Lead isotope distribution and enrichment factors in soil profiles around an abandoned Pb-smelter plant

Abstract

Todos os Santos (all Saints) Bay area on Brazil’s east coast is known for one of the most significant cases of lead contamination in the country owing to the past activities of a Pb-smelter plant. This work was carried out to assess the concentration and sources of Pb based on Pb isotopes and enrichment factor of soil profiles surrounding Todos os Santos Bay in order to understand the expansion of contamination and to help the establishment of Pb regulatory standards for the region. Forty-four samples were collected from soil genetic horizons of six pedons that represent the range of dominant soil properties and geologic materials in the region. Concentrations of Pb and the isotopes 204Pb, 206Pb, 207Pb, and 208Pb were determined on an inductively coupled plasma (quadrupole) mass spectrometry. The soil enrichment factor was calculated using Al and Fe as conservative index elements. Average Pb concentration (15.87 mg kg−1) in uppermost horizons (from all six pedons) is slightly higher than soil background concentrations commonly reported in Brazil. Samples feature a wide range of Pb isotope ratios, ranging from 36.71 to 47.38 for 208Pb/204Pb, 15.00 to 15.65 for 207Pb/204Pb, 16.86 to 20.59 for 206Pb/204Pb, and 1.10 to 1.31 for 206Pb/207Pb. For the enrichment factor calculations, only Fe demonstrated a good agreement with Pb isotopic ratios. Both Pb isotopic composition and enrichment factor were useful tools to distinguishing natural and anthropogenic influence on the Pb soil concentrations.