Dioxins

There are 29 different dioxins and dioxin-like compounds from three broad chemical families representing several hundred individual chemicals; these families are chlorinated dibenzo-p-dioxins (CDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). Because they are structurally similar, the body metabolizes the dioxins in the same way although they have varying potential to affect health as described in the US Environmental Protection Agency (EPA) 2010 Recommended Toxicity Equivalence Factors (TEFs) for Human Health Risk Assessments of 2,3,7,8- Tetrachlorodibenzo-p-dioxin and Dioxin-Like Compounds (PDF).

The Minnesota Department of Health (MDH) considers "dioxins" to be a group of related compounds that exhibit a similar spectrum of health effects. Dioxins are extremely persistent and once released remain in the environment a very long time. Since the 1980's regulatory and voluntary actions have dramatically reduced the amount of dioxins released into the environment and the amount of dioxins to which people are exposed. Based on recent measures it appears that levels in our bodies are decreasing. However, when current body burdens in the population are compared to the levels of concern derived from animal and human studies it is clear that it is desirable and necessary to further reduce human exposure.

The CDDs and PCDFs are not purposely produced. They mainly are formed by burning organic matter that contain chlorine (incinerators, fires, etc.), the bleaching of wood pulp to make paper, and are produced in small amounts when the wood preservative pentachlorophenol and other pesticides are made. PCBs were once manufactured and widely used in a variety of industrial and commercial applications. Visit the EPA's Inventory of Dioxin Sources and Environmental Releases webpage for information and links to inventories and reports about dioxin sources.

When dioxins are released into the air, they disperse and may travel long distances before eventually settling onto land, surface water and vegetation. Dioxins that are released to or deposited onto land tend to bind strongly to soil. Because they do not dissolve easily in water, most dioxins in surface waters attach strongly to sediments. Dioxins enter the food web when animals eat contamination on plants, sediment, and soil. Dioxins are hard for the body to breakdown and leave the body slowly. This means that dioxins build up in the fat of wildlife and people, especially those who eat other animals.

Dioxins from both human-made and natural sources remain in the environment for a very long time. Since the 1980's, dramatic decreases in the amounts released to the environment has reduced the levels of dioxins people are exposed to. Although biomonitoring surveys show that levels in our bodies are decreasing, amounts of dioxins measured in the general population remain sufficiently high that it is still wise to minimize exposures further where possible. In Minnesota, low levels of dioxins and dioxin-like compounds (referred to as "background") are likely present in soil, air, and water due to local and global sources. However, the potential for exposures to dioxins at concentrations above background are most likely to be associated with pentachlorophenol (PCP) contaminated soil at former wood treatment facilities.

The effects of dioxins on human health are difficult to evaluate for many reasons. Available human data are limited to studies involving occupational or accidental exposures to mixtures of dioxins and other toxic chemicals. Such circumstances make it difficult to determine which chemical caused observed effects. Adult occupational or accidental exposure to dioxins has been associated with chloracne, hyperpigmentation of the skin, and mild liver toxicity (e.g., transient elevations in liver enzymes). The most obvious sign of dioxin exposure is chloracne. Visit the National Library of Medicine article Chloracne and Hyperpigmentation Caused by Exposure to Hazardous Aryl Hydrocarbon Receptor Ligands, Int J Environ Res Public Health.2019 Dec; 16(23): 4864. Published online 2019 Dec 3.doi:10.3390/ijerph16234864 for more information and images.

Some studies have reported additional health effects such as changes in thyroid hormone levels, endometriosis, diabetes, and immune system alterations; however, these effects have not been consistently reported and may be attributed to study design differences. Significant uncertainty exists in our current understanding of the relationship between dioxin exposure and the risk of human health effects.

Animal studies, which administer known amounts of dioxins under controlled laboratory conditions, provide most of the current information on the health effects that may be associated with dioxin exposure. Based on animal studies, the most sensitive effects are immune, endocrine, and development effects. Because humans and test animals metabolize dioxin in a similar manner, it is reasonable to assume these are also the most sensitive effects in humans.

Cancer is also a concern for dioxins and dioxin-like chemicals. Several studies suggest that workers exposed to high levels of dioxins over many years have an increased risk of developing cancer, but the relationship between cancer and dioxins exposure remains uncertain. Animal studies have conclusively shown that 2,3,7,8-TCDD (the most potent form of dioxin) is capable of causing increased tumors.

The Agency for Toxic Substances and Disease Registry provides several resources that describe the potential health effects of dioxins and dioxin-like compounds. Visit Chlorinated Dibenzo-p-dioxins (CDDs) | Toxic Substances | Toxic Substance Portal | ATSDR (cdc.gov) for more information.

Because dioxins have been in our environment for a long time and are so widespread, we all have small, but measurable amounts of dioxins in our bodies. Current exposures to dioxins are largely due to past practices that caused releases.

The risk of harm from dioxins depends on many factors. The amount of dioxins and dioxin-like chemicals that a person takes in varies on several factors, such as the amount and duration of exposure(s) and the amount of dioxin in the media (e.g., food, soil, water, air) that a person contacts.

