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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:
weight of evidence
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
Experimental test result performed using standard OECD test guideline
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
yes
Remarks:
DMSO was used as a vehicle.
Details on test solutions:
The stock solution 10.0 g/l was prepared by dissolving white powder in DMSO. Test solutions of required concentrations were prepared by mixing the stock solution of the test sample with OECD growth medium and inoculum culture.
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM
- Strain: 86.81 SAG
- Source (laboratory, culture collection): Institute of botany of the ASCR
- Initial biomass concentration: 5x10(3) cells /ml
- Method of cultivation: No data available
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
23±2°C
pH:
without adjustment
the sample at concentration: 5.6 mg/l: pH 8.0 did not change during the test
control: pH = 8.0 changed to pH = 8.1 during the test
Nominal and measured concentrations:
Nominal test chemical conc. used for the study were 0, 0.35, 0.70, 1.4, 2.8 and 5.6 mg/l, respectively.
Details on test conditions:
TEST SYSTEM
- Test vessel: 100 ml Glass vessel
- Type (delete if not applicable): closed (with air permeable stopper)
- Sample volume: 30 ml
- Initial cells density: 5x10(3) cells/ml
- No. of vessels per concentration (replicates): 3

GROWTH MEDIUM
- Standard medium used: yes

OTHER TEST CONDITIONS
- Adjustment of pH: No
- Photoperiod: Continuous
- Light intensity and quality: 6000-8000 lx

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: microscope with counting chamber Cyrus I or electronic particle counter.
- Other: ErC50 was calculated using non-linear regression by the software Prism 4.0
Reference substance (positive control):
yes
Remarks:
Potassium dichromate (K2Cr2O7)
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
4.93 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Remarks on result:
other: 95% CL: 4.83 to 5.02 mg/l
Results with reference substance (positive control):
- Results with reference substance valid
- EC50: 0.65 mg/L (24 hours)
Reported statistics and error estimates:
EC50 was calculated using non linear regression by the software Prism 4.0
Validity criteria fulfilled:
yes
Conclusions:
Based on the growth rate inhibition of algae Desmodesmus subspicatus (previous name: Scenedesmus subspicatus) due to the exposure of test chemical, the 72hr median effective concentration (ErC50) value was determined to be 4.93 mg/l (95% CL: 4.83 to 5.02 mg/l).
Executive summary:

Toxicity to aquatic algae study was conducted for 72 hrs for assessing the effect of test chemical on Desmodesmus subspicatus. The test was performed in accordance to OECD Guideline 201 (Alga, Growth Inhibition Test). Desmodesmus subspicatus (previous name: Scenedesmus subspicatus) of strain 86.81 SAG obtained from Institute of botany of the ASCR with an initial biomass conc. 5x10(3) cells /ml was used as a test organism. The stock solution 10.0 g/l was prepared by dissolving white powder in DMSO. Test solutions of required concentrations were prepared by mixing the stock solution of the test sample with OECD growth medium and inoculum culture. Nominal test chemical conc. used for the study were 0, 0.35, 0.70, 1.4, 2.8 and 5.6 mg/l, respectively. Study was performed using Desmodesmus subspicatus as a test organism in a static fresh water system. Desmodesmus subspicatus were exposed to test chemical in 100 ml glass vessel in a volume of 30 ml of liquid solution containing both the chemical and media. The beakers were placed in a room at a temperature of 23±2°C with a continuous light intensity of 6000-8000 lx, respectively. Alongwith the test chemical, one positive control Potassium dichromate (K2Cr2O7) was also run simultaneously. Solvent control was also run simulatenously during the test. Cell counting was carried out using microscope with counting chamber Cyrus I or electronic particle counter. ErC50 was calculated using non-linear regression by the software Prism 4.0. On the basis of the effect of test chemical on the growth rate of the test organism Desmodesmus subspicatus, the 72 hr median effect concentration (ErC50) value was determined to be 4.93 mg/l (95 % CI 4.83 - 5.02 mg/l). Thus, based on the EC50 value, test chemical can be considered to be toxic to aquatic algae and considered to be classified in 'aquatic chronic category 2' as per the CLP classification criteria.

