2,3,7,8-Tetrachlorodibenzo-/?-dioxin TCDD

Helder, T. 1980. Effects of 2,3,7,8-tetrachlorodibenzo-/)-dioxin (TCDD) on early life stages of the pike Esox lucius L.). Sci. Total Environ. 14 255-264. 

The toxicologic profile for these agents, particularly that of 2,4,5-T, has been confusing because of the presence of chemical contaminants (dioxins) produced during the manufacturing process (see below). 2,3,7,8-Tetrachlorodibenzo-/ -dioxin (TCDD) is the most important of these contaminants. 

Perhaps the most renowned example is the extensively-used 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), or rather the 2,3,7,8-tetrachlorodibenzo- -dioxin (TCDD) impurity which sometimes accompanies it. During massive use of the herbicide as a defoliant in the Vietnam war, TCDD was found almost by accident to be one of the most toxic synthetic substances ever tested. Soon, it was shown to be present in domestic 2,4,5-T as well as in the chemical warfare agents. Tests in laboratory animals demonstrated that some of the observed levels indeed were quite high enough to cause toxic effects (32). 

Figure 2 Electrostatic potentials on the molecular surfaces of (a) dibenzo-p-dioxin, 5, and (b) 2,3,7,8-tetrachlorodibenzo-/>-dioxin (TCDD), 6, computed at the Hartree-Fock STO-5G level. Color ranges, in kcal/mol red, more positive than 17 blue, more negative than —20 (see legend).

Cook R, Townsend J, Ott MG and Silverstein L Mortality experience of employees exposed to 2,3,7,8-tetrachlorodibenzo-dioxin (TCDD). J Occup Med 22 530-532, 1980. 

These compounds have been much in the news, mainly because of the extreme toxicity of the congener 2,3,7, 8-tetrachlorodibenzo-/ -dioxin (TCDD), usually called dioxin in the news media. Like the PCBs, PCDDs and PCDFs are families with many congeners there are 75 PCDDs and 135 PCDFs (Figure 12). 

Negative Cl of l,2,3,4-tetrachlorodibenzo-/ -dioxin (TCDD) and of a series of dioxin congeners containing one to eight chlorine atoms332 was studied employing hydrogen,... 

Dioxin and Furan Emissions. The emissions of polychlorinated dibenzo-/)-dioxins (PCDD) and polychlorinated dibenzo-furans (PCDF) from incinerators (4) are of interest to the pubHc, scientists, and engineers. The U.S. EPA classifies 2,3,7,8-tetrachlorodibenzo-/)-dioxin (2,3,7,8-TCDD) as the most potent carcinogenic compound it has evaluated. It is also Hsted as the agency s most potent reproductive toxin (4). 

Organohalogen compounds are of serious concern also as contaminants. The most feared material in this category is dioxin (2,3,7,8-tetrachlorodibenzo-para-dioxin, TCDD) that has already caused several catastrophes and has even been detected in effluent and sludge from paper mills that use chlorine bleach and also in... 

Chlorinated dibenzo ip-dioxins are contaminants of phenol-based pesticides and may enter the environment where they are subject to the action of sunlight. Rate measurements showed that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is more rapidly photolyzed in methanol than octachlorodi-benzo-p-dioxin. Initially TCDD yields 2,3,7-trichlorodiben-zo-p-dioxin, and subsequent reductive dechlorination is accompanied by ring fission. Pure dibenzo-p-dioxin gave polymeric material and some 2,2 -dihydroxybiphenyl on irradiation. Riboflavin-sensitized photolysis of the potential precursors of dioxins, 2,4-dichlorophenol and 2,4,5-trichloro-phenol, in water gave no detectable dioxins. The products identified were chlorinated phenoxyphenols and dihydroxy-biphenyls. In contrast, aqueous alkaline solutions of purified pentachlorophenol gave traces of octachlorodibenzo-p-dioxin on irradiation. 

Tetrachlorodibenzo-p-dioxin (TCDD) (I), an occasional contaminant in 2,4,5-T and other trichlorophenol derivatives, is the most toxic of the commonly-encountered dioxins (8) and it received most of our attention. Its low solubility in common solvents and water (ca. 2 ppb) limited our experiments since the products were difficult to identify by the conventional techniques of organic chemistry. However, TCDD has an absorption maximum at 307 nm in methanol—well within the solar spectrum observed at the earth s surface and near the region of maximum intensity (310-330 nm) of the UV lamps used in previous experiments (H 29). 

TAetection of the highly potent impurity, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), necessitated an environmental assessment of the impact of this contaminate. Information was rapidly needed on movement, persistence, and plant uptake to determine whether low concentrations reaching plants, soils, and water posed any threat to man and his environment. Because of the extreme toxicity of TCDD, utmost precautions were taken to reduce or minimize the risk of exposure to laboratory personnel. Synthesis of uniformly labeled C-TCDD by Muelder and Shadoff (I) greatly facilitated TCDD detection in soil and plant experiments. For unlabeled experiments it seemed wise to use only small quantities of diluted solutions in situations where decontamination was feasible and to rely on the sensitivity afforded by electron capture gas chromatography... 

Tetrachlorodibenzo-p-dioxin (TCDD) is a contaminant in 2,4,5- trichlorophenoxyacetic acid (2,4,5-T) which may occur in the manufacturing process. Before 1971 some samples of 2,4,5-T contained from 2-50 ppm TCDD (i) in the technical acid. Highest concentrations of TCDD occurred before 1968. 

Data from NIOSH. 1984. Current Intelligence Bulletin 40 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD,... 

Data from Kociba, R.J. and B.A. Schwetz. 1982b. A review of the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with a comparison to the toxicity of other chlorinated dioxin isomers. 

Chapman, D.E. and C.M. Schiller. 1985. Dose-related effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in C57BL/6J and DBA/2J mice. Toxicol. Appl. Pharmacol. 78 147-157. 

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