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Ecological Risk Assessment
Published in Ted W. Simon, Environmental Risk Assessment, 2019
Most dioxins, furans, and dioxin-like compounds lack individual screening benchmarks. However, the congener-specific dioxin and furan data can be consolidated into a single measure called the toxic equivalence (TEQ) of the sample. The TEQ is calculated by multiplying the concentrations of each congener or congener containing chlorine at the 2,3,7, and 8 positions in a sample by a toxicity equivalence factor (TEF) and summing those products. The TEF normalizes the toxicity of those congeners to the toxicity of the 2,3,7,8-TCDD congener, generally considered to be the most toxic of the dioxin, furan, and dioxin-like compounds. A great deal of effort by internationally known scientists have gone into developing the TEF scheme for dioxin-like chemicals.40,41 In effect, the TEQ indicates the concentration of 2,3,7,8-TCDD that would have the same toxicity as the mixture of dioxins and furans being evaluated. The TEFs used here reference the World Health Organization values for mammals, birds, and fish.42Figure 7.3 shows the structure of some PCDD/Fs.
Fate and Behavior of Endocrine Disrupters in Sludge Treatment and Disposal
Published in Jason W. Birkett, John N. Lester, Endocrine Disrupters in Wastewater and Sludge Treatment Processes, 2002
PCBs, Polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) compounds represent a challenge in terms of analysis. (There are 207 possible congeners for the PCB alone). Some consideration may be given to the relative toxicity of each compound/congener in terms of toxic equivalence factors (TEF).72 It is also important when considering comparison of data that historically workers may have quantified samples using commercial mixtures of PCB as standards. However, more recent (post-1990) data are more likely to have been generated through quantification of individual congeners. The presence of these compounds in sludges and digested sludges has been well-documented for over a quarter of a century and reports of their occurrence have been included in Table 5.2. Data from the United Kingdom demonstrate the changes in analytical techniques and priorities of analysis. In 1982, McIntyre and Lester73 reported values based on Arochlor 1260. However, by 1993, a range of 29 specific congeners were quantified,74 and in 2001, the nonortho-(planar) congeners which are deemed to be more toxic have been quantified.75,76 Data from the United States in the late 1970s showed concentrations of PCB (as Arochlors) in dry sludge ranging from 238 to 1700 mg kg−1.77 More recent analysis of samples of sludge from Switzerland has indicated that concentrations of PCB do appear to be decreasing.78
Industrial and Hazardous Waste Incineration
Published in Gaetano Joseph Celenza, Specialized Treatment Systems, 2020
Dioxin is the name given to the family of polychlorinated dibenzo-para-dioxins (PCDD), whose primary derivative is the basic structure shown in Figure 1.18 and which can be chlorinated in multipositions resulting in 75 possible compounds. Similarly, furans are derivatives of polychlorinated dibenzofurans (PCDF) with the structure shown in Figure 1.19, which can also be chlorinated in multipositions resulting in 135 possible compounds. Most data has concentrated on what is considered the most toxic of the possible compounds, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), equating related compounds to TCDD equivalence (TEQ), using toxic equivalent factors (TEF) [1].
Signature tracing of PCBs congeners in breastmilk of mothers living in selected urban centers of Pakistan
Published in Human and Ecological Risk Assessment: An International Journal, 2023
Shagufta Tahir, Abdul Qadir, Mehvish Mumtaz, Nadia Jamil, Mujtaba Baqar, Asad Ullah Saeed, Naeem Khan, Richard Halbrook
PCB congeners could be classified based on their degree of chlorination, tendency for substitution, and affinity for binding to receptors. PCBs that bind strongly to the aryl hydrocarbon receptor (AhR) are called DL-PCBs (Van den Berg et al. 2006). The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most dangerous of all dioxins, is used to compare congeners to determine their toxic equivalency factor (TEF). As a result, a toxic potency 1 (TEF 1), or toxic equivalent factor, is assigned (Chirollo et al. 2018). Toxic equivalents (TEQ) were calculated for selected DL-PCB congeners PCB-77, PCB-169, PCB-118, PCB-156, and PCB-189. The concentration of each congener was multiplied by its TEF value, and the resulting TCDD equivalents are toxic equivalents validated by WHO (Van den Berg et al. 2006) explained in Eq. (1).
Differential expression of hepatic genes with embryonic exposure to an environmentally relevant PCB mixture in Japanese quail (Coturnix japonica)
Published in Journal of Toxicology and Environmental Health, Part A, 2018
Meredith E. Bohannon, Tom E. Porter, Emma T. Lavoie, Mary Ann Ottinger
Some PCB congeners exert more deleterious effects than others based upon their chlorination pattern. The less ortho-substituted congeners enable the two phenyl rings to lie planar to each other and therefore behave in a dioxin-like manner by binding to the AhR (Hestermann, Stegeman, and Hahn 2000). The ability of a compound to bind in this manner yields a higher Toxicity Equivalency Factor (TEF), which has been held as the standard for toxicity comparison across compounds, where tetrachlorodibenzo-p-dioxin is generally the reference compound to which other compounds are compared (Van Den Berg et al. 2005). As reported by the World Health Organization, PCB 126 has a TEF of 0.1 while PCB 77 has an avian TEF of 0.05 (El-Shahawi et al. 2010; Van Den Berg et al. 1998, 2005). Knerr and Schrenk (2006) reported a mammalian TEF of 0.0001 for PCB 77, lending evidence to the possibility that birds may be more susceptible to this congener than mammals. Both of these congeners are non-ortho-substituted, making them very planar and therefore hypothetically able to activate the AhR. However, different PCB congeners exhibit varying levels of toxicity and are typically found as mixtures in the environment, as is the case at the upper Hudson River (Frame, Cochran, and Bowad 1996a; Frame et al. 1996b; Dean KM, University of Maryland, College Park, MD, USA, Personal communication).
Assessment and ecological indicators of total and polycyclic aromatic hydrocarbons in the aquatic environment of lake Manzala, Egypt
Published in Journal of Environmental Science and Health, Part A, 2018
Ahmed A. El-Kady, Terry L. Wade, Stephen T. Sweet
Toxic equivalency factor (TEFs) are used to characterize the toxicity and assess the risk of PAH mixtures since human exposure rarely occurs as a single compound. Benzo(a)pyrene (BaP) has been used as a reference compound with a TEF of 1.0 and the carcinogenicity of other PAHs are estimated relative to BaP.[58,59] The overall toxicity or toxic equivalents (TEQs) of a mixture are defined by the sum of the concentration of individual compounds in a mixture multiplied by their relative potencies or TEFs.[60] Toxic equivalents (TEQs) were calculated based on the TEF reported by Nisbet and Lagoy.[59] The highest potential toxicities were found in fish collected from Legam site (0.316) followed by Bahr Al-Baqar drain (0.254) and Al-Boghaz site (0.246). Fish collected from Al-Hamra and Al-Ginka sites were the least toxic (TEQs of 0.141 and 0.137, respectively). These toxicity estimates are below levels of concern for human consumption.