In 1976, the U.S. Centers for Disease Control and Prevention’s (CDC) Environmental Services Division revealed blood lead levels related to gasoline exposure, leading to decreased lead amounts in gasoline, implemented by the U.S. Environmental Protection Agency (EPA).

Since 1971, the United States has seen a dramatic and sustained decline in population-level lead exposure. Blood lead levels (BLLs), a time-integrated measure of past and recent exposure, are the most common indicator of human exposure.

An understanding of the sources of lead in the environment and the pathways of exposure is imperative to the development and implementation of regulations to reduce exposures. Lead is a naturally occurring heavy metal in the earth’s crust. Widespread extraction and use of lead have contaminated the environment, exposed people to lead, and created significant public health problems in many parts of the world. The primary pathways for human exposure to lead are inhalation and ingestion.