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Thallium

Thallium is a silvery-grey metal that tarnishes easily in air. This metal is so soft and malleable that it can be cut with a knife.

Although its physical characteristics may seem similar to many other elements on the periodic table, thallium and its compounds are extremely toxic. For this reason, its use is restricted to few applications.

The commercial industry uses this element primarily in insecticides and rat poison. Because thallium sulphate is odourless and tasteless, insects and rats are not able to detect its toxic presence. Thallium sulphide's electrical conductivity changes with exposure to infrared light. Hence, it has practical use in photocells, an area being studied by the National Research Council Canada (NRC).

Due to thallium's toxicity, its presence poses a serious health hazard. Thallium and its compounds can be absorbed through the skin, and its effects are cumulative. One may not know that he/she has been poisoned as it takes several days for the poison to act. Symptoms of this poisoning include quick hair loss and adverse effects on the nervous system.