Toxicity equivalent factors

I-TEF International toxic equivalency factor UASB Upflow anerobic sludge blanket... 

Ah-receptor-mediated toxicity is particularly associated with the highly toxic compound 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD), commonly referred to as dioxin. TCDD, and the concept of toxicity equivalency factors (TEFs) based on TCDDs, will be dealt with in Chapter 7. The main point to make at this juncture is that the toxicity of each individual coplanar congener in a mixture can be expressed in terms of a toxic equivalent calculated relative to the toxicity of dioxin. Summation of the toxic equivalents of the individual coplanar PCBs gives a measure of the toxicity of the whole mixture, as expressed through the Ah receptor mechanism. 

Safe, S. (1990). An authoritative account of the toxicology of PCBs, and the development of toxic equivalency factors. 

Toxic equivalency factors (TEFs) are estimated relative to 2,3,7,8-TCDD, which is assigned a value of 1. They are measures of the toxicity of individual compounds relative to that of 2,3,7,8-TCDD. A variety of toxic indices, measured in vivo or in vitro, have been used to estimate TEFs, including reproductive effects (e.g., embryo toxicity in birds), immunotoxicity, and effects on organ weights. The degree of induction of P450 lAl is another measure from which estimations of TEF values have been made. The usual approach is to compare a dose-response curve for a test compound with that of the reference compound, 2,3,7,8-TCDD, and thereby establish the concentrations (or doses) that are required to elicit a standard response. The ratio of concentration of 2,3,7,8-TCDD to concentration of test chemical when both compounds produce the same degree of response is the TEF. Once determined, a TEF can be used to convert a concentration of a dioxin-like chemical found in an environmental sample to a toxic equivalent (TEQ). 

Ahlborg, U.G., Becking, G.C., and Birnbaum, L.S. et al. (1994). Toxic equivalency factors for dioxin-like PCBs. Chemosphere 28, 1049-1067. 

Safe, S. (1998) Hazard and Risk Assessment of Chemical Mixtures Using the Toxic Equivalency Factor Approach. Environmental Health Perspectives, 106(Suppl. 4), 1051-1058. 

Newsted, J.L., J.P. Giesy, G.T. Ankley, D.E. Tillitt, R.A. Crawford, J.W. Gooch, P.D. Jones, and M.S. Denison. 1995. Development of toxic equivalency factors for PCB congeners and the assessment of TCDD and PCB mixtures in rainbow trout. Environ. Toxicol. Chem. 14 861-871. 

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). 

Clemons, J.H., L.E.J. Lee, C.R. Myers, D.G. Dixon, and N.C. Bols. 1996. Cytochrome P4501A1 induction by polychlorinated biphenyls (PCBs) in liver cell lines from rat and trout and the derivation of toxic equivalency factors. Canad. Jour. Fish. Aquat. Sci. 53 1177-1185. 

Safe, S. 1987b. Determination of 2,3,7,8-TCDD toxic equivalent factors (TEFs) support for the use of the in vitro AHH induction assay. Chemosphere 16 791-802. 

Safe, S. 1990. Polychlorinated biphenyls (PCBs), dibcnzo-p-dioxins PCDDs), dibenzofurans (PCDFs), and related compounds environmental and mechanistic considerations which support the development of toxic equivalency factors (TEFs). Crit. Rev. Toxicol. 21 51-88. 

Zabel, E.W., P.M. Cook, and R.E. Peterson. 1995. Toxic equivalency factors of polychlorinated dibenzo-p-dioxin, dibenzofuran and biphenyl congeners based on early life stage mortality in rainbow trout (Onco-rhynchus mykiss). Aquat. Toxicol. 31 315-328. 

Toxic equivalence factors (TEFs), 13 140 Toxic free radical activity, herbicides that enhance, 13 297... 

The dioxin toxic equivalency factor (TEF) approach is currently used worldwide for assessing and managing the risks posed by exposure to mixtures of certain dioxin-like compounds (DLCs). World Health Organization-TEF (WHO-TEE) values have been established for humans and mammals, birds, and (For new, refined values, see Ref. 12g.) It should be mentioned that 16 PCBs, the coplanar isomers with nonortho, monoortho, and diortho substitution by chlorine (overall, there are 209 isomers for this class of compounds) show dioxin-like toxic behavior. I-TE values are smaller, in the range of 0.0001-0.1. The most toxic isomers is 3,3, 4,4, 5-pentachlorodiphenyl with I-TE of 0.1. Polybrominated dibenzodioxins and furans with the 2,3,7,8 pattern also show dioxin-like toxicity, but their I-TE values are lower compared to PCDD/F. 

TABLE 8.3 Toxic Equivalency Factors (TEFs) for Toxic PCDD/F Isomers According to NATO/CCMS (1988) and WHO I-TE... 

Simple similar action serves as the basis for the use of toxic equivalency factors (TEF, Section 10.5.1.4) often used to describe the combined toxicity of isomers or structural analogues. Additive... 

The approaches discussed are the hazard index (HI) (Section 10.5.1.1) and the weight-of-evidence (WOE) modification to the HI (Section 10.5.1.2), the point of departure index (PODl) (Section 10.5.1.3), toxicity equivalency factors (TEFs) (Section 10.5.1.4), the margin of exposure (MOE) procedures (Section 10.5.1.5), and the cumulative risk index (CRl) method (Section 10.5.1.6). 

Toxicity Equivalency Factors (WHO-TEFs) for Dioxins and Dioxin-Like PCBs... 

Nisbet, I.C. and P.K. LaGoy. 1992. Toxic equivalency factors (TEFs) for polycyclic aromatic hydrocarbons (PAH). Regul. Toxicol. Pharmacol. 16 290-300. 

Van den Berg, M., L. Bimbaum, A.T.C. Bosveld, et al. 1998. Toxic Equivalency Factors (TEFs) for PCBs, PCDDs, PCDFs for Humans and for Wildlife. Environ. Health Perspect. 106 775-792. 

Van den Berg, M., L.S. Bimbautn, M. Denison, M. De Vito, et al. 2006. The 2005 World Health Organization reevaluation of human and mammalian toxic equivalency factors for dioxins and dioxin-Uke compounds. Toxicol. Sci. 93 223-241. 

The WHO-TEF values are internationally accepted toxic equivalent factors for dioxins, furans, and dioxin-like PCBs, as stated by the WHO and derived from both in vivo and in vitro studies. The relative toxic potency of dioxins, furans, and dioxin-like PCBs, relative to... 

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