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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.
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Dioxins*
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Toxic Equivalency
Factor (TEF)**
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2,3,7,8-TCDD
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1
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1,2,3,7,8-PnCDD
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1
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1,2,3,4,7,8-HxCDD
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0.1
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1,2,3,6,7,8-HxCDD
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0.1
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1,2,3,7,8,9-HxCDD
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0.1
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1,2,3,4,6,7,8-HpCDD
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0.01
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OCDD
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0.0001
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2,3,7,8-TCDF
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0.1
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1,2,3,7,8-PnCDF
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0.05
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2,3,4,7,8-PnCDF
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0.5
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1,2,3,4,7,8-HxCDF
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0.1
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1,2,3,6,7,8-HxCDF
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0.1
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1,2,3,7,8,9-HxCDF
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0.1
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2,3,4,6,7,8-HxCDF
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0.1
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1,2,3,4,6,7,8-HpCDF
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0.01
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1,2,3,4,7,8,9-HpCDF
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0.01
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OCDF
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0.0001
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*
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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Dioxin
TRI Data - Cl2 Sector