Periodic table entry for thallium that includes the atomic number, abbreviation and mass
CAS Number: various

Thallium is a metal that occurs in nature.  It is used in various specialized applications in electronics, medicine, and research.  Historically, it was used as a rat poison, but this use was banned in 1972 because thallium is very toxic to humans.  Thallium is released into the environment at very low levels from raw materials used by some industries, such as oil and gas operations, cement plants, and steel manufacturers.

Fact Sheet

Thallium is found in:

  • Components used in electronics, such as semiconductors.
  • Some drinking water sources, such as well water that has been affected by industrial or wastewater discharges.
  • Air and dust near certain industrial facilities that can release thallium, such as cement plants and steel manufacturers.
  • Cigarette and other tobacco smoke, at very low levels.

Possible health concerns of thallium

Thallium is highly toxic and can harm many vital processes in the body.  Thallium:

  • Can harm the nervous system.
  • Can impair vision.
  • Can cause hair loss.

Possible ways to reduce exposure to thallium

  • If your water comes from a private well, have it tested for metals, including thallium.  (If your water comes from a public water supplier, it is already tested regularly for thallium.)
  • If you work with materials that contain thallium or at facilities where thallium may be released into the air, follow all occupational safety guidelines for your industry. 

Biomonitoring California Information

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