Volume II Chapter 3.0 Pages 1 of 10 page next page 2

3.0 SOURCES 3-1

3.1. OVERVIEW OF SOURCES 3-1

3.2. PULP AND PAPER MILLS 3-14

3.2.1. Bleached Chemical Wood Pulp and Paper Mills 3-14

3.2.2. Nonchemical and Nonwood Pulping and Bleaching Mills 3-18

3. SOURCES

3.1. OVERVIEW OF SOURCES

The purpose of this chapter is twofold:
(1) to identify sources that release dioxin-like compounds into the environment and
(2) to derive national estimates for releases from these sources in the United States.

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 vs. 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 chlorinated and brominated dioxins and furans have never been intentionally produced other than on a laboratory-scale basis for use in chemical analyses. Rather, they are generated as byproducts from various combustion and chemical processes. 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 in industrialized countries, but continue to be released to the environment through the use and disposal of these products.

 

Dioxin-like compounds are released to the environment in a variety of ways and in varying quantities depending upon the source. For example,

• Releases to the air occur primarily from combustors and appear to have the most direct influence on human exposure. As discussed in Chapter 4, atmospheric deposition and subsequent accumulation through the food chain appears to be the major pathway of human exposure to dioxin-like compounds.

• Solid residues such as combustor ash, still bottoms, etc. can contain high levels of CDD/CDFs and can collectively contain more of these compounds than are found in air or water discharges. However, these solid residues are not generally released to the environment in an uncontrolled manner. Rather, they are usually disposed at secure landfills and any leaching to ground water is minimal due to their very low water solubility.

• Water discharges from paper mills, sewage treatment plants, and possibly other industries can contain low levels of CDD/CDFs. These releases can bioaccumulate via the aquatic food chain and ultimately lead to human exposure via fish ingestion.

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 resulted in the presence of CDDs and CDFs in paper products as well as in liquid and solid wastes from this industry. Municipal sewage sludge has been found to frequently contain CDDs and CDFs. Influents from industrial facilities, stormwater runoff, microbial metabolism of chlorophenols, and domestic household wastewater have been identified by various researchers as the sources(s) of the CDDs/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, continued, limited use and disposal of these compounds can result in releases of CDDs, CDFs, and PCBs to the environment. High levels of CDFs have been found in sludge from graphite electrodes used in chloralkali process to manufacture chlorine.

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 sources 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 causes 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 various processes such as dust or sediment resuspension resulting in the potential for exposure. Releases from these "reservoirs" are not original sources in a global sense, but can be on a local scale. For example, past air emissions causing deposition onto a watershed with subsequent erosion may have resulted in accumulation in downstream sediments. Future sediment dredging operations could result in short-term significant resuspension of dioxins that had accumulated over a much longer period of time. Similarly, leaf composting operations could lead to releases of the dioxins that had, over the course of a growing season, deposited on or been sorbed to the leaves of deciduous trees in an area. Such leaf reservoirs could also be resuspended during forest fires.

As awareness of these possible sources has grown in recent years, a number of changes have occurred that should reduce the release rates (Rappe, 1992a). 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.

Some investigators have raised the possibility that major sources exist that have not yet been identified. This suggestion is acknowledged to be quite speculative, but is important to consider. Three studies addressing this issue are summarized below.

Travis and Hattemer-Frey (1991) used the Fugacity Food Chain (FFC) model to predict the contribution of municipal solid waste incinerators, motor vehicles, hospital waste incinerators, residential wood burning, and pulp and paper mill effluents, to the U.S. total environmental input of 2,3,7,8-TCDD. It was estimated that the total input from all five sources combined accounted for only 11 percent of the total 2,3,7,8-TCDD found in the different media in the United States. The authors concluded that this low value indicated: (1) the source term used in the FFC modeling exercise for 2,3,7,8-TCDD may have been too high; (2) some unidentified major source(s) of 2,3,7,8-TCDD exist; or (3) multiple environmental sources of 2,3,7,8-TCDD with no one source dominating the total input.

