2,2,5-trimethyl-5-pentylcyclopentan-1-one

Toxicity to aquatic algae and cyanobacteria

Description of key information

OECD Guideline 201, GLP, key study, validity 1:
72h-ErC50 (Pseudokirchneriella subcapitata) > 3.4 mg/L, the highest attainable test substance concentration over the study period; 
72h-ErC10 (Pseudokirchneriella subcapitata) = 1.7 mg/L (95% confidence interval: 1.4 - 2.0 mg/L).
72h-NOEC = 0.46 mg/L.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

0.46 mg/L

Additional information

One valid key study is available to assess the toxicity of the registered substance to aquatic algae.

The freshwater green algal Pseudokirchneriella subcapitata were exposed to the registered substance at concentrations of 1.0, 3.2, 10, 32 and 100% of a Water Soluble Fraction (WSF) prepared at a loading rate of 100 mg/L, during 72 hours under static conditions, according to OECD Guideline 201 with GLP statement. Three replicates were tested for each test item concentration and six replicates for the control. The test substance was known to be volatile and hence testing was conducted in sealed test vessels in order to minimize possible losses due to volatilization. In order to prevent inhibition of growth due to the restriction of gaseous exchange, additional sodium bicarbonate was added to the culture medium to provide a source of carbon dioxide for algal growth. At the start of the test, the actual test concentrations were 0.12, 0.36, 1.2, 3.7 and 12 mg/L in 1.0, 3.2,10, 32 and 100% of the WSF, respectively. These concentrations decreased to 3-5% of initial at the end of the test period. The lowest initial concentration of 0.12 mg/L decreased below the limit of detection (LOD=0.0049 mg/L) at the end of the test. Based on these results, the TWA concentrations were calculated to be 0.037, 0.12, 0.46, 1.3 and 3.4 mg/L (28-51% of initial). The two lowest test concentrations were not needed and therefore not used for the calculation of the EC-values. Growth rates were in the range of the control at concentrations up to and including 0.46 mg/L during the 72-hour test period, whereas the growth rate of algae exposed to 1.3 and 3.4 mg/L were increasingly reduced. Statistically significant inhibition of growth rate was found at test concentrations of 1.3 mg/L and higher. Microscopic observations at the end of the test revealed a normal and healthy appearance of the exposed cells when compared to the control.

In conclusion, under the test conditions, test item inhibited growth rate of this fresh water algae species at a TWA concentration of 1.3 mg/L and higher although the 72h-ErC50 was >3.4 mg/L (24% effect at this concentration) the highest achievable concentration averaged over the test period despite precautions being taken; the 72h-ErC10 could be statistically obtained and was 1.7 mg/L with a 95% confidence interval ranging from 1.4 to 2.0 mg/L, and the 72h-NOECr was 0.46 mg/L.