Volume II Chapter 4.0 Pages 4 of 4 page    


4.7.1. U.S. Data 4-44

4.7.2. European Data 4-45

4.7.3. Air Summary 4-47






Tables B-14 through B-16 (Appendix B) contain summaries of data from studies of ambient air measurements of CDDs, CDFs, and PCBs in the United States and Europe. Environmental levels of PCBs in air are based on a single source of information (Hoff et al., 1992).

Relatively few studies have been conducted to measure ambient air levels of CDDs/CDFs because of the low analytical detection limits required to detect the expected low concentrations of specific CDD/CDF congeners. These detection limits in ambient air samples were not achieved until the mid 1980s.

To obtain subparts-per-trillion levels of analytical detection, sampling relatively large volumes of air (e.g., 350 to 450 cubic meters of ambient air over a 24-hour period) is required. The results of several of these recent studies are summarized in the following paragraphs.

table Table 4-8 Concentrations of Dioxins & Furans . table Table 4-9 Maximum CDD/CDF Levels in Foods Collected in Canada (pg/g fresh weight) as Reported by Birmingham et al. (1989).
expand table Table V2 4-8 expand table Table V2 4-9

4.7.1. U.S. Data

The most extensive ambient air monitoring study of CDDs/CDFs conducted to date is a multiyear monitoring effort conducted at eight sampling locations in the Southern California area by the Research Division of the California Air Resources Board from December 1987 through March 1989 (Hunt et al., 1990). The monitoring network "included a number of sites situated in primarily residential areas (San Bernadino, El Toro, and Reseda), as well as several sites in the vicinity of suspected sources of CDDs/CDFs (Cal. Trans, Commerce, North Long Beach, and West Long Beach)."

The seven sites mentioned above were classified as urban locations by the definitions used in this document, while one site was classified as an industrial site (i.e., Carson--on site at manufacturer of gas cooking equipment). Additionally, four of the eight sites were part of the South Coast Air Quality Management District (SCAQMD) monitoring network.

All totaled, there were nine sample collection intervals throughout this study. "Typically, five to seven stations were in contemporaneous operation during a particular session" (i.e., samples were not collected from each location at each interval).

Total tetra- through octa- chlorinated CDDs and CDFs were screened for in the study as well as various 2,3,7,8-substituted CDD and CDF congeners. A total of 34 analyses were performed throughout the study for all congeners except for OCDD and OCDF, respectively, for which only 31 analyses were performed. Samples were collected over a maximum of seven intervals at each site throughout the study (i.e., Reseda and El Toro--six dates, duplicate samples on one date), while a sample was collected from the Commerce site during only a single collection interval. Sample collection intervals generally averaged 24 hours in duration.

Generally, higher substituted CDD and CDF congeners accounted for the majority of positive samples containing quantifiable CDD/CDF residues in this study (i.e., Total HxCDD/HxCDF and above). In fact, over 90 percent of the samples collected contained quantifiable levels of 1,2,3,4,6,7,8-HpCDD, Total HpCDD, and OCDD. Additionally, approximately 50 to 70 percent of the samples collected contained quantifiable levels of Total HxCDD; 2,3,7,8-TCDF; Total TCDF; Total PeCDF; Total HxCDF; 1,2,3,4,6,7,8-HpCDF; Total HpCDF; and OCDF.

For all other congeners, quantifiable residues were detected in less than 25 percent of the samples collected. All CDD congener concentrations ranged from nonquantifiable levels (low limit of 0.0026 pg/m3) to an upper limit of 18.0 pg/m3. Additionally, CDF congener levels ranged from nonquantifiable levels (low limit of 0.0040 pg/m3) to an upper limit of 2.70 pg/m3.

According to Hunt et al.(1990), "The highest concentration of CDDs/CDFs congener class sums (Cl4-Cl8) and 2,3,7,8-substituted species were noted during a period predominated by off-shore air flows in December 1987, suggesting a regional air mass and transport phenomena. Concentrations of the CDDs/CDFs were diminished markedly in subsequent sessions where air flow patterns were primarily off-shore or of coastal origin." Hunt et al. (1990) indicated that the "CDD/CDF congener profiles (Cl4-Cl8) and 2,3,7,8-substituted isomeric patterns strongly suggest combustion source influences in the majority" of the samples collected.

In a long-term study of CDD/Fs in the ambient air around Bloomington, Indiana, methods were developed for measuring individual CDD/Fs at concentrations as low as 0.001 pg/m3 (Eitzer and Hites, 1989).

