COLLOIDAL AND PARTICULATE SILVER IN RIVER AND ESTUARINE WATERS OF TEXAS

Concentration and phase speciation of Ag in selected Texas rivers and in the Trinity River estuary were measured in order to establish the m ajor factors that control its fate in the aquatic environment from sou rce to sink. Concentrations of Ag in the filter-passing fractions in T exas 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-co nservative estuarine mixing behavior. An internal source of filter-pas sing (less than or equal to 0.45 mu m) and colloidal (1 kDa-0.45 mu m) Ag was observed in the upper Trinity Bay. Silver, associated with col loidal macromoecular organic matter, which was isolated using cross-fl ow ultrafiltration techniques, amounted to 15-70% of the filtered (les s than or equal to 0.45 mu m) Ag concentration, decreasing with increa sing salinity. Such a trend was similar to that of dissolved and collo idal organic carbon. Estuarine distributions of colloidal Ag were also broadly similar to those of suspended particulate matter. The ratio o f colloidal Ag to filter-passing Ag was similar to the ratio of colloi dal organic carbon to total dissolved organic carbon, suggesting not o nly that Ag is complexed by organic macromolecules but also that funct ional groups with high affinity for Ag were evenly distributed over th e different molecular weight fractions. Particulate Ag was found assoc iated mainly with a iron-manganese oxyhydroxide/sulfide phase. The clo se relation between Ag and Fe in colloidal and particulate phases sugg ests common surface complexes, probably sulfhydryl groups. In river wa ters of Texas, 33-89% of the operationally defined dissolved (less tha n or equal to 0.45 mu m) Ag fraction was present in a large colloidal form (0.1-0.45 mu m). The high affinity of Ag for suspended particulat es in river and estuarine water was reflected by a high mean particle/ water partition coefficient of log K-d = 5.0 +/- 0.6 (based on filtrat ion through a 0.45-mu m filter) and 5.5 +/- 0.5 (based on filtration t hrough a 0.1 mu m filter). Particle/water partition coefficients for t he surface-adsorbed phase showed particle concentration effects, which , however, disappeared (log K-p1 = 5.0 +/- 0.3) when the dissolved Ag data were corrected for the presence of a colloidal fraction.