Numerous polluted sites have been left unmanaged since the end of the industrial era in Europe, in the mid 20th century. Metals such as cadmium and zinc are accumulated in leaves, in quantity depending on tree species. At abscission, leaves still contain metals which can be transferred to adjacent ecosystems (terrestrial or aquatic) and are then susceptible to affect organisms and associated functional processes. In the present study, we aimed to assess the effects of contaminated litter entering small streams, highly dependent on allochthonous organic matter for their functioning. We first assessed the leaching of metals from contaminated litter, showing its fast and high release in water. Then, we tested the impact of leachates on the common freshwater shredder Gammarus fossarum following survival, metal bioconcentration, physiological (osmoregulation, digestive enzymes, lipid peroxidation, energy reserve) and behavioral responses (locomotion & ventilation). Finally, in an in situ experiment, we conjointly assessed the effects metal contaminated litters on their decomposition and on their consumption by G. fossarum. Despite behavioral modifications, litter decomposition and consumption did not differ between contaminated and un-contaminated litters suggesting that in spite of detrimental effects of contaminated litters, ecosystem functions can be maintained, at least in the short term.