sodium 2-{N-[(3,5-difluorophenyl)carbamoyl]ethanehydrazonoyl}nicotinate

Toxicity to aquatic algae and cyanobacteria

Description of key information

Key study with freshwater diatom, navicula pelliculosa:
The 5-day EC50 was calculated to be 0.10 mg A.E./L (95% confidence limits of 0.033 and 0.36 mg A.E. (acid equivalent)/L). The 5-day No-Observed-Effect Concentration (NOEC) was determined to be 0.0030 mg A.E. (acid equivalent)/L.
Key study with marine water diatom, Skeletonems costatum:
The effects of the test substance observed on the growth of Skeletonema costatum were clearly concentration related and yielded a 5-day EC50 value, based on cell density, of 0.14 mg A.E.(acid equivalent)/L. The 5-day No-Observed-Effect Concentration (NOEC) was determined to be 0.0064 mg A.E. (acid equivalent)/L.

Key value for chemical safety assessment

EC50 for freshwater algae:

0.1 mg/L

EC50 for marine water algae:

0.14 mg/L

EC10 or NOEC for freshwater algae:

0.003 mg/L

EC10 or NOEC for marine water algae:

0.006 mg/L

Additional information

Key study (freshwater diatom)

A 5-day toxicity test with the freshwater diatom, navicula pelliculosa was performed in accordance with FIFRA Guidelines 122-2 and 123-2. The mean measured concentration were: 0.0030, 0.0052, 0.011, 0.024, 0.042, 0.084 and 0.17 mg A.E. (acid equivalent)/L.

Based on the analytical results generated during this study, the concentrations of the test substance (difluenzopyr sodium salt) were relatively stable during the 5-day exposure period. The mean measured test concentrations ranged from 83 to 96% of nominal concentrations. Based on mean measured concentrations, the 5-day EC50 was calculated to be 0.10 mg A.E.(acid equivalent)/L (95% confidence limits of 0.033 and 0.36 mg A.E.(acid equivalent)/L). The 5 -day No-Observed-Effect Concentration (NOEC) was determined to be 0.0030 mg A.E.(acid equivalent)/L.

In addition to the worst case key study, several supporting studies with diverse algae species (Anabaena flos-aquae and Selenastrum capricornutum (new name: Pseudokirchnerella subcapitata) were performed according to FIFRA guidelines 122 -2 and 123 -2 (guidelines equivalents to US. EPA, 1982). The measured reference figures support the findings of the key study. NOEC values were in the range of 0.0064 mg/L to 0.0078 mg/L. EC50 values were between 0.11 mg/L and 0.14 mg/L.

Key study (marine water diatom):

A 5-day toxicity test with the marine diatom, Skeletonems costatum, was performed in acordance with FIFRA guidelines 122-2 and 123-2. Based on the analytical results generated during this study, the concentrations of the test subbstance were relatively stable during the 5-day exposure period. The mean measured test concentrations of the test substance (difluenzopyr sodium salt) ranged from 87 to 100% of nominal concentration. The mean measured concentrations were: 0.0064, 0.013, 0.024, 0.043, 0.092 and 0.18 mg A.E. (acid equivalent)/L.The effects of the test substance observed on the growth of Skeletonema costatum were clearly concentration related and yielded a 5-day EC50 value, based on cell density, of 0.14 mg A.E. (acid equivalent)/L (corresponding 95% confidence limits of 0.075 to 0.27 mg A.E. (acid equivalent)/L). The 5-day No-Observed-Effect Concentration (NOEC) was determined to be 0.0064 mg A.E.(acid equivalent)/L.