Overview of Dioxin Biomonitoring Data in the 2005 CDC National Exposure Report

July 21, 2005


With its Third National Report on Human Exposure to Environmental Chemicals, released July 21, 2005, the U.S. Centers for Disease Control and Prevention (CDC) provides a glimpse of the levels of 148 chemicals in a representative sample of the U.S. population. This short interpretive document focuses exclusively on one group of those chemicals-dioxins1 . Blood levels of dioxins were measured in the U.S. population as part of the National Health and Nutrition Survey (NHANES) in 1999-2000 and in 2001-2002, and were reported in the CDC's second and third national exposure reports in 2003 and 2005, respectively.

CDC's Third National Report confirms that dioxin levels in human tissues are very low. CDC affirms the new data support the observation that human blood levels of dioxins have decreased by more than eighty percent since the 1980s. Findings also show that there are generational differences in dioxin levels.

Is there an increase in dioxin blood levels measured between the 2003 and 2005 reports? No. Dioxin levels in humans have been decreasing since the early 1970s and scientific models project continued declines in all age groups. The appearance of an increase between the last two CDC reports is due to the following:

  • Additional dioxin/furan compounds were analyzed for in the 2005 report compared to the 2003 report2.
  • Missing data in the 2003 and 2005 reports were treated in calculations3 as "zero" levels of dioxins. An "artificially" low average dioxin level resulted because there was more missing data in the 2003 report than the 2005 report.
  • The volume of individual blood samples available for dioxin analysis in the 2003 report was too small to detect low levels of dioxins. (This was corrected in sampling for the 2005 report.)
Dioxin Levels: Historically .And Looking Ahead
Figure 1
(See Appendix 1 for data sources and notes for Figures 1 and 2.)
Figure 2

Scientific models show levels of dioxins are declining in all age groups.

Since the 1970s, levels of environmental dioxins have decreased significantly. Dioxins accumulate in human tissue and are slowly eliminated at a rate determined by the amount of dioxin in the body. Scientists tell us that levels of dioxins in human blood are related to a person's birth year: children today have lower levels of dioxins in their blood than their parents and grandparents did when they were children. Moreover, with today's lower exposures, babies born today will likely never reach the levels of dioxins of their grandparents.

How low can they go?

Humans will always be exposed to some low level of dioxins because there are natural sources of these compounds from which we cannot escape. For example, dioxins are formed in forest fires and volcanoes.

Low body levels of dioxins are the result of low average intake of dioxins.

The main source of human exposure to dioxins is the diet. The U.S. Environmental Protection Agency (EPA) and U.S. Food and Drug Administration (FDA) have estimated daily intake levels of dioxins, and these intake amounts fall well below safe intake guidelines set by the U.S., Europe, Canada, Japan and the World Health Organization.

Figure 3: The Current Daily Dioxin Intake of the
Average American is Below Government Guidelines

Daily Intake in pg-TEQ/kg/day

WHO, World Health Organization; JECFA, Joint FAO/WHO Expert Committee on Food Additives; ESCSF, European Commission Scientific Committee on Food; ATSDR, Agency for Toxic Substances Disease Registry; TEQ, Toxic Equivalency; pg-TEQ/kg/day, picogram-TEQ per killogram per day.

EPA data show a significant decline in emissions of dioxins.

(See Appendix 1 for data sources and
notes for Figure 4.)

Dioxins have never been manufactured for commercial purposes. They are formed in trace amounts in a variety of combustion environments, both natural (e.g., forest fires and volcanoes) and those controlled by man (e.g., energy generation, chemical manufacturing, backyard trash burning, vehicle fuel combustion and various types of waste incineration). Government regulators, industry and environmentalists have worked hard to reduce emissions of dioxins to the environment. These pollution control efforts resulted in estimated declines in emissions from EPA-quantified sources of 92 percent between 1987 and 2004.

Where do dioxins come from today?

The pie chart below illustrates the estimated contributions of dioxin sources in 2004. The CDC states in its 2005 National Exposure report, "Releases from industrial sources have decreased approximately 80% since the 1980s. Today, the largest release of these chemicals (dioxins) occurs as a result of the open burning of household trash and municipal trash, landfill fires, and agricultural and forest fires."

(See Appendix 1 for data sources and notes for Figure 5.)

For More Information:

Appendix 1: Data Sources and Notes for Figures

Figure 1

Data for 1965, 1985 and 1995 are modeled average dioxin-TEQ for ages 20 to 70 (Lorber, 2002).

