Volume II Chapter 5.0 Pages 1 of 2 page next page 2


    • 5.1. INTRODUCTION 5-1
      • 5.3.1. North American Exposures 5-12
      • 5.3.2. Comparison of Previous North American Studies to This Study 5-12
      • 5.3.3. Comparison of Previous European Studies to this Study 5-1


The purpose of this chapter is to assess background exposures to the dioxin-like compounds. Recent assessments of background exposures cited in the scientific literature are summarized, and background exposures that have been estimated from the data presented in Section 4 of this report are presented. The term "background," as applied to exposure, can be used to represent different concepts.

Two common definitions are
(1) the level of exposure that would occur in an area without known point sources of the contaminant of concern or
(2) the average level of exposure occurring in an area whether sources are present or not.

For the purposes of this document, "background" is defined as suggested in the first definition above. To the extent possible, background exposures estimated in this chapter are based on monitoring data obtained from sites removed from known contaminant sources (or food data representative of the general food supply). These data are considered to be the most useful for describing background exposure levels.


Several researchers have published quantitative assessments of human exposures to CDDs and CDFs. Some of the more recent assessments are discussed below (Travis and Hattemer-Frey, 1991; Fürst et al.,1990; Fürst et al., 1991; Henry et al., 1992; Theelen, 1991; and Gilman and Newhook, 1991). It is generally concluded by these researchers that dietary intake is the primary pathway of human exposure to CDDs and CDFs. Over 90 percent of human exposure occur through the diet, with foods from animal origins being the predominant sources.

Travis and Hattemer-Frey (1991) estimated that the average daily intake of 2,3,7,8-TCDD by the general population of the United States is 34.8 pg/day. Ingestion exposures were estimated by multiplying the concentration of 2,3,7,8-TCDD in beef, milk, produce, fish, eggs, and water (estimated using the Fugacity Food Chain model) times the average U.S. adult consumption values for these products reported by Yang and Nelson (1986).

The calculations assume that 100 percent of the 2,3,7,8-TCDD ingested are absorbed through the gut. Intake via inhalation was estimated by multiplying the concentration in air times the amount of air inhaled per day (20 m3) assuming that 100 percent of inhaled 2,3,7,8-TCDD are absorbed through the lung.

The results of their assessment, summarized in Table 5-1, indicate that foods from animal origins comprise 95 percent of the estimated total daily exposure. These foods include milk and dairy products, beef, fish, and eggs. Exposure resulting from consumption of vegetables and other produce was estimated to account for 3.4 percent of the total intake. Exposure from ingestion of water, ingestion of soil, and inhalation of air together accounted for about 1 percent of the total daily intake.

Fürst et al. (1990) estimated human exposure to CDD/Fs based on the analysis of 107 food samples collected in the Federal Republic of Germany. The average daily TEQ intake was estimated to be 85 pg/person/day or 1.2 pg/kg body weight/day. Fürst et al. (1990) concluded that foods of animal origin contribute significantly to the human body burden of CDD/Fs. In a subsequent study, Fürst et al. (1991) assessed human exposure to CDDs and CDFs from foods using data from more than 300 randomly selected food samples and food consumption data reflective of consumption habits of the German population.

These authors estimated that the German population's average daily intake of CDDs and CDFs from food is 158 pg TEQ per person of which 25 pg is 2,3,7,8-TCDD. Dairy products, meat and meat products (primarily beef), and fish and fish products each contribute about 32 to 36 percent of the daily intake of TEQ. Based on the levels of CDD/Fs observed in human samples, the average daily intake via food was estimated to be in the range of 1 to 3 pg TEQ/kg body weight.

Henry et al. (1992) of the U.S. Food and Drug Administration estimated the average exposure to the U.S. population from 2,3,7,8-TCDD through the food supply using the following assumptions:

(1) all dairy products have background lipid 2,3,7,8-TCDD levels equivalent to those found in milk and half-and-half, i.e., about 55 ppq (whole dairy food levels were estimated using percent fat in each food);

(2) levels averaging 35 ppq in beef tissue are present in all meat products;

(3) ocean fish with tissue levels equal to half of the detection limit (about 0.5 ppt) are the sole fish source in the diet;

(4) average food consumption figures (total-sample-basis) available from nationally representative data bases were used for frequency of eating (Market Research Corporation of America's (MRCA) Menu Census VI (1977-78)) and for serving sizes (U.S. Department of Agriculture's 1977-78 National Food Consumption Survey).

