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

ABSTRACT

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.

KEYWORDS:

• Metal trace elements
• lichens
• air pollution sources
• Pb isotope ratio
• biomonitoring

Acknowledgements

We warmly thank the members of the French association of lichenology (AFL) for their contribution to the identification of certain species during the determination session at the laboratory of the forest ecology station of Fontainebleau (France, 2016). We also thank Claude Roux for the contribution to the determination of corticolous species (December 2019).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Essilmi Mohamed

Essilmi Mohamed is a graduate in biological sciences from Cadi Ayyad University, Morocco. Essilmi Mohamed is a researcher in lichenology, ecotoxicology and environment at the Faculty of Sciences Semlalia in Marrakech, trainer at the regional centre of pedagogical training of teaching and education in Safi, and teacher at the high school Mohamed 6 of excellence in Ben guerir.

Mohammed Loudiki

Loudiki Mohammed is a graduate in hydrobiology and ecology from the University of Aix-Marseille (France). He is a professor at Cadi Ayyad University, Marrakech, Morocco. He is scientific researcher in the Laboratory of Water, Biodiversity and Climate Change, Faculty of Science Semlalia. Marrakech. Morocco.

Abdelhay El Gharmali

El Gharmali Abdelhay is a graduate in Ecotoxicology from Cadi Ayyad University, Morocco. He is a professor at Cadi Ayyad University, Marrakech, Morocco. He is scientific researcher in the Laboratory of Water, Biodiversity and Climate Change, Faculty of Science Semlalia. Marrakech. Morocco.