Thallium poisoning

Thallium poisoning
Other names	Thallium Toxicity
Thallium
Specialty	Toxicology

Thallium poisoning is poisoning that is due to thallium and its compounds, which are often highly toxic.^[1] Contact with skin is dangerous and adequate ventilation should be provided when melting this metal.^[2] Many thallium compounds are highly soluble in water and are readily absorbed through the skin.^[3] Exposure to them should not exceed 0.1 mg per m² of skin in an 8 hour time-weighted average (40- hour working week).

Part of the reason for thallium's high toxicity is that when present in aqueous solution as the univalent thallium(I) ion (Tl⁺) it exhibits some similarities with essential alkali metal cations, particularly potassium (owing to similar ionic radii). It can thus enter the body via potassium uptake pathways.^[4] Other aspects of thallium's chemistry differ strongly from that of the alkali metals, such as its high affinity for sulfur ligands. Thus this substitution disrupts many cellular processes by interfering with the function of proteins that incorporate cysteine, an amino acid containing sulfur.^[5] Thallium was originally used as rat poison, but was discontinued due to the exposure risk.

Among the distinctive effects of thallium poisoning are peripheral nerve damage (victims may experience a sensation of "walking on hot coals") and hair loss (which led to its initial use as a depilatory before its toxicity was properly appreciated). However hair-loss generally occurs only with low doses; with high doses the thallium kills before hair loss can occur.^[6] Thallium was an effective murder weapon before its effects became understood and an antidote (Prussian blue) was discovered.^[7] Thallium is often imported for products like optical lenses and electronics. The US has not manufactured thallium since 1984. It has been called the "poisoner's poison" since it is colorless, odorless and tasteless; its slow-acting, painful and wide-ranging symptoms are often suggestive of a host of other illnesses and conditions.^[8]