PCDFs

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). 

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. 

Both CI2 and HCl have been shown to chlorinate hydrocarbons on fly ash particles. Pilot-scale data involving the injection of fly ash from municipal waste combustion (33) show that intermediate oxygen concentrations (4—7%) produce the highest levels of PCDD and PCDF. These data also show significant reductions in PCDD and PCDF emissions with the upstream injection of Ca(OH)2 at about 800°C. 

Chlorobenzenes are stable compounds and decompose slowly only under excess heating at high temperatures to release some HCl gas and traces of phosgene. It is possible, under certain limited conditions of incomplete combustion or pyrolysis, to form polychlorinated dibenzo-/)-dioxins (PCDDs) and dibenzofurans (PCDFs) from chlorobenzenes (Cm OROCARBONS and cm OROHYDROCARBONS, toxic aromatics). 

Human Health Effects. Any assessment of adverse human health effects from PCBs should consider the route(s) of and duration of exposure the composition of the commercial PCB products, ie, degree of chlorination and the levels of potentially toxic PCDF contaminants. As a result of these variables, it would not be surprising to observe significant differences in the effects of PCBs on different groups of occupationally-exposed workers. 

The specific molecular mechanisms by which PCDDs and PCDFs are initially formed and become part of the PIC remain largely unknown and are theoretical. The theoretical basis for conjecture is derived primarily from direct observations in municipal solid waste incinerators. The emissions of... 

Creosote PIC are comprised of PCDD/PCDF, flyash and soot, NO, SOj, COj, HCl, and various PAHs ... 

It is assumed that 0.5% of the PIC are comprised of gaseous forms of PCDD/PCDF. 

Available Fuel, Lbs Lbs Fuel Tor Energy Lbs Flyash Total Lbs Gaseous + PM Lbs NO., SO, CO, Other Lbs PCDD/ PCDF... 

Time, Hrs Distance from Source, m PCDD/PCDF Concentration, uglm ... 

G. Schomburg, H. Husmann and E. Hiibinger, Multidimensional separation of isomeric species of cWor inated hydrocarbons such as PCB, PCDD and PCDF , 7. High Resolut. Chromatogr. Chromatogr. Commun. 8 395-400 (1985). 

In general, capillary gas chromatography provides enough resolution for most determinations in environmental analysis. Multidimensional gas chromatography has been applied to environmental analysis mainly to solve separation problems for complex groups of compounds. Important applications of GC-GC can therefore be found in the analysis of organic micropollutants, where compounds such as polychlorinated dibenzodioxins (PCDDs) (10), polychlorinated dibenzofurans (PCDFs) (10) and polychlorinated biphenyls (PCBs) (11-15), on account of their similar properties, present serious separation problems. MDGC has also been used to analyse other pollutants in environmental samples (10, 16, 17). 

Some characteristic physical properties of PBDD/F have been determined and can be found elsewhere 8-14. An important property for environmental behaviour is the vapour pressure. Vapour pressures of some PBDD has been measured by a special new technique 30. pig. 12 shows extrapolated vapour pressures of PCDD and PCDF and of corresponding PBDD and PBDF. 

Fig. 12. Extrapolated Vapor Pressures of PCDD and PCDF and of corresponding PBDD and PBDF.

The use of aromatic brominated compounds as flame retardants has been a potential source of environmental contamination. Incomplete incineration of these compounds and wastes (plastics, textiles, oils etc...) containing brominated flame retardants caused formation of brominated/chlorinated dibenzodioxines (PBDDs/ PCDDs) and dibenzofurans (PCDFs/PBDFs) (refs. 1 - 4). 

PCDFs are similar in many respects to PCDDs but have been less well studied, and will be mentioned only briefly here. Their chemical structure is shown in Figure 7.1. Like PCDDs, they can be formed by the interaction of chlorophenols, and are found in commercial preparations of chlorinated phenols and in products derived from phenols (e.g., 2,4,5-T and related phenoxyalkanoic herbicides). They are also present in commercial polychlorinated biphenyl (PCB) mixtures, and can be formed... 

The compound should show a structural relationship to PCDDs and PCDFs. 

PCB fraction accounted for 75%+ of TEQ by either assay reduced productivity of birds in this area TEQs mainly due to PCBs, especially 3,3, 4,4 -TCB Reduced reproductive success, but less effect than expected from high TEQs PCDDs, PCDFs, and PCBs made variable, but on the whole similar contributions to TEQ values probably not high enough to adversely affect fish populations TCDD mainly 2,3,7,8-TCDD Reduced hatching... 

Induction of P450 lAl/2 provides the basis for biomarker assays for PAHs and other planar organic pollutants, such as coplanar PCBs, PCDDs, and PCDFs. 

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