Wikipedia:Today's featured article/October 20, 2024
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Heavy metals are metals with relatively high densities, atomic weights or atomic numbers, depending on the context. They are usually the denser metals in metallurgy, or the metals with higher atomic numbers in physics; chemists distinguish heavy metals by their chemical behaviour. Heavy metals tend to be less chemically reactive than light metals such as sodium, magnesium and aluminium. The earliest known metals are heavy metals, including common metals such as iron, copper and tin, and precious metals such as silver, gold and platinum. Less familiar metals such as gallium and thallium are also heavy metals, as are the essential nutrients cobalt and zinc. Some are toxic in larger amounts or certain forms; others, like mercury and lead, are highly poisonous. Sources of heavy metal poisoning may include mining and industrial waste, agricultural runoff or occupational exposure. Heavy metals are relatively scarce in the Earth's crust, but are present in many manufactured products. (Full article...)