Thallium

Thallium is known to produce alterations in the cellular gene expression machinery and the heme biosynthetic pathway. Ionic thallium appears to interfere with the process of ribosomal assembly, causing a number of structural changes in the endoplasmic reticulum in liver cells after acute in vivo injection. This is associated with alterations in the activities of several heme-pathway and heme-dependent enzyme systems [7].

It appears that thallium is capable of interfering with a number of subcellular systems and that these effects may predispose target cell populations to eventual carcinogenic susceptibility [7].

Thallium is a tasteless, odorless, and water-soluble chemical element, for which accidental and criminal intoxication has been reported. Also, the element is readily absorbed through the skin and by inhalation. Levels of 15 mg/m³ are considered immediately dangerous to the health [8].

Thallium is treated as potassium in the human body, at the cellular level. Thus the five major toxicologic effects seen with thallium toxicity are:

• tissues with high potassium concentrations also accumulate large concentrations of thallium. This causes early stimulation, followed by inhibition of potassium dependent processes. Inhibition of pyruvate kinase and succinate dehydrogenase leads to disruption of the Kreb’s cycle and glucose metabolism, resulting in decreased ATP production, swelling, and vacuolization due to impairment of the sodium-potassium ATPase [8]
• riboflavin sequestration due to thallium forming an insoluble complex with riboflavin [9]
• thallium’s high affinity for disulfide bonds disrupting cysteine residue cross-linking. This causes a reduction in keratin formation [8]
• ribosome damages by thallium’s effects on protein synthesis, especially the 60S ribosome [8]
• degeneration of myelin in the central and peripheral nervous systems, though mechanism yet unknown [8]