2-(isopropylthio)-3-(2,2,2-trifluoroethoxy)pyridine

Toxicity to aquatic algae and cyanobacteria

Key value for chemical safety assessment

EC50 for freshwater algae:

5.6 mg/L

EC10 or NOEC for freshwater algae:

2.06 mg/L

Additional information

The growth inhibition of ITTFEP (purity 82.3 %) to Pseudokirchneriella subapitata was determined in a 72 h static GLP algae growth inhibition test (Maetzler, 2001). The test design was based on the OECD 203 guideline and the EU method C.3.Since the study was performed under GLP and according the guideline and based on the good documentation the study was awarded with Klimisch 2 since one of the three validity criteria of the updated guideline was just not met. However, the results are considered acceptable for the risk assessment.

The nominal test concentrations were Control (0), 4.3, 9.4, 21, 45 and 100 mg test item/L. The mean measured concentrations were 0 (control),control, 2.54, 5.38, 12.12, 21.94 and 55.31 mg test item/L, corresponding to mean measured 0 (control), 2.09, 4.43, 9.97, 18.06, and 45.52 mg ITTFEP/L.

Six control replicates and 3 replicates from each test solution were set up. Dose verification analysis was performed. In order to determine the growth of the cultures, the cells were counted electronically. The test was started with 10000 cells/mL. The cell density was determined at 24, 48 and 72 hours. The growth of the control cultures fulfilled not all validity criteria from OECD 201 (2006).

The CV Average specific growth rate and the CV Average specific growth rate were fulfilled. The criterion for the CV Average specific growth rate was not fulfilled (to be valid CV < 35%, actual CV 36%). The value is close to the validity criterion but have not met it. When looking on the section to section specific growth rates, it becomes obvious that the 0 -1 day section has the lowest growth rate (about 0.78/d when compared to about 1.2/d during the other days). It might be speculated that the initial cell density was lower than expected or that the cells were not in the exponential growth phase. The uncertainty of the initial cell density was reported with +/- 10%. Assuming that the cell density was 3 % lower than the expected cell density would shift the validity criterion to valid. Based on these considerations, the test results are considered as relevant for the risk assessment even if not all of the validity criteria of the updated guideline were fulfilled.

The 72 -hour NOEC, ErC10 and ErC50 are 2.06, 2.63, and 5.60 mg ITTFEP/L based on the mean measured concentration.

The obtained results are considered as relevant for the risk assessment.