Dioxins/TCDD formation

Chemical Acne Many chemical compounds induce skin lesions that are similar to acne. Oils, tar, creosote, and several cosmetic products induce chemical acne. These compounds induce keratinization of the sebaceous glands of the skin, obstruction of the glands, and formation of acne. Chloracne is a specific skin lesion that is induced by chemical compounds that are structurally similar to 2,5,7,8-tet-rachloro dibenzo-p-dioxin (TCDD). Chloracne is slow to heal and difficult to... 

Tetrachlorodibenzo-p-dioxin (TCDD) is believed to be a byproduct in chemical processing generated by a halophenol or chlorobenzene starting material. An intermediate reaction will occur at an elevated temperature (equal to or greater than 160°C), an alkaline condition, or in the presence of a free halogen. The end reaction results in either direct dioxin, intermediate dioxin, or predioxin formation that will ultimately form dibenzo-p-dioxins [10]. TCDD is suspected in wastewaters from pesticide manufacture that uses such raw materials as 2,4,5-trichlorophenol (2,4,5-T) and 1,2,4,5-tetra-chlorobenzene, which are characteristic of TCDD precursors. A TCDD level as high as 111 mg/L has been found in drums of waste from the production of the pesticide 2,4,5-T. 

Langer et al. found that the corresponding octachlorodioxin formation was favored for the sodium pentachlorophenate but that the yield of 2,3,7,8-tetrachlorodibenzo-l,4-dioxin (TCDD, XIII) was low for the 2,4,5-trichlorophenate. They concluded that the formation of linear trimers and tetramers were favored over cyclizatlon of the dimer in the presence of a labile seta chlorine, and that steric effects also played an important selective role (ref. 121a). 

There has been considerable concern throughout Europe about the incineration of wastes, yet in Japan about 70% of all MSW is incinerated, and plans are that this should increase to 90% by the year 2000 [33]. Incinerators that are poorly operated may run at temperatures too low to burn potentially hazardous intermediates of the combustion process such as the products from pyrolysis which are believed to be the precursors in the combustion processes [34]. Of particular concern has been the discovery of extremely toxic materials such as dioxins (chlorinated dibenzo-/ -dioxins and benzofuran dioxins), in the flue gases of some incinerators. Such is the level of concern that many European countries have increased the legislative and environmental controls on incinerator operators, and some are moving to ban the incineration of plastics [35], and particularly PVC. In incinerators where the temperature is below about 1400 K, dehydrochlorination of PVC occurs, accompanied by the formation of polyenes. The polyenes can then cyclise and be oxidised, and then be attacked by chlorine-containing species to produce dioxins, the most toxic of which is 2,3,7,8-tetra-chlorodibenzo-/7-dioxin (TCDD), the material at the centre of the disaster at Sveso, Northern Italy, in 1979. More than 70 dioxins are known to exist (Figure 13.11). 

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. 

PCP presents a different picture from that of the lower chlorophenols and their derivatives. The corresponding dioxin shows much more stability to light than does TCDD, enough to permit its prolonged existence at low concentrations in a photoreactor. As a phenol it can directly yield dioxins, a process favored by its normal mode of application as the sodium salt. Although octachlorodibenzo-p-dioxin has much lower mammalian toxicity than TCDD (6), its formation, properties, and effects demand additional investigation. Technical preparations of PCP are frequently mixtures of tetra- and pentachlorophenols consequently, hepta-and possibly hexachlorodibenzo-p-dioxins might be expected as photolysis products in addition to the octachloro derivative. 

The objectives of the soil persistence experiments were (1) to learn the effect of soil type and concentration on the TCDD degradation rate, (2) to isolate and characterize degradation products from DCDD and TCDD, and (3) to determine whether chlorodioxins could be formed from chlorophenol condensation in the soil environment. This last study was essential since quality control at the manufacturing level could reduce or eliminate the formed dioxin impurity. But the biosynthesis of chlorodioxins by chlorophenol condensation in the soil environment could not be controlled and would have connotations for all chlorophenol-de-rived pesticides if formation did occur. The same question needed to be answered for photochemical condensation reactions leading to chloro-... 

There are 210 different isomeric possibilities, 75 of which are PCDDs and 135 are PCDFs. The toxicity of these isomers varies greatly, and only 15 exhibit extreme toxicity, the most toxic of which is 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD). The toxicity of the other isomers is therefore expressed as a toxicity equivalent of 2,3,7,8-TCDD. The PCDDs and PCDFs are poorly water soluble but are fat soluble and are therefore able to accumulate in tissue fat, thus allowing them to bio-accumulate in living organisms. The origin of dioxins in the pulp and paper industry is not entirely clear. They may be produced from the chlorination of dibenzodioxin which may be present in recycled oils used to make defoamers, but they may also arise from wood chips which have been treated with polychlorophenol to prevent sap stain formation. It is also possible that they are derived from lignin by chlorination. Dioxins are also known to be formed naturally by combustion of material such as wood, and forest fires have been particularly identified as a likely major cause of dioxin emissions. 

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. 

Pulp and paper mills are a much smaller source of PCDD/Fs in the environment than in the past. In 1988, the EPA and the US pulp and paper industry collaborated on the 104-Mill Study to measure levels of dioxins in effluent, sludge and pulp from 104 bleached chemical wood pulp and paper mills in the US. The study estimated the total discharge from all US pulp and paper mills to be 1188 g TEQ yr 1.18 In response to these findings, the pulp and paper industry expended more than SI billion dollars to reduce TCDD and TCDF formation during bleaching operations.19 The 1993 estimated discharge from all US pulp and paper mills is 97.2 g TEQ (Table 2). 

The evidence to date implies that the Ah receptor participates in every biological response to TCDD. For example, studies of stmeture activity relationships among congeners of TCDD reveal a correlation between a compound s specific binding affinity and its potency in eliciting biochemical responses, such as enzyme induction [171]. Furthermore, inbred mouse strains in which TCDD binds with lower affinity to the receptor exhibit decreased sensitivity to dioxin s biological effects, such as thymic involution, cleft palate formation, and hepatic porphyria. While there are a few... 

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