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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Description of key information

Acute toxicity to daphnia is not expected to occur upon exposure to the L-isoleucine based on information available on read-across substance L-valine.

L-valine was found to have an EC50 (mobility) > 10000 mg/L and a NOEC (slower movement) of 3200 mg/L.

Recalculation of this value taking into account the molecular weight of L-isoleucine results in a predicted EC50 value > 11200 mg/L for L-isoleucine, and a NOEC of 3583 mg/L.

The low toxicity of L-isoleucine towards daphnia is further confirmed by the result of the QSAR (EcoSAR, EpiSuite) that predicted an 48h-LC50 of 5148 mg/L.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
11 200 mg/L

Additional information

No test results for L-isoleucine 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-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 does not reveal mortality to daphnia at the highest tested concentrations (10000 mg/L) after 24 hours.

Recalculation of this value taking into account the molecular weight of L-isoleucine results in a predicted EC50 value > 11200 mg/L for L-isoleucine.

Furthermore, the EcoSAR model predicted an 48h-LC50 of 5418 mg/L. As a consequence, acute toxicity to aquatic invertebrates is not expected to occur upon exposure to the L-isoleucine.

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