October 21, 2021

European Chemicals Agency Proposes OEL for Isoprene

A new draft scientific report (PDF) published by the European Chemicals Agency includes ECHA’s recommendations regarding an occupational exposure limit for isoprene, which is primarily used as a chemical intermediate to manufacture polymers. The agency recommends an OEL of 3 ppm (8.5 mg/m3) as an eight-hour time-weighted average. According to ECHA, workers at facilities where isoprene or synthetic rubber is produced or used may be exposed to isoprene through inhalation and dermal contact. Stakeholders are invited to comment on ECHA’s report through Dec. 10.

ECHA evaluated approaches published by other organizations for cancer risk assessment and isoprene as it worked to propose its OEL. The agency’s draft report indicates that it examined AIHA’s Workplace Environmental Exposure Level for isoprene. WEELs are airborne concentration limits that provide guidance for protecting most workers from adverse health effects related to occupational chemical exposures. In 2004, an AIHA committee proposed a WEEL for isoprene of 2 ppm as an eight-hour TWA.

“The [WEEL Committee of AIHA] noted that isoprene is clearly carcinogenic in animal assays,” ECHA’s report explains. “The committee noted, however, that neurotoxic effects have been observed at lower inhalation exposure levels than carcinogenic effects and derived an OEL based on those effects.”

Since 2013, the development of WEELs has been managed by the nonprofit organization Toxicology Excellence for Risk Assessment. The table of WEEL values is available on the TERA website.

ECHA’s proposed OEL of 3 ppm follows an approach similar to that of DFG, the German Research Foundation, which established an exposure level for isoprene of 3 ppm as an eight-hour TWA. An explanation of how this value was derived by DFG can be found in the ECHA report (PDF).

ECHA’s Committee for Risk Assessment provides opinions on OELs under the Carcinogens and Mutagens Directive, which sets maximum concentrations for cancer-causing chemicals in workplace air, and the Chemical Agents Directive, which covers risks related to chemical agents at work. A table on the agency’s website summarizes ECHA’s work related to OELs.

More information about isoprene is available from PubChem, a chemistry database at the National Institutes of Health.