table Table 5-1 Predicted Average Daily Intake of 2,3,7,8-TCDD by the General Population of the United States..
... FDA's estimates of 2,3,7,8-TCDD intake were derived by multiplying the food dioxin levels by the average amounts of food consumed per day. The results of its assessment, summarized in Table 5-2, indicate an average daily exposure of 15.9 pg/day of 2,3,7,8-TCDD of which 4 percent are due to dairy and milk products, 41 percent are due to meats, and 54 percent are due to ocean fish. Theelen (1991), of the Netherlands National Institute of Public Health and Environmental Protection, estimated the average daily intake of 2,3,7,8-TCDD and total dioxin TEQ by residents of the Netherlands for various possible routes of exposure. The results, summarized in Table 5-3, indicate an average intake of 20 pg/day of 2,3,7,8-TCDD and 115 pg/day of total TEQ from food and 0.08 pg/day (2,3,7,8-TCDD) and 3.2 pg/day (TEQ) from combined direct air and soil exposure.
expand table Table V2 5-1

Milk and dairy products make up about one-third of the total daily exposure. Animal fat in meat, poultry, and fish (i.e., fish oil) also contribute about one-third. Fish consumption represents 18.5 percent of total daily exposure. In a later study, Theelen et al. (1993) reported a median daily intake for adults of 1 pg TEQ/kg body weight, and a 95th percentile rate of 2 pg TEQ/kg body weight. These values were based on CDD/F residue levels in food products and food consumption survey data.

Gilman and Newhook (1991), of the Canadian Department of National Health and Welfare and the Ontario Ministry of the Environment, respectively, estimated an average lifetime daily intake of 140 to 290 pg of TEQ for the typical Canadian. Their results, summarized in Table 5-4, indicate that between 94 and 96 percent of the estimated intake are from food sources. No breakdown of intake by food type is provided in the report.

As reported in Section 4.6.1, CDD/Fs can migrate from bleached paper packaging and paper food-contact articles to foods. Some investigators have included this pathway in estimates of background exposure.

U.S. EPA (1990a) estimated that TEQ intake due to leaching from paper products into food from paper packaging was in the range of 5.5 to 12.7 pg/d. Henry et al. (1992) estimated that daily intake of 2,3,7,8-TCDD due to migration from paper to food could amount to 12 pg/d, almost as much as the daily intake from unaffected food of 16 pg/d. (See Table 5-2.)

As shown in Table 5-3, Theelen (1991) estimated that out of a total of about 120 pg of TEQ/d, 9 pg of TEQ/d could be due to migration from paper. These estimates are based on levels in paper before recent changes in industry practices that are expected to substantially reduce dioxin levels in paper.

table Table 5-2 Predicted Average Daily Intake of 2,3,7,8-TCDD from Foods by the General Population of the United States. table Table 5-3 Daily Exposure to 2,3,7,8-TCDD and TEQ from Air, Soil, Food, and Nonfood in The Netherlands.
expand table Table V2 5-2 expand table Table V2 5-3
table Table 5-4 Estimated Lifetime Average Daily Exposure of Canadians to Dioxin TEQ.
As discussed in Section 4.6.1, these reductions are expected to have significantly lowered the CDD/CDF levels currently found in food due to any leaching of dioxin-like compounds from paper.
expand table Table V2 5-4


Background exposures to CDD/CDFs in North America were estimated using (1) the TEQ data on arithmetic mean levels in environmental media and food from Table 4-11, (2) the standard contact rates for ingestion of soil, water, and food and inhalation of ambient air, and (3) the appropriate unit conversion factors. The estimated exposures and assumptions made concerning ingestion or contact rates are presented in Table 5-5.

The background exposures reported here were estimated using standard intake rates representative of the general population. They do not account for individuals with higher consumption rates of a specific food group (e.g., subsistence fishermen, nursing infants, and subsistence farmers--these are discussed in Section 5.5).

The estimates reported here are assumed to represent typical (i.e., "central tendency") U.S. background exposures, and do not account for these types of variations in the population as a result of differences in intake rates of the various food groups.

The fish concentration used to estimate background exposures, represents the average value found in fish from fresh and estuarine waters (see Section 4.5). Correspondingly, the ingestion rate used here reflects the per capita average ingestion rate of fresh/estuarine fish (U.S. EPA, 1989).

Many individuals are likely to have higher ingestion rates of marine fish. However, the limited data on marine species indicates that the dioxin levels may be one to two orders of magnitude lower than fresh/estuarine water fish (also see Section 4.5).

The contact rates for ingestion of fish, soil, and water, and inhalation were derived from the Exposure Factors Handbook (U.S.EPA, 1989). For food products such as milk, dairy, eggs, beef, pork, and poultry, a different approach was taken because there is some evidence that consumption rates have changed since the data for the Exposure Factors Handbook were collected.

