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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

NOEC = 0.179 mg/L (based on the solid content of the test item). 
NOEC = 0.28 mg/L (based on the Proban STi included water).

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
0.179 mg/L

Additional information

No study on the activated sludge inhibition is available for the substance. However, a study performed according to OECD 303A is available (Stewart, 2007 reported in the section 5.2.2 of IUCLID 5 : Biodegradation in water and sediment: simulation tests). No toxicity to the micro organism population has been observed in this test. Therefore, the concentration used for the test (i.e. 0,179 mg/L) can be considered as a NOEC.

To assess the suitability of this NOEC value, results obtained on two analogue substances are used as a read across approach (see "read across justification" in the section 4 and 5 for explanation). Three experimental studies performed according to OECD Guideline n° 209 are available and the results obtained are described below.

Two studies were carried out with Proban CC, a structural analogue of the Perform STi. In the first study (Handley, 1992), the EC50 3h was 74 mg/L and in the second study (Mead, 1994), the EC50 3h was 190 mg/L. No NOEC values are reported in these studies, but based on the respiration inhibition observed, NOEC values of 5,6 mg/L and 100 mg/L can respectively be considered.

The third study (Croudace, 1995) was carried out with ITC 826, another structural analogue of the Perform STi. The NOEC 3h reported in this study was 10 mg/L.

 

The NOEC values obtained in activated sludge respiration inhibition studies performed on two structural analogue substances are at least 300 times higher than the NOEC of the substance deduced from an OECD Guideline 303A study. Therefore, it can be considered that this NOEC can be used as a worst case value for the derivation of the PNEC for STP. Additionnally, this NOEC value is considered as sufficiently protective to apply an assessment factor equal to 1 to derive the PNEC in accordance with the ECHA guidance R10. This approach gives a PNECSTP of 0,179 mg/L.

 

For comparaison, the PNECSTP determined for the two structural analogue substances, considering the above toxicity results, are the following:

-    Proban CC: PNECSTP = 0,74 mg/L and 1,9 mg/L (based on EC50 value)

- Proban CC : PNECSTP= 0,56 mg/L and 10 mg/L (based on NOEC value)

-    ITC 826: PNECSTP = 1 mg/L

 

Conclusion

The PNECSTP value determined for the three structural analogue substances are in same order of magnitude or above, with the value of 0,179 mg/L being the lowest one. Therefore, the PNECSTP of 0,179 mg/L is considered as a relevant worst case value for the substance.