The quantification and distribution of pollution Pb at a woodland in rural south central Ontario, Canada.

Lead concentrations and Pb isotope ratios were measured in the forest floor, mineral soil and vegetation at a white pine and a sugar maple stand in a woodland in south central Ontario. Lead concentrations decreased and ²⁰⁶Pb/²⁰⁷Pb ratios increased with mineral soil depth reflecting the mixing of pollution and natural Pb sources. Lead concentrations and ²⁰⁶Pb/²⁰⁷Pb ratios at 20–30 cm depth were ∼6–7 mg/kg and 1.31–1.32, respectively. Assuming an integrated ²⁰⁶Pb/²⁰⁷Pb ratio in deposition over time of 1.18, estimated from lichen measurements and published data for the region, approximately 65% of Pb in the surface (0–1 cm) mineral soil is from anthropogenic sources. Approximately 90% of pollution Pb is found in the 0–10 cm soil layer (Ah) and less than 3% of the pollution Pb is present in the forest biomass and mull-type forest floor combined. Despite low Pb concentrations in vegetation (<2.5 mg/kg), we estimate that between 65 and 100% of the Pb in vegetation and ∼75% of the Pb in the forest floor is from pollution sources. In total, the pollution Pb burdens at the pine and maple stands are estimated to be 860 and 750 mg/m², respectively. [Copyright &y& Elsevier]