Pollution and human mobility in the southern Levant during the Iron Age using chemical and isotopic analysis of human tooth enamel

The extent of pollution and human mobility in the Iron Age in the southern Levant is estimated in this study through lead (Pb) and strontium (Sr) concentrations and isotopic compositions in human tooth enamel. The concentrations of Pb and other trace metals (Cu, Co, Cd, Zn) and Pb/Ca along with Ba/Ca ratios are used to determine background levels of metals and exposure to metal pollution. Strontium isotopic ratios are used to trace individuals' residence as children and young adults, and Pb isotopic ratios are used for determining sources of in-vivo pollution. Seven teeth from the Natufian to the Pre-pottery Neolithic periods were used to establish metal-concentration baselines, and their Pb concentrations were compared with previous results. Forty-one additional samples (31 individuals) were selected from secure archaeological contexts, mostly urban sites, from the Iron Age (-1200 - 586 BCE; 28 individuals) and from the Persian Period (-586-332 BCE; 3 individuals). Based on their Pb/Ca ratios, five individuals were found to be in-vivo polluted, and four additional individuals were possibly polluted, all dating to the Iron Age, suggesting that just under a third of the sampled Iron Age individuals were exposed to heavy metals to some extent. All individuals except one (from the coastal site of Dor) plot within the Sr-87/Sr-86 range of local, bioavailable Sr in soils (0.7058-0.7102). The unpolluted and possibly polluted individuals from coastal sites have a different Sr-87/Sr-86 range (0.7081-0.7112) than the inland unpolluted individuals (Sr-87/Sr-86 = 0.7079-0.7084), suggesting that the former have more coastal/marine contribution in their diet. This Sr isotopic distribution pattern reflects a generally non-mobile population in both coastal and inland sites. Polluted Iron Age individuals, on the other hand, from both inland and coastal sites, have Sr-87/Sr-86 values which fall in a narrow range (0.7083-0.7086), possibly affected to some extent by coastal/ marine sediments. Lead isotopic composition of four out of five individuals clearly deviate from local soil values, indicating an external contribution of Pb, some of which possibly originated from lead-rich Cu-ores in the Arabah. We thus propose a correlation between pollution and mobility in the Iron Age southern Levant. A possible explanation might be that polluted individuals had interactions with the coast or the marine environments, where they came into contact with metals, as a result of exposure to metalworking, use and/or trade.