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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:
10 May - 22 Jun 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
no
Vehicle:
yes
Remarks:
reconstituted water
Details on test solutions:
A stock preparation with a test item concentration of 100 mg/L was freshly prepared. For that purpose, the test item was weighed in a calibrated flask and vehicle was added. The preparation was stirred with a magnetic stirrer for 24 hours. Then the formulation was passed through a filter membrane (pore size < 0.2 µm). The filtrate was used for the study. The pH value was not adjusted.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
strain 61.81 SAG, obtained from Pflanzenphysiologisches Institut der Universität Göttingen, Germany.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
72 h
Hardness:
ca. 0.24 mmol/L (about 24 mg/L CaCO3)
Test temperature:
23.5 to 24.2°C
pH:
7.81 to 8.92
Details on test conditions:
The study was performed as a static test in open vessels under culture conditions. The flasks contained 100 mL either reconstituted water or test medium (test item group).
The duration of exposure was 72 hours. The algal biomass in each flask was determined daily during the exposure period.

A 3-day old pre-culture, prepared in dilution water, was used as inoculum. Before start of exposure, the cell density was determined. The test vessels were inoculated with an appropriate volumen of algae pre-culture suspension in order to obtain an initial cell density of 10000 cells/mL.

Volumes of the algal suspension not impairing the study were taken from all test item preparations ans the controls after exposure times of 24, 48 and 72 h (+/- 1 h). The required volume depended on the cell density. The withdrawn volumes were not substituted. before the cell density measurement, the algal suspension was diluted and the cell densities were determined with an electronic particle counter. Additionally the blank values without algae were determined at the sampling time points. The respective blank values were substracted from the measured value of each replicate.
The measured cell counts were converted into cell number per mL. To identify the morphological effect of the test item on the algal cells, additional samples were taken from the control and test item group after 72 h. The morphological appearance of the treated algal cells in comparison to the controls was assessed by microscope.

The mean light intensities were 7653 Lux ± 4.7% and 7683 Lux ± 5.2% prior to and at the end of the exposure period, respectively
Reference substance (positive control):
no
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (total fraction)
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 0.076 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other:
Remarks:
limit of water solubility
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
> 100 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.:
> 0.076 mg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other:
Remarks:
limit of water solubility
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
>= 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (total fraction)
Basis for effect:
growth rate
Details on results:
The test item concentration in the reconstituted water was not quantified at the start and the end of the study.
Due to the absence og any adverse effects at the saturation concentration, the study was performed without analytical concentration verification.
No significant effect on growth rate and yield of the algae was observed at a nominal concentration of 100 mg/L, i.e. up to the maximum water solubility.
Results with reference substance (positive control):
The positive control showed 72h EC50 of 0.86 mg/L for growth rate and 0.48 mg/L for yield. The EC50 for growth rate and yield obtained in this study are in the range of ± two standard deviation of the current historical means.

Purpose

The purpose of the present study was to determine the effect of the test material on growth rate and yield of the unicellular green alga Pseudokirchneriella subcapitata.

Study Design

The information for this endpoint study record was obtained from an experimental study. The OECD GLP criteria were met and the methods applied are fully compliant with OECD TG 201
The study comprised of one control group and one test item group with six replicates each. The nominal test item concentration of 100 mg/L was dissolved in 100 mL reconstituted water. The initial algae cell density in each replicate was 10 000 cells per mL. The growth of the algae was determined over an exposure period of 72 hours and compared with the growth of the control group.

Results

The test item concentration in the reconstituted water was not quantified at the start and the end of this study. Because of the low water solubility (0.07591 mg/L), the test item cannot be detected with standard analytical methods and the development of an analytical method with a sufficiently low detection and quantification limit is complex.
Due to the absence of any adverse effects at the saturation concentration, the study was performed without analytical concentration verification.
No significant effect on growth of the algae was observed at a nominal concentration of
100 mg/L, i.e. up to the maximum water solubility.

For the test item the following EC values were determined:

Parameter (0-72h)
Growth rate
Yield
EC10
95% confidence interval
>0.07591 mg/L (nominal >100 mg/L)
n.d.
>0.07591 mg/L (nominal >100 mg/L)
n.d.
EC20
95% confidence interval
>0.07591 mg/L (nominal >100 mg/L)
n.d.
>0.07591 mg/L (nominal >100 mg/L)
n.d.
EC50
95% confidence interval
>0.07591 mg/L (nominal >100 mg/L)
n.d.
>0.07591 mg/L (nominal >100 mg/L)
n.d.


Conclusions

Under the conditions of the present study, an aqueous solution of nominal 100 mg/L of  the test material  revealed no aquatic toxicity in the test system.
The 72h EC50 for growth rate and yield were >0.07591 mg/L (nominal >100 mg/L) and, thus, could not be determined in this study.

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the study an aqueous solution of nominal 100 mg/L of the test item revealed no toxicity to algae.
The 72-h EC50 and 72-h EC10 value for growth rate were >0.07591 mg/L (nominal >100 mg/L) and thus, could not be determined in the study.

Description of key information

The toxicity to aquatic algae and cyanobacteria was studied in a GLP compliant OECD 201 assay. The 72 -h EC50 and 72 -h EC10 value for growth rate were >0.07591 mg/L (nominal >100 mg/L) and thus, could not be determined in the study.

Key value for chemical safety assessment

Additional information