Contact rates for these food groups were derived from commodity disappearance data from the United States Department of Agricultures's (USDA) report on Food Consumption, Prices, and Expenditures between 1970 and 1992 (USDA, 1993), and intake data from USDA's Nationwide Food Consumption Survey (NFCS) (USDA, 1992).

table Table 5-5 Estimated Background Exposures in the United States.
The average of USDA disappearance and NFCS intake rates were used in this study to represent typical contact rates in the United States. USDA (1993) estimated per capita consumption rates using disappearance data (i.e., the quantity of marketable food commodities utilized in the United States over a specified time period) divided by the total population.

Consumption rates were calculated for several commodities including meats, eggs, milk and dairy products.

For meats, the boneless equivalent quantity was calculated by adjusting the carcass weight based on the amount of
fat and bone removed at different marketlevels.USDA (1992) reported one-day NFCS intake data for several meat categories.
expand table Table V2 5-5

These included:
beef; pork; poultry; frankfurters, sausages, and luncheon meats; fish and shellfish; and mixtures containing meat, poultry, and fish. Total intake rates for beef, pork, and poultry were estimated by assuming that the rate of consumption of these meats in

(1) frankfurters, sausages, and luncheon meats, and
(2) meat mixtures was proportional to the intake of these meats on an individual basis.

Thus, the intake in these categories was apportioned among the meat groups. In general, intake rates based on NFCS data are lower than those based on USDA disappearance data. NFCS data are believed to underestimate consumption for the general population because they may not adequately account for consumption of foods contained in mixtures (i.e., the intake rate for eggs may include eggs eaten separately or as a main ingredient in a dish, but may not be counted if they are an ingredient in a cake).

Additional uncertainty is associated with the use of data for only one day during the Spring of 1988 and the use of survey data based on recall. In contrast to NFCS data, disappearance data may overestimate per capita consumption because they are based on the quantity of marketable commodity utilized, divided by the total population.

Disappearance data do not account for losses from the food supply from waste or from the production of items not intended for human consumption (i.e., pet foods). Thus, the average of USDA disappearance and NFCS intake rates were believed to be representative of typical contact rates in the United States.

Background exposure levels are also presented for Germany based on data from Fürst et al. (1990; 1991). The total background TEQ exposure shown in Table 5-5 is 119 pg/day for North America. Based on Fürst et al. (1990; 1991), the estimated total TEQ background exposure for Germany is 79 pg/day (Table 5-6).

table Table 5-6 Background Exposures via Consumption of German Food. However, it should be noted that the estimated background level for the United States and Germany are based on limited data, and exposure to all food groups was not considered.

Also, the addition of TEQs for multiple pathways presumes that individuals are exposed by all pathways, and assumes that the fraction absorbed into the body is the same for all pathways.

The following sections present observations about CDD/CDF exposures in North America, comparisons between exposure estimates from this and previous studies, and comparisons between North American and European exposures to CDD/CDFs.
expand table Table V2 5-6

5.3.1. North American Exposures

Based on the data collected for this study, the total background CDD/CDF TEQ exposure for North America was estimated to be 119 pg/day, for all media combined. Exposure to 2,3,7,8-TCDD accounts for approximately 10.5 percent (12.0 pg/day) of the total TEQ exposure. Estimated exposures based on total CDD/CDF TEQs from the various exposure pathways are presented in Figure 5-1.

The highest exposures were estimated to occur via ingestion of CDD/CDFs in beef (37 pg/day) which accounted for over 30 percent of the total TEQ exposure. The ingestion of foods accounted for over 97 percent of the total TEQ exposure.

Exposure to CDD/CDFs via ingestion of water appears to be very low. Exposure via inhalation and soil ingestion are 2.2 and 0.8 pg/day, respectively. These exposures account for approximately 2.0 percent and <1.0 percent of the total CDD/CDF TEQ exposure in North America.

5.3.2. Comparison of Previous North American Studies to This Study

Previous studies of CDD/CDF exposures in North America were presented in Section 5.2 of this report. These studies reported CDD/CDF exposures based on the most toxic congener, 2,3,7,8-TCDD, and not on the total TEQ value for all congeners combined. For the purposes of comparison, mean background levels of 2,3,7,8-TCDD in North America from this assessment were used to calculate exposure via various pathways.

