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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
Study period:
From 2013-05-27 to 2013-07-25
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Version / remarks:
(Adopted:23 March 2006, Annex 5 corrected: 28 July 2011)
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: Testing Methods for New Chemical Substances; 2011.03.31, No. 0331-07, Ministry of Health, Labor and Welfare; 2011.03.29 No 5, Ministry of Economy, Trade and Industry; No. 110331009, Ministry of Environment, Japan; IV. Algae growth inhibition test.
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
- Lot No.: KNC110310
- Purity: 100.0%
Analytical monitoring:
yes
Details on sampling:
- Concentrations: control, 100 mg/L
- Sampling method: An aliquot was taken from the remaining unused test solution of each test group at initiation and termination of the test. The samples were taken from mid-depth of each replicate without agitation.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: A 0.0802 g aliquot of the test substance was weighed. A stock solution of concentration 100 mg/L was prepared to make a volume to 800 mL with the medium.
- Eluate: no
- Differential loading: no
- Controls: yes, test medium control
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Common name: Unicellular green algae
- Strain: ATCC22662
- Source (laboratory, culture collection): in-house culture originates from American Type Culture Collection (received 01 Aug 1996)
- Method of cultivation: aseptic culture
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Test temperature:
21.7 - 23.5 °C
Measured by Thermometer SK-1250MC (Sato Keiryoki Mfg. Co., Ltd.)
pH:
7.6 - 7.7 at the begining
8.1 - 8.3 at the end
Measured by pH meter F-22 (Horiba Ltd.)
Nominal and measured concentrations:
nominal: 0, 100 mg/L
measured: < LOQ, 100 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 300 mL Erlenmeyer flasks with an air-permeable silicone stopper
- Volume of test solution: 100 mL/vessel
- Aeration: continuously shaken at 100 rpm
- Initial cells density: 1 E+04 cells/mL
- Control end cells density: 1.77 E+06 cells/mL
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 6

TEST MEDIUM / WATER PARAMETERS
- Standard medium used: yes (OECD 201 recommended test medium)

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: continuous fluorescent illumination
- Light intensity and quality: cool-white light, 400-700 nm, 60-65 µE/m²/s (± 15%) at the surface of the cultures
- Revolution rate: maintained at a constant rate of 100 rpm throughout the exposure period.

EFFECT PARAMETERS MEASURED:
- Determination of cell concentrations: electronic particle counter after 24, 48 and 72 h
- Appearance: once daily
- Morphological changes: microscopic observation at the end of the test

- Range finding study
- Test concentrations: 0, 10, 100 mg/L
- Results used to determine the conditions for the definitive study: 3.7% inhibition of growth rate at 10 mg/L, 2.3% inhibition of growth rate at 100 mg/L.
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
100 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
growth rate
Details on results:
- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): not reported
- Unusual cell shape: The microscopic observation of algal cells for morphological changes showed no abnormality at 100 mg/L.
- Colour differences: not reported
- Flocculation: not reported
- Other observations: Appearance of the test solution was clear at the preparation, and no precipitation or floating material was observed during the exposure period.
- Aggregation of algal cells: not reported
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Latest ErC50(0-72h): 1.07 mg/L
- Other: conducted at approximately 6-month intervals.
Reported statistics and error estimates:
Student t-test, using a computer program (StatLight#3 comparison of 2 groups, ver. 2.0, Yukms Co. , Ltd, Japan).

Table 1: Growth inhibition rates

Nominal concentration [mg/L]

Vessel No.

Growth rate 0 - 72 h [day -1]

Percent inhibition [%]

Medium control

1

1.7337

-

2

1.7124

-

3

1.7293

-

4

1.7244

-

5

1.7355

-

6

1.7213

-

Mean

1.7261

-

SD

0.0086

-

CV

0.5

-

100

1

1.6741

3.0

2

1.7172

0.5

3

1.7003

1.5

4

1.6884

2.2

5

1.7179

0.5

6

1.7120

0.8

Mean

1.7016

1.7*

SD

0.0176

-

* Statistically different

 

It is considered that the significant difference at 100 mg/L was not the results of the test substance treatment but of incidentally small relative variation between replicates of each test group. Although statistical significance was detected, the difference in the growth inhibition rate between 100 mg/L and control group was very small and was not considered biologically relevant. The statistical significance should be attributed not to the treatment of test substance but to the incidentally small relative variation of the values between replicates in each test group.

Validity criteria fulfilled:
yes
Conclusions:
A 72-hour median effect concentration (ErC50) and no observed effect concentration (NOECr) of test item for freshwater green alga, Pseudokirchneriella subcapitata was >100 and 100 mg/L, respectively, based on the mean measured concentration.
Executive summary:

The 72-hour median effect concentration (ErC50) and no observed effect concentration (NOECr) of test item for freshwater green alga, Pseudokirchneriella subcapitata were determined in accordance with OECD 201.

The test was conducted with static test system-shake culture (continuous at 100 rpm) for 72 hours at 100 mg/L.

Growth inhibition rate at 100 mg/L was 1.7% after 72-hour exposure. The 72 h ErC50 and NOECr were >100 and 100 mg/L, respectively, based on the mean measured concentration.

Description of key information

The 72-hour median effect concentration (ErC50) and no observed effect concentration (NOECr) of test item for freshwater green alga, Pseudokirchneriella subcapitata were determined in accordance with OECD 201.

The 72 h ErC50 and NOECr were >100 and 100 mg/L, respectively, based on the mean measured concentration.

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC10 or NOEC for freshwater algae:
100 mg/L

Additional information