Data for 1996-2001 are measured average TEQs from individuals age 15 to over 60 from LA, MO, NC, and NY (588 people) and includes 4 PCBs (Patterson et. al., 2004).

Data for 1999-2000 are from CDC (2003) for people aged 20 and over.

Data for 2001-2002 are from CDC (2005) for people aged 20 and over.

Range for governmental exposure guidelines is 8 - 32 ppt, which includes dioxins and PCBs with TEFs.

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Figure 2

Chlorine Chemistry Division of the American Chemistry Council modeled the future body levels (from 2002 to 2020) starting with the mid-point measurement for the average dioxin ppt-TEQ for each reported age group (20 years and older) reported in the Third National Exposure Report (2005).

Chlorine Chemistry Division of the American Chemistry Council based projections for the 15 year old age group on the 2001-2002 pooled blood samples (Needham, 2005).

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Figure 4

Data for 1987 and 1995 are from the "US Environmental Protection Agency Inventory of Sources of Dioxin-Like Compounds in the United States-1987 and 1995" http://cfpub.epa.gov/ncea/cfm/dioxindb.cfm?ActType=default.

Year 2000 data are from the "External Review Draft: The Inventory of Sources and Environmental Releases of Dioxin-Like Compounds in the United States: The Year 2000 Update," EPA (March, 2005). http://www.epa.gov/NCEA/pdfs/dioxin/2k-update/pdfs/Dioxin_Frontmatter.pdf

The 2002/4 data are based on EPA projections assuming full compliance with regulatory levels by this period and the closure of a copper smelter (personal communication, Dwain Winters, US EPA, 9-9-02).

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Figure 5

*With the exception of forest fire data, dioxin emissions source data are based on EPA projections for 2002/4, assuming full compliance with regulatory levels and the closure of a copper smelter (personal communication, Dwain Winters, US EPA, 9-9-02).

#The dioxin contribution from forest fires was calculated using National Interagency Fire Center acreage burned in year 2004 wildland fires; an emission factor of 20 ng-TEQ/kg biomass burned [Gullett and Touati (2003)]; and a biomass consumption rate of 9.43 metric tons/acre in areas consumed by wildfires from Ward et al. (1976), as cited in the EPA Draft Dioxin Reassessment (September, 2000).

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End Notes

1"Dioxins" refers to 7 dioxins and 10 furan chemical compounds. There are 210 known chlorinated dioxins and furans, but only 17 of interest. [return to top]

2Of the 17 dioxin compounds of interest, 15 were measured for the 2003 report, but all 17 were measured for the 2005 report. [return to top]

3Calculations were performed by the Chlorine Chemistry Division of the American Chemistry Council. [return to top]

4Government guidelines are set to be protective of individuals over a lifetime. [return to top]


CDC (2005). Third National Report on Human Exposure to Environmental Chemicals, Atlanta, GA., NCEH Pub. No. 05-0570. July 2005. See http://www.cdc.gov/exposurereport/

CDC (2003). Second National Report on Human Exposure to Environmental Chemicals, Atlanta, GA., NCEH Pub. No. 02-0716. Revised March 2003. See http://www.cdc.gov/exposurereport/

Gullett, B.K. and Touati, A. (2003). PCDD/F emissions from forest fire simulations, Atmospheric Environment 37, p. 803-13.

Lorber, M. (2002). A pharmacokinetic model for estimating exposure of Americans to dioxin-like compounds in the past, present, and future. Science of the Total Environment. 288. 81-95.

Needham, L.L. (2005). Exposure Levels as Determined by Serum Levels from Control Data Sets and National Health and Nutrition Examination Survey (slides show preliminary data), presentation to the National Academy of Sciences, Expert Panel on Review EPA's Exposure and Human Health Reassessment of TCDD and Related Compounds, Project BEST-K-03-08-A. February 2, 2005. Slides are available by contacting NAS staff. http://www4.nas.edu/cp.nsf/Projects+_by+_PIN/BEST-K-03-08-A?OpenDocument.

Patterson, D.G., Canady, R., Wong, L-Y., Lee, R., Turner, W., Caudill, S., Needham, L., Henderson, A. (2004). Age specific dioxin TEQ reference range. Organohalogen Compounds 66, 2878-2883.

Ward et al., 1976 An update on particulate emissions from forest fires. Presented at: 69th Annual Meeting of the Air Pollution Control Association, Portland, OR June 27-July 1, 1976] as cited in the EPA Draft Dioxin Reassessment, September, 2000.

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