The experimental exposures of aquatic organisms to metals have led to many scientific advances. For example, the toxicity of metals and their biological consequences can be now formalized within Biotic Ligand Model. However, the metal ecotoxicity is more complex to assess in real environments, often lowly contaminated, because it depends on physicochemical, biological and ecological processes. In this purpose, the determination of biota contamination in situ offers promising perspectives. Indeed, this biological endpoint allows to integrate the whole of environmental processes controlling both the speciation and bioavailability of metals in environmental conditions. Since Gammarus pulex is widely distributed in temperate freshwaters and plays an important role in the functioning of these ecosystems, this autochthonous invertebrate could constitute a specific-substrate early warning of bioavailable contamination.