The History and Biological Basis of Occupational Exposure Limits for Chemical Agents

Abstract

Over the past 50 years, many organizations in numerous countries have proposed occupational exposure limits (OEL) for airborne contaminants. The limits or guidelines that have gradually become the most widely accepted both in the United States and in most other countries are those issued annually by the American Conference of Governmental Industrial Hygienists (ACGIH) and are termed Threshold Limit Values® (TLVs). The usefulness of establishing OELs for potentially harmful agents in the working environment has been demonstrated repeatedly since their inception. It has been claimed that whenever these limits have been implemented in a particular industry, no worker has been shown to have sustained serious adverse effects on his health as a result of exposure to these concentrations of an industrial chemical. Although this statement is arguable with respect to the acceptability of OELs for those chemicals established before 1980 and later found to be carcinogenic, there is little doubt that hundreds of thousands of persons have avoided serious effects of workplace exposure due to their existence. The contribution of OELs to the prevention or minimization of disease is widely accepted, but for many years such limits did not exist, and even when they did, they were often not observed. Although it is not possible for any single book chapter to discuss how each of the various biological issues that need to be considered when establishing an OEL should be quantitatively accounted for, most of them have at least been generally addressed here. It should be clear from the discussion that the process for setting OELs remains remarkably similar to those that were used in the late 1940s but that the quality and quantity of data used to set these limits, as well as the methodology, has evolved with our increased level of scientific understanding. It is also clear that as occupational health professionals develop a better understanding of toxicology and medicine, techniques for quantitatively accounting for pharmacokinetic differences among chemicals, and better knowledge of the mechanisms of action of toxicants, more refined approaches for identifying safe levels of exposure will be developed. Hopefully, the end result will be that future occupational exposure limits will be based on the best scientific principles and, therefore, our confidence that workers will be protected at these limits will be even greater than it is today. Keywords: Occupational exposure limits; Uncertainty factors; Limits; Reference concentrations; Ceiling limits; Neurotoxic agents; Odors Persistent chemicals; Mixtures; Chemical carcinogens; Threshold Limit Values; Corporate OELs; Brief and Scala Models; Haber's Law; Exposure limits; U.S.; Exposure limits; International