Dioxins toxic equivalency factors

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. 

Thi s guidance for dioxin and dioxin-like compounds i s unique because of the potency of TCDD itself, and the needto considerthetotal potency of all dioxin and dioxin-like compounds detected in soil. The toxicity of a dioxin-like compound is commonly referred to in terms of its dioxin toxicity equivalency factor (TEF). See Background section for further information. 

Hejtmancik, Miiton Batteiie Memoriai institute, Coiumbus, OH Evaluation of dioxin toxic equivalency factors NIEHS... 

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. 

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. 

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). 

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. 

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

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... 

Hamm JI, Chen CY, Birnbaum LS A mixture of dioxin, furans, and non-ortho PCBs based upon consensus toxic equivalency factors produces dioxin-like reproductive effects. Toxicol Sci 2003 74 182. [PMID 12730615]... 

S. Safe, Polychlorinated Biphenyls (PCBs), Dibenzo-p-dioxins (PCDDs), Dibenzofurans (PCDFs) and Related Compounds Environmental and Mechanistic Considerations Which Support the Development of Toxic Equivalency Factors (TEFs), C. R. C. Crit. Rev. Toxicol. 21 (1990) 51-88. 

NORTH ATLANTIC TREATY ORGANISATION, COMMITTEE ON THE CHALLENGES of MODERN SOCIETY. International Toxicity Equivalency Factor (I-TEF) method of risk assessment for complex mixtures of dioxins and related compounds. Pilot study on international information exchange on dioxins and related compounds . CCMS Report Number 176, Environmental Protection Agency, Washington D.C., 1988. 

AHLBORG U G, BECKING G C, BIRNBAUM L S, BROUWER A, DERKS H G M, FEELEY M, GOLOR G, HANBERG A, LARSEN J C, LIEM A K D, SAFE S H, SCHLATTER c, W/ERN f, younes M and YRJANHEIKKIE Toxic equivalency factors for dioxin-like PCBs Report on a WHO-ECEH and IPCS consultation, December 1993 , Chemosphere, 1994 28 1049-1067. 

Although this public health statement will focus on CDDs, it is important to note that CDDs are found in the environment together with other structurally related chlorinated chemicals, such as chlorinated dibenzofurans (CDFs) and polychlorinated biphenyls (PCBs). Therefore, people are generally exposed to mixtures of CDDs and other classes of toxicologically and structurally similar compounds. 2,3,7,8-TCDD is one of the most toxic and extensively studied of the CDDs and serves as a prototype for the toxicologically relevant or dioxin-like CDDs. Based on results from animal studies, scientists have learned that they can express the toxicity of dioxin-like CDDs as a fraction of the toxicity attributed to 2,3,7,8-TCDD. For example, the toxicity of dioxin-like CDDs can be half or one tenth or any fraction of that of 2,3,7,8-TCDD. Scientists call that fraction a Toxic Equivalent Factor (TEF). More information on TEFs can be found in Section 2.5. 

Ahlborg UG, Brouwer A, Fingerhut MA, et al. 1992. Impact of polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls on human and environmental health, with special emphasis on application of the toxic equivalency factor concept. Europ J Pharmacol 228 179-199. 

Niimi AJ, Oliver BG. 1989b. Assessment of relative toxicity of chlorinated dibenzo-p-dioxins, and biphenyls in Lake Ontario salmonids to mammalian systems using toxic equivalent factors (TEF). Chemosphere 18(7-8) 1413-1423. 

Olson JR, Beilin JS, Barnes DG. 1989. Reexamination of data used for establishing toxicity equivalence factors (TEFs) for chlorinated dibenzo-para-dioxins and dibenzofurans (CDDs and CDFs). Chemosphere 18 371-381. 

Safe SH. 1998b. Development validation and problems with the toxic equivalency factor approach for risk assessment of dioxins and related compounds. J Anim Sci 76 134-141. 

Stahl BU, Kettrup A, Rozman K. 1992. Comparative toxicity of four chlorinated dibenzo-p-dioxins (CDDs) and their mixture. Part I Acute toxicity and toxic equivalency factors (TEFs). Arch Toxicol 66(7) 471-7. 

WHO. 1998. WHO toxic equivalent factors (TEFs) for dioxin-like compounds for humans and wildlife. Environ Health Perspect 106(12) 775-792.. 

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