Field Measurements of PCB Partitioning between Water and Planktonic Organisms:  Influence of Growth, Particle Size, and Solute−Solvent Interactions

Due to long equilibration times, growth of planktonic organisms significantly dilutes cell concentrations of adsorbed highly hydrophobic organic compounds (HOCs). Behavior of polychlorinated biphenyls (PCBs) in field samples of 0.2−2, 2−25, and >100 μm particle size fractions confirmed this. The in-situ log K oc values showed a near linear relationship with hydrophobicity (log K ow) with a slope of 1.2 for the 0.2−2 μm size fraction, whereas the in-situ log K oc values remained within 1 log unit throughout the entire log K ow interval for the 2−25 μm size fraction. In the largest size fraction, there was a weak positive relationship between log K oc and log K ow with a linear regression slope of 0.28. The results imply that equilibrium concentrations in planktonic organisms cannot be used in food chain modeling. Observed high equilibrium log K oc values relative to log K ow values are discussed in terms of solute−solvent interactions in the octanol−water system as opposed to the organic carbon−water system in the field.