Tl Toxicity Research Articles

Thallium Use, Toxicity, and Detoxification Therapy: An Overview

Thallium (Tl) is released into the environment, where is present at very low levels, from both natural and anthropogenic sources. Tl is considered as one of the most toxic heavy metals; it is a non-essential metal, present in low concentrations in humans. Tl toxicity causes dermatological and gastrointestinal diseases and disorders of the nervous system, and may even result in death. Many isotopes of Tl exist, with different uses. One of the isotopes of this metal (201Tl) is used in cardiovascular scintigraphy and for the diagnosis of malignant tumors such as breast or lung cancer and osteosarcoma bone cancer. Many Tl compounds are tasteless, colorless, and odorless. Due to these characteristics and their high toxicity, they have been used as poisons in suicides and murders for criminal purposes, as well as instances of accidental poisoning. Impaired glutathione metabolism, oxidative stress, and disruption of potassium-regulated homeostasis may play a role in the mechanism of Tl toxicity. Solanum nigrum L. and Callitriche cophocarpa have been suggested as promising agents for the phytoremediation of Tl. In addition, macrocyclic compounds such as crown ethers (18-crown-6) are good candidates to absorb Tl from wastewater. Through this review, we present an update to general information about the uses and toxicity of Tl. Furthermore, the attention is focused on detoxification therapies.

Thallium in aquatic environments and the factors controlling Tl behavior.

Although thallium (Tl) usually exists in a very low level in the natural environment, it is highly toxic. With the development of mining and metallurgical industry and the wide application of Tl in the field of high technologies, Tl poses an increasing threat to the ecological environment and human health. This paper summarizes the research results of the toxicity of Tl as well as the distribution, occurrence forms, migration, and transformation mechanism of Tl in rivers, lakes, mining areas, estuaries, coastal waters, and oceans. It also discusses the influence mechanisms of pH, redox potential, suspended particulate matters, photochemical reaction, natural minerals, cation/anion, organic matters, and microorganisms on the environmental behavior of Tl. This paper points out the shortcomings of Tl research methods in water environment, and looks forward to the future development directions: First, the technology for separating Tl(III) and Tl(I) is still immature, especially it is difficult to effectively separate Tl(III) and Tl(I) in seawater. Second, the development of many advanced in situ detection technologies will bring great convenience to the studies of the dynamic mechanisms of Tl migration and transformation in the environments. Third, adsorption is the most effective mechanism to remove Tl from water, in which modified metal oxides or macrocyclic organic compounds have high application potential.

Releasing Characteristics and Biological Toxicity of the Heavy Metals from Waste of Mercury-Thalliummine in Southwest Guizhou of China

In this paper, the releasing characteristics and biological toxicity of Tl, Hg, As and Sb in waste of Lanmuchang mercury-thallium mine were studied. The results indicated that strong acidity can significantly promote the release of Tl from waste. With the increase of pH, the release of Sb grew steadily, while Hg and As showed a trend of first increasing and then decreasing. Fe2(SO4)3 contributed less to the release of As and Sb than to that of Hg and Tl. FeCl3 significantly inhibited the release of As, Sb and Tl. In the leaching experiments of litter and root exudates, the lixiviums appeared neutral, and the litter and root exudates solution significantly reduced the release of Tl, and showed less toxicity to luminescent bacteria. However, they promoted the release of Hg, As and Sb at different levels.

Chronic toxicity of waterborne thallium to Daphnia magna.

There is limited information regarding the toxicity of the trace element thallium (Tl) to aquatic biota, most of which assesses acute toxicity and bioaccumulation. The relative lack of chronic Tl toxicity data compromises the establishment of water quality criteria for this trace metal. In the presented work, chronic toxicity endpoints (final body weight (a proxy measure of growth), survival, and reproduction) and Tl body burden were measured in the freshwater crustacean Daphnia magna during a 21-day exposure to dissolved Tl. Thallium caused complete mortality in daphnids between exposure concentrations of 424 and 702μgL-1. In contrast with previously published work examining acute Tl toxicity, exposure to Tl for 21 days was not associated with changes in whole-body potassium concentration. This was despite a 710-fold increase in Tl body burden in animals exposed to 424μgL-1 relative to the control. Median effect concentrations (EC50's) for growth and reproduction (total neonates produced), were 1.6 (95% confidence interval: 1.0-3.1) and 11.1 (95% confidence interval: 5.5-21.8) μg Tl L-1, respectively. A no observable effect concentration (NOEC) of 0.9μgTl L-1 for growth, and a NOEC range of 0.9-83μgTl L-1 for a variety of reproductive metrics, was measured. A lowest observable effect concentration (LOEC) of 8.8μgTl L-1 was determined for the effects of Tl on growth and most of the reproductive endpoints examined. These data indicate that under controlled laboratory conditions D.magna is significantly less sensitive to Tl than the species on which the current Canadian Council of Ministers of the Environment regulatory guideline value of 0.8μgL-1 is based.

