Service Area

Occupational Exposure Limit

Occupational exposure limits (OELs) for pharmaceuticals and industrial chemicals are health-based limits for workplace exposure.  OELs are typically developed to address chemical exposure via inhalation and to a lesser degree dermal exposure.  At Gradient, board-certified toxicologists, board-certified industrial hygienists, exposure scientists, and chemists work collaboratively to provide our clients with qualified OELs.  We are skilled in assessing data poor chemicals and chemical classes through well-developed in silico and read-across methodology.  Gradient conducts peer-review of established OELs and is actively involved in organizations that establish these limits.

  • Occupational Exposure Limits (OELs)
  • Threshold Limit Values (TLVs)
  • Exposure modeling
  • No Expected Sensitization Induction Levels (NESILs)
  • In silico predictions and expert review
  • Data gaps and read-across

Gradient has a team of board-certified toxicologists, board-certified industrial hygienists, exposure scientists, and chemists who work in collaboration, as needed, on OELs.

Sample Projects

Development of an Occupational Exposure Limit (OEL)

Gradient evaluated the human health toxicity of a fluorocarbon chemical and reviewed the toxicology literature to identify No Observed Adverse Effect Levels (NOAELs) suitable for derivation of an OEL for this chemical.  We identified point-of-departure doses for three toxicological endpoints, and considered the strengths and weaknesses of the three approaches for deriving an OEL.  We recommended an approach for calculating an OEL and identified uncertainties that may require additional data collection.

Occupational Exposure Limit (OEL) Development and Risk Evaluation for Fragrance Substances

Gradient developed OELs to conservatively assess potential risk to workers exposed to fragrance substances.  We developed OELs after evaluating the toxicology literature.  We also estimated worker exposures with the use of air-modeling approaches and publicly available tools, such as the Targeted Risk Assessment (TRA) tool from the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) and ChemSTEER from the US Environmental Protection Agency (US EPA).  The client used the OELs and risk evaluations we created to assess worker safety and define benchmarks for occupational health goals within the company.

Evaluation of the Manganese Threshold Limit Value (TLV)

Gradient evaluated the methodology used by the American Conference of Governmental Industrial Hygienists (ACGIH) to derive the manganese TLV.  To analyze ACGIH’s interpretation of data, we reviewed the manganese occupational studies, including welding studies, that ACGIH reviewed.  We offered a more scientifically robust approach to the derivation of the TLV, and recommended a range of TLV values that are protective of welders and other workers exposed to manganese.  Our analysis was used in industrial hygiene assessments and was published in a peer-reviewed journal.  Gradient conducts annual updates to this analysis.

Developmental and Reproductive Toxicity (DART) Assessments

On an ongoing basis, Gradient evaluates potential DART risks posed to pregnant employees at a workplace.  These evaluations assist the employer in determining the need for exposure controls.

Critique of a Non-health-based Occupational Exposure Limit (OEL) for Bisphenol A

For a trade association, Gradient critically reviewed the draft recommendation for a non-health-based bisphenol A (BPA) OEL proposed by the Dutch Expert Committee on Occupational Health and Safety (DECOS) of the Health Council of the Netherlands.  We evaluated the methodology used by DECOS to derive the proposed OEL, as well as the underlying toxicity data upon which the OEL was ultimately based.  We also recommended a health-based BPA OEL that is consistent with the weight of the evidence for BPA toxicity and with European Commission directives.  Our critique was submitted to DECOS in a set of written comments.

Health Analyses Regarding Carbon Nanotube (CNT) Manufacture

For a CNT manufacturer, Gradient addressed worker and customer health concerns, specifically with regard to potential exposures to polycyclic aromatic hydrocarbons (PAHs) formed unintentionally during production.  Our work helped the client take proper steps to ensure appropriate product stewardship.

Our Team