Metals discharged into aquatic systems are mostly adsorbed on suspended particles and finally accumulate in sediments. Since the toxicity of metals have been recognized as important environmental hazard, extensive research was conducted on the dose-effect relationship under different geochemical conditions. In those studies during the 1970s and 1980s, exposure was focused on waterborne metals and factors affecting metal bioavailability. Especially the influence of water composition on toxicity such as hardness and pH was discovered. Regulatory authorities developed Water Quality Criterias, which based on a compilation of measurements and on mechanistic statistical relationships.