3-methyl-5-(2,2,3-trimethyl-3-cyclopenten-1-yl)pent-4-en-2-one

Toxicity to aquatic algae and cyanobacteria

Description of key information

The toxicity of Ebanone to the freshwater algae Pseudokirchneriella subcapitao is estimated to give a 72-Hour growth rate EC50 value of 24 mg/l based on read-across from an appropriate structural analogue.

Key value for chemical safety assessment

EC50 for freshwater algae:

24 mg/L

Additional information

An appropriate structural analogue (3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pent-4-en-2-ol), tradename Ebanol, has been tested for toxicity to aquatic algae. Exposure of Pseudokirchneriella subcapitata to the test material gave the following results based on the nominal test concentrations:

TiPoint (Hours)	Response Variable	EC50 (mg/l)	95% Confidence Limits (mg/l)			No Observed Effect Concentration (NOEC) (mg/l)	Lowest Observed Effect Concentration (LOEC) (mg/l)
72	Growth Rate	24		*		3.1	9.9
	Yield	13	12	-	15	9.9	31
	Biomass	13	12	-	15	3.1	9.9
96	Growth Rate	26		*		3.1	9.9
	Yield	13	11	-	14	3.1	9.9
	Biomass	13	11	-	15	3.1	9.9

*It was not possible to calculate 95% confidence limits for the ErC5 0values as the data generated did not fit the models available for the calculation of confidence limits.

Analysis of the test preparations at 0 hours showed measured test concentrations to be near nominal with the exception of the 0.31 and 3.1 mg/l test concentrations which showed measured test item concentrations of 164% and 133% of nominal respectively. Analysis of duplicate samples which had been stored frozen confirmed these results (127% and 136% of nominal respectively). A significant decline in measured test concentration was observed at 96 hours in the range of less than the limit of quantitation (LOQ) of the analytical method employed (which was determined to be 0.017 mg/l) to 3% of nominal.

Given that the results obtained from the preliminary stability analyses and additional stability analyses conducted under test conditions indicated that the test item was stable over the test period this decline was considered to be due to adsorption to the algal cells present. Whilst the preliminary recovery analyses conducted in the presence of algal cells indicated that no significant adsorption occurred this does not preclude long term adsorption over the test period to the increasing algal biomass. Given that the decline in measured concentrations was attributable to adsorption of the test item to the algal cells present it can be considered that the algae were exposed to near nominal test item concentrations for the duration of the test. As such it was considered appropriate to calculate the results based on nominal test item concentrations alone.

A re-growth test was performed which showed the test item to be algistatic but not algicidal in effect.

The study met the acceptability criteria prescribed by the Study Plan and hence was considered valid.

The preferred observational endpoint in this study is algal growth rate inhibition because it is not dependent on the test design (ECHA guidance Chapter R.7b v1.1). Since exponential growth occurred throughout the test duration of 96 hours the ErC50 values at 72 hours (24 mg/L) and 96 hours (26 mg/L) are equally valid. The lowest effect value of 24 mg/L has been used for the chemical safety assessment.

The aquatic toxicity of the analogue test substance (Ebanol) is anticipated to be similar to that of Ebanone. They are expected to exhibit the same mode of action, non-polar narcosis, and have similar physical-chemical properties (see read-across justification document in section 13 for more details). Therefore, the EC50 of Ebanone is also considered to be 24 mg/L.