Toxicity equivalent quantities

Thirty soil samples extracted and purified using the official method employed in Japan were subjected to an on-bead assay, and the values obtained were compared with the toxic equivalent quantity (TEQ) obtained by GC/MS analysis.35 Dioxin is a generic term for a group of chemicals, which consists of many congeners and the toxicity of each congener is different. Environmental samples contain mixtures of... 

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. 

TEQ is toxic equivalency quantity determined by using intematiomd equivalency ctors. 

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. 

A special case that falls under the present definition of risk assessment methods is provided by the methods for analysis of dioxins and related compounds included in the calculation of toxic equivalent quantity (see Section 11.4.1). 

PCDD/F emission data are expressed in terms of the NATO-CCMS (North Atlantic Treaty Organization - Committee on the Challenges of Modem Society) toxic equivalence quantities (TEQ) for most important processes [31]. These processes include public power/heat plants based on coal and residual oil, non-industrial and industrial combustion of coal, oil, gas and wood, blast furnaces, sinter plants, non-ferrous and aluminum production, electric furnace steel plants, road transport, incineration of domestic, municipal and hospital waste. Emissions of dioxins from the combustion of kerosene with dichloroethane or dichlorobenzene are significant... 

The concentration of dioxins in the slag is greatly reduced compared with the dioxins concentration in the fly ash. In a typical case more than 98% of dioxins are decomposed by plasma melting. In terms of TEQ (Toxic Equivalent Quantity), the dioxins concentration is only 0.01 ng (Table 2. ). 

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). 

Since dioxins and furans have varying levels of toxicity, emissions of mixtures of these compounds are typically expressed in TEQs (Toxic EQuivalents). TEQs relate the toxicity of all dioxin and furan compounds to the known toxicity of 2,3,7,8-TCDD using a weighting scheme adopted by the EPA and most European countries.1,2 Therefore, a quantity of combined PCDDs and PCDFs... 

The toxicity of a complex mixture of PCBs can be expressed in terms of TCDD equivalent quantity (TEQ), which is the quantity of TCDDs that give the same toxic effect as the mixture considered. 

Many carotenoids function in humans as vitamin A precursors however, not all carotenoids have provitamin A activity (Table 3). Of the biologically active carotenoids, -carotene has the greatest activity. Despite the fact that theoretically one molecule of -carotene is a biological source of two molecules of vitamin A, this relationship is not observed and 6 p.g -carotene is equivalent to 1 p. vitamin A. Although -carotene and vitamin A have complementary activities, they caimot totally replace each other. Because the conversion of -carotene to vitamin A is highly regulated, toxic quantities of vitamin A cannot accumulate and -carotene can be considered as a safe form of vitamin A (8). 

A V -Carbonyldiimidazole (CDI) is prepared in a convenient and safe procedure from phosgene and imidazole as a non-toxic crystalline compound (m.p. 116-118 °C).[5],[6] It reacts almost quantitatively at room temperature or by short and moderate heating with an equimolar quantity of a carboxylic acid in tetrahydrofuran, chloroform, or similar inert solvents within a few minutes to give the corresponding carboxylic acid imidazolide, which is formed under release of carbon dioxide, together with one equivalent of readily separable and recyclable imidazole.Thus, this reaction leads under very mild conditions to the activation of a carboxylic acid appropriate for transacylation onto a nucleophile with an alcohol to an ester, with an amino compound to an amide or peptide, etc. 

It is essential to ensure that employees are not exposed to toxic materials at levels above or for durations beyond those permitted by TLV s or the equivalent. It is thus necessary to ensure by periodic measurement that atmospheric levels of toxic materials throughout the work shift do not exceed the permitted levels. Measurement of atmospheric toxic exposures has been discussed in Chapter 11. The frequency of this air sampling depends on the potential for exposure and injury. Where the hazard is relatively low and actions have been taken to control it, occasional checks by a knowledgeable but not necessarily professional person are desirable to ensure that the control is effective. Where there is a potential for serious hazard, for example, where high-hazard materials are handled in quantity,... 

Toxicity. Cadmium pigments are cadmium compounds with a low solubility, however, small quantities of cadmium dissolve in dilute hydrochloric acid (concentration equivalent to stomach acid), and in cases of long-term oral intake of cadmium pigments, they can accumulate in the human body. On inhalation of subchronic amounts of cadmium pigments, a small proportion of cadmium is biologically available [3.115], [3.116]. 

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