SKELETAL CONCENTRATIONS OF LEAD, CADMIUM, ZINC, AND SILVER IN ANCIENT NORTH-AMERICAN PECOS INDIANS

Bone samples of 14 prehistoric North American Pecos Indians from circa 1400 A.D. were analyzed for lead, cadmium, zinc, and silver by graphite furnace atomic absorption spectrometry to establish the baseline levels of these elements in an ancient North American population. Measurements of outer and inner bone fractions indicate the former were contaminated postmortem for lead, zinc, and cadmium. The contamination-adjusted average (xBAR +/- SD) level of lead (expressed as the ratio of atomic lead to atomic calcium) in bones of the Indians was 8.4 +/- 4.4 x 10(-7), which was similar to ratios in bones of ancient PeruVians (0.9 to 7.7 x 10(-7)) and significantly lower than ratios in bones of modern adults in England and the United States (210 to 350 x 10(-7)). The adjusted average concentrations (microgram per gram dry weight) of biologic cadmium, silver, and zinc in the Pecos Indian bones were 0.032 +/- 0.013, 0.094 +/- 0.044, and 130 +/- 66, as compared to concentrations of 1.8, 0.01 to 0.44, and 75 to 170 in the bones of modern people, respectively. Therefore, cadmium concentrations in Pecos Indian bones are also approximately 50-fold lower than those of contemporary humans. These data support earlier findings that most previously reported natural concentrations of lead in human tissues are erroneously high and indicate that natural concentrations of cadmium are also between one and two orders of magnitude lower than contemporary concentrations.