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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:
OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)
Version / remarks:
OECD Guideline nº 201 (2011)
Deviations:
not specified
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
not specified
Details on sampling:
The primary stock solution used in the range-finding test was prepared by dissolving 0.025 g of the test substance in volume completed to 250 mL with OECD medium, resulting in a concentration of 100 mg.L-1. The stock solution of 10 mg.L-1 was prepared from dilution of the primary stock solution.

The stock solution used in the definitive test was prepared by dissolving 0.1 g of the test substance in volume completed to 1000 mL with OECD medium, resulting in a concentration of 100 mg.L-1.

The analyses were carried out using gas chromatograph coupled to a mass spectrometer (GC-MS).
Vehicle:
no
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
- Common name: Green algae
- Strain: SAG 86.81
- Source (laboratory, culture collection): Originally obtained from Culture Collection of Algae at Goettingen University - SAG 61.81 on October, 08th, 2013, and is recommended by the Guideline OECD 201 (2011).
- Age of inoculum (at test initiation): 3 days growth
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
22.0 to 22.2 °C
pH:
7.96 - 8.12
Nominal and measured concentrations:
nominal: 0 (control); 1; 3.2; 10; 32 and 100 mg.L-1
mean measured: , -, 0.88, 3.28, 9.9, 30.85 and 95.81 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 mL Erlenmeyer flasks
- Material, size, headspace, fill volume: glass beaker plugged with gas permeable silicone sponge caps, 100 mL fill volume
- Initial cells density: 5 x 103 cells.mL-1
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 6

GROWTH MEDIUM
- Standard medium used: yes

- Light intensity and quality: 4656 lux (average), the photoperiod is continuous light

- Determination of cell concentrations: A Neubawer chamber and a microscope were used to determine the cell number (cells.mL-1).
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
ca. 10.44 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
other: yield
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
ca. 84.64 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
ca. 1 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Key result
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
ca. 3.2 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
growth rate
Details on results:
The 72-hours EyC50 value of test substance, obtained in this study with Pseudokirchneriella subcapitata, was 10.44 mg.L-1 (95% confidence limits = 8.46 to 12.88 mg.L-1) and the 72-hours ErC50 value was 84.64 mg.L-1 (95% confidence limits = 66.76 to 107.31 mg.L-1). The highest concentration of the test substance in which was not observed any statistically significant adverse effect on algal growth (NOEC) over the test period (72 hours) was 1 mg.L-1 and the lowest test substance concentration at which was observed significant reducing effect on growth (LOEC) was 3.2 mg.L-1.

The 72-hours EyC50 value of the reference substance potassium dichromate was 0.66 mg.L-1 (confidence limits at 95% = 0.60 to 0.72 mg.L-1), demonstrating that the toxic sensitivity of the algae was within the accepted range (ISO, 1989), which report toxicity ranged between 0.60 and 1.03 mg.L-1.

The growth curve of the test system (Pseudokirchneriella subcapitata) at different concentrations of test substance during 72 hours of exposure in the definitive test is shown.

In order to check the validity of the test, the biomass in the control cultures should increase exponentially by a factor of at least 16 within 72 hours. The mean coefficient of variation (CV) for section-by-section specific growth rates in the control cultures must not exceed 35% and the CV of average specific growth rate during the entire test period in replicate control cultures must not exceed 7%. In fact, in the present study, the biomass in the control cultures increased 509 times at end of the test. The mean coefficient of variation (CV) of the growth rate in the control group was 34.7% and the CV of average specific growth rate during the entire test period in replicate control cultures was 0.3%, showing therefore, the validity of this study.
Results with reference substance (positive control):
- Results with reference substance valid? yes
- EC50: 0.66 mg/L (based on yield)
Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the study, the 72 hour EC50 (growth rate) of the test material was determined to be 84.64 mg/l.
Executive summary:

In this guideline (OECD 201) study conducted with GLP certification, the objective of this study was to evaluate the toxicity of 1,3,2-Dioxathiane, 2,2-dioxide on alga Pseudokirchneriella subcapitata. A range-finding test was conducted to find the concentrations that cause algae growth inhibition. Based on the results of the range-finding test, a definitive test was carried out with the following concentrations of test substance: 0 (control); 1; 3.2; 10; 32 and 100 mg.L-1. The test was incubated during 72 hours inside chambers with controlled conditions of luminosity, temperature, and agitation. The 72-hours EyC50(yield) value was 10,44 mg/L and the 72-hours ErC50(growth rate) value was 84,64 mg/L. The highest test substance concentration which no observed significant adverse effect (NOEC) on algal growth was 1 mg/L and the lowest test substance concentration at which was observed significant reducing effect on growth (LOEC) was 3.2 mg/L.

Description of key information

Study carried out according to guideline and with GLP compliance.

Key value for chemical safety assessment

EC50 for freshwater algae:
84.64 mg/L
EC10 or NOEC for freshwater algae:
1 mg/L

Additional information

The key study for the determination of the inhibition of algal growth was conducted according to the Study Plan and procedures described in the Guideline 201 of the Organisation for Economic Co-operation and Development (OECD, 2011). The 72-hours EyC50 value of test substance, obtained in this study with Pseudokirchneriella subcapitata, was 10.44 mg/L (95% confidence limits = 8.46 to 12.88 mg/L) and the 72-hours ErC50 value was 84.64 mg/L (95% confidence limits = 66.76 to 107.31 mg/L). The highest concentration of the test substance in which was not observed any statistically significant adverse effect on algal growth (NOEC) over the test period (72 hours) was 1 mg/L and the lowest test substance concentration at which was observed significant reducing effect on growth (LOEC) was 3.2 mg/L.