Interactions of thallium with marine phytoplankton

Thallium (Tl) is the most toxic metal for mammals, likely due to its chemical similarity to the bioessential potassium (K). The biogeochemical cycle of Tl is susceptible to perturbation from a number of anthropogenic activities. Tl accumulation in the food chain may cause chronic Tl poisoning from dietary intake for human beings. However, Tl accumulation in the marine biosphere has largely been overlooked because high concentrations of K are thought to inhibit any uptake of Tl by organisms. Here, for the first time, high accumulation of Tl in the cytosol by the ubiquitous and abundant marine phytoplankton Emiliania huxleyi was found, making it readily transferable to higher trophic levels. Dose-response and physiological data were presented from a range of 9 species of phytoplankton under a wide range of Tl concentrations (1 ng L−1 to 1 mg L−1), spanning modern open ocean concentrations of 10–20 ng L−1, and higher concentrations in the coastal and fresh waters. Of all phytoplankton studied here, the cyanobacteria Synechococcus and the haptophytes Isochrysis galbana and Pavlova granifera have the largest tolerance to Tl toxicity, while the chlorophyte Micromonas pusilla has the least tolerance to elevated Tl. Haptophytes, especially isochrysidales, accumulated significantly more Tl intracellularly (up to 300-fold higher) than chlorophytes, making them good candidates for Tl bioremediation studies. Potassium transporters from E. huxleyi are found to be different from all other phytoplankton in this study based on analyses of the proteome. Since Tl is well known to be taken into cells by mistake through potassium channels, the difference of K channels in E. huxleyi may be responsible for its highest accumulation of Tl. As one of the most widely distributed phytoplankton in the ocean, the bioaccumulation of Tl in E. huxleyi may transfer and concentrate through the marine food chain and have significant impacts on the Tl biogeochemical cycle in the modern ocean.

The Effect of Major Ions and Dissolved Organic Matter on Complexation and Toxicity of Dissolved Thallium to Daphnia magna.

Thallium (Tl) is a trace element associated with base metal mining and processing, but little is known regarding how its toxicity is influenced by water chemistry. In the present study, the 48-h median lethal concentration (LC50) of Tl to Daphnia magna was determined in a standard laboratory water, and toxicity was reassessed under conditions of varying cation (Ca2+ , K+ , Na+ ), anion (Cl- , HCO-3 ), and dissolved organic matter (DOM) concentrations. The calculated 48-h LC50 of 1.86 mg Tl/L was consistent with previous work on Tl toxicity to D. magna. At the 48-h LC50 concentration, changes in water chemistry had no statistically significant effect on mortality, although there was a trend toward lower Tl toxicity with elevated water K+ . Test waters containing 10 mM CaCl2 did not support control survival. The measurement of Tl complexation with DOM using asymmetric flow field flow fractionation confirmed the outcomes of biogeochemical speciation modeling: Tl speciation was relatively unaffected by water chemistry, and the majority of Tl remained in the ionic form across all treatments. These data indicate that Tl toxicity is largely independent of speciation, a property that will greatly simplify risk assessments for this metal in freshwaters. Environ Toxicol Chem 2019;38:2472-2479. © 2019 SETAC.

Solid-phase distribution and mobility of thallium in mining-metallurgical residues: Environmental hazard implications

Thallium (Tl) and its compounds are non-essential and highly toxic for living organisms, even at low concentrations. In this paper, we analyzed the presence and geochemical distribution of Tl in different mining-metallurgical and sediment samples collected from several mining zones of Mexico. A modified BCR sequential extraction procedure was also applied to the samples to investigate the geochemical behavior and potential environmental risk of Tl according to types of ore deposit and mineral processing method applied. Results revealed the presence of Tl in the majority of the mining-metallurgical samples, with labile concentrations reaching up to values of 184.4 mg kg−1, well above the environmental standards. A comparison of Tl partitioning in different samples showed that Tl was usually found associated with labile fractions instead of entrapped in the environmentally-passive residual fraction. Specifically, high levels of Tl were extracted from the exchangeable/acid-extractable and poorly-crystalline reducible fractions, suggesting its association with both soluble and amorphous Fe-Mn oxyhydroxides, respectively. Besides, Tl was also frequently found associated with the crystalline reducible fraction, presumably bonded to manganese oxides and jarosite-like minerals. Lastly, little amounts of Tl were extracted from the oxidizable fraction. Considering the fractionation of Tl in these mining-metallurgical samples, they may pose a significant environmental hazard. This study provides useful insights into the potential sources of Tl pollution in Mexico and emphasizes the need for further research to determine the extent of its impact and to develop effective remediation protocols to protect the environment from Tl toxicity.