Total CDD/F concentrations were 0.480 pg/m3 and 1.360 pg/m3 for the vapor phase and the particle-bound phase, respectively. For individual congeners, CDFs were found to decrease in concentration with increasing levels of chlorination, and CDD concentrations were found to increase with increasing levels of chlorination (Eitzer and Hites, 1989).

4.7.2. European Data

Clayton et al. (1993) conducted a study of CDDs and CDFs in the ambient air of three major cities and an industrial town in the United Kingdom. The annual average TEQ concentrations of CDDs and CDFs ranged from 0.04 to 0.10 pg/m3.

The hepta- and octachlorinated dioxin congeners contributed the most to the total concentration of 2,3,7,8-substituted CDD/Fs, and a large number of nondetect values were reported for the tetra-, penta-, and hexachlorinated dioxins.

The congeners that contributed most to the total TEQ concentrations were 2,3,7,8-TCDF; 1,2,3,4,7,8-; 1,2,3,6,7,8-; and 2,3,4,6,7,8-HxCDF. These values are relatively consistent with the concentrations in ambient German air observed by Liebl et al. (1993) and König et al. (1993a). Liebl et al. (1993) analyzed ambient air samples collected from 10 sites in Hessen, Germany, from 1990 through 1992. Concentrations ranged from 0.04 to 0.15 pg TEQ/m3.

The higher concentrations were presumed to result from direct local industrial sources. König et al. (1993a) collected air samples from six sites located in Hessen, Germany. CDD/F concentrations ranged from 0.048 pg TEQ/m3 at a rural reference site to 0.146 pg TEQ/m3 at an industrial site.

The results of the study also indicated that concentrations of CDDs and CDFs are typically higher in the winter than in the summer. Sugita et al. (1993) also observed higher concentrations of CDDs and CDFs in winter than in summer in an ambient air study in urban Japan. The average concentration of CDDs and CDFs was 0.788 pg TEQ/m3 in the summer and 1.464 pg TEQ/m3 in winter.

In a Swedish study, air samples were collected from a city center, suburb, remote countryside, and open coastal area (Broman et al., 1991). Analyses of the samples for dioxins and furans indicated that the concentrations of these compounds decreased with increasing distance from the city center.

Total CDD/F concentrations were 1.40 pg/m3, 1.10 pg/m3, 0.40 pg/m3, and 0.22 pg/m3 for the city center, suburb, countryside, and open coastal areas, respectively. Similar patterns of decreasing concentrations with increasing distances from urban areas were also observed for individual CDD/F congeners (Broman et al., 1991).

In a study of ambient air concentrations of CDDs and CDFs in Flanders, samples were collected and analyzed at rural, industrial, and urban sites (Wevers et al., 1993). Average ambient air concentrations ranged from 0.0696 pg TEQ/m3 at a rural site to 0.254 pg TEQ/m3 at a site believed to be influenced by a chemical industry and a highway.

PCBs have also been evaluated in European air samples (Halsall and Jones, 1993; König et al., 1993b). Halsall and Jones (1993) monitored urban air at two sites in the United Kingdom. The annual mean total PCB concentrations were 520 and 590 pg/m3.

PCBs existed in ambient air predominantly in the vapor phase. This study also indicated that summer PCB concentrations were higher than winter concentrations. These researchers attributed the differences in seasonal patterns to volatilization from soil during summer months. Ambient air concentrations of PCBs in Hessen, Germany, ranged from 350 to 1630 pg/m3 during the period of 1990 to 1992 (König et al., 1993b). Urban areas characterized by industry and/or heavy traffic had the highest PCB concentrations in ambient air.

4.7.3. Air Summary

Based on the limited ambient air measurements that have been made in selected cities in the United States and Europe, there appears to be good agreement with respect to the magnitude of specific congeners of CDDs and CDFs in urbanized areas in the United States and Europe. Most of these measurements tend to be very close to the current analytical detection limit. This increases the probability that congeners indicated as not detected (ND) may actually be present.

A total of 84 samples from the studies summarized in Tables B-14 and B-15 was selected as representative of "background" conditions in the United States. Samples collected from pristine sites and from rural and urban locations not expected to be impacted by industrial point sources were assumed to represent "background" conditions. The mean TEQ level for these 84 samples is 0.095 pg/m3 assuming that values reported as not detected are equal to one-half the detection limit.

