The speciation and physico-chemical forms of metals in surface waters and sediments

Surface waters can be contaminated in many ways, e.g., by solutions and suspended matter. Moreover, insoluble substances in colloidal form, in suspension or adsorbed on solid bodies can dissolve in response to changing physical and chemical conditions and become a secondary source of surface water pollution, thereby endangering wildlife. In addition, if we take into account varying rates of flow, contaminants can be transported over considerable distances. Hydrological processes, which determine factors, such as the rate of sedimentation, also influence the quality of surface waters; bottom sediments can contain large quantities of accumulated organic and inorganic compounds, including heavy metals. The physical and chemical properties of aquatic ecosystems are characterized by a number of interdependent parameters. Hence, factors such as temperature, oxygen content and pH of a water body can alter the solubility of the salts present in it, the forms of occurrence of particular species, as well as their bioavailability and toxicity. Thus it is necessary to determine the various species of metals present in the different compartments of the aquatic ecosystem.