What are dioxins? Why the concern?

Main Category: Cancer / Oncology
Article Date: 12 Dec 2004 - 11:00 PDT


'Dioxins' refers to a group of chemical compounds that share certain chemical structures and biological characteristics. Several hundred of these compounds exist and are members of three closely related families: the chlorinated dibenzo-p-dioxins (CDDs), chlorinated dibenzofurans (CDFs) and certain polychlorinated biphenyls (PCBs). Sometimes the term dioxin is also used to refer to the most studied and one of the most toxic dioxins, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). CDDs and CDFs are not created intentionally, but are produced inadvertently by a number of human activities. Natural processes also produce CDDs and CDFs. PCBs are manufactured products, but they are no longer produced in the United States.

Dioxins are formed as a result of combustion processes such as commercial or municipal waste incineration and from burning fuels (like wood, coal or oil). The draft dioxin reassessment makes the finding that anthropogenic emissions dominate current releases in the United States, but acknowledges the need for more data on natural sources. Dioxins can also be formed when household trash is burned and as a result of natural processes such as forest fires. Chlorine bleaching of pulp and paper, certain types of chemical manufacturing and processing, and other industrial processes all can create small quantities of dioxins. Cigarette smoke also contains small amounts of dioxins.

Over the past decade, EPA and industry have worked together to dramatically reduce dioxin emissions. It is important to note that dioxin levels in the United States environment have been declining for the last 30 years due to reductions in manmade sources. However, dioxins break down so slowly that some of the dioxins from past releases will still be in the environment many years from now. Because dioxins are extremely persistent compounds, levels of dioxins still exist in the environment from both manmade and natural sources. A large part of the current exposures to dioxins in the United States is due to release of manmade dioxins that occurred in the past, even decades ago. Even if all human-generated dioxins could somehow be eliminated, low levels of naturally produced dioxins will remain, as will reservoirs. EPA is working with other parts of the government to look for ways to further reduce dioxin levels entering the environment and to reduce human exposure to them.

Why are people concerned about dioxins?

Studies have shown that exposure to dioxins at high enough doses may cause a number of adverse health effects. Because dioxins from natural and anthropogenic sources have been widely distributed in exist throughout the environment since the early 1900's (and before), almost every living creature, including humans, has been exposed to dioxins. (See G9) The health effects associated with dioxins depend on a variety of factors including: the level of exposure, when someone was exposed, and how long and how often. Because dioxins are so widespread, we all have some level of dioxins in our bodies.

The most common health effect in people exposed to large amounts of dioxin is chloracne. Such levels have typically been the result of accidents or significant contamination events. Chloracne is a severe skin disease with acne-like lesions that occur mainly on the face and upper body. Other effects of exposure to large amounts of dioxin include skin rashes, skin discoloration, excessive body hair, and possibly mild liver damage.

One of the main health effects in question for dioxins is the risk of cancer in adults. Several studies suggest that workers exposed to high levels of dioxins at their workplace over many years have an increased risk of cancer. Animal studies have also shown an increased risk of cancer from long-term exposure to dioxins.

Finally, based on data from animal studies, there is some concern that exposure to low levels of dioxins over long periods (or high level exposures at sensitive times) might result in reproductive or developmental effects.

What happens to dioxins when they enter the environment?

When released into the air, some dioxins may be transported long distances. Because of this, dioxins are found in most places in the world. When dioxins are released into water, they tend to settle into sediments where they can be further transported or ingested by fish and other aquatic organisms. Dioxins decompose very slowly in the environment and can be deposited on plants and taken up by animals and aquatic organisms. Dioxins may be concentrated in the food chain so that animals have higher concentrations than plants, water, soil, or sediments. Within animals, dioxins tend to accumulate in fat.

How might I be exposed to dioxins?

Most of the population has low-level exposure to dioxins. Although dioxin is an environmental contaminant, most dioxin exposure occurs through the diet, with over 95% coming through dietary intake of animal fats. Small amounts of exposure occur from breathing air containing trace amounts of dioxins on particles and in vapor form, from inadvertent ingestion of soil containing dioxins, and from absorption through the skin contacting air, soil, or water containing minute levels.

Do all dioxin compounds pose the same amount of danger?

No. Different dioxin compounds have different toxicities and dioxins are most often found in mixtures rather than as single compounds in the environment. The most toxic forms of dioxin are 2,3,7,8-TCDD and 1,2,3,7,8-PeCDD. Scientists use a shorthand method for comparing the toxicity of different types or mixtures of dioxins to the toxicity of 2,3,7,8- TCDD and 1,2,3,7,8-PeCDD. This method is called the "Toxicity Equivalence" or TEQ.

Have we made progress in reducing environmental dioxins?

Yes. Dioxin levels in the United States environment have been declining for the last 30 years due to reductions in manmade sources. In fact, as a result of the efforts of EPA, state governments and industry, known and quantifiable industrial emissions of dioxin in the United States have been reduced by more than 90% from 1987 levels. However, dioxins break down so slowly that some of the dioxins from past releases will still be in the environment many years from now. Dioxins that remain in the environment from past releases are sometimes called "reservoir sources" of dioxins. Because of natural processes, dioxin levels in the environment will never go to zero.

Based on recent measurements in a few states, it appears that levels in our bodies are going down too. We are continuing to monitor to see if these trends continue. Because of background occurrence of dioxin in the environment, the levels will probably never go to zero.

What is meant by "natural background" and "current background" for dioxins?

In addition to manmade sources, natural processes, such as brush and forest fires, produce dioxins. The term "natural background" for dioxins refers to the dioxins that are in the environment because of these natural processes. We do not know what the natural background level of dioxins is. The term "current background" refers to the level of dioxin in the environment today. Current background is primarily made up of dioxins from manmade sources.

