Thallium

The chemical properties of Tl can be used as key parameters to explain its ecological behaviour and occurrence as well as its action on living biota. This review presents recent knowledge from the molecular level to symptoms of illness. Tl mainly occurs in Sulfides and acid silicates. After weathering or thermal volatilization, it is quite mobile in soils, sediments and subsurface clays as a monovalent cation. Monovalent Tl is similar to K with respect to fit into the silicate lattice, complex formation, solubility and Sorption properties. Inside the living cell, however, stronger affinities towards S‐ and P‐ containing ligands lead to substitution of K at specific adsorption sites. This interferes with K‐metabolism and, in many cases, with the formation of ATP by respiration. Pathological changes have been documented in mitochondria and ribosomes, as well in peripherous nerve cells, liver cells and renal tissues. Muscle cells are activated by Tl similar to K. Contrary to many other metal cations, actions of Tl are mainly reversible. Some microorganisms get accustomed to higher Tl‐levels by using Tl like K. Main toxic effects on animals and man are observed in the nervous and digestion/excretion systems. The blood‐liquor barrier protects man and animals, leaving the plankton in aquatic ecosystems more sensitive to Tl pollution than fish. In green plants, protein binding is limited and uptake and effects are highly variable. Rape strongly accumulates thallium, bound to a low molecular species, without showing symptoms. As a therapy against intoxication, enforced excretion and supply of K have been successfully used.

Key words:

• Thallium
• review
• geochemical cycling of Tl
• toxicology of Tl
• effects of Tl