TEQ vs. TM-17

The reason two types of units exist for dioxin reporting has to do with the fact that "dioxin," rather than denoting one chemical compound, denotes the family of PCDD/F compounds. Dioxin is always produced as a mixture of its family member compounds. Furthermore, the toxicities of individual family member compounds vary greatly.

TEQ Method

Toxic Equivalents, or TEQs, are used to report the toxicity-weighted masses of mixtures of PCDD/Fs. The TEQ method of dioxin reporting is more meaningful than simply reporting the total number of grams of a mixture of variously toxic compounds because the TEQ method offers toxicity information about the mixture.

Within the TEQ method, each PCDD/Fs compound is assigned a Toxic Equivalency Factor, or TEF (see the table below). This factor denotes a given dioxin compound's toxicity relative to 2,3,7,8-TCDD, which is assigned the maximum toxicity designation of one. Other dioxin compounds are given equal or lower numbers, with each number roughly proportional to its toxicity relative to that of 2,3,7,8-TCDD. Developed by the World Health Organization, TEFs are used extensively by scientists and governments around the world (Van den Berg, et al., 1998). The EPA uses units of grams-TEQ to report emissions of PCDD/Fs from known sources to the open environment in its Inventory of Sources of Dioxin in the United States.

To obtain the number of grams-TEQ of a PCDD/Fs mixture, one simply multiplies the mass of each compound in the mixture by its TEF and then totals them.

Dioxins*
Toxic Equivalency Factor (TEF)**
2,3,7,8-TCDD
1
1,2,3,7,8-PnCDD
1
1,2,3,4,7,8-HxCDD
0.1
1,2,3,6,7,8-HxCDD
0.1
1,2,3,7,8,9-HxCDD
0.1
1,2,3,4,6,7,8-HpCDD
0.01
OCDD
0.0001
2,3,7,8-TCDF
0.1
1,2,3,7,8-PnCDF
0.05
2,3,4,7,8-PnCDF
0.5
1,2,3,4,7,8-HxCDF
0.1
1,2,3,6,7,8-HxCDF
0.1
1,2,3,7,8,9-HxCDF
0.1
2,3,4,6,7,8-HxCDF
0.1
1,2,3,4,6,7,8-HpCDF
0.01
1,2,3,4,7,8,9-HpCDF
0.01
OCDF
0.0001
* The term "Dioxins" here refers to 7 dioxin and 10 furan chemical compounds.
**Developed by the World Health Organization [Van den Berg, et al. (1998). Toxic Equivalency Factors (TEFs) for PCBs, PCDDs, PCDFs for Humans and for Wildlife. Environmental Health Perspectives 106, 775.]

TM-17 Method

"TM-17" denotes the "total mass" of the 17 PCDD/Fs compounds of interest in any given sample of PCDD/Fs. Dioxins almost always occur as a complex mixture of individual compounds. The EPA requires facilities to report the 2000 TRI dioxin data in units of total grams, or grams-TM-17 (g-TM17).

"TM-17" reporting is different from "TEQ" reporting of PCDD/Fs quantities. The TEQ method is a toxicity-weighted reporting method whereby the masses of individual PCDD/Fs compounds are scaled by Toxic Equivalency Factors (TEFs). Unlike the TM-17 method, the TEQ method offers meaningful information about the total toxicity of a PCDD/Fs sample. PCDD/Fs commonly are reported using the TEQ method. The US EPA lists dioxin quantities in grams-TEQ in its Inventory of Sources of Dioxin in the United States.

In contrast, the TM-17 method simply adds the masses, in grams, of all constituent compounds in the mixture. Clearly, without knowing the TEQ measure of a given mass (in grams) of dioxin (and understanding that toxicities of individual PCDD/Fs vary widely), one cannot know the toxicity of a particular reported amount.

 
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