TA7 Bioaccumulation and Kinetics of POPs
201 Oregon Ballroom
8:00 AM - 12:00 PM, Tuesday
() Partitioning of hydrophobic organic chemicals to plankton and suspended sediments: Are slow kinetics the answer?
Baker, J.1, Ko, F.1, Chang, C.1, Schneider, A.1, 1 University of Maryland Chesapeake Biological Laboratory, Solomons, Maryland, USA
ABSTRACT- Thirty-five years after Karickhoff's seminal papers describing partitioning of PAHs to sediments, considerably uncertainty surrounds modeling of hydrophobic organic contaminant (HOC) behavior in surface waters. Hydrophobicity, as typically quantified by the octanol-water partition coefficient, explains broad trends in HOC partitioning across several orders of magnitude. Normalization of partitioning by the organic matter content of the solids often further reduces variance, but not always. Most field studies demonstrate highly variable HOC partitioning in surface waters, with measured distribution coefficients between filterable solids and the dissolved phase varying several orders of magnitude for individual chemicals. Slow adsorption/desorption kinetics, the presence of colloids and, more recently, soot-like particles with extremely high HOC affinities have been proposed explanations for this variance. We have measured the distribution of polycyclic aromatic hydrocarbons and PCB congeners in several hundred surface water samples from the Chesapeake Bay and studied the rates of PCB adsorption to pure cultures of estuarine phytoplankton and the rates of PCB desorption from contaminated sediments. PAH partitioning in field samples is especially variable, with little correlation between dissolved and particulate PAH concentrations. This variability likely results from input of combustion-derived particles that contain tightly-bound PAHs that do not undergo water column partitioning. In contrast, PCB congener distributions are better predicted by classical Karickhoff-type partitioning, although the field-measured distribution coefficients of individual congeners still vary more than an order of magnitude. Slow sorption kinetics and the complex mixture of particles encountered in estuaries may account for this variance. Finally, our laboratory studies show that adsorption and desorption rates of PCBs to natural solids are reasonably fast, with approaches to equilibrium on the time scales of hours. This implies that hindered sorption rates may only explain observed HOC partitioning behavior only under restricted conditions.
Key words: PCBs, partitioning, PAHs, Chesapeake Bay