Description of key information

On the basis of the experimental studies of the functionally similar read across chemical and applying the weight of evidence approach, the 72/96 hr EC50 value (ErC50) of the test chemical on test organism green algae was determined to be in the range 4.93 to 9.571 mg/l, respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:
4.93 mg/L

Additional information

Data available for target chemical and structurally & functionally similar read across analogues, has been reviewed to determine the effect caused on fresh water algae. The studies are summarised below:

In an experimental study, toxicity to aquatic algae study was conducted for 72 hrs for assessing the effect of test chemical on Desmodesmus subspicatus. The test was performed in accordance to OECD Guideline 201 (Alga, Growth Inhibition Test). Desmodesmus subspicatus (previous name: Scenedesmus subspicatus) of strain 86.81 SAG obtained from Institute of botany of the ASCR with an initial biomass conc. 5x10(3) cells /ml was used as a test organism. The stock solution 10.0 g/l was prepared by dissolving white powder in DMSO. Test solutions of required concentrations were prepared by mixing the stock solution of the test sample with OECD growth medium and inoculum culture. Nominal test chemical conc. used for the study were 0, 0.35, 0.70, 1.4, 2.8 and 5.6 mg/l, respectively. Study was performed using Desmodesmus subspicatus as a test organism in a static fresh water system. Desmodesmus subspicatus were exposed to test chemical in 100 ml glass vessel in a volume of 30 ml of liquid solution containing both the chemical and media. The beakers were placed in a room at a temperature of 23±2°C with a continuous light intensity of 6000-8000 lx, respectively. Alongwith the test chemical, one positive control Potassium dichromate (K2Cr2O7) was also run simultaneously. Solvent control was also run simulatenously during the test. Cell counting was carried out using microscope with counting chamber Cyrus I or electronic particle counter. ErC50 was calculated using non-linear regression by the software Prism 4.0. On the basis of the effect of test chemical on the growth rate of the test organism Desmodesmus subspicatus, the 72 hr median effect concentration (ErC50) value was determined to be 4.93 mg/l (95 % CI 4.83 - 5.02 mg/l).

Another algal growth inhibition test was conducted for 96 hrs for assessing the growth inhibition potentialof test chemical on green algae.The test was performed following the ASTM International Standards method (1988) under static condition for 96 hrs. Analytical monitoring of test chemical concentrations were carried out by GC analysis.Test organism green algae (10000 cells/ml) were exposed to five different conc. of test chemical, i. e.,0, 12.5, 25, 50 and 100 mg/l in 125 ml flasks for a period of 96 hrs. These test vessels were shaken continuously. All experiments were performed in four replicates. IC50 was calculated using a linear interpolation program. On the basis of the effect on growth of the test organism green algae,the 96 hrs IC50 value was determined to be 9.57 mg/l (95% C. I. = 7.434 to 13.274). 

In a supporting weight of evidence study, toxicity to aquatic algae study was conducted for 72 hrs for assessing the effect of test chemical on Desmodesmus subspicatus. The test was performed in accordance to OECD Guideline 201 (Alga, Growth Inhibition Test). Desmodesmus subspicatus (previous name: Scenedesmus subspicatus) of strain 86.81 SAG with an initial biomass conc. 5x10(3) cells /ml was used as a test organism. The stock solution 100 g/l was prepared by dissolving white powder in acetone and it was 10 times diluted by acetone. Test solutions of required concentrations were prepared by mixing the stock solution of the test sample with OECD growth medium and inoculum culture. Nominal test chemical conc. used for the study were 0, 0, 2, 3.6, 6.5, 12 and 21 mg/l, respectively. Study was performed using Desmodesmus subspicatus as a test organism in a static fresh water system. Desmodesmus subspicatus were exposed to test chemical in 50 ml glass vessel in a volume of 15 ml of liquid solution containing both the chemical and media. The beakers were placed in a room at a temperature of 23±2°C with a continuous light intensity of 6000-8000 lx, respectively. Alongwith the test chemical, one positive control Potassium dichromate (K2Cr2O7) was also run simultaneously. Solvent control was also run simulatenously during the test. Cell counting was carried out using microscope with counting chamber Cyrus I or electronic particle counter. ErC50 was calculated using non-linear regression by the software Prism 4.0. On the basis of the effect of test chemical on the growth rate of the test organism Desmodesmus subspicatus, the 72 hr median effect concentration (ErC50) value was determined to be 8.9 mg/l (95 % CI 8.0 - 10.0 mg/l).

On the basis of the experimental studies of the functionally similar read across chemical and applying the weight of evidence approach, the 72/96 hr ErC50 value of the test chemical on test organism green algae was determined to be in the range 4.93 to 9.571 mg/l, respectively. Thus, based on the ErC50 value, test chemical can be considered to be toxic to aquatic algae and considered to be classified in 'aquatic chronic category 2' as per the CLP classification criteria.