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II.2.2.Estimates of Annual Releases of Dioxin-Like Compounds

PCBs were produced in relatively large quantities for use in such commercial products as dielectrics, hydraulic fluids, plastics and paints. They are no longer produced, but continue to be released to the environment through the use and disposal of products manufactured years ago. The chlorinated and brominated dioxins and furans, on the other hand, have never been intentionally produced other than on a laboratory scale basis for use in chemical analyses. They are, however, generated as byproducts from various combustion and chemical processes.

Dioxin-like compounds are released to the environment in a variety of ways and in varying quantities depending upon the source. The dioxin like compounds have been found in all media and all parts of the world. This ubiquitous nature of these compounds suggests that multiple sources exist and that long range transport can occur. An unresolved issue is how the relative impacts from local versus distant sources compare at a particular location. Presumably in industrial areas local sources will dominate and in rural areas distant sources will dominate.

However, site specific considerations such as stack height, wind patterns, magnitude of local sources, etc. could influence these comparisons.
The major identified sources of environmental release have been grouped into four major types for the purposes of this report:

. Industrial/Municipal Processes:
Dioxin-like compounds can be formed through the chlorination of naturally occurring phenolic compounds such as those present in wood pulp. The formation of CDDs and CDFs resulting from the use of chlorine bleaching processes in the manufacture of bleached pulp and paper has in the past resulted in the presence of CDDs and CDFs in paper products as well as in liquid and solid wastes from this industry, although more recently this industry has made process changes to minimize CDD/CDF formation. Occasionally, municipal sewage sludge has been found to contain CDDs and CDFs.

. Chemical Manufacturing/Processing Sources:
Dioxin-like compounds can be formed as by-products from the manufacture of chlorine and such chlorinated compounds as chlorinated phenols, PCBs, phenoxy herbicides, chlorinated benzenes, chlorinated aliphatic compounds, chlorinated catalysts, and halogenated diphenyl ethers. Although the manufacture of many chlorinated phenolic intermediates and products, as well as PCBs, was terminated in the late 1970s in the United States, the continued limited use and disposal of these compounds can result in releases of CDDs, CDFs, and PCBs to the environment.

. Combustion and Incineration Sources:
Dioxin-like compounds can be generated and released to the environment from various combustion processes when chlorine donor compounds are present. These processes can include incineration of wastes such as municipal solid waste, sewage sludge, hospital and hazardous wastes; metallurgical processes such as high temperature steel production, smelting operations, and scrap metal recovery furnaces; and the burning of coal, wood, petroleum products, and used tires for power/energy generation.

. Reservoir Sources:
The persistent and hydrophobic nature of these compounds cause them to accumulate in soils, sediments and organic matter and to persist in waste disposal sites. The dioxin-like compounds in these "reservoirs" can be redistributed by dust or sediment resuspension and transport. Such releases are not original sources in a global sense, but can be on a local scale. For example, releases may occur naturally from sediments via volatilization or via operations which disturb them such as dredging. Aerial deposition and accumulation on leaves may lead to releases during forest fires or leaf composting operations.

As awareness of these possible sources has grown in recent years, a number of changes have occurred which should reduce the release rates (Rappe, 1992). For example, releases of dioxin-like compounds have been reduced due to the switch to unleaded automobile fuels (and associated use of catalytic converters and reduction in halogenated scavenger fuel additives), process changes at pulp and paper mills, new emission standards and upgraded emission controls for incinerators, and reductions in the manufacture of chlorinated phenolic intermediates and products.

Table II-2 presents CDD and CDF air emission estimates for Germany, Austria, the United Kingdom, the Netherlands, Switzerland and the U.S. All the countries except Austria estimate that municipal waste incinerators are an important source (new emission standards in Germany indicate that the emissions from this source are now nearer the lower end of the range listed in Table II-2). Medical waste incinerators, wood burning and metal smelters/refiners also appear to be generally important sources. Rappe (1992) and Lexen et al. (1992) have identified emissions from ferrous and non-ferrous metals smelting and refining facilities as potentially the largest current source in Sweden. Rappe (1992) reported that changes in various industrial practices have lead to reductions in dioxin emissions in Sweden from 400 - 600 g of TEQ/yr in 1985 to 100 - 200 g TEQ/yr in 1991.


