Preferential sorption of planar contaminants in sediments from Lake Ketelmeer, The Netherlands

Organic carbon normalized sediment-water distribution coefficients (K-oc) o f a series of in situ and (mass-labeled) added chlorobenzenes, PCBs, and PA Hs were determined in an aged and a more recently deposited sediment layer from Lake Ketelmeer, The Netherlands, using the cosolvent method. The resul ting log K-oc's for both in situ and added compounds are rather high compar ed to literature data (up to 9.3 for benzo[ghi]perylene), with the ones in the recently deposited layer being generally higher than those in the aged layer (up to 1.6 log units). The results do not show the well-established e ffects due to increased contact time of contaminants with sediments (i.e. " aging" or "slow sorption") and indicate that after only short equilibrium t imes (11 days) K-oc's can even be higher than after several decades of cont act time in the field. In addition, distribution coefficients show a remark able dependence on sorbate planarity, manifested by significantly different log K-oc-log K-ow relationships for planar (chlorobenzenes, PAHs, and mono -ortho-substituted PCBs) and nonplanar (multiple-ortho-substituted PCBs) co ntaminants in both sediment layers. The confirmed presence of sootlike mate rial for which planar aromatic compounds probably have strong affinity is b rought up to explain these observations. Differences in K-oc's between both layers are discussed in relation to contact time and analyzed soot fractio ns.