Thallium poisoning is poisoning that is due to thallium and its compounds, which are often highly toxic. Contact with skin is dangerous and adequate ventilation should be provided when melting this metal. Many thallium compounds are highly soluble in water and are readily absorbed through the skin. 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. 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. 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. Thallium was an effective murder weapon before its effects became understood and an antidote (Prussian blue) was discovered. 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.
Interactions
Thallium compounds The odorless and tasteless thallium sulfate was previously used as rat poison and ant killer. Since 1975, this use in the United States and many other countries is prohibited due to safety concerns.
Symptoms Thallium can enter the body through inhalation, absorption through the skin, or through ingestion. It can spread to the nervous system, liver, kidneys, adipose tissue, skin, and appendages. Acute symptoms of thallium exposure include stomach pain, diarrhea, and vomiting. More serious neurological symptoms do not appear until days after the metal has been ingested. These include: tremors, headache, insomnia, seizures, ataxia, ascending peripheral neuropathies, coma, and possible death. Nystagmus, diplopia, and other ocular effects are also common. After many weeks, those with thallium poisoning begin to present with dermatological symptoms such as acne-like abrasions, hypohidrosis, and alopecia.
Main causes Exposure from work Accidental ingestion Contaminated foods or drugs Exposure to hazardous waste sites Malicious intent (poisoning)
Diagnosis Thallium may be measured in blood or urine as a diagnostic tool in clinical poisoning situations or to aid in the medicolegal investigation of suspicious deaths. Normal background blood and urine concentrations in healthy persons are usually less than 1 μg/litre, but they are often in the 1–10 mg/litre range (1,000–10,000 times higher) in survivors of acute intoxication. Thallium is present in the blood for a very short time so urine testing is usually most appropriate. A quick way to assess possible thallium poisoning is to perform a microscopic analysis of a hair and its root. In thallium poisoning this analysis will show a tapered anagen hair with black pigmentation at the base (anagen effluvium). This is pathognomonic for thallium toxicity. Other ways of testing thallium levels include CBC blood tests, liver function tests, blood urea nitrogen, calcium, or electrolytes.
Treatment There are two main methods of removing both radioactive and stable isotopes of thallium from humans. The first known was to use Prussian blue (potassium ferric hexacyanoferrate), which is a solid ion exchange material, and absorbs thallium. Up to 20 g per day of Prussian blue is fed by mouth to the person, and it passes through their digestive system and comes out in the stool. Hemodialysis and hemoperfusion are also used to remove thallium from the blood stream. At a later stage of the treatment additional potassium is used to mobilize thallium from the tissue. Other methods of treatment are stomach pumping, use of activated charcoal, or bowel irrigation, depending on the prognosis.
Notable cases
There are numerous recorded cases of fatal thallium poisoning. Because of its use for murder, thallium has gained the nicknames "the poisoner's poison" and "inheritance powder" (alongside arsenic).
Australia's "Thallium Craze" In Australia, in the early 1950s, there was a notable spate of cases of murder or attempted murder by thallium poisoning. At this time, due to the chronic rat infestation problems in overcrowded inner-city neighbourhoods (notably in Sydney), and thallium's effectiveness as a rat poison, it was still readily available over the counter in New South Wales (NSW), where thallium(I) sulfate was marketed as a commercial rat bait, under the brand Thall-rat.
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