Based on the results of European studies, ambient air concentrations of CDDs and CDFs appear to be similar to those found in the United States. For the purposes of this study, a TEQ value of 0.10 pg/m3 was used to represent concentrations in Europe. This value represents the mean of the midpoints of the European studies for which TEQ concentrations were reported (Clayton et al. 1993; Liebl et al. 1993; König et al. 1993a; Wevers et al. 1993). Data for these European studies are not included in Tables B-14 and B-15 because individual congener data were not reported.

It is interesting to compare these values with the CDD/CDF concentrations in air recently measured by Lugar (1993) in and around McMurdo Station, Antarctica, a logistics and staging facility with a population of about 1,100.

Four locations were sampled: a site upwind of the station, downwind of the station, in the center of the station, and a remote unpopulated island 30 kilometers distant from the station. CDDs/CDFs were not detected in the samples from the upwind site (congener detection limits ranged from <0.01 to 0.03 pg/m3) and the remote island sites (congener detection limits ranged from 0.001 to 0.008 pg/m3) and only sporadically at the downwind site (some congeners detected in three of five samples). CDDs/CDFs were detected in all five samples collected from the station center site (mean TEQ concentration of 0.0153 pg/m3).


Small amounts of dioxin-like compounds may be formed during natural fires suggesting that these compounds may have always been present in the environment.

However, it is generally believed that much more of these compounds have been produced and released into the environment in association with man's industrial and combustion practices, and as a result, environmental levels are likely to be higher in modern times than they were in prior times. However, the trend may now be reversing (i.e., releases and environmental levels may be gradually decreasing) due to changes in industrial practices (Rappe, 1992).

As discussed in Chapter 3, the potential for environmental releases of dioxin-like compounds has 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, improved emission controls for incinerators, and reductions in the manufacture and use of chlorinated phenolic intermediates and products.

Smith et al. (1992, 1993) analyzed sediment core layers from Green Lake, located near Syracuse, New York, to determine temporal trends in the deposition of CDDs and CDFs since the beginning of the industrial era (i.e., circa 1860). This deep lake (200-foot depth) is thought to be impacted only by atmospheric deposition because no industrial inputs are present and motorboats are not allowed.

Relatively constant but low concentrations of CDDs and CDFs (10 ng/kg or less) are observed in sediments deposited from 1860 to 1930. However, concentrations increase rapidly thereafter, reaching a peak in the mid-1960s when total CDD concentrations exceeded 1,300 ng/kg and total CDF concentrations exceeded 250 ng/kg.

The concentrations of CDDs and CDFs have rapidly declined since the mid-1960s, and now (1986-1990) are measured at 750 ng/kg as total CDD/CDF. The authors speculate that the decline may be due to the switch to unleaded fuels for vehicles. Similar trends have been reported by Czuczwa and Hites (1984) for Great Lakes sediment.

Rappe (1991) reports testing of archived soils and plants collected in southeast England between 1846 and 1986. CDDs and CDFs were found in all samples and showed generally increasing levels of dioxins. Rappe further notes that the congener pattern is typical of those for combustion sources until about 1950 when the pattern becomes more dominated by hepta- and octa-CDDs corresponding to increases in production of chlorinated compounds.

Schecter (1991) analyzed ancient liver tissues (estimated to be 100- to 400-years old) recovered from frozen bodies of Native American (Eskimo) women. He found that the dioxin levels were much lower than those commonly found in livers of people currently living in industrial areas.

Studies that may be used to assess temporal trends in human exposure to dioxins and furans are extremely limited. The use of indirect exposure assessment techniques for detecting temporal trends is difficult because large-scale, long-term, nationally- representative environmental monitoring for dioxins and furans has not been conducted.

Short-term studies are generally not comparable because of differences in sampling protocols and analytical techniques used in these studies. A potentially useful study for evaluating changes in human exposure over time is EPA's National Human Adipose Tissue Survey (NHATS). The purpose of NHATS is to monitor the human body burden of selected chemicals in the general U.S. population (U.S. EPA, 1991a). NHATS uses direct measurement techniques to estimate exposures.

Nationwide samples of adipose tissue are collected from surgical patients and autopsied cadavers and analyzed annually. In 1982, broadscan analysis of composited adipose tissue specimens revealed that chlorinated dioxins and furans could be detected and quantified in the U.S. population across all geographic regions and age groups (U.S. EPA, 1986). In 1987, NHATS specimens were also analyzed for dioxins and furans making temporal comparisons possible. Statistical analyses were performed to determine if significant differences existed between the concentrations of these compounds in 1982 and 1987 adipose tissue specimens.

