Book excerpt: This book presents new results on metal fluxes from society to the environment, on metal speciation in water, soil and sediment, and its mobility, biological uptake and toxicity. New approaches, like the Acid Volatile Sulphide (AVS) concept to predict metal bioavailability in sediments, and the Biotic Ligand Model to calculate the toxicity of metals to aquatic organisms, are critically evaluated, with a focus on copper, nickel, zinc, and, chromium.