2.1.9 Carcinogenicity

Most national and international agencies have not classified ethylbenzene for potential genotoxicity or carcinogenicity. In Germany the Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (“MAK Commission”) has classified ethylbenzene as having very low cancer potency. The International Agency for Research on Cancer (IARC) has concluded that there is inadequate evidence to classify ethylbenzene as a carcinogen in humans and sufficient evidence in experimental animals.

Ethylbenzene is carcinogenic in animals following lifetime exposures to high vapor concentrations. The strongest evidence of cancer was kidney tumors found in male rats that inhaled 750 ppm ethylbenzene, a concentration that also significantly reduced the male rats’ survival. There was some evidence of kidney tumors in female rats at this concentration that was detected only after extended evaluation. Exacerbation by ethylbenzene of chronic progressive nephropathy, a pathway that is considered to have no relevance for extrapolation to humans, is postulated as the mode of action underlying the development of the rat renal cancer. There was some evidence at 750 ppm ethylbenzene of liver and lung tumors in mice. The incidences of lung tumors in male mice and liver tumors in female mice were greater than those in concurrent control but were within the historical control ranges observed for these tumor types. There is evidence suggesting that increases in regenerative cell proliferation play a key role in the mouse tumor findings; the significance of these effects at non-toxic exposure levels is therefore expected to be limited.

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