Metals occur naturally and are commonly found as contaminants in areas where industrial and municipal effluents are discharged. Aquatic sediments/environments are often polluted by heavy metals due to the temporal variations in anthropogenic input of contaminants via atmospheric deposition, catchment runoff, effluent inflow and dumping from industrial transportation, mining, agricultural and waste disposal sources [EPA, 1989]. The transfer of contaminants associated with settling inorganic particulates and/or biotic detritus from the water column to the sediments, no disturbance of sediments by physical mixing, slumping or bioturbation after deposition, no post-depositional degradation or mobility of the contaminants and the establishment of a reliable time axis. Therefore, metal contamination in aquatic environment is one of the problems. Rivers, coastal waters, sediments, soils, etc. were mostly contaminated by industrial and mining activities. Recently, the metal discharged from the industries have been controlled in the most developed countries. Even so, till the heavy metals dispersed in river sediments still need to be dealt with. Mainly, characterization, transformation, transport and fate of metal contaminants in the sediment to the aquatic environment need to be studied, because the sediment has great capacity to accumulate the contaminants. Exploitation and utilization of mines discharges heavy metals into the environment and contaminates neighboring aquatic ecosystem ...

Bioavailability refers to the extent to which humans and ecological receptors are exposed to contaminants in soil or sediment. The concept of bioavailability has recently piqued the interest of the hazardous waste industry as an important consideration in deciding how much waste to clean up. The rationale is that if contaminants in soil and sediment are not bioavailable, then more contaminant mass can be left in place without creating additional risk. A new NRC report notes that the potential for the consideration of bioavailability to influence decision-making is greatest where certain chemical, environmental, and regulatory factors align. The current use of bioavailability in risk assessment and hazardous waste cleanup regulations is demystified, and acceptable tools and models for bioavailability assessment are discussed and ranked according to seven criteria. Finally, the intimate link between bioavailability and bioremediation is explored. The report concludes with suggestions for moving bioavailability forward in the regulatory arena for both soil and sediment cleanup.

In experiments with sediment-water systems the effects of Copper, Cadmium, Zinc and Lead on electron transport system activity (ESTA), rate of nitrate reduction (except Pb) and nitrification were studied. All experiments were performed with eutrophic surface sedoments, contaminated with salts of different metals.

V.3 ... consists of individual chapters that describe 1) the conceptual background for radionuclides, including tritium, radon, strontium, technetium, uranium, iodine, radium, thorium, cesium, plutonium-americium and 2) data requirements to be met during site characterization.

The mechanisms controlling the transport of three heavy metals: cadmium, chromium, and silver, in natural water systems are evaluated following a review of the scientific literature and laboratory studies of adsorption/desorption behavior and the interaction of these metals with phytoplankton. In fresh water, chromium as chromate is not appreciably taken up by model inorganic or organic particulates, but after reduction to Cr(III) is rapidly and irreversibly taken up by clay particles, hydrous iron oxide and phytoplankton. Cadmium and silver are more reversibly adsorbed by clay particles, are strongly adsorbed by hydrous manganese oxide, and are concentrated by phytoplankton. Once a part of reducing bottom sediments, the availability of all three metals to the aqueous phase is further reduced so that they are not released by short term resuspension. With prolonged resuspension of anoxic sediments some cadmium may redissolve, but chromium and silver will remain in the solid phase. (Author).