3,5,5-trimethylhexyl acetate

Toxicity to aquatic algae and cyanobacteria

Description of key information

The growth rate of freshwater green algae exposed to the substance was inhibited. The 72-hour and 96-hour ErC50 values were greater than the highest concentration that could be maintained under test conditions (3.8 mg/L). The ErC10 after 72-hours was 0.65 mg/L (mean measured).

 

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

0.65 mg/L

Additional information

The effects of the test item 3,5,5-trimethylhexyl acetate on the growth of the freshwater green alga Pseudokirchneriella subcapitata were examined after 72 and 96 hours of exposure in a closed test system, according to OECD TG 201, EC No. L383 Method C.3 and OCSPP Number 850.4500.

Nominal concentrations were 1.0, 2.6, 6.4, 16 and 40 mg/L. All test solutions appeared clear and colorless and were otherwise unremarkable at test initiation. At test termination, there were no visible particulates or surface-slicks in any of the test chambers. Results of the study were based on geometric mean, measured test concentrations, calculated using the measured concentrations at 0, 24, 48, 72 and 96 hours of exposure, of 0.51, 1.2, 1.9, 3.0 and 3.8 mg/L, equivalent to 51, 46, 30, 19 and 10 % of nominal concentrations, respectively. The controls showed that the substance may adhere to the algae.

The toxicity of 3,5,5-trimethylhexyl acetate to P. subcapitata was determined by evaluating changes in cell density over a 72- and 96-hour exposure period. Cell densities of algae in exponential growth phase were used to determine area under the growth curve, growth rates and yield at 72 and 96 hours of exposure.

The 72-hour ErC50 value for growth rate was >3.8 mg/L. Reductions in area under the growth curve, growth rate and yield were statistically significant (Dunnett’s test; p < 0.05) in all treatment groups at 72 hours of exposure. The 72-hour NOEC was determined to be < 0.51 mg/L.

The 72 and 96-hour ErC10 values for growth rate were calculated as 0.65 and 3.3 mg/L, respectively.

After 96 hours of exposure, the ErC50 value for growth rate was >3.8 mg/L. Area under the growth curve was significantly reduced (Dunnett’s test; p < 0.05) in all treatment groups at 96 hours of exposure. The 96-hour NOEC was determined to be < 0.51 mg/L.

After 96 hours of exposure, there were no signs of noticeable aggregation or flocculation of cells in the negative or solvent control groups or in any treatment groups. Cells were not observed to be adhering to the test vessels in any of the experimental groups. P. subcapitata cells in the treatment levels and the solvent control appeared normal when compared to cells present in the negative control.