Sunday, March 16, 2014

Comments on NIOSH Update of Carcinogen Classifications and Risk Levels

NIOSH is proposing an update of their “Carcinogenic Classification and Target Risk Level Policy for Chemical Hazards in the Workplace”.  My friend and colleague Chris Laszcz-Davis asked that I comment on these changes so that she could forward comments to the American Industrial Hygiene Association.  I thought I would share these comments below on this blog.

The new classification policy proposes using the assessment schemes used by the NTP, EPA and IARC which makes plenty of sense because to do so will enhance harmonization and will keep NIOSH from reinventing the wheel. 

The use of risk based exposure limits (RBOEL) for carcinogens is a step directly into the 21st century for NIOSH.   The chosen benchmark of one in 1000 risk of cancer at the 95th lower confidence limit for a 45 year working lifetime seems imminently appropriate to me.   Mention is made in the document that this risk is at least an order of magnitude higher than the cancer risk permitted in the US for the general public.   What is not mentioned in the document is that, according to the Bureau of Labor Statistic, the risk for accidental death occurring during employment in a working lifetime in the United States is slightly higher than 1 in 1000 over the entire US worker population and very much higher for some classifications of workers (e.g., construction workers, commercial fisherman).  Note to viewers of TV show:  Deadliest Catch.  It really is perhaps the most dangerous occupation in the US.   It is certainly the most dangerous of the occupations that I know of that are tracked.

What is even more interesting is that these accidental deaths of workers represent actuarial data; that is, this the portion of working folks who actually died as evidenced by historical records.   The risk of cancer from exposure to a carcinogen on the other hand is putative and the result of low dose extrapolation of animal data.   The extrapolation also assumes that there is a linear dose-response all the way down to exposures that are many orders of magnitude below those tested on animals.   It also estimates the occurrence of cancer and not the rate of death from cancer.  

Low-dose extrapolation modeling will be the topic of at least one future blog but suffice it to say here that when you extrapolate with one model (linearity) far below the level of data you are essentially presenting an argument without data.

Given all these factors, the criterion outlined by NIOSH for RBOELs for carcinogens seems perfectly reasonably to me.

I also agree with the decision to make the RELs risk-based; that is, NIOSH will no longer consider the technical achievability (i.e., ability to control exposure) in establishing these limits.

I disagree with one area of the proposal; namely, the treatment of RELs set when the reliable analytical quantification limit is higher than an REL set using the above criteria (i.e., the 1 in 1000 quantitative risk level).   Here NIOSH is proposing using a higher REL with an AF notation for Analytical Feasibility.  This policy implicitly ignores the ability of modern exposure science to estimate exposures in essentially any scenario by physical-chemical modeling.    My suggestion would be to have two RELs in this instance.   The first would be the standard REL using the above criteria and the second an REL-AF to reflect the analytic realities. 

For many, perhaps most, carcinogens this will bring down the OEL significantly and this will undoubtedly present problems for some who need to comply with these new lower levels.   A colleague asked me to comment on this issue which I will do in the next blog.


  1. The fact that the current national occupational accidental death risk level is 1/1000 doesn't justify selecting it as an acceptable level of risk for workers, whether from accidents or from exposure to carcinogens (which is clearly not an "accidental" risk). Furthermore, the NIOSH proposed acceptable risk level is based on the risk of cancer (cases), not deaths so comparison to the national risk of worker accidental deaths isn't appropriate. Under the Clean Air Act of 1990, Congress set a target risk level from exposure to toxic chemicals for the most highly exposed population at 1/10,000 - why should the target risk level for workers be an order of magnitude higher? Finally, given that occupational exposures to chemicals are typically much higher than those of the general population, the issue of low dose extrapolation is not necessarily "many orders of magnitude" lower than those used in animal studies, and is certainly not the case for risk assessments based on epidemiological studies.

    1. Anonymous,

      The risk of dying on the job in the US is a historical fact. It could actually be thought of by some as being incidental to employment. Indeed, I would love to hear any expert's opinion as to whether this overall rate could be driven down by a factor of 10. Clearly there is a constant push or pressure to lower occupational accidents; however, I do not sense any intense and sweeping drive by society to dramatically lower this highly certain number.

      I see the real and actual risk of dying on the job in the US today as an important and reasonable benchmark. These are real bodies whereas the 1 in 1000 risk for cancer cases at an exposure limit is a modeled estimate. I do not think that anyone can prove that there will actually be 1 in 1000 cancers at these exposures. It does indeed represent orders of magnitude extrapolation. Most animal tests can detect a rate of 1 in 10 so a prediction of 1 in 1000 is still 100 fold below the data and, IMHO, still quite a significant extrapolation.

      It may or may not be justified but the established fact is that we have always subjected the worker population to more putative risk than members of the general public. EPA and California Prop 65 typically use 1 in a million and 1 in a hundred thousand putative risk for carcinogens; however, ever since the Benzene Supreme Court ruling the 1 in 1000 for workers has become standard.

  2. I agree with the points made in this article. According to recent survey it is found that about 19% of the accidents happen due to failure in understanding of the work. We can reduce the risk by 19% by giving awareness to the employees regarding what they are meant to do in the company.

    Arnold Brame