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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Description of key information

48hr EC50 value for surrogate substance propylene glycol butyl ether: measured >1000mg/l, QSAR: 460mg/l

48hr EC50 value for surrogate substance propylene methyl ether: ~23000mg/l, QSAR: 5700mg/l

QSAR value for ethoxypropanol: 2500mg/l

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
5 000 mg/L

Additional information

There is no measured data available on this substance but there is measured data on two closely related substances and there is a reliable QSAR that can also be used and together these allow interpolation to be used to predict with some confidence the likely toxicity to daphnia of this substance.

In a GLP study, the 48 -hr EC50 of methoxypropanol (a close structural analogue of ethoxypropanol) in Daphnia magna was measured to be 23,300 mg/L.

In a GLP guideline study, Daphnia magna less than 24 hours old were exposed for 48 hours to concentrations of 0, 0.01, 0.1, 1, 10, 100, or 1000 mg/liter water of propylene glycol butyl ether (PnB). No immobilization occurred at PnB concentrations of 560 mg/liter or less. 10% of the daphnia exhibited immobilization when exposed to the highest concentration of 1000 mg after 48 hours. The 48-hour EC50 is greater than 1000 mg/liter.

In addition, the measured data is supported by information from the US EPA ECOSAR software (v1.11), which predicts the 48hr daphnia EC50 for ethoxypropanol to be 2500 mg/L, based on structure activity relationship models for neutral organic compounds. Estimates for the surrogate materials using the same QSAR were 5700mg/l for methoxypropanol and 460mg/ml for propylene glycol butyl ether, suggesting that the model is consistent with and likely more conservative than experimental results, probably by a factor of between ~2 to 5. The mode of action of this substance is likely to be non-polar narcosis (see overall summary to chapter 6.1 for further information.) This means that toxicity is likely to be linked with the partition coefficient. This would suggest increasing toxicity with increasing length of the alkyl group and decreasing toxicity with increasing number of PO units in the molecule. This is reflected in the QSAR results and the measured values available are consistent with this trend. The QSAR can be considered highly reliable and conservative in predicting relative toxicity.

According to annex XI of the REACH regulation, testing for this substance does not appear to be scientifically necessary for the following combined reasons:

  • Through a grouping approach, there is adequate measured data available on similar substances that allow interpolation within the group to predict the acute daphnia toxicity of the substance that is the subject of this registration. The grouping approach is fully justified in a document attached to chapter 13 of the lead company registration dossier. The approach fully meets the requirements of annex XI.
  • Results are available from a valid QSAR model which fully meets the requirements of annex IX. The QSAR can be used to support the interpolation from the measured data on surrogate substances.

These results consistently indicate that the acute EC50 for ethoxypropanol to daphnia is clearly >1000mg/l. The value from the QSAR increased by a factor of 2 is taken as a predictor of the EC50 in daphnia.

An extensive justification for read across is contained in the read across justification attached to chapter 13 of this dossier.