Dioxin – Scientific Analysis

This letter is reprinted with permission from the Environmental Working Group, a CHE partner. See the original letter with full science analysis on EWG’s website.  

Dr. Timothy Buckley, Chair
Dioxin Review Panel
Science Advisory Board
Environmental Protection Agency (EPA)
Washington, DC

Dear Dr. Buckley,

Twenty-five years after publishing its first assessment of dioxin, a common industrial pollutant and food contaminant, the Environmental Protection Agency (EPA) has yet to establish a safe daily dose for human exposure to this potent chemical.

Dioxin (2,3,7,8-Tetrachlorodibenzo-p-dioxin, also known as 2,3,7,8-TCDD, or TCDD) may well be one of the most-studied of all chemical pollutants. The U.S. National Toxicology Program has listed dioxin as a known human carcinogen since 2001 (NTP 2005), and the U.S. Environmental Protection Agency has proposed to do the same (EPA 2010a). There is a large and persuasive body of research dating from the 1950s showing that dioxin undermines fetal development, damages the reproductive and immune systems and causes severe skin ailments and other disorders.

As U.S. industrial data demonstrate, dioxin is released from municipal waste incinerators; industrial and military hazardous waste treatment facilities; pesticide manufacturing and paper bleaching plants; and a wide range of other industrial processes. In the 1970s, dioxin was identified as a contaminant in Agent Orange, the notorious defoliant deployed by the U.S. during the Vietnam War and blamed for diabetes and other diseases among exposed personnel (Chamie 2008; Cranmer 2000; Gupta 2006).

This widespread, persistent pollutant accumulates in animal and human fat. It contaminates meat, fish, milk, cheese, and human breast milk.

We applaud EPA Administrator Jackson’s commitment to complete the long-awaited dioxin assessment this year (EPA 2009a; EPA 2010b). We urge the Science Advisory Board (SAB) to expedite its review of EPA’s latest dioxin assessment and help the agency meet its goal. This important assessment, once completed, would serve as a cornerstone and working model for the agency’s efforts to protect public health from chemical contaminants.

We recommend that the EPA Science Advisory Board:

  • Urge EPA to finalize its proposed safety standard that would protect Americans from the carcinogenic effects of dioxin. EWG estimates that the general public may be exposed to as much as 1,200 more dioxin contamination in common foods than the amount considered negligible as a cancer risk.
  • Confirm EPA’s decision that the best current human data for determining the safe exposure limit (technically, reference dose, or RfD) for dioxin lies in two key studies, Mocarelli 2008 and Baccarelli 2008, of infants and children in Seveso, Italy, where a 1976 chemical plant explosion exposed thousands of people to dioxin in unprecedented intensity and left large quantities of the chemical in the soil (Cerlesi 1989).
  • Support EPA’s characterization of dioxin as carcinogenic to humans. This definition would be consistent with the National Toxicology Program classification of dioxin as a known human carcinogen in 2001 and the 1997 classification of dioxin as a group 1 carcinogen by the International Agency for Research on Cancer (IARC). The classification is amply supported by the weight of evidence presented by the EPA draft dioxin reanalysis.
  • Advise EPA on how best to strengthen the proposed safe daily dose (RfD) for dioxin over time, to protect children from early life exposures to this contaminant, as data continues to emerge further illuminating the unique sensitivity of the fetus, infant and child to this toxic compound.

Detailed suggestions and technical comments on the EPA draft reassessment are provided in the attached Science Analysis on dioxin’s risks to human health and the need for expedited action. Briefly, EWG’s review of the scientific literature on dioxin has determined that EPA should accelerate its dioxin assessment on these grounds:

