In summary, epidemiologic evidence supports the position that airborne lead in the concentrations found in the general ambient atmosphere is, at most, a minor contributor to lead in blood. The increment of quantity of the airborne lead contribution even if it can be deduced, is biologically meaningless.
Dr Jerome F. Cole, director of environmental health for the Lead Industries Association. From Los Angeles Times, Showdown On Lead Pollution Issue Takes Shape”, by W.B. Rood.