Fig. 4. Sources of Pb were identified using (a) trace element ratio and (b) isotopic ratio (measured by inductively coupled plasma mass spectrometry (ICP–MS)) analysis techniques. Both graphs represent data (n = 4) from a nonurban residence with a known and isolated Pb-based paint Pb source. The data in (b) is compared to the isotope ratio range for Pb-based paint and a leaded gasoline signature measured by Rabinowitz (1986).