Importance and difficulties of research on metal speciation in the aquatic ecosystem: an ecologist's viewpoint

Post-war research on the role of heavy metals in the environment was stimulated by a new sensitivity towards nature, the increasing impact of human activities on the environment, continuous progress in analytical chemistry and the development of radioecology. Nowadays, very low concentrations of total metal can be quantified in the various compartments of the ecosystem (e.g. water, sediment, suspended particles, plants and animals), and the physical and chemical forms of the metal identified. A current difficulty is how to evaluate the role of the various metal forms in the natural ecosystem. The major issues to be tackled are: variations over time of metal species in relation to the influence of environmental variables; the fact that the availability of the metal varies with the plant and animal species; the ability of the organism to select the metals and their forms; the influence of suspended particles and chelating substances on metal uptake, detoxification strategies and synergic and antagonistic effects. The advantages and disadvantages of monitoring using bioaccumulator organisms are discussed.