News of possible interest only to me. It seems obvious that oil present in sediment enhances sorption and storage of PCBs than soot/black carbon. After all, it is a liquid phase and is present in higher amounts than black carbon. PCBs are so hydrophobic that almost any organic material has a higher affinity for PCBs than water/sediment. Carbon is a strong PCB adsorbent only for planar PCBs, and then only if it is itself graphitic, hence planar. In all other cases, oil should outcompete carbon for PCBs. Glad they found experimental evidence. In all my (three) years of analyzing for PCBs, the oily samples are always the highest concentration ones.
Oil Is a Sedimentary Supersorbent for Polychlorinated Biphenyls
Michiel T. O. Jonker and Arjan Barendregt
Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80176, 3508 TD Utrecht, The Netherlands
Received for review January 18, 2006
Revised manuscript received April 10, 2006
Accepted April 11, 2006
The often-observed enhanced sorption of hydrophobic organic chemicals (HOCs) to sediments is frequently attributed to the presence of soot and soot-like materials. However, sediments may contain other hydrophobic phases, such as weathered oil residues. Previous experiments have shown that these residues can be efficient sorbents for certain PAHs. In this study we investigated sorption of PCBs to sediments contaminated with different concentrations and types of oils, and from that derived oil-water distribution coefficients (Koil). Sorption of PCBs to both fresh and weathered oils was proportional to sorbate hydrophobicity, and no effects of PCB planarity were observed. Furthermore, the experiments demonstrated that different oils sorbed PCBs similarly and extensively (Koil up to 108.3 for PCB 169), and that weathering caused an almost 2-fold increase in sorption of the lower chlorinated PCBs. Koil values indicated that at the PCB equilibrium concentrations tested (pg-ng/L range), for many congeners weathered oil is a stronger sorbent than pure soot and soot-like materials. Due to attenuation of adsorption to the latter materials in sediments (caused by competitive adsorption with organic matter), sedimentary weathered oil will therefore, if present as a separate phase, defeat sedimentary soot, coal, and charcoal as PCB sorbent in most cases. Consequently, weathered oil probably is the ultimate sedimentary sorbent for PCBs and should be included in HOC fate models.