Nitrogen trifluoride

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Short description of key information:

7.6.1: KS: May (2012) - Ames study.  The increases in revertants in strains TA100, TA1535 and WP2uvrA indicate that the type of damage induced was base pair changes, likely resulting from an indirect DNA damaging effect (i.e. oxidative damage) or chromosomal effects.

Chrom abs: Waiver

Endpoint Conclusion:No adverse effect observed (negative)

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

Justification for selection of genetic toxicity endpoint

The collective conclusion is that NF3 is not considered to be mutagenic in eukaryotic cells

Short description of key information:

SS: Lee (1997) - MLA study. NF3 was concluded to be negative up to a concentration of 10% (v/v) a maximum practicable concentration in both the absence and presence of S9 mix.

7.6.2: KS: Baldwin & O'Loughlin (1996) - bone marrow micronucleus study.  NF3 did not exhibit an increase in the frequency of micronucleated polychromatic erythrocytes in male or female mouse bone marrow cells when tested up to a dose considered to be a MTD (evidence of bone marrow effects [erythropoiesis]).

Endpoint Conclusion: No adverse effect observed (negative)

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Gene mutation (bacterial)

A robust, Ames GLP, guideline compliant key study (May, 2012) confirms under the conditions of a 4 strain S. typhimuriumtest (TA98, TA100, TA1535 and TA1537) and a single E.colistrain (WP2uvrA (pKM101)) thatNF₃exhibits evidence of mutagenic activity in two S. typhimurium (TA100 and TA1535) and one E. coli(WP2uvrA (pKM101)) in both the absence and presence of exogenous metabolic activation. The effect of metabolic activation did not alter the mutagenic potential. The increases in revertants in these strains indicate that the type of damage induced was base pair changes, likely resulting from an indirect DNA damaging effect (i.e. oxidative damage) or potentially chromosomal type effects (with crossover of sensitivity with strain WP2uvrA and the chromosomal aberration study. Of note, thein vivo study returned no evidence of chromosomal effects).

Other Ames studies conducted back in 1997 and 1998 also returned positive results in the same strains at similar levels to the GLP study. These increases in revertants were due to the presence of N₂F₂. A higher, purifiedNF₃sample (1995) showed no evidence of mutagenic activity. This data suggests that the mutagenic response observed in the current Ames study was attributed to the presence of the impurity.

 

Mammalian chromosome aberration (in vitro)

Waiver requested as a robust,in vivo bone marrow mouse micronucleus study has been conducted.

 

Mammalian gene mutation (in vitro)

The mammalian gene mutation study conducted (Lee, 1997), confirmed thatNF₃did not increase the background mutant frequency of L5178Y cells when tested up to a concentration of 10% (v/v), deemed to be a maximum practicable concentration in both the absence and presence of S9 mix.

 

In vivobone marrow micronucleus

In the mouse bone marrow micronucleus study onNF₃(Baldwin & O’Loughlin, 1996) a single 4-h nose only exposure to the test material was undertaken with the bone marrow sampled at time points of 24, 48 and 72 h post dosing. Data from the 72 hour sample time has not been reported in this submission as this time point is inconsistent with current guidance (a later time point is only required when there is evidence of cell cycle delay – there was no evidence in this study [i.e. decrease in %PCE]). Data from the 24 and 48 hour sample time were in line with the guideline requirements. A negative result was obtained from this study, with a dose level considered to be the MTD due to proliferative effects on the bone marrow (i.e. evidence of erythropoiesis).

 

Genetic Toxicology Summary

These results together suggest thatNF₃does not cause genotoxicityviathe clastogenic / aneugenic endpoint. Concerns obviously result from the current GLP bacterial (Ames) study, where evidence of increases in revertants were observed. At concentrations where increases in revertants were observed in the GLP study these increases in the same strains were comparable to the data generated back in 1997 and 1998 in NF₃containing high levels of N₂F₂. Furthermore, when the Ames result is examined alongside the mouse lymphoma assay, it can be seen that no evidence of gene mutation was observed in mammalian cells. These data would suggest that NF₃ shows evidence of mutagenic activity in prokaryotic and not eukaryotic cells, resulting from high levels of impurities.

 

Due toNF₃oxidising potential, concerns are raised over its carcinogenic potential, not from direct DNA damage but rather due to its oxidising properties (resulting in depletion of free radical protective mechanisms).

Further supporting evidence in the form of Na fluoride (WHOP, 1984) reported that Na fluoride did not induce reverse mutations inS. typhimuriumeither in the absence or presence of S9. 

 

Under REACH for the registration of up to 1000 tons/annum the minimum requirements for the genetic toxicology endpoint are bacterial gene mutation assay,in vitromammalian gene mutation andin vitrochromosome aberration assay. In the absence of thein vitro chromosome aberration study, thein vivostudy fulfils this data gap. The available data for the clastogenic / aneugenic endpoint confirms thatNF₃does not induce genotoxicity through this mode of action. Regarding the gene mutation end point, the bacterial system returned positive results, whilst thein vitro mammalian study returned negative results. When these data are examined in conjunction with other fluoride containing compounds (which returned negative Ames data) the data are suggestive thatNF₃shows evidence of mutagenic activity in prokaryotic and not eukaryotic cells, with other fluoride containing compounds being devoid of mutagenic activity in bacteria. The overall conclusion from these data confirm under the requirements of this registration the genetic endpoint has been adequately addressed and this chemical is devoid of direct DNA damaging effects in eukaryotic cells.

Justification for classification or non-classification

Nitrogen trifluoride is considered not to interact directly with DNA. Therefore classification is not required.