Category: Illness or disabilities
Introduction and description
Thallium is classified as a heavy metal. It is a chemical element with the symbol Tl and atomic number 81. When isolated, thallium resembles tin, but discolours when exposed to air.
Chemists William Crookes and Claude-Auguste Lamy discovered thallium independently in 1861, in residues of sulfuric acid production. Both used the newly developed method of flame spectroscopy, in which thallium produces a notable green spectral line. Thallium, from Greek θαλλός, thallós, meaning "a green shoot or twig", was named by Crookes. It was isolated by both Lamy and Crookes in 1862; Lamy by electrolysis, and Crookes by precipitation and melting of the resultant powder. Crookes exhibited it as a powder precipitated by zinc at the International exhibition, which opened on 1 May that year.
Above: Pieces of very pure thallium in glass ampoule under argon. Image: W. Oelen
Thallium and its compounds are extremely toxic, with numerous recorded cases of fatal thallium poisoning. Although it seems extraordinary, thallium salts were used in the past to treat syphilis, gonorrhoea, tuberculosis and ringworm (tinea corporis). Needless to say, by the early 1930s numerous cases of thallium poisoning, with some causing death were being reported.
Thallium poisoning is via ingestion, inhalation or absorption through the skin. The lethal dose for humans is 15-20 mg/kg, although much smaller doses have also led to death. Non-lethal doses cause toxic effects. Prolonged exposure may lead to build-up and chronic poisoning. Thallium poisoning has been caused by:
- Occupational exposure - from the maintenance and cleaning of ducts and flues at smelting plants where thallium particles can be breathed in.
- Accidental ingestion of rat poison – thallium is water soluble and nearly tasteless so any residue from touching rat poison could be ingested or absorbed through the skin.
- Drug contamination - Cocaine, heroin and herbal products have been contaminated with thallium.
- Food - Eating food such as fish and shellfish contaminated with thallium.
- Living near hazardous waste sites - containing thallium that have contaminated the air and soil and have resulted in higher than normal exposures.
- Deliberate poisoning. - we also have an observaton that provides some examples
Right above Thallium sulphate
MMWR Morb Mortal Wkly Rep. 2008 Sep 19;57(37):1015-8. Thallium poisoning from eating contaminated cake--Iraq, 2008. Centers for Disease Control and Prevention (CDC).
Thallium is an odorless, tasteless, heavy metal formerly used in rodenticides and still used in some manufacturing processes (e.g., electronics, pharmaceuticals, and glass). Thallium has also been used for intentional poisonings. …… On January 22, 2008, 10 of 12 members in two families in Baghdad, Iraq, developed gastrointestinal symptoms; four of those 10 persons subsequently died from acute thallium poisoning, and five developed neurologic symptoms but survived. The Jordan Field Epidemiology Training Program investigated this cluster at the request of the World Health Organization (WHO) representative in Iraq. The preliminary investigation indicated this was an intentional poisoning, PMID: 18802411
The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for thallium exposure in the workplace as 0.1 mg/m2 skin exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) also set a recommended exposure limit (REL) of 0.1 mg/m2 skin exposure over an 8-hour workday. At levels of 15 mg/m2, thallium is immediately dangerous to life and health. Thallium(I) compounds have a high aqueous solubility and are readily absorbed through the skin, cutaneous absorption can exceed the absorbed dose received by inhalation at the permissible exposure limit (PEL).
Thallium is also extremely dangerous environmentally and becoming more of a problem. Its main entry into the environment is from coal-burning and smelting where it stays in the air, water and soil for a long time. It is absorbed by plants and can build up in fish and shellfish, where it enters the food chain.