Thallium Intoxication in Relation to Drug Abuse and Cigarette Smoking in Iran

Thallium (Tl) is a highly toxic heavy metal with atomic number 81. It is a soft, bluish-white or gray water-insoluble metal but the salt forms are colorless, tasteless, and odorless. Tl is readily absorbed via ingestion, inhalation, and dermal contact. Any amount of Tl in the body is abnormal. The clinical manifestation of thallotoxicosis has a wide spectrum but painful ascending peripheral neuropathy, gastrointestinal, and dermatologic manifestations are major characteristics in Tl toxicity. Tl intoxication has been identified in drug abuse and cigarette smoking leading to various signs and symptoms. Substance abuse and cigarette smoke are a major public health hazard across the world.

Physiological response of Arundo donax L. to thallium accumulation in a simulated wetland

A simulated wetland experiment was used to investigate the effect of thallium (Tl) accumulation on the growth of Arundo donax L., its photosynthetic characteristics and its antioxidant enzyme activities. Tl accumulated in the order of stems<leaves<roots and increased gradually with increasing Tl concentrations (from 0 to 2.5µgL–1). Moderate Tl applications (from 0.2 to 2.5µgL–1) increased the rate of both photosynthesises (Pn) and transpiration (Tr), as well as catalase and peroxidase activity. Tl significantly affected stomatal conductivity, but had no effect on the relative chlorophyll content (SPAD values) or the potential and effective photochemical efficiency of photosystem II. However, intercellular CO2 concentrations and superoxide dismutase decreased in response to increasing Tl concentrations. Although 50µgL–1 Tl significantly decreased the SPAD values, as well as the potential and effective photochemical efficiency of photosystem II, it had no effect on Pn or Tr. These results suggest that root restriction and oxidative stress are involved in the mechanism of Tl toxicity, but the photosynthetic system of A. donax was not harmed by certain concentrations of Tl, indicating the strong tolerance of this species to increased Tl pollution.

Redox-controlled release dynamics of thallium in periodically flooded arable soil

To our knowledge, this is the first work to mechanistically study the impact of the redox potential (EH) and principal factors, such as pH, iron (Fe), manganese (Mn), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), chlorides (Cl−) and sulfates (SO42-), on the release dynamics of thallium (Tl) in periodically flooded soil. We simulated flooding using an automated biogeochemical microcosm system that allows for systematical control of pre-defined redox windows. The EH value was increased mechanistically at intervals of approximately 100 mV from reducing (−211 mV) to oxidizing (475 mV) conditions. Soluble Tl levels (0.02–0.28 μg L−1) increased significantly with increases in EH (r = 0.80, p < 0.01, n = 30). Thallium mobilization was found to be related to several simultaneous processes involving the gradual oxidation of Tl-bearing sulfides, reductive dissolution of Fe-Mn oxides and desorption from mineral sorbents. Manganese oxides did not appear to have a considerable effect on Tl retention under oxidizing conditions. Before conducting the microcosm experiment, Tl geochemical fractionation was assessed using the modified BCR sequential extraction procedure. The BCR revealed a majority of Tl in the residual fraction (77.7%), followed by reducible (13.3%) and oxidizable fractions (5.9%). By generating high levels of Tl toxicity at low doses, Tl released under oxidizing conditions may pose an environmental threat. In the future, similar studies should be conducted on various soils along with a determination of the Tl species and monitoring of the Tl content in plants to achieve more detailed insight into soluble Tl behavior.

Thallium Toxicity in Mediterranean Horticultural Crops (Fragaria vesca L., Mentha pulegium L., Ocimum basilicum L.)

