Understanding risk of contaminants to humans is a difficult task. Since toxicologists can't ethically conduct controlled experiments on humans, the agencies evaluating the risk have to rely on many different types of studies - for example, epidemiological studies from accidental exposures to humans (as in Vietnam), laboratory studies with animals (in vivo), and laboratory studies without animals (ex vivo). Some of the studies support toxicity, some don't. The level at which effects are seen depends on what the effect is and what the test organism is... it just isn't easy. Period. Most of the work, however, does support that dioxins are quite bad for humans and one specific dioxin (2,3,7,8-TCDD) has been called one of the most toxic chemicals known to man. Dioxins can be lethal, they can cause a skin condition called chloracne, they can cause reproductive damage and birth effects, they can weaken the immune system, and they can cause cancer (ATSDR, 1998), but again, whether these effects occur and at what exposure level they occur depends on what animal is being tested and how the exposure occurs.
And so, the EPA is charged with determining how much of a toxic substance like dioxins can be in our food without causing an increased risk of cancer and non-cancer effects to humans. This was last completed in the 1980s. Reassessments of dioxins risks, based on new science since the last assessment has been on-going. The short story is that there was a reassessment completed in 2003 and evaluated by the National Academy of Sciences (NAS). Three years later, the NAS provided comments to the EPA on that reassessment. In 2010, the EPA released a draft reassessment incorporating comments from the NAS. They also decided in 2010 to separate cancer risk from non-cancer risk and had a goal of releasing the final Dioxin Reassessment for non-cancer risk by the end of January, 2012, which hasn't happened yet. According to Bottemiller (2012), the allowable level for non-cancer effects is expected to be 0.7 picograms per kilogram of body weight per day. The problem... industry, such as the American Chemical Council isn't happy about this level (see Bottemiller for a great summary of all of this). In the meantime, we are all exposed to dioxins from the meats, dairy products, and fish that we eat.
As of now, I suppose we watch what happens and make comments whenever the public gets a chance... this is a story to pay attention to.
Additional Information:
- Hamilton. A Chemical Conundrum: How Dangerous is Dioxin. NPR Morning Edition: Dec 28, 2010.
- World Health Organization. Dioxins and Their Effects on Human Health. Fact sheet N°225: May 2010.
- Tomson. EPA Misses Deadline on Dioxin Guidelines. The New York Times: Feb 1, 2012.
- Williams. EPA misses deadline to issue dioxin health assessment. NPR Environment: Feb 2, 2012.
- Bottemiller. EPA Misses Key Deadline for Dioxin Assessment. Food Safety News: Feb 3, 2012.
