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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Read across to Cyclamen Aldehyde; 96h Growth Rate EC50 = 3.8 mg/L, NOEC = 0.70 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
3.8 mg/L
EC10 or NOEC for freshwater algae:
0.7 mg/L

Additional information

A valid study is available for the analogue substance, 3-p-cumenyl-2-methylpropionaldehyde (trade name, cyclamen aldehyde). It is a GLP compliant study conducted in compliance with agreed protocols, with no or minor deviations from the standard test. Important considerations for the use of read-across are:

i) Bourgeonal (the target chemical) is structurally similar to cyclamen aldehyde (the source substance). Both substances are 3-(4-alkylphenyl)propionaldehydes.

ii) The OECD QSAR toolbox assigns the same acute aquatic toxicity classification and mode of action to both chemicals.

iii) Hydrophobicity (as modelled by log Kow) can be an important aspect in aquatic toxicity. Bourgeonal and Cyclamen Aldehyde have similar measured log Kow values of 3.2 and 3.4 respectively.

iv) Both chemicals have been tested for ready biodegradability, acute toxicity to daphnia, and toxicity to microorganisms. Both chemicals gave similar results.

Therefore read-across is justified. The study on the analogue substance is summarised below.

A study was performed on Cyclamen Aldehyde to assess the effect of the test item on the growth of the green alga Pseudokirchneriella subcapitata. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Regulation (EC) No 761/2009 and the US EPA Draft Ecological Effects Test Guideline OPPTS 850.5400.

A decline in measured concentration observed in the range-finding test followed a concentration dependant pattern. Therefore it was considered likely that the test item was adsorbing to the algal cells present. Further study of samples without the presence of algal cells confirmed this theory. It was therefore considered appropriate to base the results on the geometric mean measured test concentrations using the 72 and 96 hour results obtained from the samples prepared with the omission of algal cells as these reflect more accurately the concentrations of test item to which the algae were exposed.

A positive control test showed that the use of a modified test system to reduce losses of test item through volatility (completely filled and sealed test vessels) had a slightly lowering effect on the EC50values obtained, and, a notable effect on the No Observed Effect Concentration (NOEC) compared with that obtained in a conventional test system. As such it can be considered that the results obtained from the definitive test give a worst case result for the test item.

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 effect values at 72 and 96 hours are equally valid. The ErC50 values are respectively 4.3 mg/L and 3.8 mg/L, and the NOEC values 0.72 and 0.7 mg/L. The lowest effect values have been used for the chemical safety assessment.