Hundreds of U.S. air marshals and federal Bureau of Prisons employees were exposed to dangerous levels of lead while pursuing required firearms proficiencies at gun ranges sanctioned by the federal government, according to an investigation by the Seattle Times.

After the paper reported that two Seattle-area gun ranges repeatedly violated lead-safety regulations while benefiting from federal contracts, the Transportation Security Administration (TSA) issued a mandate that at least some gun ranges that do business with the federal government prove that their facilities are not tainted with lead.

Lead enters the body primarily through inhalation and ingestion. When exposure occurs through breathing in lead-containing dust and fumes, the lead passes through the lungs into the blood where it can cause neurological effects, gastrointestinal effects, anemia, and kidney disease.

Shooting ranges that lack adequate ventilation and cleanup procedures can expose shooters to high levels of lead vapor and dust which is emitted when lead-based ammunition is fired.

Air marshals must train with firearms at TSA-approved gun ranges. After the Times’ expose the TSA announced that bids from firing range companies in Houston and Detroit must show that their indoor air has recently met federal safety standards and to provide results from recent lead level tests or an OSHA compliance inspection report.