Thallium is a toxic metal from electronics production and coal burning. It enters water through industrial waste. Even small amounts can damage nerves and organs.

Thallium, discovered in 1861, was once used in rat poisons and insecticides. Today, it's primarily released through electronics manufacturing and coal combustion. It enters water supplies via industrial waste discharge or by leaching from contaminated soil. The EPA regulates thallium in drinking water, measuring it in parts per billion (ppb). While essential for some electronics, thallium has no known biological role and is highly toxic to humans, even in small quantities.