Concentrations of hydrophobic organic contaminants in zooplankton have been hypothesized to be governed by either near-equilibrium partitioning with surrounding water, growth dilution, or biomagnification. Concentrations of 17 polychlorinated biphenyls (PCBs) were measured in size-fractionated zooplankton, in phytoplankton (> 0.7 mu m), and in the dissolved water phase (< 0.7 mu m) in the surface water of the northern Barents Sea marginal ice zone east and north of Spitsbergen (Norway) and in the central Arctic Ocean at 89 degrees N. The linear partition model was used to indirectly assess if PCBs were equilibrated between water and the extractable organic matter (EOM) of zooplankton. As an independent test, the relation between the EOM-normalized partition coefficient (log K-EOM) and trophic level (TL) of the zooplankton (based on delta N-15) was investigated. All log K-log K-OW regressions were significant (n = 18, p < 0.05, r(2) = 0.65-0.95), being consistent with near-equilibrium partitioning and indirectly suggesting the absence of biomagnification. No correlation was found between log K-EOM and TL, further supporting the apparent absence of biomagnification in zooplankton. One implication of these results is a reduced uncertainty in modeling of food web uptake, in which kinetic parameterizations of biodilution or biomagnification in zooplankton may be replaced by a simpler parameterization based on equilibrium partitioning.