Lead and strontium isotopes as palaeodietary indicators in the Western Cape of South Africa

Abstract

We analysed the isotopic compositions of bioavailable strontium (Sr) and lead (Pb) in 47 samples of animals and plants derived from the various geological substrates of southwestern South Africa, to explore the utility of these isotope systems as dietary tracers. Measurements were made using high-resolution multi-collector inductively-coupled-plasma mass spectrometry (MC-ICP-MS). 87Sr/86Sr could efficiently discriminate between geologically recent sediments of marine origin in near-coastal environments and older geologies further inland. However, 87Sr/86Sr was not able to distinguish between the Cape Granite Suite and the Cape System (Table Mountain sandstones), whereas Pb isotopes could, demonstrating the utility of this hitherto underused isotope system. Bioavailable 87Sr/86Sr in near-coastal terrestrial environments is influenced by marine input, whereas Pb isotopic ratios are not, because of low concentrations of Pb in seawater. There is considerable potential to use Pb isotopes as a dietary and palaeodietary tracer in near-coastal systems in fields as diverse as archaeology, palaeontology, wildlife ecology and forensics. Significance: • This study is the first investigation of the potential of Pb isotopes as a dietary tracer in southwestern South Africa. • Pb isotopes are a valuable dietary tracer; used in combination with 87Sr/86Sr, they can extend our knowledge of landscape usage in coastal-marine environments. • Pb isotopes have also shown to be useful in samples from the 1980s, collected during the time when leaded petrol was in use in South Africa; however, these samples were from remote areas with low motor vehicle emissions.