Table 4-10 presents the estimated national average concentrations for the two time periods and the relative changes from 1982 to 1987. The estimated concentrations of 1,2,3,7,8-PeCDD; 2,3,4,7,8-PeCDF; and HxCDD in human adipose tissue were significantly lower in 1987 than in 1982 (U.S. EPA, 1991a).

Similar survey designs were used in the two studies, but changes in some of the analytical methods were made in 1987 that may account for some of the differences in estimated concentrations. These changes include lower limits of detection and the use of additional internal quantitation standards that provided more accurate measurements.

The levels of 2,3,7,8-TCDD; 1,2,3,4,6,7,8-HpCDD; and OCDD were also lower in 1987 than in 1982, but the differences were not found to be statistically significant. No statistical comparisons were possible for 2,3,7,8-TCDF; HxCDF; 1,2,3,4,6,7,8-HpCDF; or OCDF because one or both of the annual estimates were based on data that did not meet the minimum criteria for statistical modeling (i.e., the chemical was not detected in at least 50 percent of the composites analyzed, and/or fewer than 30 composite samples were analyzed in each year).

The results of this study indicate that exposure to certain dioxins and furan congeners may have decreased over this 5-year time period. However, further studies are needed to verify that these changes are not a result of protocol changes, but actual reductions in exposures.


This chapter has summarized data on CDD/F levels in environmental media and food with emphasis on "background levels." Data representative of background conditions in environmental media are considered to be those collected in rural, pristine, and urban (air only) areas not believed to be impacted by any local sources (e.g., incinerators and highways).

table Table 4-10 Estimated National Average Concentrations of Dioxins and Furans from the 1982 and 1987 NHATS.
Only food data from the general food supply (i.e., collected from grocery stores) were used to represent background conditions (except fish).

Tables B-17 through B-30 in Appendix B present the geometric and arithmetic averages of environmental background monitoring data for CDD and CDF congeners in various media, compiled from the published literature.

The geometric averages are consistently lower than the arithmetic averages. This results from the fact that the data span several orders of magnitude with the distribution skewed toward the lower end due to the large number of not detected values.
expand table Table V2 4-10

... To calculate a total TEQ for all CDD/CDFs for each media, the arithmetic mean background concentration for each congener was multiplied by its respective TEF value, and individual TEQs for each congener were totaled.

These total TEQs are presented at the end of Tables B-17 through B-30 and summarized in Table 4-11. These total background level TEQs are used in Chapter 5 to estimate typical exposure levels in the United States. Exposure levels for Europe are based on the levels of CDD/Fs in food reported by Fürst et al. (1990), and the levels in environmental media are based on data collected from several European countries.

Standard deviations of the total mean TEQs for each media were also calculated to depict the "range" of probable CDD/CDF levels in various media. Because the total TEQs were actually a summation of mean TEQs for various congeners, the use of typical methods for calculating standard deviations was not possible.

Therefore, standard deviations were based on the standard deviation of the congener that contributed most to the total TEQ. The percentage deviation from the mean for that congener was applied to the total mean TEQ for all congeners combined. The congeners selected for use in the standard deviation estimates are presented in Table 4-12. The data in this table indicate that the pentachlorinated dioxins were the highest contributors to total TEQs in most foods in the United States.

The media levels presented in Table 4-11 are shown graphically in Figure 4-1. Except for the TEQ levels in European food which are based on data reported for German food by Fürst et al. (1990) and the TEQ levels in European air which are based on data repoted for air in Germany, Belgium and the United Kingdom by König et al. (1993), Liebl et al. (1993), Wevers et al. (1993), and Clayton et al. (1993), all other TEQ levels presented in Figure 4-1 are based on the data analyzed in this study.

table Table 4-11 Summary of CDD/CDF Levels in Environmental Media and Food (whole weight basis). table Table 4-12 CDD/CDF Congeners that Contribute the Highest Percentage of TEQ to the Total TEQ for All Congeners Combined.
expand table Table V2 4-11 expand table Table V2 4-12
table Figure 4-1 Background Environmental Levels in TEQ.  
expand table Figure V2 4-1

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 4-1. For most media, the average levels appear to be similar between North America and Europe. However, differences were noted in three areas:

. 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 dairy products data 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 suggest that North America levels are higher than European levels. The low number of samples collected in Europe 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 human tissue data (discussed in Section 5.4) 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 food surveys are clearly needed to confirm these levels.


