2.3.7.8- Tetrachloro TCDD

As shown by several investigations [91], the bromine-rich polybromide phase by itself is hardly flammable and fireextinguishing properties have been reported occasionally. The formation of polybrominated dibenzo-dioxins (PBrDD) and furans (PBrDF) due to the plastic-containing housing of a zinc-flow battery cannot be totally neglected in the case of a fire, but their concentrations are far away from the tetrachloro dibenzodioxine (TCDD) toxic equivalents even in a worst-case scenario. 

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. 

For some toxins it is possible to demonstrate an apparent improvement in functional response at levels of exposure which are below a threshold. This effect, which has been termed hormesis , is most effectively demonstrated in the consistently improved longevity of animals whose caloric intake is restricted rather than allowing them to feed ad lib (Tannenbaum, 1942). Clearly in this instance, the observed effects are the result of exposure to a complex mixture of chemicals whose metabolism determines the total amount of energy available to the organism. But it is also possible to show similar effects when single chemicals such as alcohol (Maclure, 1993), or caffeic acid (Lutz et al., 1997) are administered, as well as for more toxic chemicals such as arsenic (Pisciotto and Graziano, 1980) or even tetrachloro-p-dibenzodioxin (TCDD) ( Huff et al., 1994) when administered at very low doses. It is possible that there are toxins that effect a modest, reversible disruption in homeostasis which results in an over-compensation, and that this is the mechanism of the beneficial effect observed. These effects would not be observed in the animal bioassays since to show them it would be necessary to have at least three dose groups below the NOAEL. In addition, the strain of animal used would have to have a very low incidence of disease to show any effect. 

Neubert, R., G. Golor, R. Stahlmann, H. Helge, and D. Neubert. 1992. Polyhalogenated dibenzo-p-dioxins and dibenzofurans and the immune system. 4. Effects of multiple-dose treatment with 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) on peripheral lymphocyte subpopulations of a non-human primate (Callithrix jacchus). Arch. Toxicol. 66 250-259. 

NP NPEC OC OP OPEC PCB PCDBT PCDD PCDF PCP PFB RA TCA TCDD TCF TCMTB TOC VSC VOC Nonylphenol Nonylphenol ethoxycarboxylate Organo chlorine Octylphenol Octylphenol ethoxycarboxylate Polychloroinated biphenyls Polychlorinated dibenzothiophene Polychlorin ated dib enzo-p - dioxins Polychlorinated dibenzo-p-furans Pentachlorophenol Pentafluorobenzyl Resin acids 2,4,6-Trichloroanisole Tetrachloro dibenzo dioxin Totally chlorine- free 2-(Thiocyanomethylthio)-benzothiazole Total organic carbon Volatile sulphur compounds Volatile organic compounds... 

Chlorinated dibenzo-p-dioxins and dibenzofurans are among the most toxic substances known, especially 2,3,7,8-tetrachloro-p-dibenzodioxin (TCDD). These extremely hazardous compounds can be produced from 3,4,5- and 2,4,5-trichlorophenols by peroxidases [207]. However, the biological formation of such toxicants in nature or by microorganisms has not been described. 

Fungal peroxidases may also dimerize 3,4-dichloroaniline to 3,4,3, 4 -tetrachloro-azobenzene, a compound similar in toxicity to TCDD [209,210]. 

Figure 3 is the resulting advice for an example of a good QA/QC match with the user s needs. In this example, a high level of confidence was established, the methodology was both verified and validated, two samples were to be taken and analyzed by gas chromatography-mass spectrometry (GC-MS) at levels below 10 parts-per-billion (ppb). These conditions might be typical of analyses for 2,3,7,8-Tetrachloro- -dioxin (TCDD) in polluted water. 

Ward, C.T. and Matsumura, F. Fate of 2,3,7,8-tetrachloro-p-dioxin (TCDD) in a model aquatic environment. Arch. Environ. Contam. Toxicol, 7(3) 349-357, 1978. 

