PARTITIONING OF CU, PB, AG, ZN, FE, AL, AND MN BETWEEN FILTER-RETAINED PARTICLES, COLLOIDS, AND SOLUTION IN 6 TEXAS ESTUARIES

There are few methodical studies of processes controlling trace metal behavior in estuaries, where river water gradually mixes with seawater leading to systematic changes in ionic strength, pH, DOC, nutrient concentrations, and alkalinity. We report here data on Cu, Zn, Pb, and Ag behavior in six Texas estuaries using state-of-the-art ultra-clean techniques. In addition, Fe, Al, and Mn data are presented for one of Texas's major estuaries, Galveston Bay. It was found that suspended matter concentration (SPM) was the only variable related to systematic variations in partitioning of trace metal and Fe and Al concentrations between filter-retained and filter-passing fractions across salinity gradients. Inverse relationships were observed between empirically defined particle/solution distribution coefficients, K(D), for the different metals and SPM concentrations. This inverse dependence can be explained by the ''particle concentration effect'', which can be caused by the presence of Fe, Al, and trace metals associated with colloidal matter in the filtrate fraction. Our argument is supported by the direct analysis of colloids (> 10,000 Daltons) ultrafiltered from Galveston Bay waters. Colloidal Fe, Al, Pb, and Zn (but not Cu) account for most of the filter-passsing form of these metals. The results of this study have important implications for regulatory agencies and regulated industries, allowing for algorithms to predict Pb, Cu, Zn, and Ag partitioning between particle and solution phases.