The effects of sediment contact time on Koc of nonpolar organic contaminants

Mobility of nonpolar organic contaminants depends upon partitioning between sediment solids and interstitial water. The objective of this study was to measure the constancy of Koc values for polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs) over time. Two PCBs and one PAH were incubated and sampled periodically over a 6 month period. Results demonstrated that as time of contact increased, the value of Koc increased, reflecting a decrease in the truly dissolved contaminant concentration in the interstitial water. The data also showed a marked dependence of Koc on the source of organic carbon and a 2 to 17 fold deviation of measured Koc values from values predicted by empirical relationships. Therefore, empirical data may be the only truly reliable alternative for determining mobility potential of these contaminants.