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2012 EPA Research Progress Report

Final Non-Cancer Science Assessment for Dioxins Released

On February 17, 2012, EPA reached a major milestone by completing its non-cancer health assessment for dioxin. Dioxins are toxic chemicals that exist naturally and can be released to the environment through forest fires, backyard burning of trash, certain industrial activities, and residue from past commercial burning of waste.

Over the past two decades EPA has worked to significantly reduce emissions from all of the major industrial sources of dioxins. Today, the largest remaining source of dioxin emissions is backyard burning of household trash.

EPA’s final report, Reanalysis of Key Issues Related to Dioxin Toxicity and Response to NAS Comments, Volume 1 (Dioxin Reanalysis), describes the health effects (other than cancer) that may result from exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic of the many different forms of dioxin (also known as congeners).

The assessment also establishes, for the first time, a non-cancer oral reference dose (RfD) that represents the amount of dioxin a person can be exposed to every day over a lifetime that is not likely to cause harmful effects. Scientists can use this RfD to calculate the toxicity of the many other dioxin congeners relative to TCDD. This provides a way to add up the toxicity of all dioxin congeners that appear together in an environmental mixture.

Most Americans have low-level exposure to dioxins. The health effects associated with dioxins depend on several factors, including: how much dioxin a person is exposed to, when someone was exposed and for how long, and how often someone is exposed. Based on data from animal and human epidemiology studies, there is concern that exposure to low levels of dioxins over long periods (or exposures at sensitive times during the lifespan) might result in reproductive or developmental effects and other health effects.

The non-cancer health assessment for dioxin is a significant achievement for EPA and will contribute to the Agency’s mission of protecting public health. The information in the assessment will be considered in a variety of Agency activities, such as establishing cleanup levels at Superfund sites, reviewing the drinking water standard for dioxin, and evaluating whether additional Clean Air Act limits on dioxin emissions are warranted.

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