Propanoic acid, 2-hydroxy-, (1R,2S,5R)-5-methyl-2-(1-methylethyl)cyclohexyl ester, (2S)-

Toxicity to aquatic algae and cyanobacteria

Description of key information

No valid study for menthyl lactate is available. Therefore read-across to the structural very similar menthyl acetate was done. Based on experimental data obtained for menthyl acetate, the EC50 growth rate was determined to be 3.11 mg/L for menthyl lactate. The EC10 growth rate is 0.7 mg/L, the NOEC growth rate is 0.18 mg/L. 

Key value for chemical safety assessment

EC50 for freshwater algae:

3.11 mg/L

EC10 or NOEC for freshwater algae:

0.7 mg/L

Additional information

A valid study on algal toxicity with menthyl lactate is not available. Therefore read-across to the structural very similar menthyl acetate was done. The influence of the menthyl acetate racemic on the growth of the freshwater green algal species Pseudokirchneriella subcapitata was investigated in a 72-hour static test according to the OECD Guideline 201 (2006) and the Commission Regulation (EC) No 761/2009, C.3. The preparation of the test media was based on the OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures, 2000. At the start of the test, the analytically determined concentrations of Menthyl Acetate racemic in the test media were 0.0368, 0.127, 0.35, 1.27, 4.12 and 13.2 mg/L, respectively. During the test period of 72 hours, a decrease of test item concentration in the test media occurred. At the end of the test, the measured test item concentrations in the test media with algae (dilutions 1:320 to 1:3.2) were below the Limit of Quantification (LOQ=0.0218 mg/L). In the undiluted filtrate with algae, 12.5 mg/L was found. Additionally, the test media were incubated over the test duration, but without algae. The measured test item concentrations in the test media without algae (dilutions 1:320 to 1:3.2) were below the LOQ. In the undiluted filtrate without algae, 9.2 mg/L was found. Therefore the losses in the test media with algae during the test period were not considered to be due to adsorption of the test item onto the algae.

Since most of the test item was degraded at the end of the test, the analytical measurements were also based on Menthol rac. (CAS 89-78-1), a degradation product of the test item. At the end of the test, the total determined concentrations of Menthol rac. (expressed as test item) plus test item were 0.0596, 0.191, 0.58, 1.955, 4.999 and 13.26 mg/L, respectively. The biological results were related to the mean measured test item concentrations calculated as the geometric means of the concentrations measured at the start (test item concentration) and end (Menthol rac. concentrations expressed as test item + test item) of the test.

The biological results (based on geometric mean measured concentrations of menthyl acetate) of the study were as follows: EC50 growth rate is 2.7 mg/L. EC10 growth rate is 0.61 mg/L. NOEC growth rate is 0.16 mg/L. After adjustment to the molecular weight of menthyl lactate (228.33, compared to 198.3 of menthyl acetate), these results correspond to an estimated ErC50 value of 3.11 mg/L, an estimated ErC10 value of 0.7 mg/L and a NOEC of 0.18 mg/L for menthyl lactate. This conclusion is also supported by a valid study with L-menthol (Bruns, Caspers 2002b) (for applicability of read across refer to justification document in chapter 13).