The long, convoluted path toward assessing the toxicity of a class of persistent, bioaccumulative chemicals called dioxins and dioxin-like compounds is scheduled to reach another milestone in late January 2012. This is the latest step in a decades-long process that still has some ways to go, but the new EPA assessment of noncancer toxicity should offer information that will provide guidance going forward, as well as fodder for critics on all sides to seize upon. At a later, unspecified date, EPA says it will release a similar assessment of cancer threats posed by dioxins.
The assessments could have wide-ranging direct and indirect effects in realms such as toxic site cleanups, brownfield development, manufacturing processes, domestic food production and sales, and international trade of food and possibly other goods. EPA officials declined to say if any related rulemaking will occur.
The noncancer assessment is expected to be posted on the agency's Integrated Risk Information System (IRIS) Web site. Some background information on dioxins and the various steps taken so far by EPA and others is available on the agency's main dioxin page.
- IRIS. 
- EPA, Dioxin ; media, Tisha Petteway,  202-564-3191.
- "EPA's Reanalysis of Key Issues Related to Dioxin Toxicity and Response to NAS Comments,"  May 2010 (can provide considerable background for the upcoming IRIS posting).
There are more than 400 dioxins and dioxin-like compounds, with about 30 currently considered to be of most concern for health impacts (including 2,3,7,8- tetrachlorodibenzo para dioxin, or TCDD, which at the moment is usually considered the most toxic). They are created as byproducts of a wide range of manufacturing and human-instigated and natural combustion processes, including electricity generation, medical, municipal, industrial, and residential waste incineration, manufacture and use of certain herbicides, chlorine bleaching of pulp and paper, smelting, forest fires, and volcanoes.
The growing consensus is that they are quite toxic, even at relatively low concentrations, and may cause or contribute to health problems such as heart disease, diabetes, liver and skin disorders, birth defects, damage to reproductive, neurological, immune, and endocrine systems, and several types of cancer.
Since the threat of dioxins was generally recognized a few decades ago, some steps have been taken to reduce their formation. Nonetheless, dioxins are very persistent in the environment and build up in the food chain, leading to their presence in many foods, which are now considered the primary sources of exposure for most people (with some occupational exposures also occurring).
The most contaminated foods tend to be animal products that contain fat, including meat and dairy products, as well as fish and shellfish. Other foods can also be contaminated. The FDA has tested some foods for their dioxin contamination.
- FDA, data for certain foods analyzed for selected dioxins in 2001-2003  (dated November 2007; covers many dairy products, eggs, meats, fats, oils, fruits, vegetables, grains, cereals, seafoods, nuts, and a few dietary supplements).
- FDA, additional information on dioxins and PCBs  (some of which are dioxin-like).
Another way to gauge the potential effects of dioxins on human health is to measure their occurrence in people, in a process known as biomonitoring. The CDC's latest dioxin biomonitoring data remain spotty, but it provides a starting point for understanding the possible threat posed by 25 dioxins and their cousins, including a number of furans and PCBs.
- Fourth National Report on Human Exposure to Environmental Chemicals, Dioxin-Like Chemicals. 
The volume of dioxins generated by industries and voluntarily reported as part of the Toxics Release Inventory is relatively small (54,426 grams in 2010, including 1,234 grams of air releases), though their potency makes even these small quantities a concern to public health officials. Despite preventive measures taken in recent decades, the total quantity of dioxins released in 2010 increased 18% from 2009, and air releases rose 10%. Electric utilities, which accounted for 35% of all air releases in 2010, rose 5% from 2009 to 2010. The biggest overall increase from 2009 to 2010, via land disposal, subsurface injection, air releases, or other pathways, came from the hazardous waste management and primary metals sectors.
- 2010 TRI National Analysis, Q&A  (page 4).
To find specific sources generating dioxins in your audience area, check:
- Right-to-Know Network, Toxics Release Inventory  (search for "dioxin*" in order to capture the term "dioxin and dioxin-like compounds").
Various industries that either create dioxins or have to deal with them in food continue to vigorously challenge EPA's toxicity assessment process and findings to date. For instance, the Food Industry Dioxin Working Group says EPA's process and data have numerous flaws, and contends the agency's findings could "mislead the public and potentially create a health scare that doesn't exist."
- Food Industry Dioxin Working Group, December 2011 letter to EPA  (the 13 industry association members of the group are listed at the bottom of page 1).
The American Chemistry Council says EPA's separation of the cancer and noncancer assessments makes this a flawed process, and isn't consistent with the National Research Council's recommendations in 2006 on how the agency could improve its efforts. The ACC also says EPA is being overly cautious in its determination of what constitutes a toxic level, and will create a situation leading to unnecessary alarm and regulation.
- American Chemistry Council, Dec. 20, 2011, letter to EPA ; and "Dioxin Risk Assessment Receives Harshest Criticism Yet as Key Scientist Calls Out EPA's Assumptions as 'Policy Masquerading as Science',"  Sept. 1, 2011.
For a summary of the National Research Council report and the full document, see:
- Health Risks from Dioxin and Related Compounds; Evaluation of the EPA Reassessment (the committee members are a source for scientific comment).
For two environmental health advocacy group perspectives on the toxicity of dioxins, and protective measures that could be taken, see:
For some other points of view, and sources for experts, see:
- World Health Organization, Dioxins and Their Effects on Human Health,  May 2010 (includes brief mention of a number of notorious food contamination incidents in the past 15 years or so, as well as a few other major dioxin exposure disasters in recent decades).
- National Institute of Environmental Health Sciences, Dioxins. 
- Agency for Toxic Substances and Disease Registry (ATSDR), Toxicological Profile for Chlorinated Dibenzo-p-dioxins,  March 2011.
- ATSDR, ToxFAQs for Chlorinated Dibenzo-p-dioxins,  (summary information).
Thumbnail photo credit: NIEHS/Dioxins.