Multiple sources of lead in soils from a Hawaiian chronosequence

We report lead isotopic ratios and concentrations from a basaltic soil chronosequence in Hawaii. Substrate ages at the sites range from 300 years to 4.1 million years. All soils show a net addition of Pb above the contributions made by basaltic weathering, indicating that atmospheric deposition of natural or pollutant sources is important across the sequence. Isotopic ratios from the chronoseqence soils indicate a mixture of basalt, mineral aerosol, and anthropogenic Pb sources derived from both long range and local inputs. Locally derived anthropogenic Pb dominates young soils. Intermediate age soils in remote locations have a strong mineral aerosol signature and likely contain some anthropogenic lead of Asian origin. Older soils have undergone extensive leaching of both basaltic and eolian lead. While the anthropogenic inputs in most sites are from less radiogenic local and Asian sources, we find evidence of “J-type” lead of North American origin in a remote soil on Kauai. The diversity of anthropogenic lead sources suggests that at least two different weather patterns dominate atmospheric Pb transport across the Hawaiian island chain.