Analyte	US EPA 1 TEF	WHO 2 TEF
2,3,7,8-TCDD	1.0	1.0
1,2,3,7,8-PeCDD	0.5	1.0
1,2,3,6,7,8-HxCDD	0.1	0.1
1,2,3,7,8,9-HxCDD	0.1	0.1
1,2,3,4,7,8-HxCDD	0.1	0.1
1,2,3,4,6,7,8-HpCDD	0.01	0.01
1,2,3,4,6,7,8,9-OCDD	0.001	0.0001
2,3,7,8-TCDF	0.1	0.1
1,2,3,7,8-PeCDF	0.05	0.05
2,3,4,7,8-PeCDF	0.5	0.5
1,2,3,6,7,8-HxCDF	0.1	0.1
1,2,3,7,8,9-HxCDF	0.1	0.1
1,2,3,4,7,8-HxCDF	0.1	0.1
2,3,4,6,7,8-HxCDF	0.1	0.1
1,2,3,4,6,7,8-HpCDF	0.01	0.01
1,2,3,4,7,8,9-HpCDF	0.01	0.01
1,2,3,4,6,7,8,9-OCDF	0.001	0.0001

1) Taken from Interim procedures for estimating risks associated with exposures to mixtures of PCDD & PCDFs and 1989 update, EPA/625/3-89/016, March 1989.

2) WHO TEFs for human risk assessment based on the conclusions of WHO meeting in Stockholm, Sweden, 15-18 June 1997 (Van den Berg et al; 1998).