ECHA RAC Releases Scientific Evaluation On Occupational Exposure Limits For 1,3-Butadiene

The European Chemicals Agency's Committee for Risk Assessment (RAC) has released an evaluation of occupational exposure limits (OELs) for 1,3-butadiene, determining that no health-based limit can be established due to the compound's classification as a non-threshold carcinogen. Instead, RAC has derived an exposure-risk relationship to address the risk of cancer among exposed workers, reflecting findings that link 1,3-butadiene to increased cancer risks in the haematolymphatic system, particularly leukaemia.

Carcinogenicity Of 1,3-Butadiene

The evaluation recognises 1,3-butadiene (1,3-BD) as a potent carcinogen, particularly affecting workers in industries involving synthetic rubber production. The International Agency for Research on Cancer (IARC) classified 1,3-BD as “carcinogenic to humans” based on occupational studies, animal models, and evidence of a genotoxic mechanism driven by reactive metabolites. Epidemiological data from studies in the US and Canada show an association between prolonged exposure to 1,3-BD in styrene-butadiene rubber manufacturing workers and increased rates of leukaemia​​.

No Health-Based OEL, But Cancer Exposure-Risk Relationship Established

Given 1,3-BD’s non-threshold carcinogenic nature, RAC found it impossible to establish a safe OEL for long-term occupational exposure. Instead, the committee proposed an exposure-risk relationship (ERR), which calculates an excess lifetime cancer risk based on 1,3-BD concentrations. According to the ERR, a workplace air concentration of 0.065 ppm of 1,3-BD corresponds to an excess lifetime cancer risk of 4 cases per 100,000 workers over a 40-year exposure period​.

Critical Health Effects And Metabolic Differences

Although 1,3-BD poses significant cancer risks, RAC’s analysis also highlighted ovarian atrophy as a critical non-cancer effect in animal models. However, species-specific metabolic differences hinder establishing a direct human relevance. Studies showed that mice, in particular, displayed ovarian toxicity at relatively low concentrations, but the varied metabolism of 1,3-BD across species raises uncertainties for human risk assessment​.

Recommendations For Monitoring And Risk Management

RAC recommends biomonitoring for 1,3-BD exposure using specific urinary biomarkers like DHBMA and MHBMA in workplaces, especially where workers are also exposed to compounds such as chloroprene or smoke. However, RAC did not suggest a biological limit value (BLV) due to the limited data on baseline levels in the EU population and the influence of external factors like smoking​.

Groups At Extra Risk

The RAC’s evaluation identified particular groups at higher risk, including workers with certain genetic polymorphisms that increase sensitivity to 1,3-BD metabolites. Additionally, women of reproductive age may be at elevated risk due to the compound’s potential ovarian toxicity.