Lead in archaeological samples: an isotopic study by ICP-MS

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS) has been used to measure the concentration and isotopic composition of Pb in archaeological human and animal skeletal remains, soil from a village site of the Omaha tribe (U.S.A.) and cosmetic pigments. Lead concentrations in human bones from the Omaha tribe vary between 4.8 and 2570 μg/g, with younger people having the highest concentrations. Lead concentrations in animal bones from an Omaha village vary between 0.6 and 3.7 μg/g, and those of three soil samples range between 18 and 21 μg/g. Lead concentrations found in human bones from Anasazi (Utah, U.S.A.) and Alta (Peru) populations vary between 0.7 and 3.2 μg/g. Isotope ratios of a reagent grade Pb(NO 3) 2 solutions were measured by thermal ionization 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 206Pb/ 204Pb, 0.02–0.55% for 207Pb/ 204Pb, and 0.16–0.56% for 208Pb/ 204Pb. The precision of measurements on artifacts was 0.42–0.65% for 206Pb/ 204Pb and 0.41–0.62% for 207Pb/ 204Pb, whereas the precision for the same ratios for the bones was 0.85–1.8 and 0.82–1.67%, respectively. For the cosmetic lead-bearing pigments, a precision of 0.07–0.15% was found for both 206Pb/ 204Pb and 207Pb/ 204Pb ratios. Lead isotope ratios of artifacts give a radiogenic Pb signature, of which are close to signatures from Pb Zn mines of the central U.S. region. Lead isotope ratios of the pigments give non-radiogenic Pb signatures. Lead isotope ratios of the bones differ from those of the artifacts, and although similar in isotopic ratio to the pigments, they are more scattered, suggesting potential mixing of Pb from different regions.