Lead
Lead has been used by humans for a variety of purposes for more than 5,000 years.
Over time, as we've better understood the risks to people and the environment, how lead is used has also changed.
Today, lead is used as a pure metal, alloyed with other metals, or as a chemical compound.
Its principal use is in lead-acid storage batteries, which provide critical stand-by power for hospitals and telecommunications systems, as well as energy storage for wind and solar energy systems and hybrid-electric vehicles.