Organic and Inorganic Components in Estuarine Colloids: Implications for Sorption and Transport of Pollutants

Abstract

In colloids isolated from Chesapeake Bay and its subestuaries the concentrations of Al, Fe, and a number of trace elements were determined to vary with the clay mineral fraction that was most abundant in freshwater samples collected during the winter. The elements As, Ba, Sb, and Zn, however, increased with increasing organic content, indicating a covariance with the organic component. Organic analyses for amino acids (proteins), carbohydrates, and lipids indicate that these biopolymers comprised 4 to 22%, 20 to 60%, and less than 1%, respectively, of the colloidal organic carbon in these samples. The results are significant because amino acids and carbohydrates contain oxygen, nitrogen, and sulfur functional groups capable of reacting with trace metals and organic pollutants. The sorption properties of several neutral hydrophobic organic compounds, including PAHs and herbicides, and several aromatic amines were investigated using the estuarine colloidal material. The effects of several environmental variables on these sorption properties were determined. The results indicate that colloids have the capacity to sorb and transport relatively insoluble pollutants that otherwise might remain immobile in the environment. Colloidal organic matter in natural water systems (lakes, rivers, estuaries and the oceans, as well as groundwater) may serve as substrates for the sorption or binding of organic contaminants. Although most of the data has been developed using neutral hydrophobic organic compounds, data also exist for selected polar compound groups such as aromatic amines. The chemical behavior of these compound groups in interaction with DOM appears to have some similarity to their chemical interaction with sediments and soils. Partitioning constants are linear, except for polar compounds, and appear to be closely correlated to fundamental compound properties such as solubilities and octanol-water partition coefficients. Even though a variety of methods were used to collect the colloids for study and to determine partition coefficients, no single method appears to be superior. Ultrafiltration techniques appear to be optimal for collecting the colloids, since this method subjects the materials to less extreme chemical conditions than the preparation of humic extracts, whereas equilibrium techniques such as dialysis and head space analysis appear to yield the best results for partitioning constants. However, each of these techniques has limitations with respect to the classes of compounds that can be studied successfully.