Combustion sources, PCDD

Fiedler 1999). An overview of combustion sources known to generate and emit PCDD/PCDFs (Fiedler, 1999) is presented in Table 2. 

Combustion processes. Combustion is still a major source of these substances. PCDDs and PCDFs have been found in exhaust gases from a wide variety of combustion processes - from cigarette smoke to emissions by fossil fuel power plants. Stringent controls have been introduced on waste incinerators in the UK and several other countries. It is likely now that most formerly significant sources have been controlled, leaving diffuse combustion sources, e.g. bonfires and car exhausts, as major contributors to the environmental background. 

Dioxins (PCDDs) occur as contaminants in many agricultural pesticides and can occur in the environment as a result of pesticide usage, although many other industrial sources and natural sources have been identified. The National Dioxins Program (2004) has revealed that major sources of dioxins in the environment are uncontrolled combustion sources such as bush fires and accidental fires which contribute 70% of the total to the air and 80% to the soil whereas waste disposal and land filling contribute 75% of the total to water. 

Yamamoto T, Fukushima M. 1993. Modeling study on contribution of combustion source complex to PCDD/PCDF levels in urban air. Chemosphere 27(l-3) 295-300. 

It is now generally accepted that combustion is the almost exclusive source of the carcinogen and endocrine-disrupting chemical family of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F or dioxins for short). Dioxins are part of a broader class of chlorinated organic air pollutants that are produced by most combustion sources. All that is necessary are a small source of chlorine (that may even be in the combustion makeup air), a catalytic metal, and a hydrocarbon. 

It is now known that endocrine disrupting chemicals are emitted from combustion sources. Interest has focused on the emissions of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F), which are also known carcinogens. However, oxy-PAH, epoxides, and other oxygenated species are known EDCs. These can also be emitted from combustion sources, although they are not well characterized. They are semipolar compounds that are difficult to analyze. Thus, improved methods of analysis are needed in conjunction with biological testing to determine the nature and quantity of EDC emissions from combustion sources. 

Chlorinated and brominated materials are burned or thermally treated in a variety of combustion sources including hazardous and municipal waste incinerators, industrial processes, backyard trash burning, and accidental fires. Chlorinated materials are used in a wide range of applications and brominated compounds are fire retardants used in many devices including electronic circuits. Although there has been some research on the reactions of CHCs and BHCs in the past 20 years, too little is known about their reactions considering the magnitude of the environmental impact. Elementary reaction studies of gas-phase reactions of Cj and C2, CHCs, and BHCs are needed to understand their most fundamental reaction properties. Reactions of the chlorinated and brominated benzenes and phenols are important intermediate steps in the formation of PCDD/F. Recent kinetic models indicate that the gas-phase reactions may be quite important and elementary gas-phase reaction studies have been overlooked by researchers. 

Sources From Combustion Processes. In 1977, PCDD and PCDF were detected in particulate emissions from municipal incinerators (5). Similar data were soon reported from around the world. In 1980, workers at Dow Chemical Company, using the most sensitive and specific analytical techniques of that time, detected a range of PCDD in residues from many combustion processes (6). These workers postulated that all combustion processes that contain chlorine sources produce PCDD. Although this postulate is not supported in all situations, dioxin emissions from combustion sources are major contributors to PCDD in the environment (7). 

Energy recovery from packaging waste is discussed, with particular reference to the co-combustion of mixed plastics with other conventional fuels such as wood, coal and peat. Experimental work is described in which a project was established to evaluate the possibility of energy recovery from a circulating fluidised bed boiler using packaging from different sources as fuel. The role of sulphur in the formation of PCDD/F in the combustion process was also studied. 

Heating of houses with wood, charcoal or mazut also results in formation of trace amounts of dioxins. Hazardous source of PCDD and PCDF constitutes the combustion of engine oil and gasoline with chlorine- or bromine-organic additives. Over the long period of time, pesticides containing dioxins (2,4,5-T, copper trichlorophenolate etc.) [4] were used in agriculture. 

