Monday, October 13, 2014

USE is KING in Ranking Human Exposure Potential to Chemicals but No One is Listening

Mandates that require the estimation of exposure and human health risk posed by large numbers of chemicals present regulatory managers with a significant challenge.   Although these issues have been around for a long time, the estimation of human exposure to chemicals from their use of products in the workplace and by the consumer has been generally hindered by the lack of good tools. Indeed, one would think that the logical and most cost-effective approach would include an initial attempt to rank-order or prioritize the chemicals according to the human exposure potential that each might pose.  
This is not so easily done.   Indeed, chemicals used in general commerce, that is, chemical used in the workplace and in commercial and consumer products have always presented a number of challenges for regulators. First, there are a large number of chemicals in use, for example, European Inventory of Existing Commercial Chemical Substances lists about 100,000 chemicals whereas the current US inventory of existing chemicals under the Toxic Substances Control Act (TSCA) is approximately 70,000.  Second, there are a wide range of chemicals and products used in the workplace and by consumers. Third, one product may result in a number of different exposures to different individuals by different routes over the product’s life cycle. Finally, the nature of the chemical exposures that result from the use of these products is highly variable because of differing use patterns.
In general formal efforts to “rank” or prioritize chemical sources have been primarily based on surrogates of exposure (e.g., annual produc­tion volume or physical and chemicals characteristics). Clearly, these approaches at best can only provide qualitative or quasi-quanti­tative results with questionable effectiveness. 
Consider a chemical with a nasty physical/chemical profile (an organic with high volatility, high octanol water partitioning coefficient) that is manufactured in very large quantities but mostly in enclosed manufacturing facilities and mostly gets reacted before it ever gets to expose either workers or consumers.   Compare that to a product with very limited production volume and what might be considered “mild” physical/chemical properties from an exposure potential BUT is used in intimate contact with millions of person during its use. The above ranking tools could dramatically miss classify the exposure and potential risk of these two hypothetical chemicals.
A number of years ago, my colleagues in The LifeLine Group and I worked on this problem for Health Canada.  We ultimately developed and published an approach we call CEPST.  This particular prototype tool was developed for “nearfield” sources of exposure.  We explicitly separated these “nearfield” sources from those in the “far field.”   Farfield sources are defined as relatively large but initiated as typically distant sources or emissions to the general environment (air, water, soil). Think of smoke stacks and large discharges to water.  Nearfield sources are those that occur within the microenvironment of a residence or literally at arm’s length for the exposed person.  Think of hair spray.  The nearfield has been shown to be the dominant milieu for human exposure for many if not the vast majority of chemicals especially those that neither are persistent, bioaccumulative nor discharged at relatively high levels to the general environment. Thus, a critical challenge for any regulatory approach designed to really understand human (especially consumer) exposure to chemicals lies first in the recognition and elucidation of both the farfield and the nearfield exposures. 

CEPST in its current form focuses on the nearfield but it could easily be expanded to include exposures from the farfield.

CEPST functions on the input received during four activities conducted for each chemical under consideration:

  1. Chemical identification and physical properties (Chemical Abstract Service (CAS) number, physical properties from available sources)
  2. Internet search for chemical use
  3. Expert panel deliberation and determination of sentinel product(s) for that chemical
  4. Modeler assignment of chemical/scenario dependent variables

The important thing to understand here is that CEPST focuses on the chemicals’ USE in products as it primary aim.   Indeed, we continue to believe that this is the most direct and accurate manner of understanding and ranking the human exposure potential of a large number of chemicals. Unfortunately, it has not been embraced for further developed by any large regulatory entity and I personally think that failure has been a lost opportunity.

I would be happy to send you a pdf copy of the CEPST paper if you email me at  Also, I would be most interest in your response to the following questions:

Do you have to rank order chemical exposures in your professional life and if so what tool or approach do you use?

Even if you do not have to do it in your current job, how would you approach the exposure/risk ranking of hundreds or thousands of chemicals used in commerce?


  1. One of the biggest shortcomings of HHRA - we don't rank the chemicals. We just evaluate risks from exposure to each individual chemical one at a time...

    1. Indeed, there is a real need to do worst things first...