244For more information on the uses and releases of chemicals in your state, contact the Community
Right-to-Know Hotline: (800) 424-9346.
How will I know if Thallium is in my Drinking Water?
When routine monitoring indicates that thallium levels are above the MCL, your water supplier must
take steps to reduce the amount of thallium so that it is below that level. Water suppliers must notify
their customers as soon as practical, but no later than 30 days after the system learns of the
violation. Additional actions, such as providing alternative drinking water supplies, may be required
to prevent serious risks to public health.
How will Thallium be Removed from my Drinking Water?
The following treatment method(s) have proven to be effective for removing thallium to below 0.002
mg/L or 2 ppb: activated alumina; ion exchange.
How do I learn more about my Drinking Water?
EPA strongly encourages people to learn more about their drinking water, and to support local
efforts to protect the supply of safe drinking water and upgrade the community water system. Your
water bill or telephone book's government listings are a good starting point for local information.
Contact your water utility. EPA requires all community water systems to prepare and deliver an
annual consumer confidence report (CCR) (sometimes called a water quality report) for their
customers by July 1 of each year. If your water provider is not a community water system, or if you
have a private water supply, request a copy from a nearby community water system.
Thallium Explained
Thallium is a chemical element with symbol Tl and atomic number 81. This soft gray poor metal is
not found free in nature. When isolated, it resembles tin, but discolors 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, thallos, meaning "a green shoot or twig," was named by Crookes. It was isolated by
electrolysis a year later, by Lamy.
Thallium tends to oxidize to the +3 and +1 oxidation states as ionic salts. The +3 state resembles
that of the other elements in thallium's group (boron, aluminum, gallium, indium). However, the +1
state, which is far more prominent in thallium than the elements above it, recalls the chemistry of
alkali metals, and thallium(I) ions are found geologically mostly in potassium-based ores, and (when
ingested) are handled in many ways like potassium ions (K+) by ion pumps in living cells.
Commercially, however, thallium is produced not from potassium ores, but as a byproduct from
refining of heavy metal sulfide ores. 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. It is also used in infrared detectors.
The radioisotope thallium-201 (as the soluble chloride TlCl) is used in small, nontoxic amounts as
an agent in a nuclear medicine scan, during one type of nuclear cardiac stress test. Soluble thallium
salts (many of which are nearly tasteless) are highly toxic in quantity, and were historically used in
rat poisons and insecticides.