Nationwide emission estimates for the United States have not previously been compiled. This task was attempted as part of this project and the air emissions are summarized in Table II-2 and a detailed estimate of emissions to all media are presented in Table II-3. For each source, emissions to air, water, land, and product are estimated where appropriate and where data are adequate to enable an estimate to be made. The term "product" is defined to include substances or articles (e.g., paper pulp or sewage sludge that is distributed/marketed commercially) that are known to contain dioxin-like compounds and whose subsequent use may result in releases to the environment.

In order to make each source emission estimate, information was required concerning both the "emission factor" term for the source (e.g., grams TEQ per kg of material processed) and the "production" term for the source (e.g., kg of material processed annually in the U.S.). Because the quantity and quality of the available information for both terms for each emission source varies considerably, a confidence rating of "high", "medium", or "low" was assigned to both terms. In addition, the uncertainty in these national release estimates is reflected by presenting (where possible) for each source category both a central or "best guess" value and a possible range from a lower to an upper estimate.
table Table II-2. CDD and CDF air emission estimates for West Germany, Austria, United Kingdom, Netherlands,Switzerland, and the United States. table Table II-3. Current CDD and CDF multi-media emission estimates for the United States.
expand table Table VX X-X expand table Table VX X-X

In general, the emission estimates are quite uncertain since the nationwide approximations were derived by extrapolating only a few facility tests. Insufficient data were available to statistically derive estimates of the range of uncertainty surrounding the central emission estimates. Instead, a judgement-based approach was used that assigned a factor of 10 from the low to high end of the range for the low confidence class, a factor of 5 for the medium confidence class and a factor of 2 for the high confidence class. It is emphasized that these ranges should be interpreted as judgements which are symbolic of the relative uncertainty among sources, and not statistical derivations of uncertainty. The emission factors and production values used to generate air emission estimates are illustrated in Figure II-3.

Key source categories are discussed below:

. Hospital Waste Incinerators:
Collectively, this may be the largest source in the United States. This is due to the facts that most of these incinerators do not rely on highly sophisticated control technologies, are high in number (over 6000 facilities) and burn high chlorine content waste.

Although the dioxin emissions from these facilities are collectively large, individually they are relatively small. Therefore, local impacts may also be relatively small. However, the area of impact is an uncertain issue in general for combustors. Germany recognized the importance of these facilities several years ago and instituted emission limits which required facilities to upgrade their technology or ship waste to hazardous waste incinerators.

. Municipal Waste Incinerators:
The current emissions from this category appear relatively high, but upgrading is occurring that should substantially reduce these emissions in the near future. Dioxin is also present in the ash generated from these facilities. The amount estimated to be in municipal incinerator waste ash nationally is the largest among the few source categories where estimates could be made concerning solid residues.

. Cement Kilns:
EPA is currently evaluating dioxin levels in the clinker dust and stack emissions from these facilities. The preliminary information suggests that collectively these facilities could be a moderate to large source. About 16% of the facilities burn hazardous waste as an auxiliary fuel; limited data suggests that the CDD/F levels in clinker dust and stack emissions of these kilns may be significantly higher than the kilns which do not burn hazardous waste.

• Wood Burning:
A large quantity of wood is burned at industrial operations, but the practice has not been well characterized. The emission estimates presented here are based on stack tests at two facilities. A number of studies have found dioxins in the emissions and ash/soot from wood fires in nonindustrial situations.
table Figure II-3 Estimated TEQ emissions to air from combustion sources in the United States.
The emission estimates for residential wood burners were made on the basis of two recent European studies. CDD/Fs may also be emitted during forest fires, but very little direct emission data are available for evaluating this issue.

The estimates shown here were derived from tests on wood stoves under conditions of uncontrolled draft.

Considering the many differences between combustion in wood stoves and forest fires, these estimates must be considered highly uncertain.

Only one test has been conducted that directly measured CDD/F in smoke of forest fires (Clement and Tashiro, 1991).
expand table Figure VX X-X

Low levels were detected, but the authors caution that some portion of these emissions could represent resuspended material from aerial deposits rather than originally formed material. The theory that much of today's body burden could be due to natural sources (such as forest fires) has been largely discounted by testing of ancient tissues which show levels much lower than those found today (Ligon et al. 1989).

