Evidencing lead deposition at the urban scale using “short-lived” isotopic signatures of the source term (Pb–Zn refinery)

To demonstrate the ability of the lead isotope signature technique to evidence the spatial extent of an industrial Pb deposition plume at a local scale, dry deposition of lead in the urban environment of a Pb–Zn refinery was investigated, as a study case, using transient (“short-lived”) isotopic signatures of the industrial source. Sampling campaigns were achieved in representative weather conditions, on an 8-h basis. Dry deposition rates measured downwind from refinery emissions (≈102–103 μg Pb m−2 h−1), cross-sectionally in a 3–5 km radius area around the plant, represent 10–100 times the urban background dry fallout, measured upwind, as well as fallout measured near other potential sources of anthropogenic Pb. The Pb–Zn refinery isotopic signature (approx. 1.100<206Pb/207Pb<1.135) is made identifiable, using the same set of Pb and Zn ores for 2 days before sampling and during field experiments, by agreement with the executive staff of the plant. This source signature is less radiogenic than signatures of urban background Pb aerosols (1.155<206Pb/207Pb<1.165) and minor sources of Pb aerosols (1.147<206Pb/207Pb<1.165). By a simple binary mixing model calculation, we established the extension of the industrial Pb deposition plume. Fifty to eighty percents of total lead settled by the dry deposition mode, 3–4 km away from the refinery, still have an industrial origin. That represents from 40 to 80 μg Pb m−2 h−1, in an area where the blood lead level exceeds 100 μg Pb l−1 for 30% of men and 12% of women living there. We demonstrate here that stable Pb isotope analysis is able to evidence the Pb dry deposition plume in stabilised aerodynamic conditions, using a short-lived source term, suggesting that this methodology is able to furnish valuable data to validate industrial Pb aerosols dispersion models, at the urban scale.