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

Abstract

Over the past 60 years, many organizations in numerous countries have proposed occupational exposure limits (OELs) for airborne contaminants (1). The limits or guidelines that have been 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 Ò (TLVs) (1-10).The usefulness of establishing OELs for potentially harmful agents in the working environment has been demonstrated repeatedly since their inception (3, 5, 6). 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 (7). 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 millions of persons have avoided serious effects of workplace exposure due to their existence.

The Global Landscape of Occupational Exposure Limits—Implementation of Harmonization Principles to Guide Limit Selection

“…This distinction between binding and non-binding limits can become blurred, however, as some regulatory authorities adopt non-binding OELs under existing rulemaking authority. For example, the ACGIH TLVs are adopted as de facto legally binding standards in many Canadian provinces, (3,15) various European countries, (2) and many other countries around the world. (16–18) Moreover, distinctions can be made between “health-based” OELs and those that are “regulatory-adjusted,” (8) with the latter involving consideration of technical and economic feasibility.…”

“…Practices in some organizations might limit the selection of the critical studies to those that are available in the open literature, whereas others might allow for the use of data sourced outside the international public domain (e.g., industrial research, internal reports), which can stimulate controversy due to limited transparency and selectivity being suspected or inferred. (17,46) Moreover, some organizations might use the highest quality studies available, resulting in a large percentage of OELs based on animal studies (e.g., in 2009, approximately 50% of the ACGIH TLVs were based on animal data), (3) whereas others might favor key study selection based on human data. Once a critical toxicity endpoint (e.g., the most sensitive effect) has been selected, organizational practices can also affect the selection of the POD, a specific exposure level that is derived from the critical studies and upon which the OEL is grounded.…”

“…Early work on OELs for airborne workplace chemicals occurred in Germany in the 1880s, when the pioneering animal experiments of Gruber and Lehmann were used to identify safe exposure levels for carbon monoxide, ammonia, and hydrogen chloride. (3) Since the publication of the first table of acute exposure limits by Kobert in 1912, (3) many organizations around the world have been added to the global capacity for establishing OELs (Table I). (4) The first list of maximum allowable concentrations (MACs)—eventually known as Threshold Limit Values (TLVs)—was published by the American Conference of Governmental Industrial Hygienists (ACGIH) in the 1940s.…”

“…(4) The first list of maximum allowable concentrations (MACs)—eventually known as Threshold Limit Values (TLVs)—was published by the American Conference of Governmental Industrial Hygienists (ACGIH) in the 1940s. (3) By the 1970s, many countries were developing or adopting their own values, such as the U.S. Occupational Safety and Health Administration Permissible Exposure Limits (OSHA-PELs) and the German Maximale Arbeitsplatz-Konzentration (MAKs). (5) The lack of OELs for many commercially important chemicals spurred the creation of non-governmental OEL-setting organizations, such as the Workplace Environmental Exposure Level (WEEL) Committee initially established under the auspices of the American Industrial Hygiene Association (AIHA), to help meet this need.…”

“…(3,8,9) However, the proliferation of international OEL-setting bodies, faced with the challenges of evaluating and interpreting complex scientific data on potential health impact of occupational exposures, has yielded a confusing landscape of OELs. As a result, occupational hygienists can be confronted with multiple relevant—but often conflicting—OELs for a particular situation, leading to difficulties in selecting the most appropriate value for health protection purposes.…”