Some authors give the dioxin concentration, pg/g and some gave the concentration pg/g WHO-TEQ. How to compare those values and how to convert TEQ to pg/g?
To convert concentration values to TEQ, you only need a set of appropriate TEFs (toxicity equivalent factors). TEQ= sum of concentration values (of every toxic congener) multiplied by corresponding TEF value.
hope it helps,
Tomas
Hi Bedigama Kankanamge Kolita Kamal Jinadasa,
For dioxins, the body burden is usually expressed in: Mass (weight) Units I-TEQ per kilogram of body weight (pg I-TEQ/kg bw). Alternatively, as dioxins accumulate in fat, the body burden can be expressed in picogram I-TEQ per gram of serum lipid, i.e. per gram of fatty substance in the blood (pg I-TEQ/g lipid). Dioxins are generally found in mixtures containing several kinds of dioxins and dioxin-like compounds, each having its own degree of toxicity. To express the overall toxicity of such a mixture as a single number, the concept of “International Toxic Equivalents” (TEQ) has been developed. The “Toxic Equivalent” (TEQ) scheme weighs the toxicity of the less toxic compounds as fractions of the toxicity of the most toxic TCDD. Each compound is attributed a specific “Toxic Equivalency Factor” (TEF). This factor indicates the degree of toxicity compared to 2,3,7,8-TCDD, which is given a reference value of 1. To calculate the total TCDD toxic equivalent (TEQ) of a dioxin mixture, the amounts of each toxic compound are multiplied with their Toxic Equivalency Factor (TEF) and then added together. The TEQ scheme refers only to adverse effects (e.g. cancer) following interactions with the cellular Ah receptors Toxic Equivalency Factor (TEF) values vary for different animal species. Regarding humans, to better understand the above values and their conversions, Dioxin Body Burdens were determined at the time of exposure:
1) Adults in industrialized countries: 2 000 to 6 000 (in pg I-TEQ per kg body weight) or 10 to 30 (in pg I-TEQ per g serum lipid);
2) Moderately exposed workers: 3 000 to 13 000 (in pg I-TEQ per kg body weight) or 15 to 650 (in pg I-TEQ per g serum lipid);
3) Highly exposed workers: 28 000 to 400 000 (in pg I-TEQ per kg body weight) or 140 to 2 400 (in pg I-TEQ per g serum lipid);
4) SEVESO incident (median values): Zone A: 90 000 * Zone B: 25 000 * Max : 10 000 000 (in pg I-TEQ per kg body weight).
Best wishes,
Ilya
I have to add a small remark:
there are several sets of TEFs. WHO-TEFs ( and corresponding WHO-TEQ) were created by the research group of Martin van den Berg and published in 1997 and than more precise set of TEFs appeared around 2008.
I-TEFs (and corresponding I-TEQ) are usually linked with a EN -1948 standard (emmissions).
With each sets of above mentioned TEFs, you will get a three different TEQ value, therefore if you want to compare TEQs, they have to be calculated having used the identical set of TEFs.
Having concentration of 17 congeners of PCDD/Fs (and/or 12 congeners of PCBs with dioxin effect) + set of TEFs, you can calculate TEQ value, but the reverse process (make 17 or 29 values out of TEQ) is impossible....
kind regards, Tomas
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