To the Editor: During recent years, increasing evidence has been presented that the alkene 1,3-butadiene can cause cancer.1 1,3-butadiene is a component in exhaust from gasoline-engine vehicles. Exhaust emissions of alkenes are highly photochemically active and 1,3-butadiene is one of the five "air toxics" that are regulated in the United States by the Clean Air amendments. In the United Kingdom, the Expert Panel on Air Quality Standards has proposed an outdoor exposure standard of 1 part per billion. It has been reported in several articles and books, including a criteria document from the International Agency for Research on Cancer,2 that 1,3-butadiene is a component in gasoline.
However, the statement that 1,3-butadiene is a constituent of gasoline is, unfortunately, a misunderstanding. This is founded on a report made by Concawe.3 A table from the Concawe report is cited in the IARC document, in which an exposure level of 1,3-butadiene during "gasoline works" as high as 32.3 mg/m3 (8-hour time-weighted average) is presented. This is an extremely high exposure level; the TLV in the United States for 1,3-butadiene is 4.4 mg/m3 (8-hour time-weighted average).
We have done a critical examination of the cited report, especially on the gas chromatographic analysis, and apparently a mistake was made during the evaluation of the results. The peak in the chromatogram that was believed to be 1,3-butadiene is in fact a mixture of C5 alkenes, but primarily 2 methyl-butene. In later reports, this has been confirmed with improved separation obtained with capillary gas chromatography.4 These measurements showed that there is no or very small amounts of 1,3-butadiene in gasoline. Analysis of fluid catalytic cracking naphtha (FCC-naphtha), which is an alkene-rich fraction from refineries, has shown very small amounts of 1,3-butadiene, below 0.001%.5 FCC-naphtha is used nowadays in gasoline in concentrations up to 30% and the concentration of 1,3-butadiene therefore must be much lower than 0.0005% in the gasoline. This should be compared to the 3 to 5% concentration of benzene in gasoline.
From the results of the cited literature, we therefore conclude that 1,3-butadiene is not present in gasoline to any significant amount. This is of great importance for risk assessments concerning cancer and the handling of gasoline.
Rolf G. Nordlinder, MSc
Ralph I. Nilsson, MD
Anne B. Buskhe, PhD
Institute of Internal Medicine; Section of Occupational Medicine; Göteborg University; Göteborg, Sweden
1. Landrigan PJ. Critical assessment of epidemiological studies on the carcinogenicity of 1,3-butadiene and styrene. IARC Sci Publ.
2. Occupational exposure to mist and vapours from strong inorganic acids; and other industrial chemicals. IARC Monogr Eval Carcinog Risks Hum.
3. CONCAWE. A Survey of Exposures to Gasoline Vapour.
[Report No. 4/87.] de Hague: Concawe; 1987.
4. Löfgren L, Berglund P, Nordlinder R, Petersson G, Ramnäs O. Selective assessment of C2
alkenes in air by adsorption sampling and gas chromatography. Int J Environ Anal Chem.
5. Ramnäs O, Östermark U, Petersson G. Characterization of sixty alkenes in a cat-cracked gasoline naphtha by gas chromatography. Chromatographia.
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