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.
