The 2005 World Health Organization Reevaluation of Human and Mammalian Toxic Equivalency Factors for Dioxins and Dioxin-Like Compounds

Abstract

In June 2005, a World Health Organization (WHO)-International Programme on Chemical Safety expert meeting was held in Geneva during which the toxic equivalency factors (TEFs) for dioxin-like compounds, including some polychlorinated biphenyls (PCBs), were reevaluated. For this reevaluation process, the refined TEF database recently published by Haws et al. (2006, Toxicol. Sci. 89, 4-30) was used as a starting point. Decisions about a TEF value were made based on a combination of unweighted relative effect potency (REP) distributions from this database, expert judgment, and point estimates. Previous TEFs were assigned in increments of 0.01, 0.05, 0.1, etc., but for this reevaluation, it was decided to use half order of magnitude increments on a logarithmic scale of 0.03, 0.1, 0.3, etc. Changes were decided by the expert panel for 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) (TEF = 0.3), 1,2,3,7,8-pentachlorodibenzofuran (PeCDF) (TEF = 0.03), octachlorodibenzo-p-dioxin and octachlorodibenzofuran (TEFs = 0.0003), 3,4,4',5-tetrachlorbiphenyl (PCB 81) (TEF = 0.0003), 3,3',4,4',5,5'-hexachlorobiphenyl (PCB 169) (TEF = 0.03), and a single TEF value (0.00003) for all relevant mono-ortho-substituted PCBs. Additivity, an important prerequisite of the TEF concept was again confirmed by results from recent in vivo mixture studies. Some experimental evidence shows that non-dioxin-like aryl hydrocarbon receptor agonists/antagonists are able to impact the overall toxic potency of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds, and this needs to be investigated further. Certain individual and groups of compounds were identified for possible future inclusion in the TEF concept, including 3,4,4'-TCB (PCB 37), polybrominated dibenzo-p-dioxins and dibenzofurans, mixed polyhalogenated dibenzo-p-dioxins and dibenzofurans, polyhalogenated naphthalenes, and polybrominated biphenyls. Concern was expressed about direct application of the TEF/total toxic equivalency (TEQ) approach to abiotic matrices, such as soil, sediment, etc., for direct application in human risk assessment. This is problematic as the present TEF scheme and TEQ methodology are primarily intended for estimating exposure and risks via oral ingestion (e.g., by dietary intake). A number of future approaches to determine alternative or additional TEFs were also identified. These included the use of a probabilistic methodology to determine TEFs that better describe the associated levels of uncertainty and "systemic" TEFs for blood and adipose tissue and TEQ for body burden.

Identification of Ah Receptor Agonists in Soil of E-waste Recycling Sites from Taizhou Area in China

“…PCB81 and PCB77 contributed the second greatest proportion It should be noted that the brominated analogues such as polybrominated diphenyl ethers (PBDEs) and polybrominated dibenzo-p-dioxins/furans (PBDD/Fs) have not been studied in this work. Though PBDEs, which were widely used as flame retardants in e-products, do not have AhR agonist properties by themselves, PBDD/Fs occur as trace contaminants in commercial PBDEs and can be produced during open burning of e-waste containing PBDEs (8). Both in vitro and in vivo studies have shown that PBDD/Fs are potent AhR agonists and cause dioxin-like effects (8).…”

“…Though PBDEs, which were widely used as flame retardants in e-products, do not have AhR agonist properties by themselves, PBDD/Fs occur as trace contaminants in commercial PBDEs and can be produced during open burning of e-waste containing PBDEs (8). Both in vitro and in vivo studies have shown that PBDD/Fs are potent AhR agonists and cause dioxin-like effects (8). Therefore, these compounds should be further studied in the e-waste recycling area.…”

“…The difficulty of characterizing complex mixtures of these dioxin-like compounds for risk evaluation, has led to the conceptual development of toxic equivalency factors (TEF) (8,9). Accordingly, the total dioxin-like toxic potency of a compound mixture can be expressed as a single toxic equivalency (TEQcal).…”

Effects of in ovo exposure to 3,3′,4,4′‐tetrachlorobiphenyl (PCB 77) on heart development in tree swallow (Tachycineta bicolor)

“…This lack of lethality may be ascribed to interspecific differences of PCB congeners on the activation of the AhR; according to these data, tree swallows have lower sensitivity to PCBs than other avian species [5,7,8,40]. Similarly, the potency of dioxin-like PCBs with similar chemical structures to dioxins (e.g., 2,3,7,8-tetrachlorodibenzodioxin) is toxicologically categorized by TEFs [41,42]. Thus PCB 77 (dioxin-like PCB congener), with a TEF of 0.0004 in kestrels (Falco sparverius), 0.005 in turkeys (Meleagris gallopavo), and 0.05 in chickens (Gallus gallus domesticus), should likely have significant adverse effects [6,14,43].…”

A preliminary investigation of unintentional POP emissions from thermal wire reclamation at industrial scrap metal recycling parks in China

“…For congeners with concentrations below the limit of detection (LOD), a value of half the LOD was used to calculate the total concentration and the TEQ. The WHO-TEF 2005 values reported by Van den Berg et al [18] were used to calculate the TEQs for the PCDD/Fs and dlPCBs. The TEQs for the dioxin like PCNs (dl-PCNs) and HxCBz were calculated based on the relative potency factors (RPFs) reported by Noma et al [19] and van Birgelen [20], respectively.…”