Isotopic evidence of spatial magnitude of the Pb deposition near a lead smelter

In order to determine the dry deposition of lead around a Pb-Zn refinery, two cross-sectional sampling experiments, using deposition plates, have been performed on a daily basis, under representative meteorological situations (north-easterly and south-westerly winds). The amount of lead deposited, as well as its isotopic composition (expressed by the 206 Pb/ 207 Pb ratio) are systematically measured. For a daily production of approximately 670 metric tons of (Pb+Zn), the dry fallout, greater than 1000 μgPb/h.m 2 on the edge of the plant, falls to about 100 μgPb/h.m 2 , four kilometres away from the refinery. This value is still ten times higher than the urban background (<10 μgPb/h.m 2 ). The spatial extension of the dry deposition plume is evidenced by the evolution of the isotopic signature of the refinery (1.10< 206 Pb/ 207 Pb<1.13), clearly distinct from the urban background signature (1.15< 206 Pb/ 207 Pb<1.16). As a first estimate, the extension of the deposition plume seems not to be linked to the wind speed. At the opposite, diffuse emissions from slag heaps are related to this parameter.