Do we still need traditional Occupational Exposure Limits (OELs) to compare with exposures, perform risk assessments and identify control approaches? Or have traditional OELs run their course of usefulness?

The 17 authors of the paper — “Occupational Exposure Limits: Do They Still Have A Future” — represent decades of experience in occupational health in all sectors of the profession, and believe that OELs continue to be critical to protecting workers from chemical exposures. The authors contend that OELs should be updated, consistent with current scientific knowledge. They also believe the infrastructure to generate and utilize OELs desperately needs an overhaul.

Europe has launched REACh, for example, which requires the development of DNELs (Derived No Effect Levels). These will not be consensus recommendations, but values determined by the manufacturer or supplier of the material. These manufacturers and suppliers have a very broad range of technical resources and knowledge. But small manufacturers will not have the resources to do exhaustive studies. The level of scientific review of the DNELs once submitted is unclear at this time. Plus, it remains to be seen how effective this system will be in protecting workers, according to the authors of the OEL paper.

Here is how the REACh system classifies exposures:

  • DNEL (worker) Derived No Effect Levels

  • Derived Minimum Effect Level (DMEL), based on some concept of acceptable or negligible risk, (such as the “Threshold of Toxicological Concern”)

  • The Derived No-Effect Level (DNEL) is defined in Annex 1 of REACh as the level of exposure above which humans should not be exposed.

  • Manufacturers and importers are required to calculate DNELs as part of their Chemical Safety Assessment (CSA) for any chemicals used in quantities of 10 tons or more per year.

  • The DNEL is to be published in the manufacturer’s Chemical Safety Report and, for hazard communication, in an extended Safety Data Sheet.

  • Worker DNELs (or DMELs) are reported as an allowable daily dose: — Inhalation: ppm — Dermal and Oral: “mg/kg/day”

  • This process for setting worker DNELs and DMELs primarily uses a structured algorithm utilizing NOELs and NOAELs or LOAELs and default “margins of safety”.

    The authors point out that OELs developed outside of the regulatory system as guidance have been subject to significant litigation. At the present rate of progress, it is extremely unlikely that significant numbers of new OELs will to be developed, according to the authors. Litigation could further reduce, restrict or eliminate the efforts of organizations like ACGIH to generate new OELs.

    The authors of the OEL paper state it is important to recognize that the term “OEL” refers to two distinct exposure limits. The first is widely recognized as a “health-based” OEL (or hOEL) and the second a “regulatory-adjusted” OEL (or rOEL).

    For health-based OELs, only health-driven risks are considered. The harmonizing global process for health-based OELs will have to define clearly what is to be considered detrimental or adverse, what physiological capacity is to be protected, e.g. functional reserve (transient? or permanent?), and what subpopulations are to be included. The process will have to define the degree of uncertainty permitted in the extrapolation of data from experimental biological systems or from medical surveillance.

    For the “regulatory adjusted” OELs (or rOEL), consensus from a tri-partite process will have to modify health based OEL values so that they can include non health based considerations such as economics and technical feasibility in order to serve a regulatory function in the jurisdiction that uses them.