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Key value for chemical safety assessment

Genetic toxicity in vivo

Description of key information

Hazards identified by EU Risk Assessment in May 2008:
Overall, it is considered that TCPP is not genotoxic in vivo

Additional information

Hazards identified by EU Risk Assessment in May 2008:

"The mutagenic potential of TCPP has been well investigated in vitro. Evidence from several bacterial mutagenicity studies shows that TCPP is not a bacterial cell mutagen. TCPP was also shown to be non-mutagenic in fungi. In mammalian cell studies, TCPP did not induce forward mutations at the TK locus in L5178Y mouse lymphoma cells in one study, but in a second study, the result was considered equivocal (in the presence of rat liver S9 fraction). A confirmatory mouse lymphoma was conducted in accordance with the relevant regulatory guidelines. The results of the assay indicate that TCPP shows clastogenic activity in vitro in the presence of metabolic activation. In one GLP study, TCPP did not induce unscheduled DNA synthesis in vitro. Two other in vitro UDS studies are reported. In one, TCPP gave a negative result; in the second, the result is considered equivocal. In an in vitrotransformation assay, TCPP was seen to induce transformed foci in BALB/3T3 cells, whereas in another similar study, it did not. As indicated above, the results of the most recent in vitro mouse lymphoma assay were positive. In particular in this study, there was a clear increase in the proportion of small colony mutants, giving rise to concern for a possible clastogenic effect of TCPP. Due to this positive study, industry proceeded to carry out the above-mentioned in vitro/in vivo UDS assay to further investigate the mutagenic potential of TCPP in vivo. In this study, statistically significant increases in NNG and a dose response effect at one time point were observed. However, as the counts did not exceed zero at either of the doses tested, the biological significance of the effect is doubtful and thus the result is considered equivocal. The main concern for TCPP is clastogenicity, owing to the clearly positive in vitro mouse lymphoma study. The UDS assay is not considered to be the most appropriate test for investigating a potential clastogen, as clastogenic substances are not expected to be efficient at inducing unscheduled DNA synthesis. In vivo, TCPP was not clastogenic in a mouse bone marrow micronucleus test. TCPP did not induce an increase in chromosomal aberrations in a rat bone marrow cytogenetics assay. However, there were some shortcomings in these studies and it is considered that they do not fulfil all current regulatory guidelines as described in the study summaries in 4.1.2.7.2. Therefore, in order to investigate the potential for TCPP to induce DNA damage, an in vivo Comet assay in the rat liver was conducted. The liver was chosen for comet analysis as TCPP caused an increased mutation frequency in the mouse lymphoma assay in the presence of S9 and also induced liver enlargement in repeat dose studies. Under the conditions of this study, TCPP did not induce DNA damage in the liver of rats treated with either 750 or 1500 mg/kg TCPP. Overall, it is considered that TCPP is not genotoxic in vivo."

For detailed information of studies mentioned in the Summary of the EU RAR (see above) but not in Table 5.7.1.1 or 5.7.1.2. of the CSR see Iuclid chapter 7.6.1 and 7.6.2.

 

Updated relevant information (March 2018):

Tris(chloropropyl)phosphate (M20263) [= TCPP] is on the Testing List of the National Toxicology Program (NTP) with, amongst others, peripheral blood micronucleus tests in rats and mice. According to NTP these studies are completed, but up to now only visible in table form, see description below.

http://ntp.niehs.nih.gov/testing/status/agents/ts-m20263.html

Preliminary results obtained in a peripheral blood micronucleus tests on rats were reported on the NTP-webpage. The study was included in a rat NTP 13-week toxicity study as part of the bioassay program. At the end of the 13-week exposure period (route of exposure: dosed-feed) a blood sample was obtained from male and female rats in each dose group (5 animals per treatment group per sex). 1000 to 10000 mature erythrocytes (normochromatic erythrocytes or NCEs) were scored per animal for presence of micronuclei. Doses of 1250 up to 10000 ppm for male rats and 20000 ppm for female rats were tested. There is no information available yet on the actual ingested doses.

The test result was negative for male and female rats and thus TCPP was shown to be not mutagenic in the peripheral blood micronucleus test in rats.

Preliminary results obtained in a peripheral blood micronucleus tests on mice were also reported on the NTP-webpage. The study was included in a mouse NTP 13-week toxicity study as part of the bioassay program. At the end of the 13-week exposure period (route of exposure: dosed-feed), a blood sample was obtained from male and female mice in each dose group (5 animals per treatment group per sex). 1000 to 10000 mature erythrocytes (normochromatic erythrocytes or NCEs) were scored per animal for presence of micronuclei. Doses of 1250 up to 20000 ppm were tested in both sexes. This corresponds to actual ingested doses of about 500, 1000, 2400 and 4500 mg/kg bw/day for males and 450, 900, 1800, and 3500 mg/kg bw/day for females according to a rough calculation from the tables shown.

The test result was clearly negative for female mice. In male mice the mean frequency of micronucleated polychromatic erythrocytes (MN PCEs)/1000 PCEs was 3.2 in the high-dosed animals compared to 2.6 in the control group. The high-dosed animals showed a range of MN PCEs of 2.5 to 3.7 with a statistical significance of p<0.05. The range of MN PCEs in the control animals was 2.2 to 3.2, i.e. that the ‘positive’ mean of 3.2 is within the control range and thus is only a very slight effect with questionable biological relevance. In the clearly ‘negative’ dose-group of 5000 ppm the MN-PCE range was 1.8 to 3.8 (mean 2.5). Additionally the high-dosed animals showed distinct signs of toxicity at this dose (body weight 25% lower than control males; liver and kidney toxicity). The slightly increased frequency of MN PCEs in male mice only is thus considered to be of minor relevance. For a final assessment the historical control data of the laboratory are requested. An FOIA request was send to NTP in February 2018 to get the historical control data for rat and mice peripheral blood micronucleus assays.

Justification for classification or non-classification

EU Risk Assessment of 2008: Based on the available studies, TCPP needs no classification for mutagenicity according to EU guidelines.

Update March 2018: The conclusion of non-classification for mutagenicity is confirmed and compliant with EU Regulation 1272/2008.