ABSTRACT
Establishing criteria for a maximum allowable metal content of sediments that will not cause chronic toxicity to aquatic organisms requires a science-based modeling capacity. One of the chief objections to the use of an equilibrium adsorption modeling approach to establish criteria for non-toxic metal concentrations in sediments has been the lack of evidence that adsorption and desorption can be appropriately treated as equilibrium processes. The concern as to whether metal-sediment interactions can be treated as equilibrium systems derives from two types of data. First, incomplete reversal has been reported for the adsorption of Cd onto natural sediments, of Ni and Co on clay minerals and of Cd, Ni, and Zn on goethite. Second, major differences have been reported in the time required for cationic metals to equilibrate with marine suspended sediments, depending on whether the adsorbates were added in the laboratory or had been adsorbed as a result of the prior release of the metals into the environment.
