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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Toxicity to algae is not expected to occur upon exposure to L-isoleucine based on information available on read-across substance L-tert.-Leucine.

The chronic toxicity of L-tert-Leucine towards algae was tested according to OECD 201 by determination of the inhibition of biomass production and the growth rate of the algae after an exposure period of 71.5 +/- 0.5h.

Under the conditions of the test, no NOEC value could be determined. The biomass EC10 and EC50 were 130 mg/L and > 10000 mg/L, respectively. The growth rate EC10 and EC50 were found to be 3800 mg/L and > 10000 mg/L, by extrapolation of the concentration / response curve.

The effect concentrations as determined for source substance tert-leucine do not need to be corrected for molecular weight for the read-across to target substance isoleucine, as the source and target substance have the same molecular weight. Hence, the following effect concentrations apply for L-isoleucine:

EC10 (biomass) = 130 mg/L

EC50 (biomass) > 10000 mg/L

EC10 (growth rate) = 3800 mg/L

EC50 (growth rate) > 10000 mg/L

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
3 800 mg/L

Additional information

No test results for L-isoleucine are available. However, read-across to the test results available for structural analogue L-tert.-Leucine is deemed justified based on a comparison of the main factors driving environmental toxicity: pH, water solubility, log Kow, functional groups and functional groups:

- both are amino acids that are in the zwitterion state at physiological pH

- the chemical structure differs only in that L-tert.-Leucine has a different connectivity in the alkyl side chain

- the pKa values of the α-COOH group are similar

- the pKa values of the α-NH2 group are similar

- the substances both have a high water solubility

- the substances both have a low log Kow value.

As the chemical structure and the functional groups, as well as the water solubility, log Kow and pKa values of L-tert.-Leucine and L-isoleucine are almost identical, it can be concluded that read-across for aquatic toxicity information between those 2 substances is acceptable.

The result of the QSAR (EcoSAR, EpiSuite) is an 96h LC50 for green algae (fresh water) of 10.519 mg/L. This indicates a very low level of toxicity, which is in line with the findings on read-across substance L-tert.-Leucine.