Rare earth elements (REEs) are emergent contaminants in aquatic ecosystems in parallel with their growing use in science, technology, and industry. In this study we measured the concentration of 16 REEs in freshwater marcobenthic invertebrates from 6 watercourses in northeast Italy to determine their potential use as ecological tracers of REEs in aquatic ecosystems. The total REE concentration at the sampling sites followed this order: site 6 (7.05 mg Kg−1) > site 3 (5.76 mg Kg−1) > site 4 (3.58 mg Kg−1) > site 1 (3.0 mg Kg−1) > site 5 (2.36 mg Kg−1) > site 2 (1.95 mg Kg−1). There were no significant differences in REE concentrations across the six samplings sites (Kruskal Wallis test, p = 0.1773), but two (site 3 and 6) had higher amount of REEs and were classified with the ecological status “Moderate” sensu Water Framework Directive since affected by anthropogenic activities. Light REE were always greater than heavy REE concentrations at all six sites. A positive correlation was observed between certain REEs (La, Ce, Gd) and the density of genera Caenis and Baetis (Ehemeroptera, collector-gatherers) (ρS range 0.795–0.812), suggesting that non-predatory macrobenthic invertebrates accumulate more REEs than predatory organisms and that the intake of sediment is the most effective route of assimilation.
