This study quantified the levels of heavy metals bioacumulated by two benthic macroinvertebrates  characteristic in the lower Ebro river, Ephoron virgo (Ephemeroptera: Polymitarcyidae) and Hydropsyche spp. (Trichoptera: Hydropsychidae). The pollutants present in the Flix reservoir sediments consist on several heavy metals (especially mercury), radioactivity and persistent organic pollutants (PCBs, DDT, DDE…).
The sampled area contained sites along the river affected by the remobilization of polluted sediments, and reference sites in other parts of the basin. For Ephoron virgo, we analised nymphs at diferent stages of development and also adult females, adult males and eggs in order to test temporal bioacumulation patterns and its transfer to the next generation. For Hydropsyche sp. we analysed larvae independently of its developmental stage. In both cases spatial bioaccumulation was compared. Along the river sites, significant differences in metal concentration were obtained, with mean values more han 10 times higher after the reservoir than before. For Hg, we obtained around 0.05 ppm for Hg in reference sites and 1.16 ppm downstream the reservoir. In conclusion, the relatively high concentrations of several metals in the studied macroinvertebrates suggests that they provide an important source for heavy metal transfer to higher trophic levels in the lower Ebro food web.