Characterizing and sourcing metal air contamination coupling concentrations and lead isotopes from moss biomonitoring in urban cemeteries

Abstract Populations are constantly exposed to airborne metals, in particular in urban areas. Despite their proven links to health issues, their origin and fate are still subject to debate. Bioindicators, by taking up and cumulating atmospheric metals over time, have been widely used to proxy environmental quality over large areas, at various time scales. Using the example of the Paris region, we investigated the potential for the Grimmia pulvinata moss species to both characterize air metal contamination and to identify its main sources. To this end, we coupled metal/metalloid (Al, As, Cd, Cr, Cu, Fe, Ni, Pb, Sb, Sr, V and Zn) concentrations and Pb isotope ratios from samples collected in cemeteries in the city and its suburbs. Metal enrichment factors ranged between 2 and 10 for As, Cr, Fe, Ni, Sr, V, between 50 and 100 for Cu, Pb and Zn and > 100 for Cd and Sb, indicating a dominant anthropogenic origin. Principal component analysis showed that 3 principal components explained 89% of the metal variations: (i) European atmospheric background, (ii) regional urban sources, and (iii) resuspension of regional soils. This was corroborated by Pb isotope ratios, whose variations were modelled by a ternary mixing that considered the same 3 emission sources. Using a MixSIAR isotope model, we reveal that the European atmospheric background contributes slightly (< ~ 5%) and that within 20 km of the city center bioindicators are mostly impacted by urban sources (contributions: 50–80%). Samples collected > 20 km show almost equal contributions of the endmembers representing urban activities and agricultural soil resuspension.