intensively investigated. • Typical Heavy metal(loid)s in farmland soils from ten different villages were analyzed. • Most of the studied soils still exhibited exceptionally high enrichment of Pb, Zn, Cd and As. • Zn smelting derived Fe oxides, ZnO and PbSO 4 were found in nanoscale particles in the soils. • It indicates that artisanal-smelting activity may pose long-term pollution hazards. [ABSTRACT FROM AUTHOR]