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Ecotoxicological information

Toxicity to aquatic plants other than algae

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Description of key information

Two reliable guideline studies are available; one for cloquintocet-mexyl and one for the metabolite CGA153433. In both cases the test organism was duckweed (Lemna gibba). The reported EC50 values were >0.42 mg/L and >11 mg/L for cloquintocet-mexyl and CGA153433, respectively.

Key value for chemical safety assessment

EC50 for freshwater plants:
0.42 mg/L

Additional information

Hoburg (1993) investigated the toxicity of cloquintocet-mexyl to duckweed (Lemna gibba) in a GLP compliant study performed according to EPA FIFRA Test Guidelines 122-2 and 123-2 (U. S. EPA, 1982), with minor deviations. The test was conducted as a limit test with renewal of the test solution every three days. No statistically significant adverse effect was observed based on frond density or biomass at the highest rate tested (Mean measured concentration 0.42 mg/L). Therefore, the EC50based on frond density and biomass was estimated to be > 0.42 mg/L. The 14 day NOEC based on both frond density and biomass was determined to be 0.42 mg/L.

In a similar study Hoburg 1993 investigated the toxicity of the CGA153433 (metabolite of cloquintocet-mexyl) to duckweed (Lemna gibba). Again, the study was performed according to EPA FIFRA Test Guidelines 122-2 and 123-2 (U.S. EPA, 1982), with minor deviations. No statistically significant adverse effect was observed based on frond density or biomass at the highest rate tested (Mean measured concentration 11 mg CGA153433/L). Accordingly, the EC50 based on frond density and biomass was estimated to be > 11 mg CGA153433/L, whilst the NOEC was determined to be 11 mg CGA153433/L.

Both of the above studies are considered to be reliable without restriction.

Although it provides both acute and sub-chronic endpoints, the 14 day Lemna gibba study is considered to be short-term endpoint (ECHA, 2008: Chapter R.7b: Endpoint specific guidance). Therefore, the key value used in the Chemical safety assessment is the EC50 for cloquintocet-mexyl of >0.42 mg/L.