Isolation and Characterization of the Natural Colloidal Material From the Fox River

Abstract

ABSTRACT Resuspension of aquatic sediments with HOCs (hydrophobic organic contaminants) can disrupt existing sorption equilibria and cause HOC desorption, and increase the exposure of water column biota to HOCs. Resuspension can also increase levels of aqueous colloidal material in the overlying water column. Furthermore, because colloidal material partly determines the transport and ultimate fate of sediment-derived HOCs, physical and chemical characterizations of sediment colloids that are subject to resuspension are necessary to assess the full impact of activities that disturb contaminated sediments (e.g., dredging, navigation, chemical treatment, high flow events). Colloidal material extracted from lower Fox River sediments was analyzed for chemical (total organic carbon (TOC), elemental and mineralogical analyses, isoelectric point (pHIEP)) and physical (particle size distribution (PSD), solids and moisture content, surface area) characteristics, and subjected to batch aggregation studies under controlled conditions of ionic strength (10−4-10−2 M in 1:1 and 1:2 electrolyte solutions), pH (3–7), and colloid concentration (4–10 mg L−1 as TOC equivalents). The characterization and experimental results indicate that the extracted colloidal material aggregates in a manner consistent with existing double-layer models of the solid-solution interface in aquatic systems, most notably including faster aggregation (i) in the 1:2 than in the 1:1 electrolyte solution, (ii) at acidic pH (near pHIEP), and, (iii) at high colloid concentration. The PSD of the colloidal aggregates tended to be relatively broad, indicating the potential for relatively short- as well as long-range dispersion of colloidally bound HOCs derived from resuspended Fox River sediments.