Presence of thallium in the environment: sources of contaminations, distribution and monitoring methods - Bozena Karbowska
Thallium is released into the biosphere from both natural and anthropogenic sources. It is generally present in the environment at low levels; however, human activity has greatly increased its content. Atmospheric emission and deposition from industrial sources have resulted in increased concentrations of thallium in the vicinity of mineral smelters and coal-burning facilities. Increased levels of thallium are found in vegetables, fruit and farm animals. Thallium is toxic even at very low concentrations and tends to accumulate in the environment once it enters the food chain. Thallium and thallium-based compounds exhibit higher water solubility compared to other heavy metals. They are therefore also more mobile (e.g. in soil), generally more bioavailable and tend to bioaccumulate in living organisms.
The paper indicates that it is found in fly ash originating from industrial combustion of coal, in surface and underground waters, in soils and sediments (including soil derived from different parent materials), and in numerous plant and animal tissues.
In the 1920s thallium sulfate found widespread use as a pesticide. In the South American country of Guyana, more than 40 people died from its (mis)use. The reason was that the pesticide, which was spread around in an attempt to kill rats, was absorbed by plants, and then entered the food chain, increasing in concentration, until it was eventually ingested by humans in meat or vegetable foods. Its use was not discontinued in Guyana until 1987. Of the 2,400 people who had either their blood or urine tested, 77% tested positive for thallium poisoning, showing just how widespread the thallium poisoning had become in the environment.
In Israel its use as a rodenticide wiped out the brown fish owl – a local bird of prey that used to eat fish. The thallium compound had seeped into the rivers and lakes and poisoned the fish, which were then eaten by the owls.
Sources and extraction
Thallium is not found free in nature. It is ‘modestly abundant’ in the Earth's crust, with a concentration estimated to be about 0.7 mg/kg but is mostly found in association with potassium-based minerals in clays, soils, and granites, although it is not generally economically recoverable from these sources. The major source of thallium is the trace amount that is found in copper, lead, zinc, and other heavy-metal-sulfide ores.
Thallium is also found in the minerals crookesite TlCu7Se4 [see right above], hutchinsonite TlPbAs5S9, and lorándite TlAsS2 and as a trace element in iron pyrite. Several other thallium minerals, containing 16% to 60% thallium, occur in nature as complexes of sulfides or selenides that primarily contain antimony, arsenic, copper, lead, and/or silver. These minerals are rare, and they have had no commercial importance as sources of thallium.
Thallium can be extracted as a by-product of roasting iron pyrite for the production of sulfuric acid and can also be obtained from the smelting of copper, lead and zinc ores. Commercially, thallium is produced not from potassium ores, but as a by-product from refining of heavy-metal sulfide ores.
The Allchar deposit in southern Macedonia was the only area where thallium was actively mined. This deposit still contains an estimated 500 tonnes of thallium, and it is a source for several rare thallium minerals, for example lorándite.
Approximately 60–70% of thallium production is used in the electronics industry, and the remainder is used in the pharmaceutical industry and in glass manufacturing. Despite its toxicity and its known environmental effects it is still being considered [according to Wikipedia] for a host of new applications "Thallium(I) sulfide's electrical conductivity changes with exposure to infrared light therefore making this compound useful in photoresistors. Thallium selenide has been used in a bolometer for infrared detection. Doping selenium semiconductors with thallium improves their performance, thus it is used in trace amounts in selenium rectifiers." It is also used in infrared detectors. The radioisotope thallium-201 (as the soluble chloride TlCl) is used in small amounts as an agent in a nuclear medicine scan, during one type of nuclear cardiac stress test [!]. If we look at these uses in more detail:
- Rat poisons and insecticides - Soluble thallium salts (many of which are nearly tasteless) are toxic, and they were historically used in rat poisons and insecticides. Use of these compounds has been restricted or banned in some countries, because of their nonselective toxicity Thallium poisoning is more common in developing countries where thallium rat poisons are still available and where there are less rigorous health and safety workplace practices.
- Murder and suicide – thallium has been used to poison people and commit suicide.
- Electronics manufacturing – thallium sulphide and thallium selenide are used in electronic devices, switches, and closures, primarily for the semiconductor industry.
- Optical glass manufacturing – thallium bromide and iodide are used in infrared optical materials.
