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.

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.

Stable isotope fractionation of thallium as novel evidence for its geochemical transfer during lead­zinc smelting activities.

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

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 isotopic fractionation in industrial process of pyrite smelting and environmental implications.

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 ε205Tl value of +1.28. The fluidized-bed furnace slag generated by high-temperature smelting had the heaviest ε205Tl (+16.24) in the system. Meanwhile, the boiler fly ash (ε205Tl = +8.34), cyclone fly ash (ε205Tl = +2.17), and electrostatic precipitation fly ash (ε205Tl = -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.

Thallium contamination in farmlands and common vegetables in a pyrite mining city and potential health risks.

Thallium (Tl) is a trace metal of severe toxicity. Its health concerns via consumption of contaminated vegetables have often been overlooked or underestimated. This study was designed to gain insight into the actual level and distribution characteristics of Tl and metal (loid)s (Pb, Cd, Cr, Sb, Mn, Cu, Zn, Ni, and Co) in agricultural soils and common vegetables cultivated in different zones (upstream, midstream, and downstream) of a densely populated residential area in a typical mine city, which has been open-pit exploiting Tl-bearing pyrite minerals since 1960s. The results show that most of the agricultural soils exhibit contaminated levels of Tl, with Tl contents (upstream: 1.35-4.31 mg/kg, midstream: 2.43-5.19 mg/kg, and downstream: 0.65-2.33 mg/kg) mostly exceeding the maximum permissible level (MPL) for agricultural land use (1 mg/kg). Sequential extraction procedure indicates that even Tl is predominantly retained in the residual fraction, significant levels of Tl are still present in the geochemically mobile fractions. Besides, metals like Cu, Cd, Mn, and Co are mostly distributed in the labile fractions. Almost all metal (loid)s in edible parts of the vegetables exceed their corresponding MPL for consumption. The chronic daily intake (CDI) and hazard quotient (HQ) values calculated for inhabitants at different ages indicate non-negligible Tl risks via consumption of local vegetables, especially for children. Therefore, it is critical to establish effective measures for hazardous waste management and enforceable regulations in Tl-polluted area to mitigate potential severe impacts of Tl on human health through food chain.

Provenance of uranium in a sediment core from a natural reservoir, South China: Application of Pb stable isotope analysis.

As part of ongoing environmental investigations of U mining impacts, forty-two sediment samples of a nearly-half-meter-long sediment core retrieved from a natural reservoir near an active uranium (U) mining site, South China were analyzed to quantify the extent of U release and identify U release mechanism within the riverine catchment. Enrichment levels of U was dispersed not only in the surface sediments but also in deep sediments across the depth profile. Further analysis by SEM-EDS and XRD indicated that U partitioning in the depth profile was possibly controlled by complicated interplay of leaching and precipitation cycles of U-bearing minerals. Even with the relative complexity of U dispersal processes within the catchment, the Pb isotopic fingerprinting techniques allowed quantification of source inputs of the sediments by using a binary mixing model. The results revealed that along the depth profile, only 6%-50% of the sediment material is anthropogenically derived from the U ore tailing, with the other predominant proportions originated from geogenically natural weathering of granitic bedrocks. This study highlights the use of Pb isotopes as a powerful tool for quantitatively fingerprinting the sources of U dispersal in the sediment core, and natural-occurring U contamination that may become a hidden geoenvironmental health hazard in this area.

[High-precision in situ analysis of the lead isotopic composition in copper using femtosecond laser ablation MC-ICP-MS and the application in ancient coins].

In the present study we set up a femtosecond laser ablation MC-ICP-MS method for lead isotopic analysis. Pb isotopic composition of fifteen copper (brass, bronze) standard samples from the National Institute of Standards Material were analyzed using the solution method (MC-ICP-MS) and laser method (fLA-MC-ICPMS) respectively, the results showed that the Pb isotopic composition in CuPb12 (GBW02137) is very homogeneous, and can be used as external reference material for Pb isotopic in situ analysis. On CuPb12 112 fLA-MC-ICPMS Pb isotope analysis, the weighted average values of the Pb isotopic ratio are in good agreement with the results analyzed by bulk solution method within 2sigma error, the internal precision RSEs of the 208 Pb/204 Pb ratio and 207 Pb/206 Pb ratio are less than 90 and 40 ppm respectively, and the external precision RSDs of them are less than 60 and 30 ppm respectively. Pb isotope of thirteen ancient bronze coins was analyzed via fLA-MC-ICPMS, the results showed that the Pb isotopic composition of ancient coins of different dynasties is significantly different, and not all the Pb isotopic compositions in the coins even from the same dynasty are in agreement with each other.