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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

One guideline study on freshwater green algae

Key value for chemical safety assessment

EC50 for freshwater algae:
393 mg/L
EC10 or NOEC for freshwater algae:
59.7 mg/L

Additional information

The purpose of this study was to assess the potential effects of DiEPh on the growth of the freshwater green alga, Pseudokirchneriella subcapitata. Algal growth was evaluated over a 96 -hour (4 day) exposure period at nominal concentrations of 0 (medium control), 31.3, 62.5, 125, 250, 500, and 1000 mg DiEPh/L. The medium control level included six replicate vessels and the treatment concentrations included three replicate vessels per level, all inoculated at an intial nominal loading rate of 10,000 cells/ml per vessel. In addition, blank vessels were set at each level (including the control) to serve as counting blanks to correct the daily counts for potential interference of the isoton solution and/or test material, as well as to monitor pH and concentration of the test material without the algal biomass. Cell density determinations were made at approximately 24, 48, 72 and 96 hours of exposure.

Analytical verification of the test solution concentrations was performed on samples collected on days 0 (test initiation) and 4 (test termination) of the study, Measured DiEPh concentrations ranged from 95.5 to 98% of nominal on day 0 and, in replicates with algae, ranged from 91.7 to 100% of nominal on day 4. The resulting mean measured concentrations were < LLQ (medium control), 29.7, 59.7, 121, 247, 496 and 984 mg DiEPh/L

Temperatures during the exposure period ranged from 23.8 to 24 C. Light intensity for inoculated replicates ranged from 4900 lux to 5000 lux. The pH value ranged from 7.5 to 7.6 at test initiation, from 7.7 to 8.5 in pooled replicates with algae on day 3, and from 7.7 to 8.3 in pooled replicates with algae and 7.6 to 7.7 in blank replicates without algae at test termination.

The results, based on mean measured concentrations of DiEPh, were as follows:

- 72 -hour ErC50 (95% Confidence Interval) = 393 (364, 422) mg/L

- 96 -hour ErC50 (95% Confidence Interval) = 396 (355, 437) mg/L

- 72 -hour EyC50 (95% Confidence Interval) = 254 (249, 260) mg/L

- 96 -hour EyC50 (95% Confidence Interval) = 269 (266, 272) mg/L