Fig. 5.2 Dose-response curve for 2,3,7,8-tetrachloro-p-dibenzodioxin (TCDD) in the CALUX bioassay. The concentration (expressed as TCDD) can subsequently be determined by comparing the response obtained with a sample extract with the calibration...

The widely used chlorophenoxy herbicides are chemical teratogens--as are their byproduct chlorodibenzodioxins. The symmetrical tetrachloro compound TCDD is perhaps the most toxic chemical known. 

Huuskonen H, Undila M, Pohjanvirta R, et al. 1994. Developmental toxicity of 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) in the most TCDD-resistant and -susceptible rat strains. Toxicol Appl Pharmacol 124(2) 174-80. 

TCDD, 2,3,7,8-tetrachloro-dibenzo-p-dioxin TBHQ, ter-butylhydroquinone AZT, 3 -azido-3 -deoxythymidine... 

All of the monoliths produced were dried at 150°C and fractions subsequently heat-treated at either 500°C or 850°C in a nitrogen atmosphere. The static and dynamic adsorption capacities of these monolithic composites at 30°C were determined using o-DCB as a probe molecule. This molecule was chosen since it may be considered as approximately corresponding to half a molecule of tetrachloro-dibenzene dioxin (TCDD), the most toxic isomer of the dioxin family. 

Albrecht I. D., Barkovskii A. L., and Adriaens P. (1999) Production and dechlorination of 2,3,7,8-tetrachloro-dibenzo-/)-dioxin (TCDD) in historically-contaminated estuarine sediments. Environ. Set Tecknol. 33, 737-744. 

For low volatility components such as polychlorobiphenyls or tetrachloro-para-dibenzodioxins (TCDD), it is possible to make use of a solvent effect in order to perform on-column enrichments. Thus, Poy [ 14 ] injected 4 times 2 pi of a sample containing TCDD isomers without destroying the separation performance. The low boiling components were stron y retained in the thick solvent layer formed when the solvent recondensed so that all 4 injections refocused in the column inlet before the chromatographic process took place. 

There are a wide range of chlorinated dibenzo-p-di-oxins varying in the extent of their chlorination. Dioxin nomenclature is based on the number and positions of carbon atoms that are chlorinated and include mono-, di-, tetra-, penta-, hexa-, hepta-, and octachlorinated congeners. 2,3,7,8-Tetrachloro-dibenzo-/7-dioxin (2,3,7,8-TCDD, more commonly referred to as TCDD or dioxin) is usually of greatest concern because of high toxicity in laboratory animal models, its widespread distribution and persistence in the environment, bioaccumulation potential, and because the greatest amount of data exists for this form. 

The Seveso disaster began on July 10, 1976 at the Industrie Chimiche Meda Societa Azionaria (ICMESA) chemical plant in Meda, Italy. This event became internationally known as the Seveso disaster, after the name of the most severely affected community. An increase in pressure due to an exothermic reaction in a 2,4,5-trichlorophenol-production reactor caused the rupture disk of the safety valve to burst. About 3000 kg of chemicals were released into the air. The release included 2,4,5-trichlorophenol, used in the manufacture of herbicides, and possibly up to 30 kg of the dioxin TCDD (2,3,7,8-tetrachloro-dibenzo-p-dioxin). Dioxin first came to widespread public notice during the Vietnam War, when it was identified as a component of the defoliant Agent Orange. Dioxin has also been considered to be the most toxic human-made substance. 

Alsharif NZ, Grandjean CJ, Murray WJ, Stohs SJ. 1990. 2,3,7,8-Tetrachloro-dibenzo-p-dioxin (TCDD)-induced decrease in the fluidity of rat liver membranes. Xenobiotica 20 979-88... 

Chlorophenoxy herbicides are, by themselves, of relative low toxicity to humans. They are, however, often contaminated with dioxins, of which, 2,3,7,8-tetrachloro-p-dioxin (TCDD) is the most toxic, which cause CNS and peripheral nervous system neuropathies. l8l... 

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