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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
Study period:
2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
GLP compliance:
yes
Analytical monitoring:
yes
Vehicle:
no
Remarks:
The test item is completely soluble. Therefore the test item was directly dissolved in algal medium.
Details on test solutions:
4.2.4 Preparation of the test and control vessels
The test item is completely soluble. Therefore the test item was directly dissolved in algal medium. A stock solution of 8.8 mg/L (including a factor of 1.1 to take into account the dilution caused by addition of the algal inoculum) in algal medium (OECD) was prepared.
The stock solution was used as highest test item concentration rate as well as 4 further concentrations with a spacing factor of 2.5 were tested: 0.20 mg/L, 0.51 mg/L, 1.27 mg/L, 3.17 mg/L and 7.92 mg/L.
The stock solution was stirred for 30 min. at 24.9°C with a magnetic stirrer and directly used for the preparation of the test vessels. To each test vessel 5 mL of the algal inoculum suspension (0.7 x 105 algal cells/mL) were added to obtain an algae starting concentration of 0.7 x 104 algal cells/ mL. For the controls, 5 mL algae inoculum suspension was added to 45 mL algal medium.
For chemical analysis of the test item, additional test flasks without algae were prepared with the three highest nominal test concentrations and the control. Algal medium was added to these additional flasks instead of inoculum suspension to avoid an influence of the organisms on the analytical result.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
Tests were carried out with the green alga Raphidocelis subcapitata (Strain No. 61.81 SAG) from the Culture Collection of Algae at the University of Goettingen and cultivated in suspension culture. The strain used for this study has been cultured in the laboratory of Hydrotox GmbH since July 2017. Twice a week, the stock suspension is diluted into fresh Holm-Hansen medium (see Appendix I) under axenic conditions to keep it in exponential growth.
A quality check takes place at regular intervals using a concentration range of potassium dichromate (Sigma, Steinheim, Germany, Lot No. MKBF2111V from 12 January 2011) in order to assess the validity of the test system. The last quality check was performed in November 2017. The ErC50 (Growth rate) was 1.11mg/L (95%-Cl: 0.65 – 1.86 mg/L) and the EyC50 (Yield) was 0.07 mg/L (95%-CI: 0.00 – 2.47 mg/L).

Four days before starting the test, 1.163 mL of the algae stock suspension was diluted into 50 mL algal growth medium (according to OECD 201) to obtain a starting concentration of 0.5 x 105 algal cells per mL.
The pre-culture was incubated at 22.7 – 22.9°C and 71.1 μE m-² s-1 ± 3.8 % (PAR). After four days, the cell concentration was determined using the Coulter Counter Z2. The cell concentration was 79.167 x 105 algal cells/mL. To obtain a nominal inoculum concentration of 0.7 x 105 algal cells/mL, 2.65 mL of the pre-culture was diluted into 300 mL algal growth medium.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
< 0.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
<= 0.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
1.41 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EC20
Effect conc.:
1.67 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
2.3 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
< 0.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: yield
Key result
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
<= 0.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: yield
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.16 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: yield
Key result
Duration:
72 h
Dose descriptor:
EC20
Effect conc.:
0.29 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: yield
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.92 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: yield
Reported statistics and error estimates:
Growth Rate:
NOErC < 0.20 mg/L
LOErC ≤ 0.20 mg/L
ErC 10: 1.41 mg/L (Cl 95%: 0.29 – 6.95)
ErC 20: 1.67 mg/L (Cl 95%: 0.40 – 7.29)
ErC 50: 2.30 mg/L (Cl 95%: 0.43 – 13.39)
Yield:
NOEyC < 0.20 mg/L
LOEyC ≤ 0.20 mg/L
EyC 10: 0.16 mg/L (Cl 95%: 0.03 – 0.83)
EyC 20: 0.29 mg/L (Cl 95%: 0.07 – 1.35)
EyC 50: 0.92 mg/L (Cl 95%: 0.15 – 5.72)
Validity criteria fulfilled:
yes
Remarks:
The test is valid according to OECD 201 (23 March 2006).
Conclusions:
NOErC < 0.20 mg/L
LOErC ≤ 0.20 mg/L
Executive summary:

The Algae Growth Inhibition Test was performed with five nominal concentrations between 0.20 mg/L and 7.92 mg/L. The measured TOC-concentration of the test item treatments were between 91.2 to 106.2 % of the nominal test item concentrations.

Therefore the EC values are given as nominal concentrations.

Growth Rate:

NOErC < 0.20 mg/L

LOErC ≤ 0.20 mg/L

ErC 10: 1.41 mg/L (Cl 95%: 0.29 – 6.95)

ErC 20: 1.67 mg/L (Cl 95%: 0.40 – 7.29)

ErC 50: 2.30 mg/L (Cl 95%: 0.43 – 13.39)

Yield:

NOEyC < 0.20 mg/L

LOEyC ≤ 0.20 mg/L

EyC 10: 0.16 mg/L (Cl 95%: 0.03 – 0.83)

EyC 20: 0.29 mg/L (Cl 95%: 0.07 – 1.35)

EyC 50: 0.92 mg/L (Cl 95%: 0.15 – 5.72)

Description of key information

Growth rate:

ErC 50: 2.30 mg/L (Cl 95%: 0.43 – 13.39)

ErC 10: 1.41 mg/L (Cl 95%: 0.29 – 6.95)

NOErC < 0.20 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:
2.3 mg/L
EC10 or NOEC for freshwater algae:
1.41 mg/L

Additional information