Guidance for Disposal Site Risk Characterization

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzifurans (PCDFs) comprise a family of chemicals containing 210 specific monochlorinated and polychlorinated congeners. In 1987, USEPA formally adopted an interim procedure for estimating risks associated with complex environmental mixtures containing PCDDs and PCDFs (Bellin and Barnes, 1987). The procedure used a set of toxicity equivalency factors (TEFs) to convert the concentration of congeners into an equivalent concentration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), the most toxic of the 210 congeners. The TEFs have been reviewed and updated periodically, the most recent update being USEPA (1989b) and MADEP ( ).

A list of current TEFs is presented in Table 7.2. . 

Table 7.2

MADEP Derived Toxicity Equivalency factors (TEFs)
for Polychlorinated Dioxins and Dibenzofurans

CompoundTEF
Dioxins:
Mono-, Di- and Trichlorinated dibenzo-p-dioxins0.001
2,3,7,8-Tetrachlorinated dibenzo-p-dioxin
Other Tetrachlorinated dibenzo-p-dioxins
1
0.01
2,3,7,8-Pentachlorinated dibenzo-p-dioxin
Other Pentachlorinated dibenzo-p-dioxins
0.5
0.05
2,3,7,8-Hexachlorinated dibenzo-p-dioxin
Other Hexachlorinated dibenzo-p-dioxins
0.1
0.01
2,3,7,8-Heptachlorinated dibenzo-p-dioxin
Other Heptachlorinated dibenzo-p-dioxins
0.1
0.01
Octochlorinated dibenzo-p-dioxins0.001
Furans:
Mono-, Di- and Trichlorinated dibenzofurans0.001
2,3,7,8-Tetrachlorinated dibenzofurans
Other Tetrachlorinated dibenzofurans
0.1
0.01
2,3,7,8-Pentachlorinated dibenzofurans
Other Pentachlorinated dibenzofurans
0.5
0.05
2,3,7,8-Hexachlorinated dibenzofurans
Other Hexachlorinated dibenzofurans
0.1
0.01
2,3,7,8-Heptachlorinated dibenzofurans
Other Heptachlorinated dibenzofurans
0.1
0.01
Octochlorinated dibenzofurans0.001
from MADEP (Silverman and Hutcheson, 1991)