Assessing the hazard and risk of metals to aquatic organisms poses many challenges. Previous studies have found that both total and dissolved concentrations of metals are not reliable indicators of their effects on ecosystems. The toxicity of metals can be modified by various physico-chemical water characteristics, such as dissolved organic carbon, pH, and hardness, by several orders of magnitude.
The use of bioavailability techniques, such as the Biotic Ligand Model (BLM), can help to overcome these difficulties. The BLM approach is currently recognized as the leading method for predicting metal bioavailability because it integrates existing knowledge about metal speciation in the solution surrounding the organism and the interactions between metal ions and competing ions at the binding sites on the organism-water interface, such as epithelial cells in fish gill tissue.