Bioaccumulation and sources identification of atmospheric metal trace elements using lichens along a rural–urban pollution gradient in the Safi-Essaouira coastal area

Atmospheric contamination by metallic trace elements emitted by various human activities constitutes an important threat to human and environmental health. This study aims to determine metal accumulation and the sources of air metallic pollution in the Safi urban-industrial area using lichens as biomonitors. Ten trace elements (As, Cd, Co, Cr, Cu, Ni, Pb, Ti, V and Zn) concentrations and 206Pb/207Pb and 208Pb/207Pb isotopic ratios were analyzed by ICP-MS in four lichen species: Xanthoria Parietina, Ramalina Lacera, Xanthoria Calcicola and Ramalina Pollinaria. The results showed significant differences among study sites for most elements with higher concentrations in the industrial, urban and peri-urban sites compared to the reference site chosen as a natural rural area far from any human activities. Significant differences were found between saxicolous and corticolous species especially for Cd, Cu and Zn. The values of Zn/Cu, Zn/Pb and Pb isotope ratios measured in lichens revealed that vehicular traffic and industrial emissions are the main sources of atmospheric Pb contamination. Other anthropic activities (waste incineration, artisanal pottery …) might be the source of other trace metal elements accumulated by lichens. Airborne contaminants in Safi appear to be exported from their sources by air mass movements driven by the regional wind profile.