Determination of the extent of anthropogenic Pb migration through fractured sandstone using Pb isotope tracing

The extent of vertical migration of anthropogenic Pb beneath a medieval smelting site in Derbyshire, U.K. has been estimated using the determination of total Pb concentrations and 206Pb/207Pb isotope ratio from samples taken down 6 m of drill core. Preliminary studies of total Pb concentrations established that the surface slag derived from the smelting contained up to 16% Pb and that the normal background levels in uncontaminated sandstone were 10±2 ppm. Sample analyses beneath the site revealed elevated Pb concentrations in fracture infill clays (270 ppm Pb) and sandstone (76–83 ppm Pb). Both are well above the background Pb concentration. Lead isotope analysis of the slag wastes, the underlying contaminated sandstone and fracture infill has shown that all 3 contain very similar isotope ratios for 206Pb/207Pb (1.1802–1.1820). However, matched control sandstone samples show that the background 206Pb/207Pb isotope ratio (1.1670 ± 0.003) is distinctly different.