FATE, BIOAVAILABILITY AND TOXICITY OF SILVER IN ESTUARINE ENVIRONMENTS

The chemistry and bioavailability of Ag contribute to its high toxicit y in marine and estuarine waters. Silver is unusual, in that both the dominant speciation reaction in seawater and the processes important i n sorbing Ag in sediments favour enhanced bioavailability. Formation o f a stable chloro complex favours dispersal of dissolved Ag, and the a bundant chloro complex is available to biota. Sequestration by sedimen ts also occurs, but with relatively slow kinetics. Amorphous aggregate d coatings enhance Ag accumulation in sediments, as well as Ag uptake from sediments by deposit feeders. In estuaries, the bioaccumulation o f Ag increases 56-fold with each unit of increased Ag concentration in sediments. Toxicity for sensitive marine species occurs at absolute c oncentrations as low as those observed for any non-alkylated metal, pa rtly because bioaccumulation increases so steeply with contamination. The environmental window of tolerance to Ag in estuaries could be narr ower than for many elements.