Dioxins, chlorinated

The proposed mechanism by which chlorinated dioxins and furans form has shifted from one of incomplete destmction of the waste to one of low temperature, downstream formation on fly ash particles (33). Two mechanisms are proposed, a de novo synthesis, in which PCDD and PCDF are formed from organic carbon sources and Cl in the presence of metal catalysts, and a more direct synthesis from chlorinated organic precursors, again involving heterogeneous catalysis. Bench-scale tests suggest that the optimum temperature for PCDD and PCDF formation in the presence of fly ash is roughly 300°C. 

Norstrom, R.J., Simon, M., and Weseloh, D.V. (1986). Long term trends of PCDD and PCDF contamination in the Great Lakes. Proceedings of Dioxin 86, the Sixth International Symposium on Chlorinated Dioxins and Related Compounds held at Fukuoka, Japan, September 1986. 

Poiger, H. and Buser, H.R. (1983). Structure elucidation of mammalian TCDD metabolites In Tucker, R.E., Young, A.L., and Gray, A.P. (Eds.) Human and Environmental Risks of Chlorinated Dioxins and Related Compounds. New York Plenum Press, 483 92. 

Rappe, C., Nygren, M., and Linstrom, G. et al. (1987). Overview on environmental fate of chlorinated dioxins and dibenzofurans sources levels and isomeric pattern in various matrices. Chemosphere 16, 1603-1618. 

We report the crystal structures of four chlorinated dioxins—the 2,7-dichloro-, 2,8-dichloro-, 2,3,7,8-tetrachloro-, and octachlorodibenzo-p-dioxins. Thus, five crystal structures of chlorodioxins are now known. 

The biological activity of several halogenated herbicides in water is destroyed by ultraviolet irradiation (18). Irradiation seems to be a promising method for decontaminating small quantities of pesticides. The chemical similarity between the chlorinated dioxins and other chlo-rinted aromatic compounds suggested that if there were parallels in their photochemical behavior, sunlight might destroy dioxins in the environment. 

The photolysis rate of several chlorinated dioxins was determined in methanol (20) (Figure 1). Solutions of 2,7-dichlorodibenzo-p-dioxin (5 mg/liter), TCDD (5 mg/liter), and octachlorodibenzo-p-dioxin (2.2 mg/ liter) were irradiated with light having an intensity of about 100 /mW/cm ... 

Octachlorodibenzo-p-dioxin was photolyzed much more slowly than TCDD (Figure 1). The rate of dioxin photolysis increased as the number of substituent chlorine atoms decreased. Octachlorodibenzo-p-dioxin gave what seemed to be a series of chlorinated dioxins of decreasing chlorine content (20). 

The Stability of Pentachlorophenol and Chlorinated Dioxins to Sunlight, Heat, and Combustion... 

It has been suggested that the photochemical reaction of pentachlorophenol in aqueous solution to produce octachlorodibenzo[l,4] dioxin and some of the heptachloro congener could account for the discrepancy between values for the emission of chlorinated dioxins and their deposition, which is significant for the octachloro congener (Baker and Hites 2000). 

Barkovskii AI, P Adriaens (1996) Microbial dechlorination of historically present and freshly spiked chlorinated dioxins and diversity of dioxin-dechlorinating populations Appl Environ Microbiol 62 4556-4562. 

Beurskens JEM, M Toussaint, J de Wolf, JMD van der Steen, PC Slot, LCM Commandeur, JR Parsons (1995) Dehalogenation of chlorinated dioxins by an anaerobic consortium from sediment. Environ Toxicol Chem 14 939-943. 

Chlorinated dioxins occur in atmospheric deposition (Koester and Hites 1992), and will thereby enter the terrestrial environment and watercourses. The degradation of tetrachloro- through octa-chlorodibenzo[l,4]dioxins has been examined in low-nitrogen medium by Phanerochaete sor-dida YK-624 (Takada et al. 1996). All the compounds were extensively degraded, and the ring fission of 2,3,7,8-tetra- and octachlorodibenzo[l,4]dioxin produced 4,5-di- and tetrachlorocatechol. These results established important evidence for the biodegradability of even highly chlorinated dibenzodioxins. 

Koester CJ, RA Hites (1992) Wet and dry deposition of chlorinated dioxins and furans. Environ Sci Technol 26 1375-1382. 

Tanaka F, Fukushima M, Kikuchi A, Yabuta H, Ichikawa H, Tatsumi K (2005) Influence of chemical characteristics of humic substances on the partition coefficient of a chlorinated dioxin. Chemosphere 58 1319-1326... 

As described earlier, Henry s law constants can be calculated from the ratio of vapor pressure and aqueous solubility. Henry s law constants do not show a simple linear pattern as solubility, Kqw or vapor pressure when plotted against simple molecular descriptors, such as numbers of chlorine or Le Bas molar volume, e.g., PCBs (Burkhard et al. 1985b), pesticides (Suntio et al. 1988), and chlorinated dioxins (Shiu et al. 1988). Henry s law constants can be estimated from ... 

Sangster, J. (1989) Octanol-water partition coefficients of simple organic compounds. J. Phys. Chem. Ref. Data 18, 1111-1230. Sangster, J. (1993) LOGKOW, A Databank of Evaluated Octanol-Water Partition Coefficients. 1st Edition, Montreal, Quebec, Canada. Sarna, L.P., Hodge, P.E., Webster, G.R.B. (1984) Octanol-water partition coefficients of chlorinated dioxins and dibenzofurans by reversed-phase HPLC using several C18 columns. Chemosphere 13, 975-983. 

Hashimoto et al. collected chlorinated dioxins and furnaces at concentrations of 1 ppq in seawater on a XAD-2 column [244]. 

Data from Hardell, L. 1983. Epidemiological studies on soft-tissue sarcoma, malignant lymphoma, nasal and nasopharyngeal cancer, and their relation to phenoxy acid or chlo-rophenol exposure. Pages 367-374 in G. Choudhary, L.H. Keith, and C. Rappe (eds.). Chlorinated Dioxins and Dibenzofurans in the Total Environment. Butterworth, Woburn, MA. 

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. 

Clement, R., C. Tashiro, G. Hunt, L. LaFleur, and V. Ozvacic (eds.). 1990. Chlorinated dioxins and related compounds 1989. Part 2. Chemosphere 20 1263-1979. 

Josephson, J. 1983. Chlorinated dioxins and furans in the environment. Environ, Sci. Technol. 17 124A-128A. 

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