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

Figures & data

Table 1 The Early History of Institutional Occupational Exposure Limit (OEL) Development

Decade first published	Type of OEL
1910s	U.S. and South African limits (for crystalline silica/quartz only)
1920s	U.S. Bureau of Mines exposure limits
	International Critical Tables
1930s	German exposure limits
	USSR Ministry of Labor MACs
1940s	American Conference of Governmental Industrial Hygienists (ACGIH) maximum allowable concentrations of atmospheric contaminants (preceding Threshold Limit Values)
	American National Standards Institute standards
1950s	People's Republic of China's Provisional Hygienic Standards for the Design of Industrial Premises
1970s	U.S. Occupational Safety and Health Administration (OSHA) Permissible Exposure Limits (PELs)
	National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limits (RELs)
	Nordic Expert Group (NEG) for Criteria Documentation of Health Risks from Chemicals
	Deutsche Forschungsgemeinschaft (DFG) Maximale Arbeitsplatz-Konzentration (MAKs)
1980s	American Industrial Hygiene Association (AIHA) Workplace Environmental Exposure Limits (WEELs)
1990s	European Scientific Experts Group (now Scientific Committee on Occupational Exposure Limits [SCOEL]) Binding Occupational Exposure Limit Values (BOELVs) and Indicative Occupational Exposure Limit Values (IOELVs)

Based on Paustenbach et al. (2011);⁽³⁾ DFG (2013);⁽⁴⁾ Ripple (2010);⁽⁵⁾ EC (2013)^(7).

Figure 1 A hierarchy of risk-based occupational exposure benchmarks. As more toxicological and epidemiological data become available, one moves up the hierarchy. Adapted from a version of the hierarchy developed by Laszcz-Davis et al.⁽²²⁾ © AIHA. Reproduced by permission of AIHA. Permission to reuse must be obtained from the rightsholder.

Figure 2 Graphical representation of the fraction of chemicals in commerce with occupational exposure limits (OELs). (REACH data from ECHA, 2011;⁽⁴⁰⁾ data from 18 international organizations from Schenk et al., 2008a⁽³⁶⁾). © AIHA. Reproduced by permission of AIHA. Permission to reuse must be obtained from the rightsholder.

Table 2 Variability in Exposure Limits Derived for n-hexane

Type of exposure guideline	Value (ppm)∼
Traditional occupational exposure limits
Indicative Occupational Exposure Limit Value (Scientific Committee on Occupational Exposure Limits)	20
Threshold Limit Value (American Conference of Governmental Industrial Hygienists)	50
Recommended Exposure Limit (U.S. National Institute for Occupational Safety and Health [NIOSH])	50
Maximale Arbeitsplatz-Konzentration (German Ausschuss für Gefahrstoff)	50
Permissible Exposure Limit (Occupational Safety and Health Administration)	500
Alternative inhalation values
Reference Concentration (U.S. Environmental Protection Agency [EPA])	0.2
Derived No-Effect Level for general population (derived under European REACH regulations)	4.5
Derived No-Effect Level for workers	21
Immediately Dangerous to Life and Health (NIOSH)	1100
Acute Exposure Guideline Level (AEGL-2, for 30-min to 8-hr exposures; EPA)	3300

Figure 3 Potential sources of variability in science and policy decisions taken during the establishment of occupational exposure limits (OELs).

Table 3 Ideal Characteristics of Standardized Scientific Supporting Documents for Occupational Exposure Limits (OELs)

• Reflects current knowledge as presented in the scientific literature

• Includes research publications that are preferably peer-reviewed scientific papers, or are at least available publicly, and limits personal communications as references

• Communicates approaches and resulting OELs openly, particularly toward the general public

• Is developed either by a scientific committee consisting of independent scientists from academia and government, or by experts within an agency with an additional peer, stakeholder, and public review process.

• Presents and scrutinizes all relevant epidemiological and experimental studies, especially “key studies” that present data on the critical effect, and describes all observed effects

• Presents and scrutinizes environmental and biological monitoring possibilities, including toxicokinetic data

• States and describes the establishment of dose–response and dose–effect relationships and points of departure for each observed effect

• Identifies the critical effect (i.e., the effect that occurs at the lowest exposure level) in the conclusions, along with reasons as to why a certain effect is the critical one

• Highlights mutagenic, carcinogenic, teratogenic, and allergic/immunological properties

• Provides a reference list for all studies described, including a list of reviewed but unused references, and also lists databases that have been used in the literature search

Based on Zielhuis (1991);⁽²⁾ Lundberg (1994).⁽⁶⁹⁾

Figure 4 Framework for the selection of an appropriate occupational exposure limit (OEL)

Table 4 Overview of Steps Involved in the Derivation of an Occupational Exposure Limit

1. Define the scenario and develop the problem formulation.

2. Gather and summarize the scientific literature most relevant to the problem formulation (e.g., primary literature and existing reviews on toxicology, epidemiology, pharmacokinetics, physicochemical properties), using the problem formulation to guide the literature selection process.

3. Select a point of departure (e.g., NOAEL, LOAEL, BMD, or risk-based level) based on factors outlined in the problem formulation, such as protectiveness, strength of evidence, and human relevance.

4. If necessary, perform extrapolations to increase the relevance of the point of departure.

a. Adjust for route of exposure and exposure duration/patterns (using default assumptions on rates of ingestion/inhalation or physiologically based pharmacokinetic [PBPK] models).

b. Perform animal-to-human extrapolations and human variability extrapolations (using uncertainty factors, chemical-specific adjustment factors, or PBPK modeling).

c. Apply any additionally required uncertainty factors (e.g., database deficiency, severity of effect).

5. Submit value for review by external parties.

Figure 5 The Dow Chemical Company decision logic for selecting occupational exposure limits (OELs).

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