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Ecotoxicological information

Short-term toxicity to fish

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Description of key information

LC50 value for surrogate substance (DPGEE)  > 200 mg/L. by measurement, 6200mg/l by QSAR.

LC50 value for surrogate substance (PGME) = 6812mg/l by measurement, 12700mg/l by QSAR

LC50 value for surrogate substance (PGBE): 560-1000mg/l by measurement, 890mg/l by QSAR

LC50 value by QSAR = 5300

Key value for chemical safety assessment

LC50 for freshwater fish:
5 300 mg/L

Additional information

There is no measured data available on this substance but there is measured data on a number of 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 fish of this substance.

In a guideline (OECD 203) and GLP acute fish toxicity study (96 -hr; flow-through), exposure of zebra fish to dipropylene glycol monoethyl ether at concentrations up to 200 mg/L did not cause lethality. Based on these findings the acute LC0 for DPGEE is considered to be greater than 200 mg/L. These results for DPGEE are considered to be a useful surrogate for predicting the likely effects of the submission substance, ethoxypropanol (propylene glycol monoethyl ether).

In a guideline study cited, the 96 -hr LC50 of methoxypropanol (a close structural analogue of ethoxypropanol) in fathead minnows was reported to be 6812mg/L. It should be noted that this is the lowest LD50 value available for this substance and values have been reported >10000mg/l.

In a GLP guideline study, young Poecilia reticulata (guppies) were exposed for 96 hours to nominal concentrations of 0, 100, 180, 320, 560, or 1000 mg/liter of propylene glycol butyl ether. No mortality was observed at concentrations up to and including 560 mg/liter. Mortality occurred only at the highest concentration tested. At 1000 mg/liter, no fish survived the entire 96-hour exposure period.  No clinical signs were observed at concentrations of 180 mg/liter or less. At 320 mg/liter, all guppies showed an inhibition of swimming ability and some showed increased pigmentation. At 560 mg/liter, all subjects showed increased pigmentation and reduced swimming ability at all time points. Swimming ability was progressively inhibited with time to the point of immobilization and in a progressively increasing proportion of the subjects over the exposure period; touching the caudal peduncle stimulated reaction.  In survivors at any concentration, no loss of equilibrium was observed. In the negative control, mortality was zero and no clinical signs were observed. The 96 h EC50 was between 180 and 320 mg/l. The No Observed Effect Concentration (NOEC) was 180 mg/l. The 96 h LC50 was between 560 and 1000 mg/l.

In addition, the measured data is supported by information from the US EPA ECOSAR software (v1.11), which predicts the 96 -hr fish LC50 for ethoxypropanol to be 5300 mg/L, based on structure activity relationship models for neutral organic compounds. Estimates for the surrogate materials using the same QSAR were 12700mg/l for methoxypropanol, 6200mg/l for dipropylene glycol monoethyl ether and 890mg/ml for propylene glycol butyl ether, suggesting that the model is consistent with and likely more conservative than experimental results. 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 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 fish 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 LC50 for ethoxypropanol in fish is likely to be >> 200 mg/L and more likely >1000mg.l. The value from the QSAR is taken as a predictor of the actual LC50 in fish.

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