Bioaccumulation of potentially toxic elements in some lichen species from two remote sites of Tunisia

The bioaccumulation of potentially toxic elements (PTEs), namely Al, As, Cd, Cr, Cu, Fe, Ni, Pb, Sb, and Zn, was investigated at two remote sites of the Jendouba region of Tunisia in the lichens Lobaria pulmonaria, Parmotrema perlatum, Ramalina farinacea, and Flavoparmelia caperata. Additionally, to evaluate the biological impact of PTEs, the content of chlorophyll was also evaluated as indicator of lichen vitality. The results showed species-specific differences in the bioaccumulation of PTEs, with L. pulmonaria accumulating the highest amounts, and R. farinacea the lowest. The abundant presence of L. pulmonaria, a lichen species known to be very sensitive to air pollution, the overall low levels of PTEs accumulated in lichen thalli and the good vitality expressed in terms of chlorophyll content clearly indicated that the two sites are subjected to negligible or very low levels of air pollution. Special care should be devoted to monitor the somewhat high concentration of Cu that may cause chlorophyll degradation and could injury the lichen population. Based on these outcomes, the two sites could be suited for harvesting uncontaminated material to be used in lichen transplant biomonitoring studies.