4-isopropyl-m-cresol

Endpoint summary

Additional information

For acute effects:

The 48 h-EC50 for test item to Daphnia magna is between 3.7 based on a High Accuracy QSAR and 9.2 mg/L based on a laboratory study using the geometric means of the exposure concentrations. A third study, rated K4 as non-GLP and conducted after 2008 but otherwise well conducted, was also included in the mean calculation as it's 48h EC50 value of 5.7 mg/L fitted well with the other two data points. As the experimental data are very close to the predictions, the supporting experimental data are used to calculate a mean value of the studies. The mean 48 h EC50 to be used in risk assessment for this endpoint is 6.2 mg/L.

A validated High Accuracy QSAR value for acute toxicity of parathymol to fish resulted in a 96 h LC50 of 4.7 mg/L. The 96-hour LC50 for test item was 7.6 mg/L with 95% CI: 6.6–8.7 mg/L based on the geometric means of the exposure concentrations in a non-GLP study that can only be used as supporting evidence. As the experimental data are very close to the predictions, the supporting experimental data are used to calculate a mean value of the studies.The mean 96 h LC50 to be used in risk assessment for this endpoint is 6.15 mg/L.

A validated High Accuracy QSAR value for acute toxicity of parathymol to algae resulted in a 72 h ErC50 of 8.8 mg/L.

In a non-GLP study conducted in 2013 that can only be used as supporting evidence for the QSAR, the test item was found to inhibit the growth of the freshwater green algae Pseudokirchneriella subcapitata with the following effect values (geometric mean measured test item concentrations): the EC50 value after 72 h was 7.4 mg/L (95% CI: 6.8–8.3 mg/L). As the experimental data are very close to the predictions, the supporting experimental data are used to calculate a mean value of the studies.

The mean 72 h ErC50 to be used in risk assessment for this endpoint is 8.1 mg/L

The toxicity of an analogue substance to activated sludge was investigated according to OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test). 3h EC50 of 39.6 mg/L was observed (Bayer AG, 1986). Based on chemical similarity (isomers withdifferent position of the alkyl group), no significant difference is anticipated with the present dossier substance, so the read-across is considered justified.

For chronic effects

Three chronic data are available for parathymol. While none of the studies appear to have been conducted according to GLP and the results cannot be considered valid directly under the REACH Regulation as the studies were conducted after 2008, the studies are still considered technically valid as the acute values from the same publication are extremely close to the predicted values from a High accuracy QSAR.Furthermore parathymol is a polar narcotic and thus unexpectedly low effects on test organisms are not anticipted..

Thus, a weight of evidence approach is used to determine a PNEC for this substance, as follows:

1) The chronic studies are of acceptable quality for use in risk assessment except they were performed after 2008 and not under GLP. If these studies had been performed prior to the 2008 deadline for GLP studies under REACH, they would have been considered valid with restrictions (K2)and fit for use under REACH.

2) Three acute studies from the same publication are available and are in strong agreement with High Accuracy QSAR predictions (all well within a factor of 2 of the predictions) so there is no reason to expect methodological issues that would render the chronic studies unsuitable for use;

3) the substance is a polar narcotic and therefore no specific mode of action is expected that would lead to unexpectedly lower NOECs for other species).

4) A 9 day long term study was used for fish following OECD 2012 instead of a full Early Life Stage study. Nevertheless, the Guideline states that for chemicals with a non-specific, narcotic mode of action smaller differences in sensitivity between the OECD 210 and 212 woudl be expected. Due to the high water solubility and low lof Kow of the test material, the substance is expected to have reached equilibrium within the test period and therefore the 9 d study can be considered adequate to indicate chronic effects using this sub-lethal endpoint.

5) The lowest NOEC in both acute and chronic studies was for daphnids but in both acute and chronic tests, the difference between the three species is not large (<2.5 times between the most and least sensitive species).

The NOEC value for growth inhibition of the freshwater green algae Pseudokirchneriella subcapitata after 72 h was 2.5 mg/L.The 8-day NOEC from a test performed on C. dubia was determined to be 1.07 mg/L for both reproduction and for the survival of the adult test animals.The 9 day NOEC for hatching and the survival of fish larvae was 1.5 mg/L based on the geometric means of the exposure concentrations. Therefore the lowest NOEC of 1.07 mg/L for C. dubia has been taken to determine the PNEC.