Rappe (1991) found discrepancies between estimated emissions from known sources of CDDs and CDFs into the Swedish environment and calculated aerial deposition rates. The total emissions in Sweden were estimated by Rappe (1991) as 100 to 250 g TEQ/yr. The deposition rates used by Rappe (1991) were derived from a study by Marklund (1990) who made measurements in rural areas of Sweden and found an average deposition rate of 5 ng of TEQ/m2 - yr. [Later measurements by Andersson et al. (1992) indicate that deposition in this area has been reduced to about 1 ng of TEQ/m2-yr due to emissions reductions.] Rappe (1991) multiplied the deposition rate of 5 ng TEQ/m2-yr by the total land area of Sweden, yielding a total annual deposition for Sweden of 2,250 g of TEQ/yr, which appears to be 10 to 20 times higher (or 2 to 4 times higher using the deposition rate of Andersson et al. [1992]) than the total emissions from sources originating in Sweden. Possible explanations for this discrepancy are

(1) uncertainty in the emission estimates,
(2) uncertainty in the deposition estimates,
(3) long-range transport of dioxin-like compounds from sources outside of Sweden, or 4) existence of unidentified sources.

In an earlier publication, Rappe et al. (1987) compared congener patterns found in human and aquatic life tissue samples with the congener patterns found in various known emission sources and contaminated products. A poor correlation was observed between the congener patterns found in human and environmental samples and the respective potential sources. Rappe et al. (1987) speculated that the observed pattern in human and environmental samples could be the result of a combination of sources, coupled with environmental and biological degradation of the released congeners.

Harrad et al. (1992a; 1992b) have made similar estimates for the United Kingdom. They estimate that the average annual deposition from the atmosphere to the land surface in the United Kingdom is 250 kg of CDD/CDF (on a total mass basis, not TEQ), compared to about 29.1 kg/yr emitted from known sources. As with the other two studies, these discrepancies could be the result of inaccuracies in emission/deposition estimates, long- range transport from outside the country, or unidentified sources. The authors speculated that much of the discrepancy may be accounted for by secondary or "reservoir" sources (i.e. the remobilization and subsequent redeposition of CDD/CDFs already in the environment).

Table 3-1 presents CDD and CDF source-specific air emission estimates reported for West Germany (Fiedler and Hutzinger, 1992), Austria (Riss and Aichinger, 1993), the United Kingdom (ECETOC, 1992), the Netherlands (Koning et al., 1993), Switzerland (Schatowitz et al., 1993), and the United States (based on estimates generated in this document). The emission estimates for West Germany and Switzerland suggest that municipal waste incinerators and metal smelters/refiners are the largest sources of air emissions. In Austria, domestic combustion of wood is believed to be the largest source followed by emissions from the metallurgical industry. In the United Kingdom, municipal waste incinerators and coal combustion are estimated to be the major sources. Municipal waste incinerators are also estimated to be the largest source in the Netherlands. Rappe (1992a) and Lexen et al. (1992) have identified emissions from ferrous and nonferrous metals smelting and refining facilities as potentially the largest current source in Sweden. Rappe (1992a) reported that changes in various industrial practices have led to reductions in dioxin emissions in Sweden from 400 - 600 g of TEQ/yr in 1985 to 100 - 200 g TEQ/yr in 1991.

Similar nationwide emission estimates for the United States have not previously been compiled. This task has been attempted in this document, and the results are presented in Table 3-1 (air emissions only) and in Table 3-2. Table 3-2 lists emission estimates for the major known or suspected sources that could have releases of dioxin-like compounds to the environment. For each source listed in Table 3-2, estimated emissions to air, water, land, and product are listed where appropriate and where data are adequate to enable an estimate to be made. The term "product" in Table 3-2 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. Figure 3-1 is a chart that visually displays the range of emission estimates to air that are reported in Table 3-2.

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 United States). Because the quantity and quality of the available information for both terms for each emission source varies considerably, a confidence rating scheme was developed. This scheme is based on a consideration of the following factors:

Basis of Estimate -
The basis for the emission estimate varied widely from expert judgement to detailed studies. The best studies involved direct emission measurements at multiple facilities. The representativeness of emission samples was evaluated on the basis of the variability in technologies and associated release rates among individual facilities in the source category. The more variability among facilities; the more important it is to test multiple facilities. In other cases, although no direct emission measurements were available, estimates could be derived using indirect techniques. Obviously, these "indirect" estimates are much more uncertain than those based on direct measurements.

