Tetra-chlorodibenzo-p-dioxin TCDD

An environmental protocol has been developed to assess the significance of newly discovered hazardous substances that might enter soil, water, and the food chain. Using established laboratory procedures and C-labeled 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD), gas chromatography, and mass spectrometry, we determined mobility of TCDD by soil TLC in five soils, rate and amount of plant uptake in oats and soybeans, photodecomposition rate and nature of the products, persistence in two soils at 1,10, and 100 ppm, and metabolism rate in soils. We found that TCDD is immobile in soils, not readily taken up by plants, subject to photodecomposition, persistent in soils, and slowly degraded in soils to polar metabolites. Subsequent studies revealed that the environmental contamination by TCDD is extremely small and not detectable in biological samples. 

Koshakji RP, Harbison RD, Bush MT. 1984. Studies on the metabolic fate of [14C]2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD) in the mouse. Toxicol Appl Pharmacol 73 69-77. 

Blaylock B, Holladay S, Comment C, Heindel J, Luster M (1992) Exposure to tetra-chlorodibenzo-p-dioxin (TCDD) alters fetal thymocyte maturation. Toxicol Appl Pharmacol, 112 207-213. 

The Times Beach Dioxin Research Station was constructed in 1984 under the direction of the University of Missouri and the Missouri Department of Natural Resources. The station offers investigators the opportunity to conduct experiments under field conditions on a well characterized soil. During the Summer of 1984, a series of six experiments were established by Monsanto at the station to study the environmental transport of 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD) under field conditions. 

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. 

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