Thallium is a non-essential, toxic element that concerns mining areas and their acid drainage effluents. Minerals containing thallium can be eroded, and Tl can be leached into soil, thus being spread into the environment and adsorbed by plants and living organisms, entering the food chain, and inducing serious toxicity problems. In this study, the Tl cycle was observed and analyzed on basil, mint, and strawberry cultivated in a greenhouse and irrigated with Tl-contaminated water. The Tl content in both bulk and rhizosphere soils as well as thallium present in different plant organs were analyzed during the experiment, with the aim of revealing both physiological symptoms and metabolic disorders linked to the Tl toxicity. The mechanism of plants to exclude, uptake, translocate, and tolerate Tl varied among the different species, and both the bioconcentration factor (BCF) and the translocation index (TI) were calculated to highlight a different response to Tl toxicity of strawberry, mint, and basil. Basil is the less tolerant species, while mint and strawberry showed different self-defense mechanism against Tl adsorption and translocation.

Bismuth chalcohalides and oxyhalides as optoelectronic materials

Several Tl and Pb based halides and chalcohalides have recently been discovered as promising optoelectronic materials [i.e., photovoltaic (PV) and gamma-ray detection materials]. Efficient carrier transport in these materials is attributed partly to the special chemistry of $n{s}^{2}$ ions (e.g., $\mathrm{T}{\mathrm{l}}^{+}, \mathrm{P}{\mathrm{b}}^{2+}$, and $\mathrm{B}{\mathrm{i}}^{3+}$). However, the toxicity of Tl and Pb is challenging to the development and the wide use of Tl and Pb based materials. In this paper, we investigate materials that contain $\mathrm{B}{\mathrm{i}}^{3+}$, which is also an $n{s}^{2}$ ion. By combining Bi halides with Bi chalcogenides or oxides, the resulting ternary compounds exhibit a wide range of band gaps, offering opportunities in various optoelectronic applications. Density functional calculations of electronic structure, dielectric properties, optical properties, and defect properties are performed on selected $\mathrm{B}{\mathrm{i}}^{3+}$ based chalcohalides and oxyhalides, i.e., BiSeBr, BiSI, BiSeI, and BiOBr. We propose different applications for these Bi compounds based on calculated properties, i.e., $n$-BiSeBr, $p$-BiSI, and $p$-BiSeI as PV materials, BiSeBr and BiSI as room-temperature radiation detection materials, and BiOBr as a $p$-type transparent conducting material. BiSeBr, BiSI, and BiSeBr have chain structures while BiOBr has a layered structure. However, in BiSI, BiSeI, and BiOBr, significant valence-band dispersion is found in the directions perpendicular to the atomic chain or layer because the valence-band edge states are dominated by the halogen states that have strong interchain or interlayer coupling. We find significantly enhanced Born effective charges and anomalously large static dielectric constants of the Bi compounds, which should reduce carrier scattering and trapping and promote efficient carrier transport in these materials. The strong screening and the small anion coordination numbers in Bi chalcohalides should lead to weak potentials for electron localization at anion vacancies. Defect calculations indeed show that the anion vacancies (Se and Br vacancies) in BiSeBr are shallow, which is beneficial to efficient electron transport.

The acute toxicity of thallium to freshwater organisms: Implications for risk assessment

The acute toxicity of Tl(I) to the microalga, Pseudokirchneriella subcapitata, the planktonic crustaceans, Daphnia magna and Daphnia pulex, and early-life stage of the zebrafish, Danio rerio, has been studied according to OECD protocols. Toxicological end-point concentrations for the microalga ranged from 17μgl−1 for a 72h EyC25 (yield inhibition) to 80μgl−1 for a 72h ErC50 (growth inhibition). Daphnia were less sensitive to Tl, with 48h EC50s of about 1000μgl−1 and 1200μgl−1 for D. magna and D. pulex, respectively; however, end-point concentrations were reduced considerably (to about 510μgl−1 and 730μgl−1, respectively) when experiments were repeated in dechlorinated Plymouth tap water (rather than OECD medium). The 96h LC50 for D. rerio was 870μgl−1 but a variety of sub-lethal effects, including enlargement of yolk sac and reduction in heart beat rate, were observed when larvae were exposed to lower concentrations. Based on these results, a predicted no effect concentration (PNEC) for Tl in freshwaters of 0.087μgl−1 is proposed. The PNEC is an order of magnitude lower than the only (Canadian) water quality guideline for Tl that appears to exist, and is lower than Tl concentrations reported in freshwaters impacted by historical or contemporary metal mining. Our results are also consistent with previous studies that employ different organisms and end-points in that Tl toxicity is dependent on the concentration of K+, the biogeochemical analogue of Tl+. Accordingly, regulation of Tl in the freshwater environment should factor in the relative abundance of K.

