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Toxicity to microorganisms

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Description of key information

No test results for L-leucine are available. However, 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 >= 1000 mg/kg of L-leucine

Key value for chemical safety assessment

Additional information

No test results for L-leucine are available. However, 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-leucine has one extra methylene group in the aliphatic side chain

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

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

- the substances both have a high water solubility: 23 g/L for LEU, 58 g/L for VAL

- the substance both have a low log Kow value: -1.59 for LEU (calculated by EpiWin QSAR), -2.08 for VAL (calculated by EpiWin QSAR)

As the chemical structure and reactivity, and the water solubility, log Kow and pKa values of L-leucine 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-leucine at a concentration >= 1000 mg/kg.