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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:
2000
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
Monitoring of formaldehyde was unsuccessful. However, this deficiency is considered to have no influence on the integrity and validity of the results. In addition, the intitial cell concentration was 8.1 • 10exp4 cells/mL instead of ca. 10exp4 cells/mL recommended by the Guideline. Furthermore, in the test medium, NaHCO3 was twice as concentrated (100 mg/L) as indicated in the Guideline (50 mg/L). However, these deviations are considered to have no impact on the integrity of the results. In contrast, the higher concentration of hydrogencarbonate should rather stabilise the pH value. Furthermore, the pH value deviated in some vessels by more than 2 units during the test, while according to the Guideline the value should normally deviate by not more than one unit. However, this deviation is also considered as having no influence on the integrity and validity of the results.
Qualifier:
according to
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Version / remarks:
Version Jun. 07th, 1984
Deviations:
yes
Remarks:
The intitial cell conc. was 8.1 • 10exp4 cells/mL instead of ca. 10exp4 cells/mL. NaHCO3 was twice as concentrated (100 mg/L) as indicated in the Guideline (50 mg/L). In some vessels the pH value deviated by more than 2 units during the test.
GLP compliance:
yes
Analytical monitoring:
yes
Vehicle:
no
Test organisms (species):
Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)
Details on test organisms:
TEST ORGANISM
- Strain: CHODAT
- Source: Laboratory culture
- Method of cultivation: Pre-culture 3 days before start of the test incubated under the same conditions as in the test afterwards
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
72 h
Test temperature:
22.1 – 23.2 °C, mean 22.93 °C (measured daily)
pH:
7.94 – 10.55
Nominal and measured concentrations:
Initial concentrations: Screening test: 0.1, 1, 10, 100 mg/L + control; Main test: 0.625, 1.25, 2.5, 5, 10 mg/L + control
Actual concentrations: Formaldehyde could not be found in neither the t0 nor in the t72h samples at nominal concentrations of 2.5, 5 and 10 mg/L. The detection limit was 1 mg/L.
Details on test conditions:
TEST SYSTEM
- Test vessel: 50 mL
- Type: closed. Test solutions covered with plexiglass lid
- Aeration: no
- Initial cells density: 7.68 - 8.13 • 10exp4 cells/mL
- No. of vessels per concentration (replicates): 5

GROWTH MEDIUM
- Standard medium used: Composition of the medium as indicated in the OECD Guideline 201. Only exception: NaHCO3 was twice as concentrated (100 mg/L) as indicated in the Guideline (50 mg/L)

TEST MEDIUM / WATER PARAMETERS
- Intervals of water quality measurement: Temperature measured daily. pH measured at the beginning and after 72 h

OTHER TEST CONDITION
- Procedure for suspending algae: Stirring for 15 min/hour with magnetic stirrer
- Photoperiod: Continuous illumination
- Light intensity: 120 µE/m2s (8000 lux)

EFFECT PARAMETERS MEASURED: Growth rate, biomass
Biomass: determined by spectrophotometer at 578 nm.

- Determination of cell concentrations: Extinction values determined at t0, after 24 h, 48 h and 72 h
Reference substance (positive control):
no
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
1.11 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.:
1.48 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.:
4.62 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth rate
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.99 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
1.27 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
biomass
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
3.48 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
biomass
Reported statistics and error estimates:
Calculations performed according to Guideline. No information about the EC50 calculation method

 Results of main test:

Test substance
Concentration
(nominal)

[mg/L]

Cell concentrations (mean values)
[104cells/mL]

measured

Percent of control

0 h

24 h

48 h

72 h

0 h

24 h

48 h

72 h

Control

8.11

27.0

96.8

327

 

 

 

0

10

8.13

12.0

13.9

7.75

 

 

 

101.3

5

8.07

17.5

29.2

77.3

 

 

 

38.9

2.5

7.83

25.4

77.9

276

 

 

 

3.7

1.25

7.68

28.2

104

327

 

 

 

-1.4

0.625

8.03

27.5

101

327

 

 

 

-0.3

Temp. [°C]

22.1 – 23.2 °C

 

pH

7.97-8.25

 

 

7.94-10.55

 

 

Validity criteria fulfilled:
yes
Conclusions:
The test substance was found to be acutely toxic towards algae at relatively low concentrations.
Executive summary:

The toxicity ofthe reaction products of ethylene glycol with paraformaldehydeto the freshwater green algae Desmodesmus subspicatus was studied in a test according to the OECD Guideline 201.

The algae were exposed to 5 concentrations of the test substance, ranging from 0.625 to 10 mg/L. The initial cell concentration was 8.1 • 104cells/mL instead of ca. 104 cells/mL recommended by the Guideline. In the test medium, NaHCO3was twice as concentrated (100 mg/L) as indicated in the Guideline (50 mg/L).

All concentrations were tested using 5 replicates. The test was performed at 22.1 – 23.2 °C in a medium according to the OECD Guideline. The cells were counted after 0, 24, 48, and 72 hours, the pH value was measured at the start and end of the test.

All validity criteria according the test Guideline are met within the study.

A clear concentration-response relationship can be established from the study results. Both, the initial cell concentration of the algae and NaHCO3concentration were above the values recommended by the Guideline. The latter deviation is justified as the higher concentration of hydrogencarbonate should stabilize the pH value.

The test substance EGForm hydrolyses rapidly and completely in the test medium, forming ethylene glycol and formaldehyde. Formaldehyde is expected to dominate the toxicity of the EGForm in aqueous solutions. Formaldehyde is expected to be not volatile from the test solution, and no losses due to adsorption are expected.

Monitoring of formaldehyde was unsuccessful, as it could not be detected neither in the t0 nor in the t72h samples. This behaviour was not observed in test solutions of the respective tests with daphnia and fish. There is no explanation for the negative result. A possible reason for the disappearance of the test substance may be a reaction with components of the test solution (possibly ammonium).

However, in the present test a clear concentration-effect curve could be obtained, which clearly indicates the presence of the test substance. This assumption, i.e. presence of the test substance, is supported by the monitoring data obtained in the respective fish and daphnia tests. Therefore, the effective concentrations can be considered to be identical with the nominal concentrations.

Description of key information

Algal toxicity was found with EC50s of 3.48 mg/L and 4.62 mg/L for biomass production and growth rate, respectively. The NOEC based on the growth rate was determined to be 1.11 mg/L.

Monitoring in the algae test was unsuccessful, probably because of reaction of formaldehyde with a component of the test medium. Because of the clear dose-effect relationship obtained in the test and the positive monitoring results in the fish and daphnids test, the nominal concentrations in the algae test are considered as effective concentrations.

Key value for chemical safety assessment

EC50 for freshwater algae:
4.62 mg/L
EC10 or NOEC for freshwater algae:
1.48 mg/L

Additional information