Phenol, C14-18-alkyl derivs.

Toxicity to aquatic algae and cyanobacteria

Description of key information

72 h ErC50 and EyC50 > 100 mg/L WSF and 72 h NOEC (growth and yield) 100 mg/L WSF (Pseudokirchneriella subcapitata), OECD 201, EU Method C.3, ISO 8692 and OECD 23.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

100 mg/L

Additional information

In the key study, the toxicity of the test material to the freshwater green alga Pseudokirchneriella subcapitata was investigated in accordance with the standardised guidelines OECD 201, EU Method C.3, ISO 8692 and OECD 23 under GLP conditions.

The study was awarded a reliability score of 1 in accordance with the principles for assessing data quality set forth by Klimisch et al. (1997).

The batch of material tested was completely soluble in test medium at the concentrations tested. Preparation of test solutions for the final test started with the test concentration of 100 mg/L, applying two days of magnetic stirring to ensure maximum saturation was reached followed by a 22 hour settlement period. The clear and colourless Water Soluble Fraction (WSF) was then collected by means of siphoning and lower concentrations were prepared by dilution.

A final test was performed based on the results obtained in a preceding range-finding test. Six exponentially growing algal cultures were exposed to an untreated control and three replicates per group were exposed to 1.0, 3.2, 10, 32 and 100 % of a WSF prepared at a loading rate of 100 mg per litre. The initial cell density was 104 cells/mL. The total exposure period was 72 hours and samples for analytical confirmation of exposure concentrations were taken at the start, after 24 and 72 hours of exposure.

No significant differences were recorded between the values for growth rate or yield at any of the test concentrations when compared to the control group. The inhibition of yield in the lowest test group was significant but was not considered relevant as no inhibition was observed at any of the higher concentrations. Statistical analyses confirmed that the NOEC was at or above the concentration present in a WSF prepared at a loading rate of 100 mg/L. Microscopic observations at the end of the test revealed a normal and healthy appearance of the exposed cells when compared to the control.

The results of analyses should be taken with care and considered indicative. This was due to the fact that procedural recoveries at similar concentration levels ranged between 140 and 180 % and thus concentrations analysed might be a factor of 1.4 to 1.8 higher than the actual exposure concentrations. The Time Weighted Average (TWA) concentration was calculated to be 7.5 µg/L, which is just below the actual water solubility of 26 µg/L. If considering a worst-case approach and thus correcting for a factor of 1.8 (based on the higher procedural recoveries) the TWA is 4.2 µg/L with an initial exposure concentration at the study start of 22 µg/L, which approximated the water solubility.

Despite procedural recoveries being above the limits set by the guidelines it was concluded that the analysis confirmed that the actual exposure concentration in the WSF equalled the limit of solubility.

The study met the acceptability criteria and was considered valid.

Under the conditions of this study, no inhibition of growth rate or inhibition of yield was recorded at any of the concentrations tested. Both the 72 h ErC50 and EyC50 exceeded the average measured concentration in a WSF prepared at a loading rate of 100 mg/L.

The 72 h NOEC for growth rate inhibition and yield inhibition equalled the concentration in a WSF prepared at 100 mg/L.