PAH Repartitioning in Field-Contaminated Sediment Following Removal of the Labile Chemical Fraction

The effect of removing the labile chemical fraction associated with sediment particles followed by internal chemical redistribution was examined in a field-contaminated sediment. Using data from desorption equilibrium (organic carbon-water partition coefficients, K-OC) and kinetic (rate of release) experiments, estimates of polynuclear aromatic hydrocarbon biphasic partitioning and desorption rates for both the labile and nonlabile chemical fractions or organic matter compartments were obtained. Sediment K-OC values increased between 50 and 150% after removal of the labile chemical fraction. Following depletion of the labile chemical fraction during desorption experiments, sediment was stored 30 and 90 days to allow for chemical redistribution between the labile and nonlabile compartments. The subsequent desorption data indicated repartitioning had occurred with the nonlabile chemical fraction recharging the labile compartment. The results provide evidence that chemical transfer between organic matter compartments, either through interparticle porewater or via direct intraparticle compartmental exchange, is a real phenomenon that occurs over relatively short times (weeks to months). This calls into question the idea that hydrophobic organic pollutants in the nonlabile chemical fraction are sequestered or less bioavailable over the long-term and has implications for water quality impacts during contaminated sediment resuspension events, risk assessment of polluted sites, and selection of sediment remediation strategies.