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Toxicity to aquatic algae and cyanobacteria

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Reference
Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Akzo Nobel Functional Chemicals b.v. Batch no. 100000005282
- Expiration date of the lot/batch: 31 December 2021
- Purity test date:99.4%

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: Room temperature in the dark
Analytical monitoring:
yes
Details on sampling:
Samples were taken from the control and each test group from the bulk test preparation at 0 hours, from samples run alongside the test at 24 and 48 hours and from the pooled replicates at 72 hours for quantitative analysis. All samples were stored frozen prior to analysis. Duplicate samples were taken at 0 and 72 hours and stored frozen for further analysis if necessary.
Vehicle:
no
Details on test solutions:
A nominal amount of test item (1100 mg) was dispersed in 11 liters of culture medium with the aid of propeller stirring at approximately 1500 rpm for 48 hours. After 48 hours the stirring was stopped and any undissolved test item was removed by filtration through a 0.2 μm filter (first approximate 2 liters discarded in order to pre-condition the filter) to give a 100% v/v saturated solution. A series of dilutions was made from this saturated solution to give further stock solutions of 6.25, 12.5, 25 and 50% v/v saturated solution. An aliquot (900 mL) of each of the stock solutions was separately inoculated with 10 mL of algal suspension to give the required test concentrations of 6.25, 12.5, 25, 50 and 100% v/v saturated solution. Each of the prepared concentrations were inverted several times to ensure adequate mixing and homogeneity. The concentration and stability of the test item in the test preparations were verified by chemical analysis at 0, 24, 48 and 72 hours
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Source (laboratory, culture collection): Liquid cultures of Pseudokirchneriella subcapitata were obtained from the Culture Collection of Algae and Protozoa (CCAP), SAMS Research Services Ltd, Scottish Marine Institute, Oban,Argyll, Scotland.
- Method of cultivation: Master cultures were maintained in the laboratory by the periodic replenishment of culture medium (Section 3.3). The master cultures were maintained in the laboratory under constant agitation by orbital shaker (approximately 150 rpm) and constant illumination at 24 ±1 °C. Prior to the start of the test sufficient master culture was added to approximately 100 mL volumes of culture media contained in conical flasks to give an initial cell density of approximately 103 cells/mL. The flasks were plugged with polyurethane foam stoppers and kept under constant agitation by orbital shaker (100 – 150 rpm) and constant illumination at 24 ± 1 °C until the algal cell density was approximately 10e4 - 10e5 cells/mL.

Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
24 ± 1 °C
pH:
The pH value of the control cultures (see Table 2) was observed to decrease from pH 7.8 at 0 hours to pH 7.6 at 72 hours. The pH deviation in the control cultures was less than 1.5 pH units after 72 hours.
Nominal and measured concentrations:
Following a preliminary range-finding test, Pseudokirchneriella subcapitata was 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 (100 mg/L) of test item in culture medium using a propeller stirrer at approximately 1500 rpm for 48 hours. After the stirring period any undissolved test item was removed by filtration (0.2 μm Sartorius Sartopore filter, first approximate 2 liters 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.

Analysis of the test preparations at 0 hours showed measured test concentrations to range from 0.051 to 2.7 mg/L. A decline in measured test concentration was observed over the 72 Hour test period. 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. The geometric mean measured concentrations
were determined to be 0.024, 0.045, 0.093, 0.30 and 0.87 mg/L.
Details on test conditions:
TEST SYSTEM
250 mL glass conical flasks were used. Six flasks each containing 100 mL of solution were used for the control and three flasks each containing
100 mL were used for each treatment group. The control group was maintained under identical conditions but not exposed to the test item.
Pre-culture conditions gave an algal suspension in log phase growth characterized by a cell density of 4.48 x 105 cells per mL. Inoculation of 900 mL of test medium with 10 mL of this algal suspension gave an initial nominal cell density of 5.00 x 103 cells per mL and had no significant dilution effect on the final test concentration. The flasks were plugged with polyurethane foam bungs and incubated (INFORS Multitron Version 2 incubator) at 24 ± 1 °C under continuous illumination (intensity approximately 7000 lux) provided by warm white lighting (380 – 730 nm) and constantly shaken at approximately 150 rpm for 72 hours.

