Definitions for "Heavy metals"
Trace elements, such as lead, iron, cadmium, copper, mercury, nickel, and chromium, that occur naturally in rock formations and that can become concentrated to reach hazardous levels. These elements do not break down and can accumulate to toxic levels in people or plants. Accumulation of heavy metals in people can occur through eating, drinking or breathing.
Elements such as lead, mercury, zinc, copper, cadmium, and so forth, that may be required in trace amounts by organisms, but can cause damage when ingested in larger quantities.
Not rock music, but in science, a common hazardous waste that can damage organisms at low concentrations and which tends to accumulate in the food chain.