Pore-water silver concentration gradients and benthic fluxes from contaminated sediments of San Francisco Bay, California, USA

Estimates of the benthic fluxes of silver within San Francisco Bay substantiate the proposal that diagenetic remobilization is an important source of silver in surficial waters of the estuary (G.J. Smith and Flegal, 1993). Dissolved (< 0.45 mu m) silver concentrations in pore waters from relatively pristine and contaminated sediments from San Francisco Bay, as well as from sediments from Tomales Bay and Drakes Estero ranged from 4 to 4600 pM, with one exception (8900 pM). With the exclusion of four exceptionally high concentrations (> 620 pM), the average ((x) over bar +/- 1 sd) dissolved pore-water concentration of silver from these three embayments was 120 +/- 140 pM. The apparent molar partition coefficient of silver (log D-Ag *) in pore waters of benthic sediments (less than or equal to 2 cm deep) within San Francisco Bay ranged from 3.7 to 5.8 (5.1 +/- 5.2), which was consistent with the previously reported partitioning of silver within the bay surface waters (G.J. Smith and Flegal, 1993) (log D-Ag * 5.3 +/- 0.3). Estimated diffusive benthic fluxes of silver were greatest at sites affected by waste water outfalls with relatively elevated concentrations of silver in the effluent. Upper limit estimates of the integrated net benthic flux of silver to South Bay (32-290 mol yr(-1)) indicate that it could be 2.5-fold greater than the estimated fluvial input of dissolved silver (similar to 111 mol yr(-1)) to the estuary (G.J. Smith and Flegal, 1993).