By Kacee Deener
How do you know when something isn’t good for you? Sometimes it goes without saying (rattlesnake venom), and sometimes it’s not as obvious and requires deeper evaluation.
I recently kicked off a blog series about human health risk assessment and described its four-step process. Remember that hypothetical factory? How do we know if the chemicals being released are harmful? We use a process known as “hazard identification” to identify the types of health problems a chemical could cause (like cancer or respiratory effects).
Examples of two EPA programs that develop hazard identifications are: (1) the Integrated Risk Information System (IRIS) program and (2) the Integrated Science Assessment (ISA) program. Through IRIS, Agency researchers provide health effects information on environmental chemicals. ISAs provide health effects information to inform the National Ambient Air Quality Standards for the six criteria air pollutants.
So, how do we do this? We start by searching the scientific literature to compile all of the studies that look at a chemical’s effects. In IRIS assessments, we describe how we search the literature using, in part, a diagram. You can see an example of that here (pages 1-2). We then organize the information into the categories of health effects seen in the studies, (e.g., kidney or reproductive effects) and summarize certain features of each study, such as the level and route of exposure. We also look at each study’s quality (e.g., was the study designed and conducted well? was it peer reviewed?). Finally, we evaluate the overall “weight of evidence” to answer the question “does the agent cause the health effect?”
In some cases, EPA has developed “descriptors” for doing this. The Preamble to IRIS assessments provides more information (you can see an example here on page xxii). In other words, we provide text describing how likely it is that a health effect is associated with a chemical exposure. For example, in the recent IRIS assessment of 1,4-dioxane, we found that the chemical is likely to be carcinogenic to humans. In our recent ISA for Lead, we found, among other things, that there is a “causal relationship” between lead exposure and cognitive function decrements in children and a “likely causal relationship” between lead exposure and inflammatory responses in adults.
We’ve been working to improve the way we systematically review evidence when identifying hazards. In fact, we recently held a workshop on this topic. We’ve also started releasing the literature search strategy, along with evidence tables summarizing the critical studies, early in the process of developing an assessment. We follow that up with a public meeting to discuss the materials. We held the first of these meetings on December 12-13. Our next meeting is scheduled for April 23. Join us to provide your input, and don’t forget to check back in a few weeks for my next post!
About the Author: Kacee Deener is the Communications Director in EPA’s National Center for Environmental Assessment. She joined EPA 13 years ago and has a Masters degree in Public Health.