of surface-associated material, which is often highly characteristic of particles derived from a specific source. Thus, automobile exhaust particles have been shown to contain the elements Br, Cl, Cr, Mn, Ni, P, Pb, and T1 on their outer surface (25, 27).In terms of the actual results obtained, the most important conclusions are that lead derived from automobile exhaust particulates can contribute significantly to the total lead present in soils and dusts at a considerable distance from a roadway. Otherwise, it would appear that roadway dusts themselves are likely to contain lead that is almost exclusively derived from automobile exhausts.