Tributyl(ethyl) phosphonium diethylphosphate

Endpoint summary

Description of key information

A DEREK assessment, a DPRA assay and in vitro KeratinoSens^TM assay were performed. Based on these data no conclusion could be drawn on the skin sensitisation of Tributyl(ethyl) phosphonium diethylphosphate. Based on the results of the LLNA Tributyl(ethyl) phosphonium diethylphosphate was concluded sensitizing to skin

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

A Weight-of-Evidence approach has been used to fulfill information requirements about skin sensitisation potential of the test substance. The weight of evidence approach was used according to Annex XI, sections 1.2-1.5, to the REACH Regulation.

The following studies were used:

- Using DEREK NEXUS version 6.0.1, the structure of the test item did not yield any alerts for skin sensitization of the test item.

- A valid DPRA test was performed according to OECD 442C guidance and following GLP principles. For the DPRA assay, Tributyl(ethyl) phosphonium diethylphosphate was dissolved in acetonitrile (ACN) at 100 mM and formed a clear solution without precipitates or phase separation by visual inspection. Since all acceptability criteria were met this DPRA is considered to be valid. In the cysteine reactivity assay the test item showed 0.8% SPCC depletion while in the lysine reactivity assay the test item showed 0.5% SPCL depletion. The mean of the SPCC and SPCL depletion was 0.5% and as a result the test item was negative in the DPRA and was classified in the “no or minimal reactivity class” when using the Cysteine 1:10 / Lysine 1:50 prediction model. Therefore, the test item was considered to be negative in the DPRA. 

- A valid KeratinoSens^TM assay was performed according to OECD 442D guidance and according to GLP principles. For the KeratinoSens^TMassay Tributyl(ethyl) phosphonium diethylphosphate was dissolved in DMSO to a final concentration of 200 mM. From this stock 11 spike solutions in DMSO were prepared. The stock and spike solutions were diluted 100-fold in the assay resulting in test concentrations of 0.98 – 2000 μM (2-fold dilution series). The highest test concentration was considered to be the maximum testable concentration based on solubility in DMSO and is the highest dose required in the current guideline. The test item precipitated at the dose level of 500, 1000 and 2000 μM in experiment 1 only. Two independent experiments were performed.

The test item showed toxicity (IC30 values of 1196 μM, 973 μM and 1426 μM in experiment 1, 2 and 3, respectively and an IC50 value of 1549 μM and 1810 μM in experiment 1 and 3). In the first experiment a biologically relevant induction of the luciferase activity (EC1.5 692 μM) was measured with a maximum luciferase activity induction (Imax) of 9.32-fold. This led to an individual run conclusion of positive. In the second experiment no biologically relevant induction of the luciferase activity (EC1.5 1061 μM) was measured and the maximum luciferase acitivity induction (Imax) was 4.30-fold, however the induction above 1.5-fold was only observed at concentrations with cell viability < 70%. This led to an individual run conclusion of negative. As the results of first and second experiment were not concordant an additional third experiment was conducted. In the third experiment a biologically relevant induction of the luciferase activity (EC1.5 719 μM) was measured with a maximum luciferase activity induction (Imax) of 9.51-fold. This led to an individual run conclusion of positive. Overall, the test item is classified as positive in the KeratinoSensTM assay since positive results (>1.5-fold induction) were observed in two out of three experiments at test concentrations with a cell viability of >70% compared to the vehicle control.

Interpretation and conclusion of the Weight-of-evidence:

Based on a negative DEREK NEXUS assessment, a negative DPRA assay and a positive KeratinoSens^TMassay, no conclusion could be drawn on skin sensitization properties of 1,3-bis(4 -hydroxy benzoyl) benzene. Performance of an additional in vitro assay, for example the U-SENS^TMassay, would not be sufficient for potency assessment in case the test were positive and in case of negative test, the results would not be sufficient to conclude. Therefore, a third in vitro study was omitted and an in vivo study (LLNA) was been performed to determine the skin sensitizing properties of 1,3-bis (4-hydroxy benzoyl) benzene. According to the result of the in vivo study, 1,3-Bis (4-hydroxy benzoyl) benzene was considered not to be a skin sensitiser.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

According to EU CLP regulation (Consolidated version 01 -01 -2017), skin sensitisers shall be classified in category 1 where data (human or animal data) are not sufficient for sub-categorisation. Current available data are in vitro/in chemico tests (DEREK Nexus assessment, in vitro DPRA test and in vitro KeratinoSens test) and one in vivo test (LLNA according to OECD 429 guidelines).

Based on the results of these studies, 1,3-Bis (4-hydroxy benzoyl) benzene is not classified and has no obligatory labelling requirement for sensitization by skin contact according to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) of the United Nations (2015) (including all amendments) and the Regulation (EC) No 1272/2008 on classification, labelling and packaging of items and mixtures (including all amendments).