Health risks of thallium in contaminated arable soils and food crops irrigated with wastewater from a sulfuric acid plant in western Guangdong province, China

Thallium (Tl) contamination in soils poses a significant threat to human health due to the high toxicity of Tl and its ready assimilation by crops. Consumption of food crops contaminated with Tl is a major food chain route for human exposure. The health risks of Tl in contaminated food crops irrigated with wastewater from a sulfuric acid factory were investigated in this paper. Results indicate that long-term Tl-containing wastewater irrigation resulted in Tl contamination of arable soils and crops. The pollution load index values indicated that the arable soils were moderately enriched with Tl. Tl was highly accumulated in the crops. The content of Tl in the edible plant portions of crops ranged from 1.2mg/kg to 104.8mg/kg, exceeding the recommended permissible limits for food crops. The daily intake of metals (DIM) values of Tl for both adults and children via the consumption of the food crops except soya beans were higher than the reference oral dose (RfD) limit recommend by the United States environmental protection agency (US-EPA). Health risk index (HRI) values were generally higher than 1, indicating that health risks associated with Tl exposure are significant and assumed to be dangerous to the health of local villagers. Therefore, much attention should be paid to avoid consumption of these Tl-contaminated crops that can cause great potential risks.

An evaluation of the toxicity and bioaccumulation of thallium in the coastal marine environment using the macroalga, Ulva lactuca

Thallium(I) has been added to cultures of the marine macroalga, Ulva lactuca, for a period of 48h and the accumulation of the metal and its effects on the photochemical efficiency of photosystem II (PS II) measured. Thallium elicited a measurable toxic response above concentrations of 10μgL−1 in both coastal seawater (salinity 33) and estuarine water (salinity 20). The accumulation of Tl was defined by a linear relationship with aqueous Tl and accumulation factors of about 900mLg−1 in both media. Thallium accumulated by U. lactuca that was resistant to an EDTA extraction and, by operational definition, internalised, exceeded 90% in both cases. Accumulation and toxicity of Tl in the presence of a ∼105-fold excess of its biogeochemical analogue, potassium, suggests that Tl has a high intrinsic phytotoxicity and that its mode of action involves permeation of the cell membrane as Tl+ through NaCl–KCl co-transporter sites rather than (or in addition to) transport through K+ ion channels.

Reductive Dissolution of Tl(I)–Jarosite by Shewanella putrefaciens: Providing New Insights into Tl Biogeochemistry

Thallium (Tl) is emerging as a metal of concern in countries such as China due to its release during the natural weathering of Tl-bearing ore deposits and mining activities. Despite the high toxicity of Tl, few studies have examined the reductive dissolution of Tl mineral phases by microbial populations. In this study we examined the dissolution of synthetic Tl(I)-jarosite, (H(3)O)(0.29)Tl(0.71)Fe(2.74)(SO(4))(2)(OH)(5.22)(H(2)O)(0.78), by Shewanella putrefaciens CN32 using batch experiments under anaerobic circumneutral conditions. Fe(II) concentrations were measured over time and showed Fe(II) production (4.6 mM) in inoculated samples by 893 h not seen in mineral and dead cell controls. Release of aqueous Tl was enhanced in inoculated samples whereby maximum concentrations in inoculated and cell-free samples reached 3.2 and 2.1 mM, respectively, by termination of the experiment. Complementary batch Tl/S. putrefaciens sorption experiments were conducted under experimentally relevant pH (5 and 6.3) at a Tl concentration of 35 μM and did not show significant Tl accumulation by either live or dead cells. Therefore, in contrast to many metals such as Pb and Cd, S. putrefaciens does not represent a sink for Tl in the environment and Tl is readily released from Tl-jarosite during both abiotic and biotic dissolution.

Study of acute biochemical effects of thallium toxicity in mouse urine by NMR spectroscopy

Thallium (Tl) is a toxic heavy metal and its exposure to the human body causes physiological and biochemical changes due to its interference with potassium-dependent biological reactions. A high-resolution (1)H NMR spectroscopy based metabonomic approach has been applied for investigating acute biochemical effects caused by thallium sulfate (Tl(2)SO(4)). Male strain A mice were divided in three groups and received three doses of Tl(2)SO(4) (5, 10 and 20 mg kg(-1) b.w., i.p.). Urine samples collected at 3, 24, 72 and 96 h post-dose time points were analyzed by (1)H NMR spectroscopy. NMR spectral data were processed and analyzed using principal components analysis to represent biochemical variations induced by Tl(2)SO(4). Results showed Tl-exposed mice urine to have distinct metabonomic phenotypes and revealed dose- and time-dependent clustering of treated groups. The metabolic signature of urine analysis from Tl(2)SO(4)-treated animals exhibited an increase in the levels of creatinine, taurine, hippurate and β-hydroxybutyrate along with a decrease in energy metabolites trimethylamine and choline. These findings revealed Tl-induced disturbed gut flora, membrane metabolite, energy and protein metabolism, representing physiological dysfunction of vital organs. The present study indicates the great potential of NMR-based metabonomics in mapping metabolic response for toxicology, which could ultimately lead to identification of potential markers for Tl toxicity.