Citation Quality -
The quality of the supporting literature varied widely. Whenever possible, only peer reviewed final reports were used. In some cases, however, draft reports that had undergone some review were used. In a few cases, unpublished references were used such as personal communication with experts.

Table 3-1 CDD and CDF Air Emission Estimates for West Germany, Austria, United Kingdom, Netherlands, Switzerland, and the United States
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The confidence rating scheme, presented in Table 3-3, provides criteria for assigning a "high," "medium," or "low" confidence rating for both the emission factor and production terms.

Table 3-2 Current CDD and CDF Emission Estimates for the United States
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table Figure 3-1 Estimated TEQ Emissions to Air in the United States.
... As shown in Table 3-2, confidence ratings have been assigned to each emission estimate.

The first rating applies to the "production" term, and the second rating applies to the "emission factor" term.

In addition to the confidence rating, 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 upper estimate.

These lower and upper estimates are not intended to be absolute bounds, but reasonable estimates of how much higher or lower the true value might be. Insufficient data were available to statistically derive these ranges.
expand table Figure V2 3-1
Therefore, a judgement-based approach was developed. This approach uses the average or best guess estimate as the central value of the range (assumed to be a geometric average) and sets the width of the range on the basis of the confidence class as follows:

· Low confidence class: upper end of range is 10 times higher than lower end;

· Medium confidence class: upper end of range is 5 times higher than lower end;

· High confidence class: upper end of range is 2 times higher than lower end.

This approach initially assumes that the range of uncertainty is symmetrical about the central value. However, in some cases it may be more reasonable to shift the uncertainty range upwards or downwards. ...
table Table 3-3 Confidence Rating Scheme for U.S. Emission Estimates
... For example, it may be reasonable to shift the range downwards in cases where there is strong evidence that upgrades have occurred since the emissions testing. Alternatively, it is possible that the range should be shifted upwards if it can be shown that the tested facilities are more representative of the low emitting facilities than the high emitting facilities. It is emphasized that these ranges should be interpreted as judgements which are symbolic of the relative uncertainty among sources, not statistical measures. The remainder of this chapter reviews the available data for estimating CDD/CDF releases from specific source categories and provides the basis for the emission estimates presented in Table 3-2 for the United States.
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3.2. PULP AND PAPER MILLS

3.2.1. Bleached Chemical Wood Pulp and Paper Mills

During 1988, EPA and the U.S. pulp and paper industry jointly conducted a survey of 104 pulp and paper mills in the United States to measure levels of dioxins in effluent, sludge, and pulp (U.S. EPA, 1990a). This study, commonly called the 104-Mill Study, was managed by the National Council of the Paper Industry for Air and Stream Improvement, Inc. (NCASI) with oversight by EPA, and included all U.S. mills where chemically produced wood pulps are bleached with chlorine or chlorine derivatives.

In 1992, the pulp and paper industry conducted its own NCASI-coordinated survey. The collected data were summarized and analyzed in a report entitled "Summary of Data Reflective of the Pulp and Paper Industry Progress in Reducing the TCDD/TCDF Content of Effluents, Pulps, and Wastewater Treatment Sludges" (NCASI, 1993). Although the report is available from NCASI, it has not been peer reviewed nor published in an independent journal. The data used in the report were provided by individual pulp and paper companies and neither NCASI nor EPA can vouch for the accuracy or representativeness of the data.

However, NCASI (1993) reports that the pulp and paper industry has taken numerous steps to reduce CDD/CDF releases since 1988, and that NCASI considers the 1992 survey to be more reflective of current conditions than the data generated in the 104-Mill Study (U.S. EPA, 1990a).

