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Short-term toxicity to aquatic invertebrates

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Description of key information

In order to evaluate the short-term effect of cloquintocet-mexyl to aquatic invertebrates, two guideline studies were conducted with Daphnia magna. In both cases, no significant effects were observed. Therefore, the EC50 value of 100 mg/L, which corresponds to the highest concentration tested, is used for risk assessment purposes. 
In the case of the metabolite CGA153433, the 48-hour EC50 for Daphnia magna was determined to be > 9.7 mg/L.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
100 mg/L

Additional information

In the key study (Rufli, 1988), 2 groups of 10 daphnids (Daphnia magna) were exposed to cloquintocet-mexyl at nominal concentrations of 10, 18, 32, 58 and 100 mg/L, in a static test for 48 hours. The 48-hour EC50 forD. Magna was >100 mg/L, the highest concentration tested. The no observed effect concentration was 18 mg/L. This GLP-compliant study was conducted to EPA guideline EG-1 and was considered to be reliable without restrictions.

In a second study (Palmer and Krueger, 1998), daphnids (Daphnia magna) were exposed to cloquintocet-mexyl at nominal concentrations of 0.063, 0.13, 0.25, 0.50 and 1.0 mg/L, in a flow-through test for 48 hours. The 48-hour EC50 forD. magna was > 0.82 mg/L, the highest (measured) concentration tested. The no observed effect concentration was 0.82 mg/L. This GLP-compliant study was conducted to OECD guideline 202 and was considered to be reliable without restrictions.

Since both studies indicate that the EC50 is greater than the concentrations tested, it is proposed to select the upper of the two test rates as the key value for the endpoint. Therefore, for risk assessment purposes, the EC50 of 100 mg/L was used for cloquintocet-mexyl.

A study of short-term toxicity of a metabolite of cloquintocet-mexyl, CGA153433, to D. magna was carried out (Putt, 1993). This GLP-compliant study was performed to OECD guideline 202 and is considered to be reliable without restrictions. Daphnids were exposed to a nominal concentration of 9.7 mg/L, in a semi-static system. No effects were observed at the test concentration, thus the 48-hour EC50 of the metabolite CGA153433 was determined to be > 9.7 mg/L.