Thallium

Notable characteristics

 

This metal is very soft and malleable and can be cut with a knife. When it is first exposed to air, thallium has a metallic luster but quickly tarnishes with a bluish-gray tinge that resembles hydroxide is formed.

Applications

The odorless and tasteless thallium sulfate was widely used in the past as a rat poison and ant killer. In the United States and many other countries this use is no longer allowed due to safety concerns. Other uses:

• thallium sulfide's electrical conductivity changes with exposure to infrared light therefore making this compound useful in photocells.
• thallium bromide-crystals have been used as infrared optical materials, because they are harder than other common infrared optics, and because they have transmission at significantly longer wavelengths. The trade name KRS-5 referes to this material.
• thallium oxide has been used to manufacture glasses that have a high index of refraction.
• used in semiconductor materials for selenium rectifiers,
• in gamma radiation detection equipment,
• high-density liquid used for sink-float separation of minerals,
• used in the treatment of ringworm and other skin infections. However this use has been limited due to the narrow margin that exists between toxicity and therapeutic benefit.
• deuterons by the (p,3n) and (d,4n) reactions.^[6]

• combined with refractive indices.
• thallium amalgam is used in thermometers for low temperature, because it freezes at -58 °C (pure mercury freezes at -38 °C).

In addition, research activity with thallium is ongoing to develop high-temperature superconducting materials for such applications as magnetic resonance imaging, storage of magnetic energy, magnetic propulsion, and electric power generation and transmission.

History

Thallium (Greek θαλλός, thallos, meaning "a green shoot or twig")^[7] was discovered by green spectral emission lines. In 1862 Crookes and Claude-Auguste Lamy isolated the metal independently of each other.

Occurrence

Although the metal is reasonably abundant in the Earth's crust at a concentration estimated to be about 0.7 mg/kg, mostly in association with zinc, and other sulfide ores.

Thallium is found in the minerals Category:Thallium minerals.

Isotopes

Main article: isotopes of thallium

Thallium has 25 half-life of 3.78 years.

Thallium-202 (half life 12.23 days) can be made in a cyclotron^[8], while thallium-204 (half life 3.78 years) is made by the neutron activation of stable thallium in a nuclear reactor.^[9]

Toxicity

Thallium and its compounds are very toxic, and should be handled with great care^{[citation needed]}. Contact with skin is dangerous, and adequate ventilation should be provided when melting this metal^{[citation needed]}. Thallium(I) compounds have a high aqueous carcinogen.

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 ferredoxins).

Thallium's toxicity has led to its use (now discontinued in many countries) as a rat and ant poison.

Among the distinctive effects of thallium poisoning are loss of hair (which led it to its initial use as a depilatory before its toxicity was properly appreciated) and damage to peripheral nerves (victims may experience a sensation of walking on hot coals). Thallium was once an effective murder weapon before its effects became understood, and an antidote (prussian blue) discovered.

Treatment and internal decontamination

One of the main methods of removing thallium (both radioactive and normal) from humans is to use potassium. The prussian blue is fed by mouth to the person, and it passes through their digestive system and comes out in the stool.^[10]

Famous uses as a poison

• The CIA is believed (by its Inspector General) to have conceived a scheme to poison Fidel Castro by exposure to thallium salts placed in his shoes while they were being polished. The goal was to discredit him by causing him to lose his characteristic hair and beard. The scheme progressed as far as testing on animals, but the trip during which the poison was to be administered fell through.^[11]

• In 1953, Australian Caroline Grills was sentenced to life in prison after three family members and a close family friend died. Authorities found thallium in tea that she had given to two additional family members.^[12]

• It is claimed that South African agents once plotted to use it against Nelson Mandela while he was in prison on Robben Island. The Truth and Reconciliation Commission heard how agents established plans to add doses of the chemical to his medication.^[12]

• Thallium is one of the poisons that Graham Frederick Young used on his victims.

• In 1988, members of the Carr family from Central Florida fell ill from what appeared to be Thallium poisoning. Peggy Carr, the mother, died slowly and painfully from the poison and her son and stepson were critically ill but recovered. Peggy's husband was initially a suspect until thallium was discovered in his system. Two years later, the Carr's neighbor, George J. Trepal, a chemist and member of Mensa, was convicted of murdering Mrs. Carr and attempting to murder her family. The thallium was found to be slipped into bottles of Coca-Cola at Mrs. Carr's house and Trepal was sentenced to die in the electric chair.^[13]

 

• In June 2004, 25 Russian soldiers earned Honorable Mention Darwin Awards after becoming ill from thallium exposure when they found a can of mysterious white powder in a rubbish dump on their base at Khabarovsk in the Russian Far East. Oblivious to the danger of misusing an unidentified white powder from a military dump site, the conscripts added it to tobacco, and used it as a substitute for talcum powder on their feet.^[14]

• In 2005, a 17 year old girl in Numazu, Shizuoka, Japan, admitted to attempting to murder her mother by lacing her tea with thallium, causing a national scandal.^[15]

• In February of 2007, two Americans, Marina and Yana Kovalevsky, a mother and daughter, visiting Russia were hospitalized due to Thallium poisoning. Both had emigrated from the Soviet Union to the United States in 1989 and had made several trips to Russia since then. ^[16]

In Fiction

• Agatha Christie, who worked as a pharmacist, used thallium as the agent of murder in her detective fiction novel The Pale Horse — the first clue to the murder method coming from the hair loss of the victims.

• In Nigel Williams' 1990 novel The Wimbledon Poisoner, Henry Far uses thallium to baste a roast chicken in a failed attempt to murder his wife.

• "Concentrated thallium" is used as the poison of choice of the Wyoming Widow in the 2006 comedy Big Nothing

• Thallium is used to fake polio symptoms in an episode of the TV show House.

See also

• Thallium compounds

References