Dioxins/TCDD reductive

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. 

Hilarides and others (1994) investigated the destruction of TCDD on artificially contaminated soils using °Co y radiation. It appeared that TCDD underwent stepwise reduction dechlorination from tetra- to tri-, then di- to chlorodioxin, and then to presumably nonchlorinated dioxins and phenols. The investigators discovered that the greatest amount of TCDD destruction (92%) occurred when soils were amended with 25% water and 2% nonionic surfactant [alkoxylated fatty alcohol (Plurafac RA-40)]. Replicate experiments conducted without the surfactant lowered the rate of TCDD destruction. 

The parameters examined included WBC, lymphocyte levels, serum immunoglobulin levels, and lymphocyte subsets. The mean dioxin equivalent concentration (TEQ, includes CDDS, CDFs, and dioxinlike PCBs) in blood (lipid basis) from fish eaters (n=7) was 64 pg TEQ/g (range, 18-88 pg/g) compared to 21 pg TEQ/g (18-33 pg/g) for controls (n=4). CDDs and CDFs were the major contributors to the total dioxin equivalents in blood. Of all the parameters examined, only the level of NK cells was reduced in fish eaters, but the difference between groups was not statistically significant. No correlation was found between blood levels of 2,3,7,8-TCDD and the reduction in NK levels, but weak correlations existed between the latter and some non-ortho-PCB congeners and p,p -DDT. 

In addition, degradation of 2,3,7,8-TCDD in basic solutions of polyethyleneglycol and oxidants actually appears to occur by reductive processes, since the products are the lower chlorinated dioxins... 

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