- Medical imaging – trace amounts of thallium are used as a contrast agent in the visualization of cardiac function and tumours.
- Other uses – high-temperature superconducting materials, gamma radiation detection equipment, low temperature thermometers, and green fireworks [despite its toxicity].
According to the United States Environmental Protection Agency (EPA), man-made sources of thallium pollution include gaseous emission of cement factories, coal-burning power plants, and metal sewers. The main source of elevated thallium concentrations in water is the leaching of thallium from ore processing operations.
Thallium sulfate poisoning, much like the deceptive appearance of the compound itself, has initial symptoms typical of a winter virus. This generally means that poisoning is often mistaken for a common cold or flu.
The symptoms are generally seen in the hours immediately after exposure and can include severe stomach aches as well as diarrhoea. 2-5 days after exposure to thallium the body’s response takes a more neurological turn with numbness and tingling, felt especially on the palms and soles of the feet. This is followed in the weeks after exposure with an increase in neurological symptoms such as comas and blindness.
The compound also affects the heart; initially increasing heart rate and later possibly causing circulatory disturbances that can lead to death. The time that the compound will take to kill you depends on many factors and ranges from as little as 6 days or up to 8 weeks.
Common symptoms include
- Hair loss - Sudden hair loss followed by diffuse alopecia is one of the characteristic dermatological signs of thallium poisoning. Hair loss due to atrophy of the hair follicles primarily affects the scalp, temporal parts of the eyebrows, the eyelashes, and the limbs. Axillary regions are less affected. Hair discoloration may also occur. Hair roots may have dark brown or black pigmentation. With chronic exposure, these darker regions appear in bands, demonstrating multiple thallium exposures.
- Skin problems - Skin rash, redness and scaling of the palms and soles, acneform or pustular eruptions of the face, crusted eczematous lesions.
- Nail lines - Transverse white lines on the nails (Mee’s lines) appear in the nail plate about one month after the poisoning.
Other symptoms may include, hypohidrosis (reduced sweating), anhidrosis (absence of sweating), palmar erythema, painful glossitis (sore tongue) with redness of the tip of the tongue, and stomatitis.
Acute and chronic symptoms
Thallium poisoning may present as an acute poisoning or as a chronic poisoning.
Acute thallium poisoning - Where large amounts of thallium have been ingested over a short period of time patients will show signs and symptoms of acute poisoning. The classic symptoms of acute thallium toxicity are:
- - Severe stomach pain, nausea, vomiting, and diarrhoea within 3-4 hours of exposure
- - Painful and rapidly progressing peripheral neuropathies (numbness, tingling and pain, especially on the soles and palms) about 2-5 days after exposure
- - Sudden hair loss that progresses to widespread alopecia about 2-3 weeks after exposure.
Left Yassar Arafat died of Thallium poisoning
Chronic thallium poisoning - occurs over months or years of exposure to thallium. Thallium can be absorbed through the skin, respiratory, and gastrointestinal tracts and builds up to reach toxic levels. Because the presentation of chronic thallium poisoning appears similar to other diseases, many cases of industrial thallium exposure may go undetected. Signs and symptoms of chronic poisoning include tiredness, headaches, depression, hallucinations, psychosis, dementia, poor appetite, leg pains, hair loss and disturbances of vision.
All patients with significant signs and symptoms of thallium poisoning should be admitted to hospital.
One of the main methods of removing thallium (both radioactive and stable) from humans, used by the medical profession, is to use Prussian blue, a material which absorbs thallium. We have an observation that describes its use.
References and further reading
Thallium - The MOST TOXIC METAL ON EARTH! - a youtube video
- Central nervous system effects in acute thallium poisoning 029495
- Graham Young and the mass poisonings 029498
- Hallucinations mark thallium poisoning in Estonia 029497
- Thallium poisoning - Experience with 50 patients 029496
- Thallium poisoning presenting as paresthesias, paresis, psychosis and pain in abdomen 029493
- Thallium poisoning: a review. 029494