2,4,6-tri-tert-butylphenol

Toxicity to aquatic algae and cyanobacteria

Description of key information

The 72 h NOEC for both growth rate inhibition and yield inhibition was determined to be >0.040 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

0.04 mg/L

Additional information

There are two studies available to address this endpoint, one key and one supporting.

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 and the Guidance document on aquatic toxicity testing of difficult substances and mixtures, OECD series on testing and assessment number 23 under GLP conditions. The study was assigned a reliability score of 1 in line with the principles for assessing data quality as defined by Klimisch et al. (1997).

Following a combined limit/range-finding test, a full test was performed. The test material was not completely soluble in test medium at the loading rate initially prepared. A Water Soluble Fraction (WSF) was prepared at a loading rate of 100 mg/L and used as the highest concentration. The lower test concentrations were prepared by subsequent dilutions of the highest concentration in test medium. The final test solutions were all clear and colourless.

Six exponentially growing algal cultures were exposed to an untreated control, whereas three replicates per group were exposed to solutions containing 1.0, 3.2, 10, 32 and 100 % WSF. 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. As the test material was potentially volatile, the exposure was performed in airtight closed vessels, with headspace reduced to minimum and adjusted M2 medium. 

Samples taken from all groups were analysed. The actual concentrations in the two lowest groups were below the limit of detection at the start of the test. The concentrations measured in the 10, 32 and 100 % WSF increased with the applied dose. At the end of the test no concentration could be detected in the 10 % WSF. The concentrations measured in the 32 and 100 % WSF were at the level of 56 and 21 % of initial at the end of the test, respectively. Based on these results, the Time Weight Average concentrations calculated for the two highest concentrations were 0.019 and 0.040 mg/L for the 32 and 100 % WSF, respectively.

The EC50 for growth rate inhibition (72 h ErC50) and the EC50 for yield inhibition (72 h EyC50) was beyond the range tested, i.e. exceeded a TWA concentration of 0.040 mg/L (considered the maximum soluble in test medium).

Under the conditions of the study, the 72 h NOEC for both growth rate inhibition and yield inhibition was >0.040 mg/L. Due to the very low solubility of the test material in water, concentration levels that might be toxic for algae could not be reached.

 

In the supporting study, the toxicity of the test material to green algae was estimated using the ECOSAR model v1.11 (EPI Suite v4.11). The study was assigned a reliability score of 2 in line with the principles for assessing data quality as defined by Klimisch et al. (1997).

The structure-activity relationships (SARs) presented in this program are used to predict the aquatic toxicity of chemicals based on their similarity of structure to chemicals for which the aquatic toxicity has been previously measured. Most SAR calculations in the ECOSAR Class Program are based upon the octanol/water partition coefficient (Kow). The toxicity of the test material to green algae was estimated using the Phenols class of ECOSAR. The molecular weight of the test material is within the training set range.

The estimated 96 hour EC50 was 0.134 mg/L.