Occupational Cancer and the NIOSH Carcinogen Policy | CDC - NIOSH eNews - April 2011

Volume 8 Number 12 April 2011

Occupational Cancer and the NIOSH Carcinogen Policy
Guest Column by Paul Schulte, Ph.D.,
Director, NIOSH Education and Information Division

"In the 21st century, occupational cancer is still a significant cause of morbidity, mortality, and societal burden. While the number of current workers at risk of occupational cancer is not known precisely, the number of workers exposed to OSHA regulated carcinogens is still in the millions and the size of the population with past exposure is in the tens of millions. Estimates of the fraction of cancers attributable to occupation vary. At least 4% (24,000) of the approximate 600,000 deaths from cancer each year in the United States is thought to be the result of exposures in the workplace [Ward et al. 2003]. It is likely that this 4% is an underestimate. The calculation of this attributable fraction was only conducted on a few carcinogens and cancer sites. Moreover, the role of work and occupational exposures of cancers in women has not been widely studied which may contribute to the underestimate. Other estimates of cancer mortality attributable to workplace exposures range as high as 10%. If the 4% estimate for deaths is the same for cancer morbidity, an estimated 48,000 new cases of cancer each year have occupational causes. This is an important contribution to the human cancer burden, exceeded only by the contribution of cigarette smoking and diet [P. Schulte and T. Schnorr, Presentation to the President’s Cancer Panel 2008)."

NIOSH assessments of workplace carcinogens and the setting of NIOSH Recommended Exposure Limits (RELs) have been important tools in addressing the burden of occupational cancer. Historically, in 1976, to address the growing perception of an occupational cancer burden, NIOSH specified a policy to be used to classify substances as carcinogens and to develop RELs which allowed for "no detectable exposure levels for proven carcinogenic substances" [Fairchild 1976]. In 1995, NIOSH revised this policy to include advances in science and approaches in risk assessment and risk management (http://www.cdc.gov/niosh/npg/nengapdxa.html). This revised policy states that "NIOSH recommended exposure limits (RELs) will be based on risk evaluations using human or animal health effects data, and on an assessment of what levels can be feasibly achieved by engineering controls and measured by analytical techniques. To the extent feasible, NIOSH will project not only a no-effect exposure, but also exposure levels at which there may be residual risks." This policy applies to all workplace hazards, including carcinogens, and is responsive to Section 20(a)(3) of the Occupational Safety and Health Act of 1970, which charges NIOSH to "…describe exposure levels that are safe for various periods of employments, including but not limited to the exposure levels at which no employee will suffer impaired health or functional capacities or diminished life expectancy as a result of his work experience."

Over the last few years, NIOSH and stakeholders have had concerns about limitations in the NIOSH’s Carcinogen Policy and NIOSH initiated a review of the carcinogen policy in 2010. A major limitation in the policy is the use of the term "Potential Occupational Carcinogen" which dates to the 1980 OSHA hazard classification for carcinogens outlined in 29 CFR 1990.103 and is defined as "…any substance, or combination or mixture of substances, which causes an increased incidence of benign and/or malignant neoplasms, or a substantial decrease in the latency period between exposure and onset of neoplasms in humans or in one or more experimental mammalian species as the result of any oral, respiratory or dermal exposure, or any other exposure which results in the induction of tumors at a site other than the site of administration. This definition also includes any substance which is metabolized into one or more potential occupational carcinogens by mammals."

A major limitation of this definition is that the policy allows for only one cancer category, potential occupational carcinogen. The adjective "potential" conveys uncertainty that is not warranted with many carcinogens such as asbestos, benzene, and others. This approach stems from a time in the 1960s and 70s when most occupational exposures were unregulated and the science of chemical carcinogenesis was hotly debated. This policy does not allow for classification on the basis of the magnitude and sufficiency of the scientific evidence. In contrast, other organizations, such as the International Agency for Research on Cancer (IARC) and the National Toxicology Program (NTP) allow for a more differential classification.

There also are other technical and scientific issues with the current NIOSH Carcinogen Policy that require further examination. The first thing to consider is should there explicitly be a carcinogen policy as opposed to a broader policy on toxicant identification and classification (e.g. cancer, reproductive hazards, neurotoxins)? If there is a cancer policy, how should different levels of evidence be included? How are recommended exposure limits (RELs) for carcinogens determined? Should the method for determining these RELs be different than for other similarly serious outcomes?

With respect to the development of RELs, the 1995 revision of the NIOSH policy states that NIOSH RELs should be "..based on risk evaluations using human or animal health effects data, and on an assessment of what levels can be feasibly achieved by engineering controls and measured by analytical techniques." To the extent feasible, NIOSH will project not only a no effect exposure, but also exposure levels at which there may be residual risks". NIOSH continues to evaluate the technical considerations that must be addressed with the phrase "…feasibly achieved by engineering controls …" and has generally taken this to mean if a carcinogen can be controlled to the REL in one workplace then it is potentially achievable in other workplaces. However, further consideration of this interpretation is warranted as is consideration of the extent to which NIOSH RELs should be technology-forcing. That is, to achieve the REL, new technological approaches will need to be developed.

As a consequence of predicting exposure levels at which there may be residual risks, a question that must be answered is how great/large should this residual risk be? NIOSH has historically used the level of 1/1000 lifetime risk of cancer for carcinogens. This is frequently the risk level used by OSHA in setting permissible exposure limits (PELs) as a result of the Supreme Court Benzene decision. Should the NIOSH RELs use the same residual risk level as the OSHA PELs or should a lower level of residual risk, such as 1/10,000, be used? This question is increasingly of concern as new genetic tests allow for identification of subgroups in the population that have increased risk of cancer and whether this kind of research should be used in OEL development (see Schulte and Howard ARPH Vol 32, 2011).

Other issues that will be considered in the NIOSH Carcinogen Policy review are what uncertainties or assumptions should be used in the development of RELs, the utility of a standard action level, and how to address worker exposure to complex mixtures. The revision of the NIOSH Carcinogen Policy also coincides with the international realization that there is a need for more efficient and quicker means of classifying chemicals. Qualitative and semi-quantitative approaches such as hazard banding are increasingly being investigated as a means of addressing the vast numbers of unregulated chemicals. NIOSH has been in collaboration with various organizations to consider utilizing hazard banding approaches to control chemicals. This will also be reflected in the review of the carcinogen policy.

To assist NIOSH in this review and to provide stakeholders an opportunity for input, a Federal Register Notice will be published describing the process for providing input on the revision of the NIOSH Carcinogen Policy. A docket will be opened for the collection of the information and a public meeting will be held within the next few months. It is anticipated that the report on a revised NIOSH Carcinogen Policy will be available in the Spring of 2012.

"The revision of the NIOSH Carcinogen Policy reflects the fact that our science-based determinations must stay current with advances in the relevant technologies and methodologies," our Director, John Howard, maintains. I join with Dr. Howard in looking forward to the participation of all interested parties in this process as we move forward.

CDC - NIOSH eNews - April 2011