Isotopic composition of Zn and Pb atmospheric depositions in an urban/Periurban area of northeastern France.

Epiphytic lichens, ambient PM-10, and bus air-filter aerosols collected in a city and the surrounding area were used to monitor urban atmospheric metal deposition in the Metz area, NE France. According to the measured Pb and Zn concentrations, high-enrichment factors (EF) were calculated for lichens collected in 2001 and 2003, suggesting an anthropogenic origin for those metals. Pb and Zn concentrations in lichens and other samples are correlated, probably indicative of the level of pollution recorded. However, different trends and scatters in the relationship suggest decoupling of Zn and Pb sources in this area. The lead isotopic composition of lichens varies largely from downtown, near traffic roads and highways, to suburbs but indicate an overall stability of sources between 2001 and 2003, although some minor variations were noted. Remobilization of Pb from leaded gasoline is still significant. The Zn isotopic composition measured in all lichens yielded fairly homogeneous delta66Zn ranging from -0.2% per hundred to 0.5% per hundred relative to ZnJMC solution. Most lichen samples are indistinguishable from urban aerosols (PM-10 and bus air filters, delta66Zn = 0.12 +/- 0.21% per hundred) and from flue gases from the city waste combustor (delta66Zn = 0.13 +/- 0.12% per hundred). No systematic variations of Zn EF and isotopic compositions were observed for and between 2001 and 2003 samples. Some lichens having unradiogenic 206Pb/207Pb ratios displayed high Zn and negative delta66Zn, indicative of a possible traffic source for Zn. A review from the literature on the Zn isotopic composition of terrestrial materials is reported but a few reservoirs seem to have specific compositions. According to the actual precision obtained, Zn isotopes for tracing pollution sources might not be straightforward but might be potentially useful for specific studies.