Thallium(I) sulfate

Thallium(I) sulfate (Tl2SO4), archaically known as thallous sulfate, is the sulfate salt of thallium. It is colorless, odorless, and tasteless, but highly toxic.

Uses
During the last two centuries, Tl2SO4 had been used for various medical treatments but was abandoned. In the later 1900s it found use mainly for rodenticides. These applications were prohibited in 1975 in the US due to the nonselective nature of its toxicity. Thallium(I) sulfate inhibits the growth of plants by preventing germination. Tl2SO4 is mostly used today as a source of Tl+ in the research laboratory. It is a precursor to thallium sulfide (Tl2S), which exhibits high electrical conductivity when exposed to infrared light.

Structure
Tl2SO4 adopts the same structure as K2SO4. In aqueous solution, the thallium(I) cations and the sulfate anions are separated and highly solvated. Thallium(I) sulfate crystals have a C2 symmetry.

Toxicity
Thallium(I) sulfate is soluble in water and its toxic effects are derived from the thallium(I) cation. Since thallium sulfate is a simple powder with indistinctive properties, it can easily be mistaken for more innocuous chemicals. It can enter the body by ingestion, inhalation, or through contact with the skin. The thallium(I) cation is very similar to potassium and sodium cations, which are essential for life. After the thallium ion enters the cell, many of the processes that transport potassium and sodium are disrupted. Due to its poisonous nature, many western countries have banned the use of thallium sulfate in products for home use and many companies have also stopped using this compound.

A dosage in excess of 500 mg is reported as fatal. Thallium sulfate, after entering the body, concentrates itself in the kidneys, liver, brain, and other tissues in the body.

Thallium sulfate was used in Israel to control the rodent population; it is suspected that in the 1950s, this resulted in the disappearance of the Brown Fish Owl.