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Effects

Studies in humans and animals indicated that 2,3,7,8TCDD can cross the placenta and is excreted in milk. Studies on the developmental toxicity of 2,3,7,8TCDD in humans are inconclusive. Some studies have found significant increases in the risk of certain birth defects, while other found no significant alterations. However, a number of limitations (e.g., lack of exposure data, small sample sizes, and the lack of reliable data for birth defects prior to 2,3,7,8TCDD exposure) limits the interpretation of the results of these studies.
Developmental toxicity has been observed in animals orally exposed to 2,3,7,8TCDD and 2,7DCDD. The most common effects were cleft palate, hydronephrosis, impaired development of the reproductive system, immunotoxicity, and death. No studies were located regarding developmental effects in animals after inhalation and dermal exposure.

Data from studies on reproductive effects in humans are inconclusive.
Reproductive effects have been observed in oral animal studies. Increased incidences of pre and postimplantation losses were observed in 2,3,7,8TCDDexposed rodents, and monkeys. Adverse effects have also been observed in the reproductive organs (decreased weight), hormone levels, and gametes of male rats. None of the acuteduration exposure studies assessed the potential of PCDDs to impair fertility. Reduced fertility, increased incidence of abortions, altered estrus cycle, and endometriosis were observed in animals exposed for intermediate or chronic durations. Reproductive effects have also been observed in animals exposed to mixed HxCDD, but not following exposure to 2MCDD, 2,3DCDD, 2,7DCDD, 1,2,3,4TCDD, or OCDD.
Data on the reproductive toxicity of dioxins following dermal exposure is limited to a single animal study which found no adverse effects on reproductive organs of mice chronically exposed to 2,3,7,8TCDD.
No animal inhalation reproductive toxicity studies were located.

Inconclusive results were obtained regarding genotoxicity of PCDDs in human as well as in animal studies. Structural chromosomal changes were found in some groups of exposed individuals. Positive and negative results at the chromosomal level as well as at the gene level were reported in animal studies. Furthermore, negative results were obtained in dominantlethal tests and sexlinked recessivelethal tests in rats and Drosophila, respectively. In addition, mostly negative results were obtained in prokaryotic organisms. Some studies indicated that the covalent binding of 2,3,7,8TCDD to DNA is low, and that this mechanism does not operate in dioxins genotoxicity.

 


Structure formula of 2,3,7,8-Tetrachlorodibenzo-p-dioxin


3D structure of 2,3,7,8-Tetrachlorodibenzo-p-dioxin