What are the major sources of dioxins?

The amounts of dioxin released from various sources have changed significantly over time. Historically, commercial or municipal waste incineration, manufacture and use of certain herbicides and chlorine bleaching of pulp and paper resulted in the major releases of dioxins to air and water. Government regulatory actions along with voluntary industry actions have resulted in dramatic reductions in each of these sources, and they are no longer major contributors of dioxins to the environment in the United States. While the United States has taken action to control this type of emission, these sources of dioxin still occur in the world. Currently, the uncontrolled burning of residential waste is thought to be among the largest sources of dioxins to the environment in the United States. Source characterization is an ongoing effort, and if new major sources are identified, they will be factored into future inventories.

How long has dioxin exposure existed?

Dioxins have been around for a long time. There are natural sources for dioxins like brush and forest fires and volcanic eruptions, although natural sources contribute little to the current background dioxin levels. In the 1920's, as a consequence of industrialization, dioxin levels began increasing in the global environment. Declines in environmental levels began in the 1970's when dioxins were recognized as highly toxic chemicals and governments and industry took actions to prevent environmental pollution.

Why does the NAS review draft reassessment estimate of potential risk from dioxins differ from the 2000 draft?

EPA has been evaluating the health effects of environmental exposures to dioxins since 1980. The findings of the current draft are not significantly different from those of the 2000 draft. The NAS review draft differs from the 2000 SAB review draft in that it 1) reflects changes and clarifications made in response to the EPA Science Advisory Board (SAB)'s comments and 2) reflects an expansion of the quantity and quality of dioxin data, as well as refinements in how to calculate dioxin risk. The current document has an expanded analysis of background exposure, which is intended to provide a more current estimate of background exposure from diet. It also has expanded analysis of data on whether dioxin's non-cancer effects might occur at or near doses to which we are exposed, and which provides for a more robust evaluation of non-cancer effects based on body burden.

What is EPA doing to control dioxin releases into the environment?

Over the last 20 years, EPA has aggressively looked for ways to reduce and control dioxins in all environmental media in the United States. Collectively, these actions have resulted in strict controls on all of the known and quantifiable major industrial sources of dioxin releases. As a result of EPA's efforts, along with efforts by state government and private industry, known and quantifiable industrial emissions in the United States have been reduced by more than 90% from 1987 levels. For example, municipal waste combustors are estimated to have emitted collectively nearly 18 pounds of dioxin toxic equivalents in 1987, but under EPA regulations, they are now expected to emit less than 1/2 ounce per year. Similarly, medical waste incinerators emitted about 5 pounds of dioxin equivalents in 1987, but under EPA regulations they now will be limited to about 1/4 ounce annual emissions. EPA has implemented similarly strict standards for other dioxin sources. Through expanded monitoring and research collaboration with the Food and Drug Administration (FDA), the Food Safety and Inspection Service (FSIS), and the Centers for Disease Control and Prevention (CDC), EPA is also making progress in characterizing additional sources.

In response to the evolving scientific understanding of dioxin-like compounds, EPA plans to release a draft Agency-wide dioxin strategy. This draft strategy will be made available for public comment. In addition, federal agencies are already working together to coordinate federal activities related to dioxin. Further information regarding EPA efforts to reduce dioxin emissions and develop a comprehensive strategy can be found in the fact sheets available on the Internet at http://cfpub2.epa.gov/ncea/cfm/recordisplay.cfm?deid=55264

Should I (or can I) find out what my dioxin levels are?

We do not recommend dioxin testing. Tests for measuring dioxin levels in humans are not routinely available. Laboratories that offer dioxin testing generally are not certified for that testing (as is required for clinical laboratories doing medical testing). Furthermore, their detection levels may not be low enough to detect dioxin levels that occur in the general population.

How can I reduce my personal dioxin levels?

We recognize that individuals might be concerned about their potential dioxin exposure. Dioxins have existed in our environment for a long time. We all have some levels of dioxins in our bodies. Environmental dioxin has declined significantly since 1987 and recent measurements in a few states indicate that levels in our bodies are going down as well. Unfortunately, there are no safe and effective treatments to rid dioxins now in humans. Dioxins metabolize slowly (over years), but reduction of exposure reduces dioxin levels over time. The best way to reduce your personal dioxins level (and your risk from dioxins) is to reduce exposure and intake of dioxins.

Although dioxins are an environmental contaminant, exposure most often occurs through the food by consumption of animal fats. For most people, following existing Federal Dietary Guidelines will reduce fat consumption and, consequently, reduced dioxin exposure (see also G4). The dietary guidelines provide for moderate amounts of fats, which are part of a balanced diet. Eliminating all fats is not recommended. Overall, the best strategy for lowering the risk of dioxins while maintaining the benefits of a good diet is to follow the recommendations in the Federal Dietary Guidelines to choose fish, lean meat, poultry, and low or fat free (skim) dairy products and to increase consumption of fruits, vegetables and grain products. Lean meat includes meats that are naturally lower in fat, and meat where visible fat has been trimmed. For fish and poultry you can reduce fat by removing the skin. Reducing the amount of butter or lard used in the preparation of foods and cooking methods that reduce fat (such as oven broiling) will also lower the risk of exposure to dioxin. These strategies help lower the intake of saturated fats as well as reduce the risk of exposure to dioxin. For information on the Federal Dietary Guidelines see http://www.health.gov/dietaryguidelines.
CONTINUES……….www.cfsan.fda.gov/~lrd/dioxinqa.html

• Additional
• References
• Citations