What Is Lead?
QUICK ANSWER
Lead is a chemical element with atomic number 82 and the symbol Pb. It is a heavy, soft, silvery-gray metal that has been used for thousands of years for pipes, weights, ammunition, and other applications. Lead is highly toxic to humans, especially children, and has been banned from many uses since the 1970s.
Lead is one of the most useful and most dangerous metals humans have ever exploited. Easy to mine, easy to shape, and resistant to corrosion, lead has been used since Roman times for plumbing, paints, and countless other products. Modern science has revealed lead as a potent neurotoxin, leading to bans on most consumer uses. The legacy of past lead use, however, persists in old buildings and contaminated soils worldwide.
Where is lead on the periodic table?
Lead has atomic number 82, the symbol Pb (from the Latin plumbum), and sits in group 14 of the periodic table along with carbon, silicon, germanium, and tin. It is a post-transition metal with a melting point of 327°C and a density of 11.34 g/cm³, about 30% denser than iron. Four stable isotopes occur naturally (Pb-204, Pb-206, Pb-207, Pb-208), with Pb-208 being the heaviest stable isotope of any element. Lead also sits at the end of three radioactive decay chains, making it the ultimate end point for many heavier elements.
What are the properties of lead?
Lead is a soft, malleable, dense metal that can be hammered into thin sheets or cast into complex shapes at low temperatures. Its low melting point (327°C) makes it easy to work compared to other metals. Lead is highly resistant to corrosion from acids and weather, which is why it lasted so long in plumbing applications. It blocks radiation effectively, which is why x-ray aprons and nuclear shielding still use lead. Pure lead is silvery when freshly cut but quickly tarnishes to a dull gray as it forms a protective oxide layer in air.
What was lead used for historically?
Roman plumbing used lead pipes (the word plumbing comes from plumbum). Lead paint was widely used until the 1970s for its bright colors and durability. Leaded gasoline added tetraethyl lead to engine fuel from the 1920s to the 1990s to prevent engine knocking. Lead solder joined copper plumbing and electronics until banned. Lead crystal glassware used lead oxide to increase clarity and weight. Lead bullets have been standard ammunition for centuries. Most of these consumer uses have been banned or phased out as lead's toxicity became understood.
Why is lead so toxic?
Lead disrupts many biological processes by mimicking calcium and binding to proteins that should be using calcium. It crosses the blood-brain barrier, accumulates in bones, and damages the nervous system, kidneys, and reproductive system, as detailed in CDC's lead poisoning prevention resources. Children are especially vulnerable: even low-level lead exposure during brain development causes permanent IQ reduction, behavior problems, and learning disabilities. There is no safe blood lead level in children. The Flint water crisis was a major modern example of mass lead exposure from corroded pipes.
Lead is the heavy metal that built civilizations and then turned on them. From Roman pipes to American gasoline, lead's usefulness made it ubiquitous, and its toxicity has now made it a cleanup priority. Banning lead from most products has not erased its legacy: lead paint, soil contamination, and old pipes continue to cause harm worldwide.
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