Toxic equivalent quantity/factor

There are many dioxin congeners, and the toxicity of the congeners varies depending on the number and positions of the chlorine substituents. 2,3,7,8-Tetra-chlorodibenzo-p-dioxin (2,3,7,8-TCDD) shows the highest toxicity to mammals. Values for dioxin toxicity were reassessed by the World Health Organization in 2005 [1]. The toxic equivalency factor (TEF) of dioxin congener represents its toxicity relative to that of 2,3,7,8-TCDD, which is defined as having a TEF value of 1. Another parameter is the toxic equivalent quantity (TEQ), which is the total toxicity of a mixture of compounds represented as the sum of the concentrations of each compound multiplied by its TEF. Dioxin contamination is usually represented in terms of TEQ values. 

In the literature, the PCDD and PCDF results are given as Toxicity Equivalent Quantities (TEQs). Between the 210 PCDD and PCDF congeners, the most toxic molecules are those whose positions 2,3,7,8 are chlorinated. The compounds that meet these conditions number a total of 17, 10 fiuans and 7 dioxins. Since the individual toxicity of these compounds is different, the real toxicity of a mixture was assessed bearing in mind the relative toxicity of the isomers with respect to the most toxic isomer, the 2,3,7,8-TCDD a toxicity equivalence factor (TEF) equal to the unit was assigned to the 2,3,7,8-TCDD. For the toxic assessment, the 17 toxic isomers were normaUzed by multiplying their measiued concentrations by the appropriate TEFs. The sum of these products yields the total TEQs, which express these analyte concentrations as a single munber, equivalent to that of a toxicity derived exclusively from 2,3,7,8-TCDD. 

Commercial PCB mixtures frequently contain impurities that may contribute to the 2,3,7,8-TCDD toxic equivalency factor. These impurities may include other PCBs, dioxins, dibenzofurans, naphthalenes, diphenyl ethers and toluenes, phenoxy and biphenyl anisoles, xanthenes, xanthones, anthracenes, and fluorenes (Jones etal. 1993). PCB concentrations in avian tissues sometimes correlate positively with DDE concentrations (Mora et al. 1993). Eggs of peregrine falcons (Falco peregrinus) from California, for example, contained measurable quantities of various organochlorine compounds, including dioxins, dibenzofurans, mirex, hexachlorobenzene, and / ,//-DDE at 7.1 to 26.0 mg/kg FW PCB 126 accounted for 83% of the 2,3,7,8-TCDD equivalents, but its interaction with other detectable organochlorine compounds is largely unknown (Jarman et al. 1993). 

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