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Ecotoxicological information

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:
other: According to international guideline(s), GLP-compliant, performed in recognized contract research organization, no restrictions, fully adequate for assessment.
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.3 (Algal Inhibition test)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 850.5400 (Algal Toxicity, Tiers I and II)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: nominal 100 mg/L and control
- Sampling intervals: start and end of the test (0 and 72 h)
- Sampling method: samples were taken from flasks containing no algal cells
- Sample storage conditions before analysis: no storage prior to analysis
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: water accommodated fractions (WAFs)
A supersaturated solution was prepared by dispersing/dissolving the test item into the test medium (OECD Medium) at a nominal concentration of 100 mg/L. This dispersion was shaken for about 24 hours at approximately 30°C and then was equilibrated for about 24 hours at the test temperature. The non-dissolved test material was removed by filtration through a 0.22-µm filter to provide the WAF.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Strain: 61.81 SAG (identical strains: CCAP 278/4; UTEX 1648; ATCC 22662)
- Source (laboratory, culture collection): SAG: Collection of Algal Cultures, Inst. Plant Physiology, University of Göttingen, GERMANY.
- Age of inoculum (at test initiation): Three days. Algal cells used for inoculation were in the exponential phase of growth.
- Method of cultivation: Algae are cultured under standardised conditions. The pre-culture was intended to give an amount of alga suspension suitable for the inoculation of test cultures. The pre-culture was incubated under the conditions of the study in an aerated Algal Growth Medium and used when still exponentially growing (after an incubation period of 3 days). The cell count of above culture was determined by microscopic method and this cell suspension was diluted with Algal Growth Medium to 10^7 cells/mL.

ACCLIMATION
- Acclimation period: 3 days (pre-culturing)
- Culturing media and conditions (same as test or not): same
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Hardness:
24 mg/L as CaCO3 (calulated)
Test temperature:
22.9-23.2 °C (daily measurements in a flask filled with water and incubated under the test conditions)
22.6-23.4 °C (continuous measurements in the climatic chamber)
pH:
test start (0 h): 7.8
test end (72 h): 8.7-9.0
Nominal and measured concentrations:
nominal loading rate: 100 mg test material/L as WAF
measured concentrations:
start: 2.8 ± 1.7 mg test material/L (n=3)
end: 9.5 ± 8.7 mg test material/L (n=3)
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 mL Erlenmeyer flasks containing 100 mL of inoculated test medium and covered with air-permeable stoppers
- Aeration/gaseous exchange: continuous shaking on an laboratory orbital shaker
- Initial cells density: 1x10⁴ cells/mL
- Control end cells density: 71 x10⁴ cells/mL
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionised water
- Ca/Mg ratio: 1:1
- Culture medium different from test medium: no

OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: no
- Photoperiod: continuous illumination
- Light intensity and quality: about 8114 lux (equivalent to 110 µE/m2/s), provided by fluorescent lamps (spectral range 400-700 nm).

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : cell numbers counted at 24, 48 and 72 hours
- Determination of cell concentrations: counting chamber
- Algal cells were observed microscopically for abnormal appearance at 24, 48 and 72 hours.

TEST CONCENTRATIONS
- Range finding study
- Test concentrations: nominal loading rate of 100 mg/L (WAF) and dilutions 10, 1 and 0.1 mg/L
- Results used to determine the conditions for the definitive study: no inhibition of algal growth after 72 hours
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Key result
Duration:
72 h
Dose descriptor:
EL50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: growth rate, yield and biomass
Remarks on result:
other: results are expressed in terms of loading rates
Key result
Duration:
72 h
Dose descriptor:
NOELR
Effect conc.:
>= 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: growth rate, yield and biomass
Remarks on result:
other: results are expressed in terms of loading rates
Details on results:
- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): no microscopic abnormalities
- Any stimulation of growth found in any treatment: no

Control cultures:
- increase of biomass by a factor of: 71
- mean coefficient of variation for section-by-section specific growth rates (days 0-1; 1-2; 2-3): 11.9%
- coefficient of variation for the average specific growth rates during the test period (day 0-3): 0.77%
Results with reference substance (positive control):
- Results with reference substance valid? yes
- 48-hour ErC50: 0.94 mg/L (95% confidence limits. 0.85-1.03 mg/L)
Reported statistics and error estimates:
The section-by-section specific growth rates in the control cultures were assessed (calculated as the specific growth rates for each day during the course of the test (days 0-1, 1-2 and 2-3) and to demonstrate exponential growth for the entire study period.

The inhibition of alga growth was determined from the biomass (area under the growth curves, A), the average specific growth rate (r) and from the yield (y). Mean values and standard deviations were calculated for each concentration at the start, and at the end of the test using Excel for Windows software (Microsoft Co./One Microsoft Way/Redmond, WA 98052-6399).

The ErC50, EbC50 and EyC50 values of the test item were determined from the raw data.

Statistical comparisons of biomass, average specific growth rates and yield in control and in treated groups were carried out using 2 Sample t-Test (α = 0.05) by TOXSTAT software.

For the determination of the LOEC and NOEC, the calculated mean biomass, growth rates and yield at the test concentrations were tested on significant differences to the control values by 2 Sample t-Test (α = 0.05) by TOXSTAT software.

Table 1: Cell Number

 

Nominal

loading rates

(mg/L)

Replicate

number

Cell number (x 104/mL)

24 hours

48 hours

72 hours

 

Control

 

R1

 

3

 

16

 

68

R2

4

18

71

R3

5

21

69

R4

5

22

73

R5

4

18

70

R6

5

19

74

Mean

4.3

19.0

70.8

SD

0.8

2.2

2.3

100

R1

3

17

64

R2

4

18

69

R3

3

16

68

R4

5

17

70

R5

4

19

69

R6

4

19

66

Mean

3.8

17.7

67.7

SD

0.8

1.2

2.3

 

R1-R6: replicate number

Note: the initial cell density was estimated to be 1 x 104/mL

 

 

Table 2  Inhibition of growth

 

Parameter

Nominal

loading rates

(mg/L)

Sample size

Mean

Inhibition

(%)

Area under curve

0 to 72 hours

Control

6

1350

N/A

100

6

1268

6.1

Growth rate

0 to 24 hours

Control

6

0.0604

N/A

100

6

0.0553

8.4

Growth rate

0 to 48 hours

Control

6

0.0612

N/A

100

6

0.0598

2.4

Growth rate

0 to 72 hours

Control

6

0.0592

N/A

100

6

0.0585*

1.1

Yield

Control

6

69.8

N/A

10

6

66.7*

4.5

 

* : statistically significantly different compared to the control values (2 Sample t-Test;α= 0.05). However this slight deviation is considered as a biological variability of the test system due that this difference was clearly <10%.

 

Validity criteria fulfilled:
yes
Remarks:
Increase of biomass >16 after 72 hours; mean coefficient of variation for section-by-section specific growth rate <35%; coefficient of variation for average specific growth rate <7%.
Conclusions:
The results indicate that the test material is not toxic to algae up to the limits of its water solubility.

Description of key information

effect values for average specific growth rates of Pseudokirchneriella subcapitata, 0-72 h, based on loading rates (OECD 201, EU C.3):
EL50: >100 mg/L, NOELR: ≥ 100 mg/L

Key value for chemical safety assessment

Additional information

EL50 for freshwater algae: > 100 mg/L

NOELR for freshwater algae: ≥ 100 mg/L

The results indicate that the test material is not toxic to algae up to the limits of its solubility and a NOEC and thus a PNEC cannot be determined.