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Key value for chemical safety assessment

Additional information

In vitro Studies

ENB has been investigated in in vitro tests, and did not induce gene mutation in bacterial systems or chromosomal aberration in mammalian cultured cells, with or without an exogenous metabolic activation system. Several well conducted and reported studies were identified.

Reverse gene mutation assay was conducted by OECD TG 471 and TG 472. The substance was not mutagenic in Salmonella typhimuriumTA100, TA1535, TA98, TA1537 and Escherichia coliWP2uvrA at concentration of ranging from 0.00781 to 0.25 mg /plate, with and without an exogenous metabolic activation system (MHW, Japan, 1998). ENB was not mutagenic in Salmonella typhimuriumstrains TA100, TA1535, TA98, TA1537 and TA1538 at concentrations of 0.001 to 0.1 mg/plate (Ballantyne, 1998).

Chromosomal aberration test by OECD TG 473 was conducted in cultured Chinese hamster lung (CHL/IU) cells. Structural chromosomal aberrations and polyploidy were not induced up to a maximum concentration of 0.050 mg/mL on continuous treatment, and 0.1 mg/ml on short-term treatment, with and without an exogenous metabolic activation systems, respectively (MHW, Japan, 1998). ENB at concentrations ranging from 0.006 to 0.06 mg/mL did not produce increases in chromosome aberrations in Chinese hamster ovary (CHO) cells with or without metabolic activation (Ballantyne, 1998). ENB was not mutagenic in the CHO/HGPRT forward gene mutation assay at concentrations of 0.02 to 0.08 mg/mL (without activation) and 0.02 to 0.10 mg/mL (with activation), and was not mutagenic in the sister chromatid exchange test at concentration of 0.01 to 0.06 mg/mL with and without metabolic activation (Ballantyne, 1998).

In vivo Studies

The rat dominant lethal test showed a no-observed effect concentration for dominant lethality greater than 254 ppm ENB (Neeper-Bradley and Ballantyne, 1996). There are no other available data on genotoxicity in vivo.

Short description of key information:
ENB was not mutagenic with and without an exogenous metabolic activation system in bacteria and mammalian cells in vitro [OECD TG 471, 472, 473]. The chemical induced neither chromosomal aberrations nor sister chromatid exchanges in mammalian cells in culture. It also did not induce dominant lethal mutation in rats.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

On the basis of reliable negative studies (in vitro mutation, chromosome abberations and SCE; in vivo dominant lethal), no classification is proposed.