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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Determination of the acute toxicity potential of TK 12146on the growth of the green Pseudokirchneriella subcapitata.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.13 mg/L
EC10 or NOEC for marine water algae:
0.049 mg/L

Additional information

The study was performed to assess the effect of TK 12146 on the growth of the green algaPseudokirchneriella subcapitata. The method followed that described in the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Regulation (EC) No 761/2009.

 

The test item was very slightly soluble in water. Preliminary solubility work conducted indicated that it was not possible to obtain a testable solution of the test item using traditional methods of preparation e.g. ultrasonication and high shear mixing.

 

A preliminary media preparation trial indicated that a dissolved test item concentration of approximately 0.65 mg/L was obtained from a saturated solution method of preparation indicating this to be the limit of water solubility of this item under test conditions.

 

Following a preliminary range-finding test,Pseudokirchneriella subcapitatawas exposed to solutions of the test item at nominal concentrations of 6.25, 12.5, 25, 50 and 100% v/v saturated solution (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 ± 1 °C. The test item solutions were prepared by stirring an excess (50 mg/L) of test item in culture medium using a propeller stirrer at approximately 1500 rpm for 24 hours. After the stirring period any undissolved test item was removed by filtration (0.2 µm Gelman Acrocap filter, first approximate 500 mL discarded in order to pre-condition the filter) to produce a 100% v/v saturated solution of the test item. This saturated solution was then further diluted as necessary, to provide the remaining test groups.

 

Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter®Multisizer Particle Counter.

 

Results:

Analysis of the test preparations at 0 hours showed measured test concentrations to range from 0.027 to 0.95 mg/L. A slight decline in measured test concentrations was observed at 72 hours in the range of 0.018 to 0.78 mg/L (68% to 83% of the 0-Hour measured test concentrations) and hence it was considered appropriate to calculate the results based on the geometric mean measured test concentration only in order to give a “worst case” analysis of the data.

 

Exposure ofPseudokirchneriella subcapitatato the test item gave the following results based on the geometric mean measured test concentrations:

 

Response Variable

EC10(mg/L)

EC20(mg/L)

EC50(mg/L)

95% Confidence Limits (mg/L)

No Observed Effect Concentration (NOEC) (mg/L)

Lowest Observed Effect Concentration (LOEC) (mg/L)

Growth Rate

0.049

0.073

0.13

0.12

-

0.15

0.022

0.074

Yield

0.048

0.054

0.068

0.063

-

0.073

0.022

0.074