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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The effect of the test item on the growth of Pseudokirchneriella subcapitata has been investigated according to OECD Guideline 201. Given the decline in measured test concentrations observed over the 72-h test period it was considered justifiable to base the results on the time-weighted mean measured test concentrations in order to give a "worst case" analysis of the data. The EC50 values for growth rate and yield were 85 and 47 mg/L respectively. The NOEC for both growth rate and yield was 23 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
85 mg/L
EC10 or NOEC for freshwater algae:
23 mg/L

Additional information

Introduction

A study was performed to assess the effect the test item in the growth of the green alga Pseudokirchneriella 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.

Methods

Pre-study 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. ultrsonication and high shear mixing.

A pre-study media preparation trial indicated that the use if a saturated solution method of preparation was most appropriate for this test item.

Following a preliminary range-finding test, Pseudokirchneriella subcapitata was exposed to solutions of the test item at 0-hour measured concentrations of 8.8, 18, 37, 79 and 158 mg/L (3 replicate flasks per concentration) for 72 h, under constant illumination and shaking at a temperature of 24 ± 1 °C. The test item solutions were prepared by stirring an excess of the test item in culture medium using a propeller stirrer at approximately 1500 rpm for 24 h. After the stirring period any undissolved test item was removed by filtration to produce a saturated solution of the test item. This saturated solution was then diluted as necessary to provide the test concentrations.

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

Chemical analysis of the test preparations at 0 h showed measured test concentrations of 8.8, 18, 37, 79 and 158 mg/L were obtained.

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results based on the 0-Hour measured test concentrations:

Response variable

EC5-

(mg/L)

95 % Confidence Limits (mg/L)

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

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

Growth Rate

130

 

*

 

37

79

Yield

71

61

-

83

37

79

*It was not possible to calculate 95 % confidence limits for the ErC50value as the data generated did not fit the models available for the calculation of confidence limits.

Analysis of the test preparations at 72 h showed a significant decline in measured test concentration in the range of less than the limit quantitation (LOQ) of the analytical method employed (which was determined to be 0.014 mg/L) to 0.071 mg/L.

Given that a decline in measured test concentration was observed during the range-finding test it was considered appropriate to prepare additional test samples at the start of the test which were incubated under test conditions prior to analysis at 24 and 48 h. Analysis of these additional test samples showed measured test concentrations to range from 87 % to 97 % of the 0-Hour measured test concentrations after 24 h and from 41 % to 99 % of the 0-Hour measured test concentrations after 48 h.

Given the decline in measured test concentrations observed over the 72-h test period it was considered justifiable to base the results on the time-weighted mean measured test concentrations in order to give a “worst case” analysis of the data.

Exposure of Pseudokirchneriella subcapitata to the test gave the following results based on the time-weighted mean measured test concentrations:

Response variable

EC50

(mg/L)

95 % Confidence Limits (mg/L)

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

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

Growth Rate

85

 

*

 

23

53

Yield

47

40

-

56

23

53

*It was not possible to calculate 95 % confidence limits for the ErC50value as the data generated did not fit the models available for the calculation of confidence limits.