• For the general population, eating animal fats in fish, meat, and dairy products is the main source of dioxin exposure. For most people, eating a varied, balanced, low-fat diet will reduce exposure to background levels of dioxins and dioxin-like chemicals that accumulate in fat. In addition, a low-fat diet will also lower the chances of developing heart disease, high blood pressure, diabetes, and some cancers.
• The MDH Fish Consumption Advice provides guidance to help minimize intake of contaminants (including dioxins) that may be present in Minnesota fish. Generally, it is best to harvest smaller fish and to remove the body fat found on the belly before eating to limit potential exposure to contaminants found in fish fat tissue. Visit MDH Fish Consumption Guidance for more information.
• Guidance for avoiding contact with soil that is known to be contaminated is available on the MDH website. Visit How to reduce accidental intake of contaminated soils (PDF).
• The best practices in the MDH Gardening in Urban Soil webpage can help lower potential contaminant exposures from urban gardens.
• Burning trash and smoking cigarettes can produce dioxins. Unregulated trash burning is considered one of the largest dioxin sources contributing to ambient background levels. People can lower their own exposure to dioxins as well as exposure to family members and neighbors by not burning trash or smoking cigarettes.

If you think you have been exposed to dioxins or other toxic materials, talk to your health care provider about any specific health concerns or questions you have.

MDH has guidance for evaluating dioxin health risks on the MDH website. Visit Guidance for Dioxins (PDF) and Dioxins - Guidance for Air (PDF).

When requested, MDH staff also conduct public health evaluations at hazardous waste and other sites where dioxin is, or has been, found. MDH staff review available information and may recommend additional actions be taken, as necessary, if there is evidence that people are being exposed or could be exposed to site-related contaminants. If potential exposure to harmful amounts of dioxin is identified, we may work with local units of government, community groups, regulatory agencies, and those parties responsible for the contamination to prevent or reduce human exposure. Visit About Hazardous Sites and Releases in Minnesota for more information or contact the Site Assessment and Consultation Unit at 651-201-4897, or email health.hazard@state.mn.us.

Very low concentrations of dioxins are widely found in the environment. In Minnesota, the background threshold amount in soil is considered to be 7 nanograms of dioxin/kilogram of soil. The potential for people to encounter amounts significantly (100 to 1,000 times) above ambient background levels is largely limited to sites where pentachlorophenol (PCP) was historically used as a preservative to treat wood. Many such sites exist across the state.

The Minnesota Pollution Control Agency establishes Soil Reference Values (SRV) for residential and for industrial property use categories. For the residential use category, clean up goals are intended to be protective for unrestricted use of the soils on the property for a person who lives there for 26 years full time. The residential SRV for dioxin is 7 ppt—or parts per trillion-- which is also considered to be ambient background, or the amount present in soil from distant human made sources. See the MPCA Soil Background Threshold Value Evaluation (PDF) document for details of how background and site-specific background values are calculated.

Investigating and cleaning up dioxin is challenging. The science of dioxin toxicity is evolving along with the ability of laboratories to detect and measure dioxin in environmental samples at increasingly low concentrations. Currently, dioxin and dioxin-like chemicals can be reliably measured in the low parts per trillion range.

At most sites where PCP contamination is present, the dioxin is largely confined to organic matter in the soil and sediment if a water body was contaminated. Such contaminated materials can migrate with wind and/or water erosion to other areas. Deliberate disturbance and movement of soil at a contaminated site may complicate efforts to locate dioxin to determine clean up needs. Older wood treating sites where PCP was used may have been investigated and cleaned up at a time when investigative tools were not as refined as they are now and when less restrictive cleanup provided less protection compared to current best practice. As a result, people are cautioned against trespassing on former wood treating sites and those that do access such properties should observe any controls or barriers in place to prevent exposures to potentially harmful contamination.

Information for Environmental Professionals

Soil cleanup guidance and assistance is available on the MPCA webpage Cleanup guidance and assistance. The Minnesota Pollution Control Agency provides a Soil reference value (SRV) spreadsheet (c-r1-06) to evaluate potential health risks from exposure to contaminated soil. The accompanying Soil Reference Value Technical Support Document (PDF) is also useful. Detailed information on dioxin soil background levels is provided in Soil Background Threshold Value Evaluation (PDF).

Several federal documents and references, including a quality assurance plan for the assessment of soils impacted by dioxins/furans and dioxin‐like polychlorinated biphenyl (PCB) congeners are available at Contaminated Site Clean-Up Information for Dioxins.

The Agency for Toxic Substances and Disease Registry (ATSDR) provides several resources that describe the potential health effects of dioxins and dioxin-like compounds, which can be found by following links on the landing page at:

• Chlorinated Dibenzo-p-dioxins (CDDs) | Toxic Substances | Toxic Substance Portal | ATSDR (cdc.gov)

The Centers for Disease Control and Prevention (CDC) produces the National Report on Human Exposure to Environmental Chemicals. This is a series of ongoing assessments of the U.S. population's exposure to environmental chemicals using biomonitoring, which is a tool for assessing exposure to chemicals by measuring the chemical or its metabolites in human specimens such as blood or urine.

• National Report on Human Exposure to Environmental Chemicals | CDC