CDD/Fs can enter aquatic systems directly from sources in effluent discharges, indirectly from deposition of CDD/Fs in the atmosphere onto water bodies, and in stormwater runoff from areas where dioxin-containing material has been land-applied or atmospherically deposited. For any given water body, the dominant transport mechanism will depend on site-specific conditions. Aquatic organisms will bioaccumulate CDD/Fs and thereby enter the aquatic food chain.

Based on information currently available, the primary mechanism by which dioxin-like compounds enter the terrestrial food chain is via atmospheric deposition and sorption of vapors. Deposition can occur directly onto plant surfaces or onto soil.

Deposits onto the soil can enter the food chain via direct ingestion (e.g., soil ingestion by earthworms, fur preening by burrowing animals, incidental ingestion by grazing animals, etc). CDD/Fs in soil can become available to plants and thus enter the food chain by volatilization and vapor sorption or particle resuspension and adherence to plant surfaces. Although CDD/Fs in soil can adsorb directly to underground portions of plants, uptake from soil via the roots into above ground portions of plants is thought to be insignificant (McCrady et al., 1990).

Support for this air-to-food hypothesis is provided by Hites (1991) who concluded that "background environmental levels of PCD/F are caused by PCD/F entering the environment through the atmospheric pathway." His conclusion was based on demonstrations that the congener profiles in lake sediments could be linked to congener profiles of combustion sources. Further argument supporting this hypothesis is offered below:

. Numerous studies have shown that CDD/Fs are emitted into the air from a wide variety of sources and that CDD/Fs can be commonly detected in air at low concentrations. (See Chapters 3 and 4.)

. Studies have shown that CDD/Fs can be measured in wet and dry deposition in most locations including remote areas (Koester and Hites, 1992; Rappe, 1991).

. Numerous studies have shown that CDD/Fs are commonly found in soils throughout the world. (See Chapter 4.) Atmospheric transport and deposition is the only plausible mechanism that could lead to this widespread distribution.

. Models of the air-to-plant-to-animal food chain have been constructed. Exercises with these models show that measured deposition rates and air concentrations can be used to predict food levels that are similar to levels actually measured in food (Travis and Hattemer-Frey, 1991; also Chapter 7 of Volume III).

. Alternative mechanisms of uptake into food appear less plausible:

- Uptake in food crops and livestock from water is minimal due to the hydrophobic nature of these compounds. Travis and Hattemer-Frey (1987, 1991) estimate water intake accounts for less than 0.01 percent of the total daily intake of 2,3,7,8-TCDD in cattle. Experiments by McCrady et al. (1990) show very little uptake in plants from aqueous solutions.

- Relatively little impact on the general food supply is expected from soil residues that originate from site-specific sources such as sewage sludge and other waste disposal operations. Sewage sludge application onto agricultural fields is not a widespread practice. Waste disposal operations can be the dominant source of CDD/Fs in soils at isolated locations such as Times Beach, but are not sufficiently widespread to explain the ubiquitous nature of these compounds.

- The release of CDD/Fs to the environment from the use of pesticides contaminated with CDD/Fs is beleived to have declined in recent years; however, the past and current impact of pesticide use on CDD/F levels in the food supply is uncertain. CDD/Fs have been associated with certain phenoxy herbicides most of which are no longer produced or have restricted uses. EPA has issued data call-ins requiring certain pesticide manufacturers to test their products for dioxin content. The responses, so far, indicate that levels in these products are below or near the limit of quantitation. (See Chapter 3.)

- Current CDD/F levels in food resulting from the use of bleached paper products containing CDD/Fs appears to be minimal. In the early 1980s, testing showed that CDD/Fs could migrate from paper containers into food. Current levels in paper products are now much lower than in the early 1980s. Also, testing of products such as milk and beef prior to packaging has shown detectable levels which cannot be attributed to the packaging. (See Chapter 4.)

A related issue is whether the CDD/Fs in food result more from current or past emissions. Sediment core sampling indicates that CDD/F levels in the environment began increasing around the turn of the century, but also that CDF levels have been declining since about 1980 (Smith et al. 1992).

Thus, CDD/Fs have been accumulating for many years and may have created reservoirs that continue to impact the food chain. As discussed in Chapter 3, researchers in several countries have attempted to compare known emissions with deposition rates.

All of these studies (including this assessment) suggest that annual atmospheric depositions exceed annual emissions by a factor of 2 to 10. One possible explanation for this discrepancy in sources may be that volatilization or particle resuspension from these reservoir sources followed by atmospheric scavenging is responsible. These mass balance studies are highly uncertain, and it remains unknown how much of the food chain impact is due to current vs past emissions.


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