# Thallium Use, Toxicity, and Detoxification Therapy: An Overview
## 8 Thallium Phytoremediation from Soil and Water  
Volcanoes and human activities, such as industrialization, pyrite mining and cement plants, the smelting of thallium-containing ones, and burning coal to produce energy are the major causes for the presence of toxic metal compounds in the ecosystem. Toxic metal pollution of soil, water and plants is a major environmental problem; heavy metals are not degradable and their accumulation in the soil and water can contaminate drinking water and the food chain (vegetables and fruits), with serious health effects for humans. Most conventional physical, chemical, and biochemical approaches do not provide solutions to these problems, and are often expensive and invasive, causing the alteration of soil properties and disturbing the soil microflora. Phytoremediation is a technology that uses plants to remove toxic and radioactive metals and organic compounds (pesticides, crude oils, and detergents) from the environment [73; 74; 75]. In the New Zealand laboratory of [PERSON] (2001) [76], vegetables such as green bean, green cabbage, betroot, lettuce, onion, pea, radish, spinach, tomato, turnip, water chess and Iberis intermediia were grown in pot trials in the presence of TI (0.7 mg/kg to 3.7 mg/kg) to study the capability of these plants to remove this metal from polluted soils. The results showed that the uptake of thallium ranged from about 1 mg/kg in green bean to 400 mg/kg in Iberis intermediia. The TI concentrations were analyzed by flame atomic absorption spectrometry (FAAS) for samples with higher thallium levels, or by graphite furnace atomic absorption spectrometry for samples with lower thallium concentrations. [PERSON], in their laboratory in Guangzhou (China) (2015) [28], evaluated the ability of black nightshade _Solanum nigrum_ L. for TI phytoremediation in pot culture. The accumulation of thallium into roots, stems, leaves and fruits were determined under field conditions. The results of [PERSON] and collaborators were examined using different thallium concentrations (from 1 mg/kg to 20 mg/kg) after a 4-month pot culture, and suggested _Solanum nigrum_ as a good candidate for the phytoremediation of thallium. Although it reduced growth, and chlorosis and leaf senescence were observed at a thallium concentration of \(\geq\)15 mg/kg, the authors recommended the choice of _Solanum nigrum_ for the phytoremediation of moderately thallium-contaminated soil. _Callitriche cophocarpa_ has been used for the phytoremediation of water polluted by thallium, cadmium, zinc, and lead [77]. The authors pointed out that the accumulation of the elements by _Callitriche cophocarpa_ shoots (mg/kg dry weight) followed this order: Zn (1120), TI (251), Cd (71) and Pb (35), whereas the bioconcentration factors were the highest for Cd (1177) and TI (1043). The authors found that _Callitriche cophocarpa_ was able to remove TI from polluted water as well as Cd, Zn and Pb. Due its high toxicity, the removal of thallium from wastewater is very important, even though its concentration is very low. Adsorption is a method used for thallium removal and infinite types of absorbent have been used, including Prussian blue analogues and metal oxide hydrates such as iron oxide, super-magnetic Fe\({}_{3}\)O\({}_{4}\), nano-Al\({}_{2}\)O\({}_{3}\)[78], titanate nano tubes [79], etc. However, the use of these absorbents did not give excellent results. [PERSON] et al. (2020) [80] provided new macrocyclic compounds such as crown ethers as absorbents for thallium removal from wastewater. Notably, the cavity of crown ethers must be able to efficiently contain Tl\({}^{+}\) ions to form a stable complex with negatively charged oxygen atoms. Considering the cavity of several crown ethers, thallium (Tl\({}^{+}\)) settles better in the cavity of 18-crown-6. Moreover, the oxygen atoms inside circle ether can be partially replaced with sulfur atoms to increase the affinity of the crown ether towards Tl\({}^{+}\).