As part of its ongoing efforts to develop revised effluent guidelines and standards for the pulp, paper, and paperboard industry, EPA recently published the Development Document for the guidelines and standards being proposed for this industry (U.S. EPA, 1993d). The Development Document presents estimates of the 2,3,7,8-TCDD and 2,3,7,8-TCDF annual discharges in wastewater from the mills in this industry as of January 1, 1993. EPA used the most recent information about each mill from four data bases (104-Mill Study, EPA short-term monitoring studies at 13 mills, EPA long-term monitoring studies at 8 mills, and industry self-monitoring data submitted to EPA) to estimate these discharges.

The 104-Mill Study data were used only for those mills that did not report making any process changes subsequent to the 104-Mill Study and did not submit any more recent effluent monitoring data. For the purpose of this report, the release estimates from NCASI (1993) and U.S. EPA (1990a) are presented to show the possible range of releases within recent years, but the U.S. EPA (1993d) estimates are believed to be most reflective of current conditions.

NCASI (1993) found that less than 10 percent of mills had 2,3,7,8-TCDD and 2,3,7,8-TCDF concentrations in effluent above the nominal detection limits of 10 ppq and 100 ppq, respectively. Similar results were obtained in the short- and long-term sampling reported for 18 mills in U.S. EPA (1993d). 2,3,7,8-TCDD was detected at four mills, and 2,3,7,8-TCDF was detected at nine mills. Wastewater sludges at most mills (75 to 90 percent) were reported by NCASI (1993) to contain less than 10 ppt of 2,3,7,8-TCDD and less than 100 ppt of 2,3,7,8-TCDF. U.S. EPA (1993d) reported similar results but did find detectable levels of 2,3,7,8-TCDD and 2,3,7,8-TCDF in sludges from 64 percent and 85 percent of the facilities sampled, respectively. NCASI (1993) reported that nearly 90 percent of the bleached pulps contained less than 2 ppt of 2,3,7,8-TCDD and less than 20 ppt of 2,3,7,8-TCDF.

The final levels in white paper products would correspond to levels in bleached pulp, so bleached paper products would also be expected to contain less than 2 ppt of 2,3,7,8-TCDD. Overall, NCASI (1993) reports a 90 percent reduction in TEQ generation from 1988 to 1992.

The 104-Mill Study and the NCASI study measured only 2,3,7,8-TCDD and 2,3,7,8-TCDF because these two congeners are the primary contributors (90 percent or more) to the TEQ total found in pulp, sludge, and effluent (U.S. EPA, 1990b). Ninety-four mills participated in the NCASI study, and the remaining 10 (of 104) were assumed by NCASI to be operating at the same levels as measured in the 1988 104 Mill Study. All not detected values were counted as half the detection limit. If detection limits were not reported, they were assumed to be 10 ppq for effluent and 1 ppt for sludge or bleached pulp.

The U.S. annual discharge rates of 2,3,7,8-TCDD, 2,3,7,8-TCDF, and TEQs due to these two compounds are summarized in Table 3-4 for each study. As stated previously, the 1993 discharge estimate for effluent (U.S. EPA, 1993d) is believed to be the best estimate of current emissions. During the period between the conduct of the 104 Mill Study and the issuance of the U.S. EPA Development Document (U.S. EPA, 1993d), the U.S. pulp and paper industry has reduced releases of CDD/CDFs primarily by instituting numerous process changes to reduce the formation of CDD/CDFs during the production of chemically bleached wood pulp. U.S. EPA (1993d) did not provide extensive sampling of sludge and pulp samples from bleached chemical wood pulp and paper mills comparable to that provided for effluents.

However, because most of the reduction between 1988 and 1993 can be attributed to process changes of a pollution prevention nature, the percentage reduction observed in effluent emissions (from 356 g TEQ/yr to 105 g TEQ/yr or 70 percent reduction) is likely representative of the reduction that has been achieved in sludge and pulp emissions over this same time period. Table 3-4 presents best estimates of emissions in sludge and pulp of 100 g TEQ/yr and 150 g TEQ/yr, respectively, using this assumption.