• Metals Industry:
Secondary smelters which recover metal from waste products such as scrap automobiles have the potential for dioxin formation due to chlorine in the plastic in the feed material. Processes in the primary metals industry, such as sintering of iron ore, have also been identified as potential sources. Germany (see Table II-2) has identified the metals industry as potentially one of the most important.

Table II-3 estimates moderate emissions for secondary copper smelting (based on testing at only one facility) and relatively low emissions for secondary lead smelting (based on testing at three facilities). No data are available to estimate emissions from other secondary smelters or primary smelters. Accordingly, these facilities are a high priority for future emissions testing.

• Diesel Vehicles:
The literature on dioxin emissions from diesel vehicles is quite limited and somewhat contradictory. The tunnel study by Oehme et al. (1991) suggests a relatively high level of emissions. This study is based on Norwegian fuels which may differ in composition from U.S. fuels and, although aggregate samples were collected representing hundreds of vehicles, the indirect method of analysis introduces uncertainty. Much lower emissions were measured by Marklund et al. (1990) on the basis of direct tailpipe tests involving diesel fuel in a heavy-duty Swedish vehicle (Marklund et al., 1990).

This study reported no emissions at a detection limit of 100 pg/l or approximately 0.05 ng/km. This is a factor of 100 lower than the emission rate reported by Oehme et al. (1991). Because this study's results are based on only one vehicle using Swedish fuel, this emission factor is also quite uncertain. These two studies yield a very wide range of emission estimates and clearly suggests that further testing is needed.

• Coal-Fired Utilities:
The importance of these facilities remains unknown. Only one U.S. facility has been tested and no detectable levels of dioxin were found. If dioxin were present at the detection limit, an emission factor can be calculated which suggests that, due to their number, these plants could collectively represent a moderately sized source. The potential importance of this source is enhanced by several factors. In addition to being numerous, they are large in size and their high stacks indicate that they could impact very large areas. Testing is currently underway to better characterize these emissions.

• Pulp and Paper Mills:
These facilities can have dioxin releases to water, land and paper products. The paper industry has recently made process changes which they estimate have reduced dioxin emissions by 90% from 1988 to 1992 (NCASI, 1993). Extensive surveys encompassing virtually all mills have been conducted, making this industry one of the best characterized in terms of dioxin emissions.

The other combustors evaluated in this report appear to be relatively minor sources on a national scale (although their local impacts could be important to evaluate). These include sewage sludge incinerators, hazardous waste incinerators, Kraft liquor boilers, drum and barrel reclaimers, tire combustors, carbon reactivation furnaces and scrap electric wire recovery facilities. The releases associated with chemical manufacturing could not be quantified due to the lack of test data.

Potentially such releases could occur via the product itself or as emissions to the air, land or water. Such releases have lead to the termination of production of PCBs and some phenoxy herbicides. Recently, some claims have been made that significant dioxin emissions may occur during the production of vinyl chloride monomer and associated products. These claims have been strongly disputed by the industry. Insufficient emission data are currently available to make an independent evaluation. Several investigators have attempted to conduct "mass balance" checks on the estimates of national dioxin releases to the environment.

Basically, this procedure involves comparing estimates of the emissions to estimates of aerial deposition. Such studies in Sweden (Rappe, 1991) and Great Britain (Harrad and Jones, 1992) have suggested that the estimated deposition exceeds the estimated emissions by about 10 fold. These studies are acknowledged to be quite speculative due to the strong potential for inaccuracies in emission and deposition estimates. In addition, the apparent discrepancies could be explained by long range transport from outside the country, resuspension and deposition of reservoir sources, atmospheric transformations or unidentified sources.

Bearing these limitations in mind, this procedure has been used here to compare the estimated emissions and deposition in the United States.
Deposition measurements have been made at a number of locations in Europe (see Volume II) and two places in the United States (Koester and Hites, 1992). These limited data suggest that a deposition rate of 1 ng TEQ/m2-yr is typical of remote areas and that 2-6 ng TEQ/m2-yr is more typical of populated areas. Applying the values of 1 ng TEQ/m2-yr to Alaska and 2-6 ng TEQ/m2-yr to the continental United States, the total U.S. deposition can be estimated as 20,000 to 50,000 g TEQ/yr.

