We know today that trace metals in sediment and water occur not only in one single chemical form, but at the same time in a variety of physicochemical associations (species). We also know that these forms differ in their mobility and bioavailability. Plenty of analytical techniques have been developed to measure and characterize these metal forms. Assessing fate and biological effects of metals in the environment based solely on total concentrations is no longer state-of-the-art or scientifically motivated. In fact, a vast amount of knowledge has accumulated in the scientific literature during the last 3 decades, especially for those metals (Cr, Cu, Ni, Zn) that were selected in this study, that clearly illustrates the decisive role of metal speciation when metal bioavailability and toxicity in the environment have to be assessed. Although most water or sediment quality criteria for metals are still based on the total concentration of the metal in question, it is becoming more and more evident that also the regulatory society is increasingly considering speciation when environmentally relevant metals are monitored and assessed.

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