RESUMEN
This study aims to use environmental indices as complementary tools to other air quality biomonitoring techniques. The concentrations of trace elements Hg, Se, V, Mo, and Ba were analyzed by ICP-MS in four lichens: Xanthoria calcicola, Xanthoria parietina, Ramalina pollinaria, and Ramalina lacera. To assess the contamination of lichens by trace elements, different environmental indices were calculated: Contamination Index (Ic), Contamination Factor (CF), Pollution Load Index (PLI) and Enrichment Factor (EF). The results revealed that the genus Ramalina has a low tolerance to polymetallic pollution with a PLI not exceeding 0.44. The genus Xanthoria seems more resistant to polymetallic pollution with a maximum PLI of 2.58. The calculation of the enrichment factor revealed a very strong enrichment of the lichens in Mo, Hg and Se with a maximum content in Ba which reflects a strong metallic contamination of various origins especially in the urban and industrial areas of the region.