  • The U.S. food supply is widely contaminated with dioxins, including beef, pork, chicken, turkey, fish, milk, eggs, butter and other foods Americans eat daily (FDA 2006; Huwe 2009; Schaum 2003).
  • As a result, dioxin is a ubiquitous pollutant in the human body. Authoritative studies by the U.S. Centers for Disease Control and Prevention (CDC) and the EPA’s National Center for Environmental Assessment have determined that at least 13 percent of Americans test positive for dioxin (2,3,7,8-TCDD) (Lorber 2009). Furthermore, CDC has found all Americans tested to be contaminated with dioxin-like compounds, including polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDF) and polychlorinated biphenyls (PCBs), which exhibit toxic properties similar to those of TCDD (Lorber 2009; Patterson 2009). Environmental Working Group’s biomonitoring studies have detected TCDD in 11 of 34 Americans tested (EWG 2005). As a category, chlorinated dioxins and furans were found in 34 of 34 Americans tested, including all 20 tested cord blood samples from newborn babies. Clearly, the fetus is exposed to dioxins in utero (EWG 2005).
  • Americans are routinely exposed to dioxins from popular foods at levels close to EPA’s proposed safe daily dose. EWG analysis of data from the peer-reviewed literature finds that a 130-pound adult who eats a cheeseburger and drinks a glass of milk once a day can consume a third of EPA’s proposed safe daily dose of dioxin and dioxin-like compounds, and over time would accumulate an incremental dose of the carcinogens 270 times greater than that which EPA considers acceptable for the general population.
  • Breast-fed infants are among the most endangered Americans of all. Studies detect dioxin and dioxin-like compounds in human breast milk in amounts similar to highly contaminated foods such as beef, cheese and fish (Schecter 2001). Since newborns can consume nothing but breast milk for a number of months, their exposure to dioxins is greater, for their body weight, than that of older children and adults (Charnley 2006). EWG analysis of data from peer-reviewed scientific reports has found that a breast-fed infant three to six months old, with an average weight of 16 pounds, consumes up to 77 times more dioxin and dioxin-like compounds than EPA’s proposed safe daily dose (RfD).
  • Until EPA completes its assessment, other government agencies and environmental cleanup efforts lack guidance to implement remediation measures critical to public health. Finalizing the dioxin assessment is essential for strong, coordinated federal and industry efforts towards cleaning up numerous Superfund sites fouled with dioxin and similar compounds. According to EPA, 123 U.S. bodies of water are so contaminated with dioxins and other bioaccumulative chemical contaminants that the public has been warned to limit or avoid eating certain fish and water-dependent wildlife species caught there (EPA 2009c). Numerous communities across the country are plagued by dioxin pollution from historical industrial and military activities that created and released dioxin-containing hazardous wastes (Casanova 1987; EPA 2009d). Efforts to restore environmental quality at these sites will continue to languish until EPA sets a firm dioxin exposure standard.

Every year, 4 million newborns are exposed to dioxin daily, beginning in utero and continuing throughout life. Ubiquitous dioxin contamination of food has a lifelong impact on Americans’ health. Government and industry efforts to reduce dioxin emissions since the 1970s have not been enough: Americans are still routinely overexposed to this uniquely toxic food pollutant. Countless manufacturing and incineration facilities continue to release it into the environment.

With the growing number of studies of dioxin, scientists are finding it to exhibit greater toxicity at progressively smaller doses. Thus, EPA’s present findings on the potency of dioxin to spur cancer and non-cancer health effects may still underestimate the true scope of the problem. The proposed safe daily dose is not the most health-protective and most conservative choice, as demonstrated by EPA’s proposal to establish both the RfD and exposure limits to protect against cancer in the mid-range of values supported by the scientific literature. Also, EPA’s proposed limits may well become obsolete in the future as more scientific evidence adds to our knowledge of the deleterious effects of long-term exposure to dioxin. Such facts support the need for EPA to finish its dioxin assessment and consider plans for strengthening its recommendations as new data emerge.

The societal cost of the dioxin-induced health burden may never be fully understood. But we know this much: it is already too high. It is EPA’s responsibility to address this problem with resolve, making decisions based only on the public good, without regard to pressure from special interests who stand to benefit financially from weak standards and regulations.

After 25 years of study and three previous, in-depth SAB reviews, the EPA has still not completed its dioxin assessment. In this fourth SAB review, we urge you to support the agency by helping it stand by the findings and health standards presented in the current draft. We hope that the Science Advisory Board’s timely, focused review will serve as a closing step in guiding EPA to establish a safety level for dioxin that will truly protect the health of Americans, particularly the youngest and most vulnerable.

Thank you for your attention and for your service on this important panel.


Jane Houlihan, MSCE
Senior Vice President for Research

Olga V. Naidenko, PhD
Senior Scientist


Casanova JN, Olfenbuttel RF. 1987. Military Sites Contaminated with 2,3,7,8-Tetrachlorodibenzo-pdioxin: Permitting Remedial Action Research. In: Solving Hazardous Waste Problems: Learning from Dioxins (Exner JH, ed): American Chemical Society, 229-43.

