Thallium is a chemical element with symbol Tl and atomic number 81. This soft gray post-transition metal is not found free in nature. When isolated, it resembles tin, but discolors when exposed to air.
Three reasons Thallium stands out
- 1
Once used in rat poisons, now has uses in medical imaging.
- 2
It is extremely insidious as a poison because it is completely colourless, odourless, and tasteless in solution.
- 3
Its distinctive symptom of causing sudden hair loss has helped forensic investigators solve several famous poisoning cases.
The poison once mistaken for potassium
Thallium ions can imitate potassium closely enough to enter biological pathways, making many compounds dangerously toxic. Its salts were once sold as rat poison before restrictions tightened. Today specialized thallium isotopes aid heart imaging, and thallium-containing crystals detect infrared light and radiation.