Urea phosphate

Endpoint summary

Additional information

Urea phopshate dissociated directly into urea and phosphoric acid in aqueous environment.

Genotoxicity in vitro

Ames test

Urea

The mutagenicity of urea was determined in the Ames test using Salmonella typhimurium (TA 1535, TA 1537, TA98, TA100, TA 1538) and Escherischia coli (WP2 uvr A), with and without S9 metabolic activation. The substance was not mutagenic at any of the 7 concentrations tested (Shimizu et al, 1985).

Phosphoric acid

Harlan Laboratories Ltd (2010) performed a bacterial reverse mutation assay (Ames test, conform OECD 471, EC B.13/14, JMAFF, EPA guidelines) in Salmonella typhimuriumstrains TA1535, TA1537, TA98, TA100 andEscherichia colistrain WP2uvrA- with and without metabolic activation. The dose range was determined in a preliminary toxicity assay and was 50 to 5000 µg/plate in the first experiment. The experiment was repeated on a separate day (pre-incubation method) using the same dose range as experiment 1, fresh cultures of the bacterial strains and fresh test material formulations. Phosphoric acid tested negative with and without metabolic activation.

Clastogenicity

Urea

Ishidate et al (1981) report the results of a chromosomal aberration assay performed in CHL cells with a number of chemicals, including urea. Approximately 10e5 cells were plated and exposed to concentrations of urea up to the concentration causing 50% growth inhibition, in the absence and presence of PCB-induced Wistar rat liver S9-fraction. Cells were harvested at 24 and 48 hours (-S9) or at 24 hours following a 3-hour pre-incubation step (+S9). Chromosomal aberrations (including numerical aberrations) were scored from 100 well-spread metaphases per concentration. A positive result is reported in this assay, however the DT20 value (the concentration at which 20% of cells or approximately 4x background) of 13.0 mg/mL or 216 mM is well in excess of the limit concentration of 5 mg/ml or 10 mM recommended by OECD 473 (1997). The authors note a very low clastogenic potential. Considering the high concentrations of urea required to produce a response in this assay, which are well in excess of the limit concentration, it cannot be concluded that urea is clastogenic. The finding in this study is very likely to be a false positive due to osmotic effects.

Diammonium hydrogenorthophosphate

In an vitro chromosome aberration test with CHO cells performed according to OECD 473 guideline, also no genotoxicity was seen with and without metabolic activation, while cytotoxicity was present.

Mammalian cell mutation

Urea

The potential mutagenicity of urea was investigated in a mouse lymphoma assay in the absence of metabolic activation. A weak positive response was seen at concentrations of 265 -662 mMol/L, concentrations which also caused cytotoxicity and which are well in excess of the limit concentration of 10 mMol/L recommended in OECD 476 (1997). The result is considered to be a false positive. The authors conclude that the effect is due to the influence of high concentrations of urea on the osmolarity of the culture medium (Wangenheim & Bolcsfoldi, 1988).

Phosphoric acid

Harlan Laboratories Ltd (2010) performed a mouse lymphoma assay according to the UK Environmental Mutagen Society guidance which is equivalent/similar to OECD Guideance 476 and EU method B.17. Concentrations of 0, 61.25, 112.5, 245, 490, 735 and 980 µg/mL were tested on the L5178Y TK+/- 3.7.2 c mouse lymphoma cell line. Solvent control and positive control (ethylmethanesulphonate without metabolic activation and cyclophosphamide with metabolic activation) were tested simultaneously. Phosphoric acid was found to be negative with (4 hours of exposure) and without metabolic activation (4 and 24 hours of exposure). Cytotoxicity was very modest: no evidence of any reductions in viability was observed. Therefore, no residual toxicity occured.

Genotoxicity in vivo

No studies available nor required.

Conclusion

Positive results obtained in vitro are associated with concentrations well in excess of the recommended limit concentrations are not considered to be of biological relevance. Considering the physiological role and presence of substantial quantities of urea in the human body, it is not considered likely that this substance is genotoxic. Further testing for genotoxicity is not proposed.

Short description of key information:
Urea phosphate will directly dissociate into urea and phosphoric acid in aqueous environment.
Both substances show negative results in Ames tests. Diammonium hydrogenorthophosphate is also negative in a chromosome aberration study. Urea shows positive results in assay for mutagenicity and clastogenicity in mammalian cells, however the value of this study is limited by the extremely high test concentration. Phosphoric acid and urea were both negative in an MLA assay. Based on the physiological role and presence in the body at high concentrations of urea, ureaphosphate is not considered to be genotoxic.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on all available data, urea phosphate does not have to be classified according to Directive 67/548/EEC and the CLP Regulation for genotoxicity.