Cerlesi S, Di Domenico A, Ratti S. 1989. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) persistence in the Seveso (Milan, Italy) soil. Ecotoxicol Environ Saf 18(2): 149-64.

Chamie K, DeVere White RW, Lee D, Ok JH, Ellison LM. 2008. Agent Orange exposure, Vietnam War veterans, and the risk of prostate cancer. Cancer 113(9): 2464-70.

Charnley G, Kimbrough RD. 2006. Overview of exposure, toxicity, and risks to children from current levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds in the USA. Food Chem Toxicol 44(5): 601-15.

Cranmer M, Louie S, Kennedy RH, Kern PA, Fonseca VA. 2000. Exposure to 2,3,7,8-tetrachlorodibenzop-dioxin (TCDD) is associated with hyperinsulinemia and insulin resistance. Toxicol Sci 56(2): 431-6.

Environmental Working Group (EWG). 2005. Human Toxome Project. 2,3,7,8-TCDD (tetradioxin). Available: http://www.ewg.org/sites/humantoxome/chemicals/chemical.php?chemid=40001

FDA. 2006. PCDD/PCDF Exposure Estimates from TDS Samples Collected in 2001-2004. Available: http://www.fda.gov/Food/FoodSafety/FoodContaminantsAdulteration/ChemicalContaminants/DioxinsPCBs/ ucm077498.htm

Gupta A, Ketchum N, Roehrborn CG, Schecter A, Aragaki CC, Michalek JE. 2006. Serum dioxin, testosterone, and subsequent risk of benign prostatic hyperplasia: a prospective cohort study of Air Force veterans. Environ Health Perspect 114(11): 1649-54.

Huwe J, Pagan-Rodriguez D, Abdelmajid N, Clinch N, Gordon D, Holterman J, et al. 2009. Survey of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and non-ortho-polychlorinated biphenyls in U.S. meat and poultry, 2007-2008: effect of new toxic equivalency factors on toxic equivalency levels, patterns, and temporal trends. J Agric Food Chem 57(23): 11194-200.

Lorber M, Patterson D, Huwe J, Kahn H. 2009. Evaluation of background exposures of Americans to dioxin-like compounds in the 1990s and the 2000s. Chemosphere 77(5): 640-51.

NTP. 2005. National Toxicology Program 11th Report on Carcinogens. 2,3,7,8-Tetrachlorodibenzo-pdioxin (TCDD); “Dioxin”. Available: http://ntp.niehs.nih.gov/index.cfm?objectid=32BA9724-F1F6-975E-7FCE50709CB4C932

Patterson DG, Jr., Wong LY, Turner WE, Caudill SP, Dipietro ES, McClure PC, et al. 2009. Levels in the U.S. population of those persistent organic pollutants (2003-2004) included in the Stockholm Convention or in other long range transboundary air pollution agreements. Environ Sci Technol 43(4): 1211-8.

Schaum J, Schuda L, Wu C, Sears R, Ferrario J, Andrews K. 2003. A national survey of persistent, bioaccumulative, and toxic (PBT) pollutants in the United States milk supply. J Expo Anal Environ Epidemiol 13(3): 177-86.

U.S. EPA. 2009a. News Releases – Research. EPA Administrator Pledges Strong Federal Cleanup Presence at Dow Dioxin Site in Michigan and Accelerated Assessment of Dioxins’ Human Health Impacts. Available:http://yosemite.epa.gov/opa/admpress.nsf/48f0fa7dd51f9e9885257359003f5342/3ffa6e8e70763f28852575 c20064b2 6b!OpenDocument

U.S. EPA. 2009b. EPA’s Science Plan for Activities Related to Dioxins in the Environment. Available: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=209690

U.S. EPA. 2009c. The National Listing of Fish Advisories. Available: http://www.epa.gov/waterscience/fish/advisories/

U.S. EPA. 2009d. Development of Draft Recommended Interim Preliminary Remediation Goals for Dioxin in Soil. Available: http://www.epa.gov/superfund/policy/remedy/sfremedy/remedies/dioxinsoil.html

U.S. EPA. 2010a. EPA’s Reanalysis of Key Issues Related to Dioxin Toxicity and Response to NAS Comments (External Review Draft). Available: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=222203

U.S. EPA. 2010b. News Release: EPA Releases Draft Dioxin Report for Peer Review and Public Comment. Available: http://yosemite.epa.gov/opa/admpress.nsf/0/6FB73A1C778FE16A8525772A0055AC5A

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