GROWTH MEDIUM
- Standard medium used: yes
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 0.87 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat. (dissolved fraction)
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.045 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat. (dissolved fraction)
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
0.093 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat. (dissolved fraction)
Basis for effect:
growth rate
Details on results:
- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): no
Results with reference substance (positive control):
A positive control (Envigo Study Number FP48BQ) used potassium dichromate as the reference item at concentrations of 0.25, 0.50, 1.0, 2.0 and 4.0 mg/L.
Exposure conditions and data evaluation for the positive control were similar to those in the definitive test.

Exposure of Pseudokirchneriella subcapitata (CCAP 278/4) to the reference item gave the following results:
ErC50 (0 – 72 h) : 1.4 mg/L; 95% confidence limits 1.2 – 1.5 mg/L
EyC50 (0 – 72 h) : 0.60 mg/L; 95% confidence limits 0.52 – 0.69 mg/L
No Observed Effect Concentration (NOEC) based on growth rate: 0.25 mg/L
No Observed Effect Concentration (NOEC) based on yield: 0.25 mg/L
Lowest Observed Effect Concentration (LOEC) based on growth rate: 0.50 mg/L
Lowest Observed Effect Concentration (LOEC) based on yield: 0.50 mg/L

The results from the positive control with potassium dichromate were within the normal ranges for this reference item.
Reported statistics and error estimates:
One way analysis of variance incorporating Bartlett's test for homogeneity of variance (Sokal and Rohlf, 1981) and Dunnett's multiple comparison procedure for comparing several treatments with a control (Dunnett, 1955) was carried out for the control and all test concentrations to determine any statistically significant differences between the test and control groups. All statistical analyses were performed using the SAS computer software
package (SAS, 1999 - 2001).
Validity criteria fulfilled:
yes
Conclusions:
The effect of the test item on the growth of Pseudokirchneriella subcapitata has been investigated over a 72-Hour period and based on the geometric mean measured test concentrations gave the following results based on the response variable growth rate, EC50: >0.87 mg/L (confidence limits not determined), NOEC: 0.045 mg/L and LOEC: 0.093 mg/L. The results based on yield were, EC50: 0.48 mg/L (confidence limits 0.32-0.73), NOEC 0.045 mg/L and LOEC 0.093 mg/L.
Executive summary:

Introduction

A study was performed to assess the effect of the test item on 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

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 1.8 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 subcapitata was 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 (100 mg/L) of test item in culture medium using a propeller stirrer at approximately 1500 rpm for 48 hours. After the stirring period any undissolved test item was removed by filtration (0.2 μm Sartorius Sartopore filter, first approximate 2 liters 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 0.051 to 2.7 mg/L. A decline in measured test concentration was observed over the 72 Hour test period, in the range of 0.036 to 1.0 mg/L at 24 hours, less than the Limit of Quantification (LOQ) of the analytical method, determined to be 0.020 mg/L and 0.73 mg/L

at 48 hours and less than the LOQ at 72 hours. 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. The geometric mean measured concentrations were determined to be 0.024, 0.045, 0.093, 0.30 and 0.87 mg/L.

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results based

on the geometric 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  >0.87*  Not determined  0.045

 0.093

 Yield  0.48  0.32 -0.73  0.045  0.093

* It was not possible to determine an ErC50 value as no concentration tested resulted in 50% inhibition of growth rate.

Description of key information

An OECD 201 study with Pseudokirchneriella subcapitata according to protocol under GLP is available.

Analysis of the test preparations at 0 hours showed measured test concentrations to range from 0.051 to 2.7 mg/L. A decline in measured test concentration was observed over the 72 hour test period, in the range of 0.036 to 1.0 mg/L at 24 hours, less than the Limit of Quantification (LOQ) of the analytical method, determined to be 0.020 mg/L and 0.73 mg/L at 48 hours and less than the LOQ at 72 hours. 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. The geometric mean measured concentrations were determined to be 0.024, 0.045, 0.093, 0.30 and 0.87 mg/L.

The ErC50 is greater than 0.87 mg/L and the ErC10 is 0.30 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.87 mg/L
EC10 or NOEC for freshwater algae:
0.3 mg/L

Additional information