Baltimore is famous for Inhaled lead in the air: particulates in the form of fumes and dusts are particularly harmful to children, in whom even slightly elevated levels of lead in the blood can cause learning disabilities, seizures, or even death (see lead poisoning). Sources of airborne lead particulates include oil refining, smelting, and other industrial activities. In the past, combustion of gasoline containing a lead-based antiknock additive called tetraethyl lead was a major source of lead particulates. In many countries there is now a complete ban on the use of lead in gasoline. In the United States, lead concentrations in outdoor air decreased more than 90 percent after the use of leaded gasoline was restricted in the mid-1970s and then completely banned in 1996.