Thallium was independently discovered by the British chemist William Crookes and the French chemist Clade-Auguste Lamy in 1861 following the development of flame spectroscopy. After observing a bright green line in his new instrument, Crookes named the new element thallium after the Greek thallós meaning "green shoot".
Thallium is distributed at low concentrations widely across the earth's crust but has very few commercial applications. Thallium is perhaps most famous for being incredibly toxic. Compounds of thallium, such as thallium sulphate, are tasteless and have previously been used in rat poisons. The use of thallium as a rat poison was banned in the UK in 1965 after numerous incidents of accidental poisoning.
Other commercial applications of thallium include the electronics industry. The electrical conductivity of some thallium compounds changes with exposure to infrared light and is therefore used in the manufacture of photoresistors. Radioactive isotopes of thallium have previously been used in nuclear medicine but have now been replaced with less toxic isotopes such as those of technetium.
Recent research has identified thallium barium calcium copper oxide (TBCCO) compounds as being suitable for use as high temperature super-conductors with potential for being used in medical imaging.
Thallium is extremely toxic to all animals and can enter the body through ingestion, inhalation, and through the skin, making it extremely dangerous. Thallium poisoning was a preferred method of political assassination used by Saddam Hussein's secret police and is also thought to have been used by agents of both the KGB and CIA during the cold war.
The exact mechanism of thallium toxicity is not well understood and has not been extensively studied. It is thought that thallium interferes with important biochemical pathways such as those regulated by potassium.
Whilst exposure to high doses of thallium can be lethal within days, exposure to much smaller amounts of thallium can also be harmful to our health as thallium accumulates within our bodies. Symptoms of thallium poisoning include hair loss, abdominal pain, paralysis, nerve and joint pain, damage to the nervous system, and heart failure.
Thallium is present in many ores and can leach into ground waters used for drinking water supplies. A 2016 academic study in northern Tuscany, Italy, led to a do not drink order being imposed by the authorities after ground water containing 9,000 ppb of thallium was found.
The US Environmental Protection Agency (EPA) has imposed a maximum contamination level for thallium of 2 ppb. Neither the World Health Organisation nor the EU guidance documents on drinking water contamination levels provide limits for thallium.
Thallium in your drinking water can be detected by the following tests.
Thallium can be reduced or removed from your drinking water using the following methods.
