Lead is released into the air by soils as they erode in wind and rain, and by volcanoes when they erupt. These natural releases are insignificant compared to those from human activities. Lead released into the environment by human activities comes mainly from metal production facilities, incinerators that burn refuse and sewage sludge, industrial boilers that burn coal and oil, and vehicles that burn gasoline. Industries reporting to EPA released 1534 tons of lead into the environment in 1995. Ash particles carrying lead settle to the ground after they are released into the air from power plants.
Most lead reaches the ground through gravity and air turbulence.
Lead compounds that dissolve in water are carried to the ground by rain and snow. Ash pond wastewater discharged into public waterways may contain small amounts of lead, but these amounts are regulated by local permits. People are commonly exposed to lead by drinking water or eating food that contains it. Lead in drinking water comes mainly from lead pipes, brass fixtures, and lead solder found in older plumbing. Lead in food comes mainly from airborne particles that fall directly on crops or contaminate the soil in which they grow.