Lead-210 is a radioactive isotope of lead with a mass number of 210. It is produced from the decay of radon-222, which is a gas that can be found in soil and rock. Lead-210 has a half-life of about 22 years, meaning it takes that long for half of a sample to decay into bismuth-210. This isotope is commonly used in environmental studies, particularly in geochronology to date sediments and understand sedimentation rates. It can also be found in some natural sources, such as uranium ores, and is monitored due to its potential health risks when ingested or inhaled.