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1J - Bioaccumulation (WEP/58) Bioavailability of HOC's depending on the colloidal state of humic substances: A case study with PCB-77 and Daphnia magna. Gallé, Tom 1, 2, Grégoire, Christian2, Bierl, Reinhard2, 1 Resource Centre for Environmental Technologies CRP-Henri Tudor, Esch/Alzette, Luxembourg, Luxembourg2 Dept. of Hydrology University of Trier, Trier, Germany, Germany ABSTRACT- The reduction of the bioconcentration factor (BCF) for hydrophobic organic compounds (HOCs) with increasing DOC concentrations of the solution phase has been documented in numerous experiments for an array of animal species. Equilibrium has often been expected to be instantaneous for colloidal humic substances at ambient pH in natural waters. Yet humic substances can adopt condensed structures as a function of pH and ionic strength, a phenomenon that is ultimately used for their isolation (precipitation). Condensed organic phases in soils and sediments are held responsible for slow desorption of hydrophobic compounds: Crosslinked, rigid structures with slow relaxation rates allow only a hampered diffusion that proceeds by jumps between structural voids. Slow desorption phases are currently assigned to diagenetically condensed matter like kerogens and coals. We intend to show that a gradient of organic matter exists, depending on a variety of intramolecular bonds from electrostatic interactions to covalent binding. The effect of variations in ionic strength and ion composition on the partition of PCB-77 between Daphnia magna and 10 ppm of colloidal humic acid has been observed during 24 hours. Results show an inverse effect of increasing concentrations of charge screening Na+ and specifically binding Ca2+ on BCF. Implications for bioavailability studies and the impact of colloids and particles on bioaccumulation will be discussed. Key words: DOC, Bioconcentration, Colloids, Sorption |
