I am often involved in issues of sediment contaminated with PCBs and PCDD/Fs that can be combined in a number of ways to generate a Toxic Equivalency (TEQ). Now I realize that toxicologists really only guarantee the usefulness of the TEQ concept when it is determined in an organism that a human or another animal might consume. Nonetheless, I know that practically people find it helpful to look at the TEQ for PCBs-PCDD/Fs in many kinds of abiotic media (e.g., wastewater, suspended solids, sludge, bed sediment, soils, and urban runoff).
My question has to do with standards that people use and/or find preferable for PCDD/Fs, PCBs, and TEQ in bed sediment in surface water. Does someone like the TEQ concept in bed sediment, and if so do you have a level that you like to at least use as a reference? Does someone prefer mass or molar concentrations of PCDD/Fs or PCBs? Do people even like to have standard, or do you find it preferable to look at everything on site-specific basis? In the US, there are not really any bed sediment standards for most of these pollutants that are legally enforced, but it would still be helpful to have a way to characterize the general level of contamination and risk without doing a full-blown food web risk analysis every time. Any suggestions?
Dear Nathan,
Interesting question. Attached a description of the Norwegian approach to set sediment quality criteria including TEQs for PCDD/PCDFs. There is a reference document giving the background for the proposed values but only available in Norwegian. Take contact if that is of interest.
Best regards,
Gijs Breedveld
This may be useful http://klamathrestoration.gov/sites/klamathrestoration.gov/files/EPA%20Klamath%20dioxin%20memo%201-13-10%20final.pdf
John, thanks for the link. I just found that document a few days ago. I've been reviewing it. Based on what's there, it seems like everyone has their own ideas about is "clean" as far as TEQ is concerned. Have you used any of the sediment guidelines in this table?
As far as I know, the Canadian council of the ministries of environment (CCME) also develop guidelines for these compounds in sediment, on the basis of TEQ. Look at http://www.ccme.ca/
Nevertheless, personally I do not support the use of TEQ in sediments. Dominant compounds in this compartment may not be taken up evenly by organisms. Moreover, CCME guidelines are based on toxicity to sediment dwelling organisms, while dioxins toxicity is much more of concern for vertebrates, in particular mammals.
Marc, thank you for that helpful answer. I am not a toxicologist, but I do think about toxicological risk. I feel that people do apply TEQs readily to abiotic media without understanding some of the limitations and assumptions in doing so, just as you pointed out with benthic organisms as compared to vertebrates and mammals. It almost seems to necessitate different TEQ schemes that are dependent on the eco-receptor. Perhaps this is already being done, or perhaps this is dealt with by simply having differing TEQ thresholds for different receptors.
If it is done with different thresholds for different receptors, it doesn't sit completely well with me because of organism differences in quantitative bioaccumulation for TEQ compounds. When considering the uptake of dioxin-like compounds, TEQ is not the basic quantity for the mass transport and thus represents a less than fundamental mechanistic approach. I think everyone knows this, but the TEQ concept seems attractive in many situations because it is easy to apply and at least appears to cut through the complexity of several different compounds at different concentrations and toxic strengths.
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