In 1974, the EPA began a phaseout of lead from gasoline in the U.S., a process that completed in 1995. The toxic element was originally added to boost engine performance, but scientists eventually discovered that it was building up in soils and becoming a serious air pollutant. The EPA estimated more than 5,000 Americans died per year from heart disease linked to lead poisoning. Since the ban, the average level of lead in the blood of Americans has decreased by more than 75%.