Heavy metals in natural aquatic environment are found in many different forms such as free hydrated ions, hydrolyzed species, inorganic complexes, organic complexes with natural organic matter, and adsorbed species on the surfaces of suspended particles. It have been well known that metal bioavailability and toxicity to aquatic organisms highly depend on the metal speciation. Therefore, ecological risk assessment and management should be conducted based on not only total metal concentration but also metal speciation. In this review, the relationship between metal speciation and bioavailability, and analytical methods of metal speciation in natural waters, and model prediction of metal speciation were introduced. Moreover, perspectives of risk assessment considering metal speciation and future research direction were mentioned.
