A Mini-Symposium on Cumulative Risk Assessment in the Occupational Setting

Posted on by R. Todd Niemeier, MS, CIH; T.J. Lentz, Ph.D; and Molly Leshner

Many of us in the occupational safety and health field have likely faced an issue similar to this: The workers in my plant are exposed to both noise and solvents. I’ve read that both of these exposures can interact to cause hearing loss. How should I control these exposures to reduce the risk of occupational hearing loss? If I control each of the exposures to their relevant occupational exposure limits, is that good enough? Or should I control these exposures to levels below their occupational exposure limits? If so, by how much?

Identifying and evaluating the combined effects of multiple exposures, known as cumulative risk assessment (CRA), is a tricky challenge. The field of mathematics has defined seven complex problems known as the Millenium Prize Problems, and if solved, are each worth US $1 million in prize money. CRA may represent this level of “problem” for us in the field of occupational safety and health – and no, there is not a million dollar prize if you solve it! So what is CRA? The US Environmental Protection Agency [2003] defined cumulative risk as “the combination of risks posed by aggregate exposure to multiple agents or stressors in which aggregate exposure is exposure by all routes and pathways and from all sources of each given agent or stressor.” CRA is a science-policy tool designed to organize and analyze data for the intended purposes of characterizing and potentially quantifying the combined risks, or cumulative risk, from co-exposure to multiple chemical and non-chemical stressors (e.g., biological, physical, or psychosocial impacts) for varying health effects [National Research Council 2009; Sexton 2012; Williams et al. 2012]. Additionally, personal risk factors such as genetics, age, personal habits, socioeconomic status, and others, can contribute to health outcomes.

In recent years, understanding the health risks associated with co-exposures to multiple stressors has received increased attention in the areas of environmental, public and occupational health. Some examples include understanding obesity and the occupational environment, the interaction of occupational and personal risk factors, and the implications of applying cumulative risk assessment in the workplace [Fox et al. 2018; Menzie et al. 2007; National Reseach Council 2009; Pandalai et al. 2013; Schulte et al. 2012; Sexton 2012;U.S. EPA 2003; Zartarian et al. 2009;]. This is an area of ongoing research at NIOSH. In July 2018, NIOSH sponsored a mini-Symposium on CRA for NIOSH employees and brought together a panel of experts from government, academia, and consulting to provide a series of diverse presentations, followed by an open forum discussion.

There are certainly many challenges to incorporating CRA in the workplace. Many of the same methodological and technical challenges that hinder complex risk assessments encountered in environmental and community settings also impact CRAs in the workplace. Additionally, there are challenges unique to the workplace including methodological limitations, data and information gaps, regulatory and public policy restraints, and social and ethical considerations. Although many challenges exist, several steps to move towards utilizing CRA in the workplace have been suggested such as:

  • Use of mode of action (MOA) hypotheses to identify potential stressors and their interactions;
  • Use checklist and audit tools to identify interactive stressors in the workplace and beyond;
  • Adjust occupational exposure limits (OELSs) to incorporate scenario-and-population-specific susceptibility factors, including non-occupational stressors.

As NIOSH and its partners begin to explore some of these options to understand and implement strategies for CRA in the workplace, the input from the occupational hygiene community can play an integral part. Towards that end, NIOSH would like feedback on the following questions:

  • Are there specific issues in the occupational environment where CRA can be applied?
  • What challenges must be overcome to make CRA a practical approach?
  • Where can we find examples of CRA concepts that have been utilized in the workplace and what were the results?

For more information on the combined effects of noise and chemicals, see the recently published NIOSH blog and NIOSH publication on this topic.

Please provide your input in the comment section below.


R. Todd Niemeier, MS, CIH, is an Industrial Hygienist in the NIOSH Education and Information Division.

T.J. Lentz, Ph.D, is the Chief of the Document Development Branch in the NIOSH Education and Information Division.

Molly Leshner is an undergraduate student at the University of Cincinnati and working on an internship in the NIOSH Education and Information Division.




Fox MA, Spicer K, Chosewood LC, Susi P, Johns DO, Dotson GS. Implications of applying cumulative risk assessment to the workplace. – Environ Int.2018 Jun;115:230-238.doi: 10.1016/j.envint.2018.03.026.Epub 2018 Mar 30.

Menzie CA, MacDonell MM, FAU – Mumtaz M, Mumtaz M. A phased approach for assessing combined effects from multiple stressors. – Environ Health Perspect.2007 May;115(5):807-16.doi: 10.1289/ehp.9331.Epub 2007 Jan 24.

National Research Council. 2009. Science and Decisions: Advancing Risk Assessment. Washington, DC: The National Academies Press. https://doi.org/10.17226/12209.

Pandalai SP, Schulte PA, Miller DB. Conceptual heuristic models of the interrelationships between obesity and the occupational environment. Scand J Work Environ Health. 2013;39:221-232.

Schulte PA, Pandalai S, FAU – Wulsin V, Wulsin V, FAU – Chun H, Chun H. Interaction of occupational and personal risk factors in workforce health and safety. – Am J Public Health.2012 Mar;102(3):434-48.doi: 10.2105/AJPH.2011.300249.Epub 2011 Nov 28.

Sexton K. Cumulative risk assessment: an overview of methodological approaches for evaluating combined health effects from exposure to multiple environmental stressors. – Int J Environ Res Public Health.2012 Feb;9(2):370-90.doi: 10.3390/ijerph9020370.Epub 2012 Jan 26.

U.S. EPA. Framework for Cumulative Risk Assessment. U.S. Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Washington Office, Washington, DC, EPA/600/P-02/001F, 2003.

Williams PR, Dotson GS, Maier A. Cumulative Risk Assessment (CRA): transforming the way we assess health risks. – Environ Sci Technol.2012 Oct 16;46(20):10868-74.doi: 10.1021/es3025353.Epub 2012 Sep 11.

Zartarian VG, Schultz BD. The EPA’s human exposure research program for assessing cumulative risk in communities. – J Expo Sci Environ Epidemiol.2010 Jun;20(4):351-8.doi: 10.1038/jes.2009.20.Epub 2009 Apr 15.


Posted on by R. Todd Niemeier, MS, CIH; T.J. Lentz, Ph.D; and Molly Leshner

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Page last updated: January 31, 2019