Hexane Fact Sheet

Source of Exposure

n-Hexane is produced by cracking of crude oil and subsequent fractional distillation, but also from natural gas and coal. Commercial n-hexane (technical grade 50-98%) also contains, inter alia, 2-methylpentane and 3-methylpentane. N-Hexane research grade is 99.98%. n-Hexane is a component of petroleum benzine and petroleum ether.

The production of n-hexane and other hexanes in the U.S. in 1975 approximated 300,000 tons, while in the European Economic Community (EEC) in 1979, it was approximately 10,000 tons. Its main use was for oil seed extraction, processing in the rubber industry, in glues (e.g. in the shoe industry), and as solvent in paints, lacquers, and printing ink. Some kinds of extraction benzine contain 50% n-hexane, petroleum ether 1 to 20%, and petrol 1.5%. Most often n-hexane is mixed with other solvents.

Absorption

The main route of absorption is through the lungs. A linear relation between the concentration in alveolar air and in venous blood has been shown in humans following 4.5 h of exposure at levels of 160 to 1400 mg/m3. Retention in the lungs was calculated to be 15%. Veulemans et al. found 24% retention following exposure to 360 to 720 mg/m3, and this was confirmed by Mutte et al. at an exposure of 243 mg/m3.

Absorption of n-hexane from the gastrointestinal tract has been demonstrated, but is hardly of any importance in occupational exposure.

Disposition

The distribution of n-hexane has not been studied in detail in humans. In rats exposed for 6 h at different levels the content on n-hexane in various organs was measured by Baker and Richert. A linear relation between exposure and organ concentrations in rats was seen by Howd et al. only in the blood and liver. Following short term exposure the concentration of n-hexane was five times higher than in the blood.

Toxic Levels

The primary adverse effects of n-hexane are caused by the 2,5-hexanedione metabolite. Experiences on the chromic neurotoxic effects of n-hexane have been collected from examinations of sniffers abusing solvent mixtures, typically solvents from glues, of which n-hexane is a constituent. Such an abuse has been quite popular in the U.S., Japan, and European countries, Experience from occupational exposure is the other main source of neurotoxicological data. Almost exclusively the PNS has been in focus, polyneuropathy being by far the most common condition induced by log-term exposure, most often as slowly progressing symptoms of sensory-motor polyneuropathy, but sometimes of subacute onset, particularly after heavy exposure. Symptoms may be accentuated even after termination of exposure, but after some additional weeks improvement starts. Restitution is slow but often compete, although some still have complaints after up to 18 months and even years. In spite of severe symptoms of neuropathy and subsequent pyramidal involvement, restitution may be achieved.

References

-Solvent Neurotoxicity, Peter Arlien-Soborg. CRC Press, Boca Raton, Florida, pp 155-183, 1992.

-Brugnone, F., Perbellini, L., Grigolini, L., and Apostoli, P., Solvent exposure in a shoe upper factory, Int.Arch.Occup.Environ.Health, 42, 51,1978.

-Veulemans, H., Van Vlem, E., Janssens, H., Masschelein, R., and Leplat, A., Experimental human exposure to n-hexane, Int.Arch.Occup.Environ.Health, 49,251,1982.