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Ecotoxicological information

Toxicity to aquatic plants other than algae

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Description of key information

Based on mean measured concentrations of the test substance (diflufenzopyr sodium salt), the 14-day EC50 for frond density was estimated to be >0.35 mg A.E.(acid equivalent)/L. The 14-day No-Observed-Effect Concentration (NOEC) for frond density was determined to be 0.0039 mg A.E.(acid equivalent)/L. Based on mean measured concentrations, the 14-day EC50 based on frond biomass was estimated to be >0.35 mg A.E.(acid equivalent)/L, the highest concentration tested. The No-Observed-Effect Concentration (NOEC) for frond biomass was determined to be 0.35 mg A.E.(acid equivalent)/L.

Key value for chemical safety assessment

EC50 for freshwater plants:
0.35 mg/L
EC10 or NOEC for freshwater plants:
0.004 mg/L

Additional information

A 14 -day toxixity test with duckweed, Lemna gibba was performed in accordance with FIFRA Guidelines 122-2 and 123-2.

Based on the analytical results generated during this study, the concentrations of the test substance (diflufenzopyr sodium salt) measured in newly prepared test solutions (days 0 and 9) closely approximated the desired nominal concentrations. Results from the 3-day-old solutions (days 3 and 12) indicated that the concentration of the test substance decreased over the 3-day period by approximately 50% from the initial measured concentrations. The decrease in test material concentrations does not appear to be related to the density of Lemna gibba but may be related to hydrolysis of the test substance in an acid medium (e.g., pH 5.0 to 6.0). Mean measured test concentrations ranged from 71 to 95% of nominal concentrations. A weak concentration-response was observed for frond density, although no adverse response was observed in frond biomass (dry weight) over the range of concentrations tested. Based on the experience of the laboratory, frond density is typically a more sensitive indicator of toxicity than frond biomass. Due to the weak response observed for frond density, the 14-day EC50 was empirically estimated to be >0.35 mg A.E (acid equivalent)./L, the highest mean measured concentration tested. The 14-day No-Observed-Effect Concentration (NOEC) for frond density was determined to be 0.0039 mg A.E. (acid equivalent)./L. Based on mean measured concentrations, the 14-day EC50 based on frond biomass was estimated to be >0.35 mg A.E.(acid equivalent)/L, the highest concentration tested. The No-Observed-Effect Concentration (NOEC) for frond biomass was determined to be 0.35 mg A.E.(acid equivalent)/L.