Pore-water silver concentration gradients and benthic fluxes from contaminated sediments of San Francisco Bay, California, U.S.A.

Estimates of the benthic t1uxes 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 /Lm) 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 ± I sd) dissolved pore-water concentration of silver from these three embayments was 120 ± 140 pM. The apparent molar partition coefficient of silver (Jog DAg ·) in pore waters of benthic sediments (s 2 em 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) (Jog DAg · 5.3 ± 0.3). Estimated diffusive benthic t1uxes of silver were greatest at sites affected by waste water outfalls with relatively elevated concentrations of silver in the eft1uent. Upper limit estimates of the integrated net benthic t1ux of silver to South Bay 02-290 mol yr- I) indicate that it could be 2.5-fold greater than the estimated t1uvial input of dissolved silver (- III mol yr" I) to the estuary (G.J. Smith and Flegal, 1993).