Issue 3

Activated carbon (AC) is currently being used to treat polychlorinated biphenyl (PCB) contaminated
field sediment. In the presence of sediment, the sorption capacity of AC for PCBs can be reduced. In
this study, sorption attenuation of AC is investigated using previously published data from 5
sampling sites where reductions in aqueous concentrations caused by AC amendment have been
reported. AC-water partitioning coefficients (KAC_clean_water) were determined at a relevant PCB
concentration in clean water using polyoxymethylene (POM) passive samplers. Logarithmic ACwater
partitioning coefficient values ranged from 7.39 to 9.59 for trichlorinated to pentachlorinated
congeners. These AC-water partitioning coefficients were used in a numerical model to predict
expected reductions in aqueous concentrations. Results reveal an overprediction of actual
reductions by a median factor ranging from 2.5 to 5.6. To obtain an estimate of AC sorption
attenuation, an AC-water partitioning coefficient more representative of sediment conditions
(KAC_apparent) was fitted via the model based on the observed reductions in aqueous concentrations.
On average, median KAC_apparent values of individual PCB congeners were smaller than KAC_clean_water
values by 1.08 log units, or a factor of 12, with corrections ranging from 0.1 to 2.3 log units. The
main controls on the reduction in sorption of PCBs to AC are PCB physico-chemical properties and
AC amendment variables. Generally AC sorption attenuation increased with PCB hydrophobicity and
decreased with increasing AC-sediment contact time and AC dose.