LEAD IN ARCHAEOLOGICAL SAMPLES - AN ISOTOPIC STUDY BY ICP-MS

Inductively coupled plasma mass spectrometry (ICP-MS) has been used to measure the concentration and isotopic composition of Pb in archaeolo gical human and animal skeletal remains, soil from a village site of t he Omaha tribe (U.S.A.) and cosmetic pigments. Lead concentrations in human bones from the Omaha tribe vary between 4.8 and 2570 mug/g, with younger people having the highest concentrations. Lead concentrations in animal bones from an Omaha village vary between 0.6 and 3.7 mug/g, and those of three soil samples range between 18 and 21 mug/g. Lead c oncentrations found in human bones from Anasazi (Utah, U.S.A.) and Alt a (Peru) populations vary between 0.7 and 3.2 mug/g. Isotope ratios of a reagent grade Pb(NO3)2 solutions were measured by thermal ionizatio n mass spectrometry (TIMS), as well as by ICP-MS to provide laboratory reference materials. The accuracy of the ICP-MS measurements relative to TIMS for the standard solution were found to be within 0.02-0.31% for Pb-206/Pb-204, 0.02-0.55% for Pb-207/Pb-204, and 0.16-0.56% for Pb -208/Pb-204. The precision of measurements on artifacts was 0.42-0.65% for Pb-206/Pb-204 and 0.41-0.62% for Pb-207/Pb-204, whereas the preci sion for the same ratios for the bones was 0.85-1.8 and 0.82-1.67%, re spectively. For the cosmetic lead-bearing pigments, a precision of 0.0 7-0.15% was found for both Pb-206/Pb-204 and Pb-207/Pb-204 ratios. Lea d isotope ratios of artifacts give a radiogenic Pb signature, of which three are close to signatures from Pb-Zn mines of the central U.S. re gion. Lead isotope ratios of the pigments give non-radiogenic Pb signa tures. Lead isotope ratios of the bones differ from those of the artif acts, and although similar in isotopic ratio to the pigments, they are more scattered, suggesting potential mixing of Pb from different regi ons.