Pacific Rim

Toxic Equivalency Factors
It has been well established that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is carcinogenic, and that other chlorinated dioxins and furans with the same 2,3,7,8- backbone are also toxic. However, each of these 2,3,7,8- congeners do not exhibit the same degree of toxicity.

A number of systems have been developed to express the total toxic contribution from dioxins and furans. In each system, the toxicity of each congener is weighted relative to 2,3,7,8-TCDD. This is called a Toxic Equivalency Factor or TEF. When results are reported, the concentration of each congener is multiplied by the corresponding TEF. These values are then summed together to give a total toxic equivalency or TEQ.

The two most common systems for determining TEQs are the World Health Organisation TEQ (WHO-TEQ) and the International TEQ (ITEQ). They are for the most part the same, with the exception of 1,2,3,7,8-PeCDD – WHO assigns a TEF of 1, while the ITEF is 0.5 – and OCDD/F – WHO-TEF is 0.0001, while ITEF is 0.001.

ITEQs are most common in North America, while Asia and Europe tend to use WHO-TEQs.

Congener

ITEF

WHO-TEF

1998

2006

2,3,7,8-TCDD

1

1

1

1,2,3,7,8-PeCDD

0.5

1

1

1,2,3,4,7,8-HxCDD

0.1

0.1

0.1

1,2,3,6,7,8-HxCDD

0.1

0.1

0.1

1,2,3,7,8,9-HxCDD

0.1

0.1

0.1

1,2,3,4,6,7,8-HpCDD

0.01

0.01

0.01

OCDD

0.001

0.0001

0.0003

2,3,7,8-TCDF

0.1

0.1

0.1

1,2,3,7,8-PeCDF

0.05

0.05

0.03

2,3,4,7,8-PeCDF

0.5

0.5

0.3

1,2,3,4,7,8-HxCDF

0.1

0.1

0.1

1,2,3,6,7,8-HxCDF

0.1

0.1

0.1

1,2,3,7,8,9-HxCDF

0.1

0.1

0.1

2,3,4,6,7,8-HxCDF

0.1

0.1

0.1

1,2,3,4,6,7,8-HpCDF

0.01

0.01

0.01

1,2,3,4,7,8,9-HpCDF

0.01

0.01

0.01

OCDF

0.001

0.0001

0.0003

To obtain a complete dioxin TEQ value, PCBs values must also be included. Twelve of the 209 PCB congeners have been assigned TEFs by the WHO. As per the dioxins, the concentration of each congener is multiplied by the corresponding TEF. These values are then summed together to give a PCB-TEQ.

PCB Congener

IUPAC #

WHO-TEF

1998

2005

3,3',4,4'-TeCB

PCB 77

0.0001

0.0001

3,4,4',5-TeCB

PCB 81

0.0001

0.0003

2,3,3',4,4'-PeCB

PCB 105

0.0001

0.00003

2,3,4,4',5-PeCB

PCB 114

0.0001

0.00003

2,3',4,4',5-PeCB

PCB 118

0.0005

0.00003

2',3,4,4',5-PeCB

PCB 123

0.0001

0.00003

3,3',4,4',5-PeCB

PCB 126

0.1

0.1

2,3,3',4,4',5-HxCB

PCB 156

0.00001

0.00003

2,3,3',4,4',5'-HxCB

PCB 157

0.0005

0.00003

2,3',4,4',5,5'-HxCB

PCB 167

0.0005

0.00003

3,3',4,4',5,5'-HxCB

PCB 169

0.01

0.03

2,3,3',4,4',5,5'-HpCB

PCB 189

0.0001

0.00003