Background exposures were calculated using background environmental levels of 2,3,7,8-TCDD, standard contact rates, and appropriate unit conversion factors, as described previously. Total 2,3,7,8-TCDD exposure for all pathways combined was 12.0 pg/day for the current assessment compared to 15.9 and 34.8 pg/day for the two previous studies of 2,3,7,8-TCDD exposure in North America (Henry et al., 1992; and Travis and Hattemer-Frey, 1991).

Figure 5-2 depicts the comparisons of the percent contribution of various exposure pathways to total exposure to 2,3,7,8-TCDD for the current assessment and for previous North American studies.

table Figure 5-1 Background TEQ Exposure for North America by Pathway. table Figure 5-2 Percent Contribution of Various Media to 2,3,7,8-TCDD Exposure in North America.
expand table Figure V2 5-1 expand table Figure V2 5-2

Figure 5-2 indicates that exposure via ingestion of meats accounted for a large portion of the exposure in all three studies. However, fish accounted for a higher percentage, and dairy products accounted for a lower percentage of the total 2,3,7,8-TCDD exposure in the Henry et al. (1992) study than in the Travis and Hattemer-Frey (1991) study and the current assessment. These differences reflect differences in assumptions for food ingestion rates as well as in TCDD levels.

All three studies indicate that beef, dairy products, and fish comprise over 94 percent of the total exposure. Because of the data base weaknesses noted earlier, it is not known if these differences can be considered significant.

5.3.3. Comparison of Previous European Studies to this Study

European CDD/CDF exposure studies may also be compared to the exposures estimated in U.S. reports and in the current assessment. Comparisons may be made based on the 2,3,7,8-TCDD congener or on total TEQ exposures (Table 5-7).

Exposures to 2,3,7,8-TCDD in North America range from 12.0 pg/day to 34.8 pg/day based on the current assessment and two other U.S. studies. These values are comparable to the 2,3,7,8-TCDD exposures reported in Germany and the Netherlands by Fürst et al. (1991) and Theelen (1991). Fürst et al. (1991) reported an estimated 2,3,7,8-TCDD exposure of 25 pg/day based on ingestion of dairy products, meat, and fish; Theelen (1991) reported an estimate of 20 pg/day based on dairy, meat, poultry, and fish intake.

Total CDD/F TEQ background exposure estimates for North America range from 119 pg/day for the current assessment to 140 to 290 pg/day based on Gilman and Newhook's (1991) Canadian study. For Europe, total TEQ exposure estimates range from 79 pg/day based on Fürst et al. (1990) to 158 pg/day based on Fürst et al. (1991). Figure 5-3 depicts the contributions of various exposure pathways to total background TEQ exposures for North America, Germany, and the Netherlands based on data from the current assessment, Fürst et al. (1990) and Theelen (1991). For all three geographic regions, over 90 percent of the exposures were attributed to ingestion of CDD/Fs in foods.

table Table 5-7 Comparison of Predicted Average Daily Intake of 2,3,7,8-TCDD and Total CDD/CDF TEQs. table Figure 5-3 Comparison of Background TEQ Exposures.
expand table Table V2 5-7 expand table Figure V2 5-3

Based on the data presented in Figure 5-3, it is reasonable to expect that the CDD/CDF body burden in vegetarians would be lower than the body burden in non-vegetarians because vegetarians avoid the consumption of meat and fish and their derivative products. Welge et al. (1993) tested this hypothesis by comparing the CDD/CDF levels in the blood of 24 German vegetarians with the blood levels of 24 non-vegetarians, matched for age, sex, body weight, and height. With the exception of two individuals, all vegetarians had practiced a diet without meat and fish for at least 3 years.

The CDD/CDF levels in the vegetarian group ranged from 14.64 to 52.85 pg TEQ/g (lipid basis) with a mean of 32.60 pg TEQ/g. In the non-vegetarian group, the CDD/CDF levels ranged from 14.26 to 97.98 pg TEQ/g (lipid basis) with a mean of 34.32 pg TEQ/g.

There was no significant difference (a = 0.05) between the vegetarian and non-vegetarian group in the mean levels of any of the 2,3,7,8-substituted congeners, in the total CDD levels, in the total CDF levels, in the total CDD/CDF levels, or in the total TEQ levels (each on a lipid and on a whole weight basis). Welge et al. (1993) suggested several reasons why no differences were found.

First, all tested vegetarians had at one time been non-vegetarians. The higher levels of exposure during this non-vegetarian period coupled with the long biological half-life of CDD/CDFs may be responsible for the apparent similarity in body burdens using blood as the measure of body burden.

Second, the vegetarians may have a higher level of consumption of dairy products than the non-vegatarians and thus have a similar CDD/CDF exposure even without consumption of fish and meat.