Owing to their chemical, physical and biological stability, PCDD/PCDFs are able to remain in the environment for a long time. As a consequence, dioxins from so-called primary sources (formed in industrial or combustion processes) are transferred to... 

Photochemical reactions can result in the formation as well as the degradation of PCDD/Fs. These reactions are carefully examined as most combustion and incineration sources produce emission directly into the atmosphere and they undergo long-distant transport. 

PCDD/Fs are emitted or spilled from many processes, but as they were found in the emissions from all combustion processes, thermal processes are recognized to be a main source, and a major public concern, especially waste incineration. But dioxins problem is attributed to all human activities, connected either with production or utilization of solid wastes and wastewaters. One of the crucial examples of the problem is sewage sludge contamination. 

Article 5 (Measures to reduce or eliminate releases from unintentional production ) of the convention generally aims at regulating the reduction of total releases derived from anthropogenic sources (combustion/burning of organic material and chlorine at the same time) of the so called Annex C chemicals, which are HCBs, PCBsand PCDD/PCDF as well as their continuous minimisation and (where feasible) ultimate elimination. 

Polychlorinated Dibenzo-(p)-Dioxins and Dibenzo-Furans. Another group of compounds that we need to specifically address are the polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzo-furans (PCDFs) (Fig. 2.15). The PCDDs and PCDFs are not intentionally produced but are released into the environment from various combustion processes and as a result of their occurrence as unwanted byproducts in various chlorinated chemical formulations (e.g., chlorinated phenols, chlorinated phenoxy herbicides see Alcock and Jones, 1996). Because some of the PCDD and PCDF congeners are very toxic (e.g., 2,3,7,8-tetrachloro dibenzo-p-dioxin, see margin), there have been and still are considerable efforts to assess their sources, distribution, and fate in the environment. Similarly to the PCBs or DDT (see above), the PCDDs and PCDFs are highly hydrophobic and very persistent in the environment. It is therefore not surprising that they have also been detected everywhere on earth (Brzuzy and Hites, 1996 Lohmann and Jones, 1998 Vallack et al., 1998). Finally, we should note that polybrominated diphenylethers (PBDEs, see margin) that, like the PBBs (see above), are used as flame retardants, are of increasing environmental concern (de Boer et al., 2000). 

In 1978, people of the Dow Company proposed the hypothesis that PCDDs are byproducts of common combustion and, therefore, have always been present in the environment. In one study (20), wood was selected as a combustion fuel for a survey study of PCDD emissions. This study suggested that additional research was necessary to confirm this hypothesis and to characterize the magnitude of this newly defined source. A recent review of the fire hypothesis is given in reference 21. 

Formation of polychlorinated dibenzo(p) dioxins and furans (PCDD/PCDF) in waste combustion has received considerable attention, because dioxins even in very small concentrations are believed to be harmful to humans. Sources of PCDD/PCDF include the waste itself, gas-phase and heterogeneous reactions within the combustion zone, and catalyzed reactions in the low-temperature region downstream [352],... 

ThuB U, Popp P, Ehrlich Chr, Kalkoff W-D (1995) Domestic Lignite Combustion as Source of Polychlorodibenzodioxins and -Furans (PCDD/F) Chemosphere 31 2591... 

Non-point source Transport, uncontrolled/ residential fuel combustion, fires etc. PCDDs/DFs, coPCBs, HCB 2004 KMOE KMOE, 2004c, 2005a... 

HCB was neither imported nor manufactured in South Korea. Domestic emission, therefore, should originate from process such as combustion of organic matters combined with chlorine and from impurities in the production of chemicals and pesticides. HCB emission for 2000 in South Korea was estimated in a preliminary study of emission inventory using top-down approach (KMOE, 2003b). Emissions from some sources in 2005 were determined by measuring concentrations in archived samples originally collected for analysis of PCDDs/DFs in 2001-2003 (KMOE, 2005a). 

---