Toxic equivalency factor (TEF) and Total Toxic Equivalency (TEQ)

Modified on: Wed, 20 Feb, 2019 at 8:47 AM

TEF expresses the toxicity of dioxins, furans and PCBs in terms of the most toxic form of dioxin, 2,3,7,8-TCDD.  2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the reference chemical to which the toxicity of other dioxins and dioxin like chemicals are compared. The toxicity of the individual congeners may vary by orders of magnitude, where dioxins are assigned a scaling factor of toxicity (TEF) in comparison to TCDD. TCDD has a TEF of 1.0.

Exposure to environmental media containing 2,3,7,8-TCDD, other dioxins and dioxin-like compounds can be harmful to humans as well as to wildlife. These chemicals are resistant to metabolism and biomagnify up the food chain. Toxic and biological effects of these compounds are mediated through the aryl hydrocarbon receptor (AhR).

With the TEFs, the toxicity of a mixture of dioxins and dioxin-like compounds can be expressed in a single number - the Total Toxic equivalency (TEQ). The toxic equivalency of a sample is the sum of the concentrations of individual compounds multiplied by their relative toxicity (TEF). TEF/TEQ values are not assigned to the Total Dioxin (PCDD) or Furan (PCDF) groups. The total toxicity information is more meaningful to toxicologists than reporting the total number of grams/micrograms. TEQs are then used for risk characterization and management purposes, such as prioritizing areas of cleanup.

*Note*: The 2,3,7,8-TCDF confirmation is performed when the value found in the primary run is above the reporting limit, as this column cannot resolve the 2,3,7,8-TCDF from two other potential tetrachlorinated isomers. Toxicity is associated only with the 2,3,7,8-TCDF in this grouping.

In order to improve the accuracy of the TEQ calculation for the sample, analysis of the same extract on a more polar column, which can separate the three tetrachlorinated isomers, is performed.

As a result of this increased separation, when taking into consideration the total toxic equivalency, this confirmation value as opposed to the original should be used for the 2,3,7,8 TCDF congener in the summation of the individual congener’s TEQs to obtain the total. (You would not add both values).

Current available TEF options.

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