An integrated interdisciplinary approach to evaluate potentially toxic element sources in a mountainous watershed

Potentially toxic elements (PTEs, i.e., Cd, Ni, Cr) and their source apportionment in waters are of major environmental concern. Different approaches can be used to evaluate PTEs sources in environment, but single-way approaches are often limited and can easily fail. PTEs sources apportionment should include the evaluation of geochemical background and spatiotemporal trends analyses. We propose an integrated approach, and we apply it to a mountain catchment in the Italian central Alps, where ultramafic terranes crop out. We collected water and glacial sediment samples during the melting season. Then, we analyzed major ions and PTEs in waters, and we quantified the total PTEs load in sediments through acid digestion. Data were then processed through spatial and temporal trends analysis, clustering of variables and the evaluation of partition between the different compartments. We found a high geochemical background of part of the PTEs, consistently with results from other areas worldwide on mafic and ultramafic terranes (high concentrations of Ni, Cr and Fe), while we identified an additional atmospheric deposition source for Zn, Cd and Ag. Also, redundant observations on Cu, As and Pb indicated a possible mixed source. This study elucidates the need for an integrated approach to avoid unnecessary or misleading assumptions in the PTE's source appointment. A single-way approach application, in fact, can fail in understanding element source in a complicated and dynamic compartment like surface water.