ET&C Spotlight: Application of a Tenax Model to Assess Bioavailability of PCBs in Field Sediments by Elizabeth M. Mackenbach, You Jing, Marc A. Mills, Peter F. Landrum and Michael J. Lydy
Jane Parkin Kullmann, Haley & Aldrich, Inc.
Polychlorinated biphenyls (PCBs) seem to be everywhere these days and not just in the sense of environmental media. They are a hot topic in many areas including government and academia and for a wide range of reasons, not the least of which is that they are common compounds of concern at contaminated sites. If PCBs are encountered in sediment, this can often be a significant driver of the remedial efforts due to the toxicity of PCBs to ecological receptors. However, much is still being learned about the characteristics of these compounds, including their environmental fate and transport, which may help inform the evaluation of the necessary level of remedial effort.
One aspect of PCBs that is very actively being explored is bioavailability of these compounds in sediment. One of the techniques that has been developed to assess sediment PCB bioavailability is Tenax extraction. Tenax is a porous polymer resin that is used to adsorb organic chemicals that desorb from sediment. The use of a Tenax extraction model to evaluate the bioavailability of PCBs in sediment is the subject of this ET&C article spotlight.
For the subject study, Mackenbach et al. (ET&C 31.10:2210–2216) constructed a model of PCB bioavailability using data from other 24-hour Tenax extraction studies and associated bioaccumulation data from laboratory-exposed and field-collected oligochaetes. They tested the model using a Ottawa River dataset. The Ottawa River sediments had a wide range of PCB concentrations, physical characteristics and particle size. Bioaccumulation tests and Tenax extractions were performed on each of the sediment samples using appropriate duplicative analyses, analytical methods and QA/QC procedures. These results were then compared to the values predicted by the literature model.
The authors found that most of the Ottawa River total PCB data fell within the 95th confidence interval of the literature-derived model, expressing very good agreement between the model and the real-world sediments. The authors then plotted the data by PCB homolog. While most of the homologs demonstrated a similar degree of agreement between the model and the Ottawa River data, this analysis made it immediately apparent that the model over-predicted bioaccumulation of mono- and di-chlorinated biphenyls (i.e., the measured bioaccumulation of these homologs was lower than predicted by the model). As noted by the authors, this would mean that the model is conservative in this respect.
The authors further discussed the Tenax extraction studies that they used in their model. They concluded that overall, the Tenax extraction method provides consistent results across different types of studies. The authors also noted that while previous studies had identified a relationship between Tenax extraction and oligochaete bioaccumulation results, the authors consider theirs to be the first Tenax extraction and oligochaete bioaccumulation study to corroborate a bioaccumulation model with an independent dataset. They concluded that corroboration makes their model more useful for future applications. The authors closed by summarizing some of the uncertainties present in their work. They recommended further study of PCB bioavailability in marine environments, bioavailability in sediments with non-aqueous phase liquids and potential interference from PCB biotransformation by exposed organisms. Additional articles related to this topic are provided here.
Author’s contact information: JParkinKullmann@haleyaldrich.com
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