Summary

Emissions of trace levels of polychlorinated aromatic compounds as products of incomplete combustion from waste incinerators cause great environmental concern. Some of these compounds are highly toxic and pose significant ecological and health effects. Polychlorinated naphthalenes (PCNs) are often formed during incineration together with polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). Some of the PCN isomers have been determined to have toxicity comparable to those of PCDDs and PCDFs. However, most of the studies on formation of toxic by-products from combustion have been concentrated on PCDDs and PCDFs;very little work has been reported for PCNs. It is very important to clarify the behavior and effect of PCNs.

First, all isomers of di-through heptachloronaphthalene have to be identified for investigation. There are only limited identification information for hexa-and heptachloronaphthalene at that time. Therefore, sixteen isomers were synthesized individually and the other isomers were obtained as several groups of definite isomers for tetrachloronaphthalene (TeCN). For pentachloronaphthalene (PeCN), by-products of TeCN synthesis were available for identification. Specific isomers were synthesized from commercial reagent by simple methods. The isomeric compositions of TeCN and PeCN in fly ash sample from municipal waste incinerator were determined using capillary columns for several stationary phases;such as OV-1701, OV-225B or SB Smectic. The isomer composition was completely different in the case of Halowax 1014 in which 1,4-substitution is dominant. Another study was performed to make quantification of PCNs possible using secondary standard. Only limited standards of individual PCN isomers are available. Halowax' is the most popular technical PCN mixture, but the composition is not clear. Here, the method to determine congener composition of PCN mixture was established using GCAED. Because AED can detect PCNs at the sensitivity proportional to the number of chlorine atoms in the molecule, the relative sensitivities were estimated for the congeners lacking for quantification.

Second, the thermal decomposition reactions of chlorinated hydrocarbons (CHC) were studied to investigate the reaction pathway. The products of thermal decomposition was changed upon the temperature, oxygen concentration, and chlorinehydrogen or chlorinecarbon ratio. Thermal decomposition of trichloroethylene or chloroform often resulted in formation of perchlorinated aromatic compounds such as hexachlorobenzene or octachlorostyrene. When these CHC were diluted by hydrocarbon, no significant formation of chlorinated aromatic compounds took place when the vapor was pre-mixed well with air. PCNs were formed when CHCs were decomposed at the absence of oxygen.

Chlorinated pesticides and plastics are also converted into chlorinated aromatic compounds by thermal decomposition. Technical Chlordane dissolved in undecane formed chlorobenzenes, chlorophenols, PCNs and small amount of chlorodibenzofurans when oxygen was decreased to stoiciomeric amount. Poly (vinylidene chloride) generated 1, 3, 5-trichlorobenzene or 1, 3, 6, 8-tetrachloronaphthalene under oxygen starved condition or very short residence time. These isomers were changed to different isomers at high temperature under oxidative atmosphere. The characteristic isomers implied that the structure of the material partially remained in the products. Tracer experiments are also effective to investigate reaction pathways. To determine the number distribution of ¹³C Atoms in chlorobenzenes, procedure to analyze mass spectral data by least-squares method was established. The number distribution of ¹³C atoms was determined by this method for chlorobenzenes generated in thermal decomposition experiment of ¹³C-labeled chloroform and unlabeled n-hexane. The determined ¹³C contents and estimated mass spectra For ¹²C-chlorobenzenes could reproduce the mass spectra of the samples in good agreement with measured spectra.

To apply this study for practical use, isomer composition of polychlorinated naphthalenes (PCNs) was measured for municipal waste incinerator fly ash samples. Two types of PCN isomer patterns were identified. One pattern contained specific PCN isomers in which chlorine atoms are substituted as if the peri position were dechlorinated from the higher chlorinated PCNs one by one. In another pattern, the isomers had a tendency for the chlorine atoms to assume successive positions on the naphthalene ring, which may be caused by specifically oriented chlorination. Some of these isomers increased together with several polychlorinated dibenzofuran (PCDF) and a few polychlorinated dibenzo-p-dioxin (PCDD) isomers.

Compositions of chemical substances have characteristics depending on their sources. In the case of polychlorinated naphthalenes (PCNs), possible sources are the technical products in the past and the incineration of wastes. In this study, isomer compositions of PCNs in several sediment samples were compared with those of PCNs in source samples. The isomer patterns of PCNs in sediment samples were different from those in incineration samples but resembled with those in technical PCNs, showing similarity indices higher than 0.6, average 0.86. However, concentrations of isomers substituted on more than three within 1-, 4-, 5-or 8-positions were exceptionally lower in environmental samples than those in technical PCNs. This phenomenon was explained to be the result of biodegradation. Thus the PCNs in the samples measured here were considered to be originating mainly from industrial production of PCNs in the past.

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