Dipraseodymium tricarbonate

Endpoint summary

Additional information

In vitro gene mutation in bacteria (Ames)

The potential of the test material to cause mutagenic effects in bacteria was assessed in accordance with the standardised guidelines OECD 471 and EU Method B.13/14. Furthermore, the test method was designed to be compatible with the guidelines for bacterial mutagenicity testing published by the major Japanese Regulatory Authorities including METI, MHLW and MAFF and the USA, EPA (TSCA) OPPTS harmonised guidelines.

Salmonella typhimurium strains TA1535, TA1537, TA98, TA100 and Escherichia coli strain WP2uvrA were treated with the test material, using the plate incorporation and pre-incubation methods, at five dose levels, both with and without metabolic activation. The dose levels assessed were 50, 150, 500, 1500 and 5000 µg/plate.

The test material caused no visible reduction in the growth of the bacterial background lawn at any dose level and was, therefore, tested up to the maximum recommended dose level of 5000μg/plate. A test material film (opaque in appearance) was noted at and above 1500μg/plate with an associated precipitate observed at 5000μg/plate. Neither of these observations prevented the scoring of revertant colonies.

No toxicologically significant increases in the frequency of revertant colonies were recorded for any of the bacterial strains, with any dose of the test material, either with or without metabolic activation or exposure method.  

The vehicle controls gave revertant colony counts within the normal range. The positive controls gave the expected increases in revertants, validating the sensitivity of the assay and the efficacy of the S9-mix.

The test material was considered to be non-mutagenic under the conditions of this test.

In vitro cytogenicity in mammalian cells (read-across from praseodymium (III,IV) oxide)

The potential of the test material to induce chromosomal aberrations was investigated in vitro in accordance with the standardised guidelines OECD 473 and EU Method B.10.

Duplicate cultures of human lymphocytes, treated with the test material, were evaluated for chromosome aberrations at three dose levels, together with vehicle and positive controls. The dose levels used in all the experiments were 0, 5, 10, 20, 40, 80 and 160 µg/mL.

Four treatment conditions were used for the study:

In Experiment 1, cells were exposed for 4 hours in the presence of an induced rat liver homogenate metabolising system (S9 at a 2 % final concentration) with cell harvest after a 20 hour expression period and a 4 hour exposure in the absence of metabolic activation with a 20 hour expression period.

In Experiment 2, the 4 hours exposure period with addition of S9 was repeated (using a 1 % final S9 concentration) whilst in the absence of metabolic activation the exposure time was increased to 24 hours.

All vehicle controls had frequencies of cells with aberrations within the range expected for normal human lymphocytes.

All the positive control materials induced statistically significant increases in the frequency of cells with aberrations indicating that the sensitivity of the assay and the efficacy of the S9-mix were validated.

The test material did not induce any statistically significant increases in the frequency of cells with aberrations in the exposure groups dosed in the presence or absence of S9, which included at least one precipitating dose level.

Under the conditions of the study, the test material was considered not to induce any statistically significant increases in the frequency of cells with aberrations and, therefore was considered to be non-clastogenic.

In vitro gene mutation in mammalian cells (read-across from praseodymium (III,IV) oxide)

The genotoxic potential of the test material was assessed in an in vitro gene mutation assay with mammalian cells. The study was performed under GLP conditions and in line with the standardised guidelines OECD 476, EU Method B.17 and EPA OPPTS 870. 5300. Chinese hamster Ovary (CHO-K1) cells were exposed to the test material in two separate experiments. Both experiments were conducted with a 4 hour exposure period and a 7 day expression period, with and without metabolic activation. In experiment 1, metabolic activation was provided by 2% S9 mix, whereas 1% was used in experiment 2. Cultures were exposed to the test material at concentrations up to 5000 µg/mL in experiment 1 ± S9 mix as well as in experiment 2 with S9, and up to 3750 µg/mL in experiment without S9 mix.

Increases in mutant frequency of greater than 20 x 10^-6were seen in the 4-hour exposure group in the absence of S9 in Experiment 1 and Experiment 2. The test material did not induce any significant or dose-related increases in mutant frequency per survivor in the presence of metabolic activation (2 % S9) in Experiment 1 but did show a clear dose related response in Experiment 2 where a reduced S9 concentration (1%) was used.

Significant cytotoxic effects were observed at concentrations ≥ 1250 µg/mL in the absence of metabolic activation, producing reductions in cloning efficiency between 21 and 89%.

Therefore under the conditions of the test, the test material was considered to be mutagenic to CHO cells at the HPRT locus in the presence and absence of metabolic activation.

Summary

The genetic toxicity profile of the test substance currently remains ambiguous. A negative result was obtained in two of the key studies (the chromosome aberration study being read-across from praseodymium (III,IV) oxide), but a positive was obtained in the in vitro gene mutation in mammalian cells study in both the absence and presence of metabolic activation (also read-across from praseodymium (III,IV) oxide). In view of this, reference to a relevant in vivo study is required in order to confirm the genetic toxicity of the test material.

A testing proposal has been made to conduct a study in accordance with OECD Guideline 486 on praseodymium (III,IV) oxide (Unscheduled DNA Synthesis (UDS) Test with Mammalian Liver Cells in vivo). It is foreseen that the results of this study could potentially also be used as read-across to support praseodymium carbonate; this approach is currently under further consideration.

Justification for selection of genetic toxicity endpoint
Three studies have been selected as key to address the genetic toxicity endpoint. All are well reported guideline studies, conducted to GLP standard. The bacterial gene mutation assay was performed on the registered substance and was thus assigned reliability scores of 1 in accordance with Klimisch (1997). The mammalian cell cytogenicity and gene mutation assays were conducted on the read-across substance praseodymium oxide and were thus assigned a reliability score of 2 in line with Klimisch (1997).

Short description of key information:
In vitro gene mutation in bacteria (Ames): Harlan (2013): Negative with and without metabolic activation.
In vitro cytogenicity in mammalian cells (Chrom. Ab.): Harlan (2013) - Praseodymium oxide: Negative with and without metabolic activation.
In vitro gene mutation in mammalian cells (CHO HPRT): Harlan (2013) - Praseodymium oxide: Positive with and without metabolic activation.

Endpoint Conclusion:

Justification for classification or non-classification

It is not possible to classify the substance for genetic toxicity on the basis of in vitro data only. Therefore, in accordance with the criteria for classification as defined in Annex I, Regulation (EC) No. 1272/2008, at this time, the test material does not require classification for genetic toxicity.