Aspects of colloid and pollutant geochemistry in marine sediments
Anthropogenic organic contaminants, like polychlorinated biphenyls (PCBs), introduced into aquatic environments associate with dissolved, colloidal, and particulate phases based on physicochemical properties. A challenge to assessing the fate and effects of these pollutants is determining their distribution among these phases. To date, contaminants associated with the particulate and 'dissolved' phases have been well studied, while the colloidal phase has remained elusive. Objectives of this work were to (1) isolate colloidal and dissolved phases from marine sediments, (2) measure the three phase distribution of PCBs in an environmentally contaminated sediment core, and (3) demonstrate the relevance of colloidal phases in assessing marine sediment geochemistry including contaminant bioavailability.^ Contaminated marine sediment cores were collected from a Superfund site. Centrifugation separated interstitial waters from the sediment. Two methods were evaluated for isolating interstitial colloidal and dissolved phases: reverse phase chromatography and ultrafiltration. Once phases were isolated, extracted PCBs were quantified using gas chromatography with electron capture detection. A core was sectioned into eight distinct horizons and dissolved, colloidal, and particulate (sediment) PCB concentrations measured. Finally, the relevance of colloid-PCB interactions was assessed by conducting (1) short-term bioaccumulation exposures, with two marine bivalve species, and (2) sediment mixing studies.^ In comparisons of isolation methods, reverse phase chromatography proved more effective than ultrafiltration for separating dissolved and colloidal phases from interstitial waters. The chromatographic method generated results agreeing with theoretical considerations and other studies in model laboratory systems. In the second study, interstitial water low molecular weight PCBs were prevalent in the dissolved phase (40-65% colloidal associated) while medium and high molecular weight PCBs dominated the colloidal phase ($\ge$80% colloidal associated). Magnitudes of the colloidal associations increased with core depth suggesting colloidal organic carbon was becoming more nonpolar. Finally, PCB bioavailability studies showed an unexpected correlation between colloidal PCBs and bivalve accumulation (r = 0.44 to 0.95, n = 15). Further, sediment mixing increased the concentration and altered the distributions of dissolved and colloidal PCBs in interstitial waters.^ In conclusion, these studies support findings of other theoretical and empirical studies of colloid-pollutant interactions and further our specific understanding of the importance of colloids as a significant aquatic phase in environmentally contaminated marine sediments. ^
Hydrology|Physical Oceanography|Environmental Sciences|Engineering, Environmental|Geochemistry
Robert M Burgess,
"Aspects of colloid and pollutant geochemistry in marine sediments"
Dissertations and Master's Theses (Campus Access).