Investigating the isotopic composition of mercury and lead in epiphytic lichens from South-western France (Pyrénées-Atlantiques) to better constrain the spatial variability of their atmospheric transport and deposition

The geographical variability of the elemental concentration and isotopic composition of mercury and lead was evaluated in epiphytic lichens collected over a mesoscale area (Pyrenees-Atlantiques, Southwestern France). The sampling points have been selected according to different parameters in order to represent the main land use classification of the investigated territory (urban, industrial, agricultural and forestal zones). Total concentrations of Hg are homogenous over the territory (mean 0.14 mg/kg dry weight) and reflect the European atmospheric anthropogenic background deposition. A significant trend is observed for lead concentrations between anthropogenized areas (~11 mg/kg) and remote areas (~6mg/kg), mainly due to local road traffic and industrial inputs. The isotopic composition of Hg reveals a relatively homogeneous signature specific of remote areas, while the lead isotopic composition is distributed along two distinct origins: past leaded gasoline and geogenic background. This study shows that the spatial concentration variability observed is globally consistent with the isotopic signatures of Hg and Pb recorded in lichens which partly explain the origin of these two metallic contaminants.