This range can be compared to the range of emissions for the United States, 3,300 to 26,000 g TEQ/yr, as presented in Table II-3. It is not clear whether this type of mass balance can ever be refined to the point where definitive conclusions can be drawn. However, it remains one of the few methods of evaluating the existence of unknown sources.

II.3. OCCURRENCE AND BACKGROUND EXPOSURES

Polychlorinated dibenzo-p-dioxins (CDDs), polychlorinated dibenzofurans (CDFs), and polychlorinated biphenyls (PCBs) have been found throughout the world in practically all media including air, soil, water, sediment, fish and shellfish, and other food products such as meat and dairy products. The highest levels of these compounds are found in soils, sediments, and biota; very low levels are found in water and air. The widespread occurrence observed is not unexpected considering the numerous sources that emit these compounds into the atmosphere, and the overall resistance of these compounds to biotic and abiotic transformation.

II.3.1.United States Food Data

All available data on background levels in United States food are summarized in Table II-4. "Background" concentrations are defined here as those for which no source of dioxin-like compound contamination was identified to have impacted the concentrations reported. The background TEQ estimates are presented first assuming that nondetects equal half the detection limits and second assuming that nondetects equal zero.

For food groups such as eggs, a wide range of TEQ estimates are seen indicating a high percent of nondetects among individual congeners. The higher of the two TEQ estimates, that calculated using half the detection limit for nondetects, are generally comparable to the TEQ estimates derived from studies conducted in Germany (Fürst et al. 1991) and Canada (Gilman and Newhook, 1991).

The German and Canadian studies did not, however, report how nondetects were treated in deriving their TEQs, but did report many nondetects in some food groups. In summary, the limited number of United States food samples and the high incidence of nondetects make an uncertain basis for estimating national background levels, although they are reasonably consistent with food level estimates reported for Canada and Germany. It is clear that more data are needed to adequately characterize the levels of dioxin-like compounds in the United States food supply.

Although a large scale survey could confirm residue levels of CDD/F, some attention also needs to be paid to sampling/analytical methodology. Since many of the detected values are only a few multiples above reported detection limits, significant uncertainty results in reported mean values when there are many nondetects in a food category.

II.3.2. Summary of Media Levels
The estimated levels of CDD/CDFs in environmental media and food are summarized in Table II-5 and shown graphically in Figure II-4. Except for the TEQ levels in European food which are based on data reported for German food by Fürst et al. (1990), all other TEQ levels presented in Figure II-4 are based on the data analyzed in this study. The background TEQ levels of CDD/CDFs in water and air were found to be lower than in any of the other environmental media evaluated and were not included in Figure II-4. For most media, the average levels appear to be similar between North America and Europe. However, differences were noted in three areas:
table Table II-4. Summary of CDD/F levels in United States food (pg/g fresh weight). table Table II-5. Summary of CDD/F levels in environmental media and food (whole weight basis).
expand table Table VX X-X expand table Table VX X-X
table Figure II-4 Background environmental levels in TEQ.  
expand table Figure VX X-X

• Sediment:
The background levels in Europe were estimated to be higher than North America. It should be noted, however, that only the 2,3,7,8-TCDD/F and OCDD/F congeners were analyzed for background sediment sites in the United States and Europe. The sediment data are quite variable and can be very high in impacted areas (i.e., 2,3,7,8-TCDD levels over 1000 ppt have been measured in industrial areas).

Also, it was difficult to interpret whether some of the European data truly represent unimpacted areas. Thus, these differences may be due more to the weakness of the data base and interpretation difficulties, rather than real differences.

• Dairy Products:
The data on dairy products suggest that North America levels are higher than European. Dairy products include a wide variety of food items with varying amounts of fat. Thus, the CDD/F levels would vary correspondingly. Differences in the mix of dairy products used for the North America and European estimates could explain these differences.

• Pork:
The pork data suggests that North America levels are higher than European levels. The low number of samples collected in both Europe and North America may mean this estimate is not representative.

In general, the differences noted above probably reflect the sparseness or inequalities in the data rather than real differences. The small number of samples available for analysis, particularly for food, should be considered when evaluating data from the United States and elsewhere. The human tissue data (see discussion below) suggest similar body burden levels in the North America, Europe and other industrial countries. Thus, it seems likely the media levels would also be similar. Large scale "market basket" type food surveys would be needed to confirm these levels.