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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Only very old test results for L-isoleucine are available. Hence, read-across to L-valine was selected as the key information.

Based on test results available for read-across substance L-valine it can be concluded that toxicity to microorganisms is not expected to occur upon exposure to >= 1120 mg/kg of L-isoleucine.

The old experiment by Dawson and Jenkins is added as supporting information to this dossier.

In the experiment, the uptake of oxygen from a Warburg manometer containing activated sludge and the test substance was monitored.

Addition of a 5% solution of the test substance to the Warburg manometer resulted in an increase of the oxygen uptake of 36%.

As a consequence, this test shows that the test substance is not toxic to the micro-organisms present in the activated sludge.

Key value for chemical safety assessment

Additional information

Only limited test results for L-isoleucine are available. Read-across to the test results available for structural analogue L-valine is deemed justified based on a comparison of the main factors driving environmental toxicity: pH, water solubility, log Kow and chemical reactivity (functional groups).

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

- the chemical structure differs only in that L-isoleucine has one extra methylene group in the aliphatic side chain

- the pKa values of the α-COOH group is very similar: 2.36 for ILE, 2.32 for VAL

- the pKa values of the α-NH2 group is very similar: 9.60 for ILE, 9.62 for VAL

- the substances both have a high water solubility: 34 - 41 g/L for ILE, 58 g/L for VAL

- the substances both have a low log Kow value: -1.72 for ILE (experimental value obtained from EpiSuite's WSKOW model database), -2.08 for VAL (calculated by EpiWin QSAR)

As the chemical structure and reactivity, and the water solubility, low Kow and pKa values of L-isoleucine and L-valine are almost identical, it can be concluded that read-across for aquatic toxicity information between those 2 substances is acceptable.

The test available for L-valine is carried out according to OECD guidelines and reveals no growth inhibition at the highest tested concentrations (9900 mg/kg) after 16 hours. As a consequence, toxicity to microorganisms is not expected to occur upon exposure to L-valine at a concentration >= 1000 mg/kg.

Recalculation of this value taking into account the molecular weight of L-isoleucine allows to concluded that no toxicity is expected to occur at a concentration of 1120 mg/L for L-isoleucine.