The confidence ratings for these release estimates were judged to be H/H based on the fact that direct measurements have been made at virtually all facilities, indicating a high level of confidence in both the production and emission factor estimates. Based on these high confidence ratings, the estimated ranges of potential annual emissions for effluent, sludge, and pulp are assumed to vary by a factor of 2 between the low and high ends of the ranges.
Assuming that the best estimates of annual emissions (i.e., the 1993 discharge-based estimates presented in Table 3-4) are the geometric means of these ranges, then the ranges are calculated to be 74 to 150 g TEQ/yr for effluent, 71 to 140 g TEQ/yr for sludge, and 105 to 210 g TEQ/yr for pulp.

table Table 3-4 Summary of Bleached Chemical Pulp and Paper Mill Discharges of 2,3,7,8-TCDD and 2,3,7,8-TCDF In 1990, approximately 20.5 percent or 500 million dry kg of the pulp and paper mill wastewater sludge generated by facilities employing chlorine bleaching of pulp were incinerated (U.S. EPA, 1993e).

The majority of the wastewater sludge generated by these facilities is landfilled or placed in surface impoundments (79.5 percent) with the remainder incinerated (20.5 percent), applied to land directly or as compost (4 percent), or distributed as a commercial product (less than 1 percent) (U.S. EPA, 1993e).


Black liquor recovery boilers used in the Kraft process for the production of paper pulp are potential sources of CDDs/CDFs. Estimates of potential CDD/CDF emissions to air from these sources are discussed in Section 3.6.4.
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3.2.2. Nonchemical and Nonwood Pulping and Bleaching Mills

Although the EPA Office of Water does not believe that secondary fiber mills (i.e., mills using recycled paper as a source of pulp) are significant sources of CDDs and CDFs, EPA is considering whether to establish effluent limitations guidelines and standards for CDD/CDFs for these mills based primarily upon data generated for the Development Document (U.S. EPA, 1993d). These data, collected by EPA or provided to EPA by industry, indicate detectable levels of 2,3,7,8-TCDD in the effluents of 2 of the 12 mills with reported monitoring data and detectable levels of 2,3,7,8-TCDF in the effluents of 4 of the 7 mills with data (U.S. EPA, 1993d).

Data on the presence of more chlorinated (i.e., penta-through octachlorinated) CDDs and CDFs in the effluents of these facilities were not generated for the Development Document (U.S. EPA, 1993d). However, Berry et al. (1993) reports that trace levels of these higher chlorinated homologs were commonly observed in the effluents from Canadian pulp mills that use recycled paper for fiber furnish (i.e., the raw materials used to manufacture pulp) and/or that do not practice chlorine bleaching. Similar results were reported by Rappe et al. (1990). The congener profile observed is not dominated by the tetra-CDDs/CDFs, as is the case with bleach plant wastewater, but rather by the higher chlorinated congeners more consistent with the congener profile found in ambient air, soil, and adipose tissue. These results lead to the hypothesis that paper and paperboard products, during their useful life, can accumulate trace amounts of CDD/CDFs from the ambient environment.

As a step in evaluating this hypothesis, Berry et al. (1993) analyzed the CDD/CDF content of pulp and paper samples from Canadian mills that use neither chlorine-containing bleaching compounds nor fibers that have been bleached with chlorine-containing compounds as well as papers from mills that use recycled paper as a furnish. All samples analyzed had detectable levels of one or more CDD/CDFs.

The congener profiles of the samples were similar with the higher chlorinated congeners dominating in terms of concentration. The order of degree of contamination on a TEQ basis, from high to low, is recycled linerboard (1 sample--2.5 ng TEQ/kg) > "totally chlorine-free" bleached kraft paper (1 sample--0.35 ng TEQ/kg) > pulp from de-inked recycled paper (1 sample--0.19 ng TEQ/kg) > newsprint (17 samples--mean = 0.07 ng TEQ/kg) > unbleached kraft paper (2 samples--mean = 0.02 ng TEQ/kg). Rappe et al. (1990) also reported finding higher levels of CDD/CDFs, particularly the hepta- and octa-chlorinated congeners, in recycled paper pulps than in virgin bleached and unbleached pulps.

Based on the results of their study, Berry et al. (1993) concluded that, although it may be possible to produce a dioxin-free pulp, it is likely that all papers will become contaminated during their first life cycle by contact with dioxin-laden dust, and contamination is inevitable if they are recycled multiple times.