Oxidative stress and DNA damage in broad bean (Vicia faba L.) seedlings induced by thallium

Thallium (Tl) is a metal of great toxicological concern because it is highly toxic to all living organisms through mechanisms that are yet poorly understood. Since Tl is accumulated by important crops, the present study aimed to analyze the biological effects induced by bioaccumulation of Tl in broad bean (Vicia faba L.) as well as the plant's antioxidative defense mechanisms usually activated by heavy metals. Thallium toxicity was related to production of reactive oxygen species in leaves and roots of broad bean seedlings following short-term (72 h) exposure to thallium (I) acetate (0, 0.5, 1, 5, and 10 mg/L) by evaluating DNA damage and oxidative stress parameters as well as antioxidative response. The possible antagonistic effect of potassium (K) was tested by combined treatment with 5 mg/L of Tl (Tl+) and 10 mg/L of potassium (K+) acetate. Accumulation of Tl+ in roots was 50 to 250 times higher than in broad bean shoots and was accompanied by increase in dry weight and proline. Despite responsive antioxidative defense (increased activities of superoxide dismutase, ascorbate peroxidase, and pyrogallol peroxidase), Tl+ caused oxidative damage to lipids and proteins as evaluated by malondialdehyde and carbonyl group levels, and induced DNA strand breaks. Combined treatment caused no oxidative alternations to lipids and proteins though it induced DNA damage. The difference in Tl-induced genotoxicity following both acellular and cellular exposure implies indirect DNA damage. Results obtained indicate that oxidative stress is involved in the mechanism of Tl toxicity and that the tolerance of broad bean to Tl is achieved, at least in part, through the increased activity of antioxidant enzymes.

Uptake of Thallium from Artificially and Naturally Contaminated Soils into Rape (Brassica napus L.)

An inductively coupled plasma mass spectrometry (ICP/MS) method was used for the evaluation of thallium transfer from naturally (pedogeochemically) and artificially contaminated soils into rape. Two sets of three different types of top soils (heavy, medium, and light) were used for pot experiments. The first set was collected from areas with high levels of pedogeochemical thallium (0.3, 1.5, and 3.3 mg kg(-1) DM). The second set of three soils with naturally low content of thallium was artificially contaminated with thallium sulfate to achieve five levels of contamination (0, 0.4, 2, 4, and 6 mg kg(-1) DM Tl). The soil samples and the samples of winter and spring rape (straw, seeds) from both sets were collected and analyzed. Plant and soil samples from fields were collected at 42 selected sites situated in South Bohemia and in Czech-Moravian Highlands where higher pedogeochemical content of thallium was expected. More intensive transport (better availability) of Tl was observed in the case of artificially contaminated soils. The physicochemical form and the total content of Tl in soil were found to be the main factors influencing its uptake by plants. The concentration of Tl in rapeseeds in the field samplings was mostly 45% of its content in the particular soil. Nevertheless the uptake of Tl from soils with naturally high pedogeochemical content can be high enough to seriously endanger food chains. These findings are very important because of the high toxicity of Tl and the absence of threshold limits for Tl in soils, agricultural products, feedstuffs, and foodstuffs in most countries including the Czech Republic.

Acute toxicity of trivalent thallium compounds to Daphnia magna

Daphnia magna was used to evaluate the aquatic toxicity of Tl(III) compounds including Tl(III) nitrate, Tl(III) chloride, and Tl(III) acetate. The results clearly show that Tl(III) is extremely toxic to daphnids. The 48-h LC 50 values for Tl(III) nitrate, Tl(III) chloride, and Tl(III) acetate are 24, 61, and 203 μg/L, respectively. Tl(III) is much more toxic than Tl(I) and many other metals such as Cd(II), Cu(II), and Ni(II); it is similar to the toxicity that of Hg(II). The formation of Tl(III)-complexes would significantly reduce Tl(III) toxicity.