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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Using a 3-week exposure study conducted with Selenastrum capricornutum, the NOEC and EC50 values for Dowfax 2A1 were 100 mg/L and >100 mg/L, respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:
840 mg/L
EC10 or NOEC for freshwater algae:
298 mg/L

Additional information

The purpose of this study was to estimate the level of phytotoxicity (50% reduction in the number of cells per milliliter in contrast to the controls and 50% reduction in total cell volume x E4 um3 per milliliter in contrast to the controls) of XDS-8174.00 to the green alga Selenastrum capricornutum.

The EC50 values are presented below and are based on measured test concentrations:

Cell Count / mL Cell Volume x E4 um3 / mL

Day 5 872(644-1101) mg/L 1016(103-1928) mg/L

Day 4 840(-37,1717) mg/L 949(197-1701) mg /L

The no observable effect level as calculated using Dunnett's t test was 297.5 mg/L in all cases for both days. Using the categorization scheme of U.S. EPA,

XDS-8174.00 is classified as not toxic to Selenastrum cavricornutum.

One published algal toxicity study with Dowfax 2A1 was available for assessment. The study was well documented and met generally accepted scientific principles, thus it was assigned a Klimish score of 2. In this study, the freshwater green algae, Selenastrum capricornutum was exposed to control and five concentrations of Dowfax 2A1 ranging from 100 to 500 mg/L. Algal cell count was measured after the growth period and at the onset of the stationary phase. There were no significant differences in cell counts between control and the 100 mg/L treatment group after 3 weeks of exposure. Algal growth was significantly less than controls beginning at the 200 mg/L dose. At 200 mg/L Dowfax 2A1, algal growth was 19.7% that of controls. Thus, according to this algal growth study, the NOEC for Dowfax 2A1 was 100 mg/L and the EC50 was greater than 100 mg/L.