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Key value for chemical safety assessment

Additional information

Various studies have been undertaken on tetrahydromethylphthalic anhydride (MTHPA). This is a structural analogue of 3 -MTHPA D4 in which the methyl substitution is not defined or fixed in a specific position on the carbon cyclic structure, as opposed to 3 -MTHPA D4 where the methyl substitution is fixed at the 3C position. 3 -MTHPA D4 is regarded as a specific isomer of MTHPA.

Bacterial cell gene mutation assay:

A reverse gene mutation assay (Ames test) has been conducted using the pre-incubation method with strains TA100, TA1535, TA98, TA1537 of S. typhimurium and Escherichia coli Wp2 uvrA. These were exposed to concentrations of 0, 62.5, 125, 250, 500, 1000, 2000 ug/plate (-S9 mix) and 0, 156, 313, 625, 1250, 2500, 5000 ug/plate (+S9 mix) in the presence and absence of a mammalian metabolic activation system. No cytotoxicity occurred and the substance did not induce mutations in the S. typhimurium and E. coli strains examined.


A chromosome aberration assay in V79 cells has been conducted using OECD test methods. There were no biologically significant increases in the number of cells showing structural chromosome aberrations, either in the absence or in the presence of metabolic activation, up to and including cytotoxic concentrations. There were no statistical differences between treatment and control groups and no dose-response relationships were noted.There were no biologically relevant increases in the rate of polyploid or endoreduplicated metaphases. The substance was therefore considered as not clastogenic in this test system

In a second study, CHL/IU cell cultures/primary lymphocyte cultures were exposed to concentrations of 0, 0.075, 0.15, 0.30 and 0.60 mg/mL with and without metabolic activation. Structural chromosomal aberrations were not induced up to 0.30 mg/mL (24 and 48 hours continuous treatment without S9). Polyploidy (1.13%) was increased at 0.30 mg/mL with 48 hours continuous treatment without metabolic activation. Polyploidy (1.25 -1.88 %) was statistically increased at 0.11 -0.43 mg/mL (all concentrations) with short-term treatment in the presence of S9, indicating a potential effect of the substance. Whereas this study showed no indication of clastogenic properties, a polyploidy inducing effect cannot be excluded. Therefore a second test was performed. However, the biological relevance of the observed variation was considered equivocal as the test design is of limited use to investigate such effects.

Mammalian cell gene mutation assay:

An in vitro mammalian cell assay has been performed in mouse lymphoma L5178Y TK+/- cells to test the potential for gene mutation and/or chromosome damage. Treatments were carried out for 3 hours with and without metabolic activation (S9 Mix) and for 24 hours without metabolic activation following OECD/EU test methods. In the first assay, mutation frequencies did not show any statistical or biological significant differences from controls. In a second assay there were one or two concentration levels where the obtained mutation frequencies were statistically significantly higher than mutation frequencies of the vehicle control. However, while the changes in mutation frequencies were dose-related, the GEF criterion for these to be regarded as positive was not achieved and the obtained statistical significances were regarded as not biologically relevant.

Short description of key information:
Genotoxicity in-vitro: Bacterial reverse mutation - Negative

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on results of the three different in vitro genetic toxicity studies tetrahydromethylphthalic anhydride (MTHPA), of which 3 -MTHPA D4 is an isomer, was not classified and labelled as genotoxic according to Directive 67/548/EEC (DSD) and to Regulation 1272/2008/EC (CLP).