Silver in river and estuarine waters of Texas: Evidence for complexation to macromolecular organic matter
Lehman RD Andren AW
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Concentration and phase speciation of Ag in selected Texas rivers and in the Trinity River estuary were measured in order to establish the major factors which control its fate in the aquatic environment from source to sink. Concentrations of Ag in the filter-passing fractions in Texas rivers ranged from <0.01 to 62 ng/L. In the Trinity River estuary (Galveston Bay), they ranged from 0.4 to 6.4 ng/L and showed a non-conservative estuarine mixing behavior. An example is shown in Figure 1. An internal source of both filter-passing ( less than or equal to 0.45 mu m) and colloidal (1kDa similar to 0.45 mu m) Ag was observed in the upper Trinity Bay. Silver, associated with colloidal macromolecular organic matter, which was isolated using cross-flow ultrafiltration techniques, amounted to 15-70% of the filtered ( less than or equal to 0.45 mu m) Ag concentration, decreasing with increasing salinity. Such a trend was similar to that of dissolved and colloidal organic carbon. Estuarine distributions of colloidal Ag were also broadly similar to those of suspended particulate matter. The ratio of colloidal Ag to filter-passing Ag was similar to the ratio of colloidal organic carbon to total dissolved organic carbon (Figure 2), suggesting not only that Ag is complexed by organic macromolecules, likely to sulfhydryl groups, but also that these functional groups were evenly distributed over the different molecular weight fractions. Particulate Ag was found associated mainly with a Fe-Mn oxyhydroxide/sulfide phase. The close relation between Ag and Fe in colloidal and particulate phases (Figures 3 and 4) suggests common surface complexes, probably again sulfhydryl groups
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