Tree species as a biomonitor of metal pollution in arid Mediterranean environments: case for arid southern Tunisia

We investigated the accumulation of Zn, Cu, Pb, and Cd in the soil and the leaves and bark of five common tree species ( Eucalyptus occidentalis Endl . , Acacia salicina Lindl . , Cupressus sempervirens L . , Casuarina equisetifolia L., and Tamarix aphylla (L.) Karst.) in the city of Gabès Tunisia to elucidate their bioaccumulation potential and determine their usefulness as biomonitors of metallic pollution in arid urban areas. Our results indicated that the bark had higher mean concentrations of Pb and Cd than leaves. In contrast, the leaves had higher mean concentrations of Zn and Cu than bark. No hyperaccumulation was detected for any of the analyzed metals in any of the studied species. E. occidentalis and T. aphylla had the highest mean concentrations of the investigated metals in leaves and bark. Based on the calculated metal accumulation index (MAI) values, these two species accumulated more metals than other studied tree species. Likewise, the concentrations of Zn, Cu, Pb, and Cd in soil had significant positive correlations with that in leaves and bark. Accordingly, E. occidentalis could be used for biomonitoring in arid areas subjected to industrial and traffic pollution. T. aphylla would be a good alternative when native species are a priority.