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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
See attached document in section 13 "Assessment report" for justification and rationale of the analogy approach.
Original letters from the French Competent Authorities requiring the read across to be done with cerium oxide isostearate are attached below.
Reason / purpose for cross-reference:
read-across source
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
>= 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
other: growth rate and biomass data
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
>= 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
other: growth rate and biomass data
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
other: growth rate and biomass data
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
> 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
other: growth rate and biomass data
Conclusions:
Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as having no toxic effects on Pseudokirchneriella subcapitata up to its solubility limit in the test water at the loading rate of 100 mg/L (=100% saturated solution) under the present test conditions.
Executive summary:

The source and target substances present similar characterization (nanoparticles of very similar parameters), and similar physico-chemical and ecotoxicological properties (high melting point, low vapour pressure, very low water solubility, no expected bioaccumulation potential when considering cerium and iron elements and isostearate parts, no acute toxicity to daphnids up to and including the saturation concentration). This similarity supports the relevance of the read-across.

Thus, the toxicity to algae is expected to be the same for the source and target substances.

Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as having no toxic effects on Pseudokirchneriella subcapitata up to its solubility limit in the test water at the loading rate of 100 mg/L (=100% saturated solution) under the present test conditions.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
experimental study
Adequacy of study:
key study
Study period:
from October 2001 to 17 January 2002
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 201 (Alga, Growth Inhibition Test)
Deviations:
yes
Remarks:
duration of test is 96 hours.
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 0 and 100 mg/L (loading rate)
- Sampling method: each sample contained 100 mL (control solution) or 50 mL (loading rate 100 mg/L). Samples were taken in triplicate (control solution) or duplicate (loading rate 100 mg/L) at the beginning and the end of the test, and analysed for Cerium content. Further samples were also taken after 96 hours from the limit test solutions (control and loading rate 100 mg/L) which contained no algae and had been run alongside the test to determine the influence of adsorption on the possible decrease of test item concentration throughout the test.
- Sample storage conditions before analysis: all samples were acidified just after sampling with 1% (v/v) of nitric acid and refrigerated at + 4 °C.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION:
As the test item, when added to water, is dissociated into a mixture of poorly soluble components (isostearate, cerium and iron), the water-soluble fractions (WSF) procedure was applied to prepare the test solutions.
Each solution was prepared by stirring the test item in test water at the appropriate loading rate during 7 days at 20-25°C ± 2°C in darkness. After a filtration through a filter of porosity 4-7µm and then a filter of porosity 0.45µm, the WSF was collected and used as the test solution.
Test organisms (species):
Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)
Details on test organisms:
TEST ORGANISM
- Strain: CCAP278/4
- Source: Culture collection of algae and protozoa, Institute of Freshwater Ecology, Far Sawrey, Ambleside, Cumbria, LA22 OLP, UK
- Age of inoculum: week-old culture
- Method of cultivation: cultured under sterile condition and maintained at exponential growth rate
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
96 h
Post exposure observation period:
none
Hardness:
34 +/- 17 mg/L as CaCO3
Test temperature:
23.2°C to 24.5°C
pH:
control: 7.38 to 8.59
at 100 mg/L: 7.36 to 9.69
Dissolved oxygen:
data not available
Nominal and measured concentrations:
Nominal loading rate: 100 mg/L (= 100% saturated solution)
Measured concentration at T0: 7.9 µg/L
Measured concentration at T96 (without algae): 3.8 µg/L
Measured concentration at T96 (with algae): 1.3 µg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 250mL conical glass flask stoppered with sterile cotton wool wrapped with lint.
- Material, size, headspace, fill volume: filled with 100mL solution
- Aeration: no, but constantly agitated
- Initial cells density: 1 x 10E4 cells/mL
- Control end cells density: 128 x 10E4 to 160 x 10E4 cells/mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6
- Further groups of vessels were prepared for chemical analysis by adding the control and the limit test solutions but no algal pre-culture.

GROWTH MEDIUM
- Standard medium used: yes

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: reconstituted water (LC)
- Culture medium different from test medium: no
- Intervals of water quality measurement: The pH values of the control and the limit test loading rate (100 mg/) was measured at the beginning of the test, and after 72 and 96 hours. Water hardness was measured once before the start of the test in LC reconstituted medium. Temperature was checked daily.

OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: no
- Photoperiod: continuously illuminated
- Light intensity and quality: a set of 15 and 30 W fluorescent tubes between "white" and "daylight" type was used (6680 to 7600 lux)

EFFECT PARAMETERS MEASURED: cell numbers were measured at 0, 24, 48, 72 and 96 hours using a Malassez cell counter. Specific growth rate and biomass were calculated from these measurements. Specific growth rate can be defined as the natural log of the cell number over specific intervals. Biomass may be defined as the cell number per mL of solution x time in hours.

TEST CONCENTRATIONS
Spacing factor for test concentrations: not relevant (limit test)
- Range finding study: yes
- Test concentrations of the range finding study: 1 and 10 mg/L (loading rate)
- Results used to determine the conditions for the definitive study: no mortality observed up to 10 mg/L (loading rate).
Reference substance (positive control):
no
Key result
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
>= 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
other: growth rate and biomass data
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
>= 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
other: growth rate and biomass data
Key result
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
> 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
other: growth rate and biomass data
Duration:
96 h
Dose descriptor:
EC50
Effect conc.:
> 100 other: % saturated solution
Conc. based on:
test mat.
Basis for effect:
other: growth rate and biomass data
Details on results:
BIOLOGICAL RESULTS:
Inhibitions of the growth rate and growth at 100 mg/L were 0% relative to control, at T72 and T96 hours. The same results were observed in the range-finding test at 1 and 10 mg/L at T72 and T96 hours.

In fact the growth rate and the growth increased with the test item loading rate at each measurement time (T24, T48, T72 and T96 hours) for the growth rate at T72 and T96 hours for the growth. This increase was statistically significant for both parameters at 10 and 100 mg/L, when compared to control, after 72 and 96 hours. It was supposed that this phenomenon was due to iron coming from the test item, a metal which is known for its stimulating action on the growth of unicellular green algae in water.


ANALYTICAL RESULTS:
The measured concentration of Cerium in the solution at 100 mg/L (without algae) at T0 was 7.9 µg/L, which is slighly higher than the water solubility determined in the OECD test No. 105 (i.e. 2.8 µg Ce/L). This slight discrepancy can be explained by the use of different water media between OECD test No. 105 and 202. It was therefore considered that the saturation level of all test item components was reached during this study.
At the end of the test (T96), the measured concentrations of cerium in the solution with (i.e. 1.3 µg/L) and without algae (i.e. 3.8 µg/L) at 100 mg/L were lower than the initial value (84% and 52%, respectively). The decrease being more important in the presence of algae, it was supposed that the decrease concentration of cerium during the test was not only due to precipitation and/or adsorption to the test vessel walls but also to adsorption at the surface of cells of the component.
Results with reference substance (positive control):
not examined.

Table 1: T72 hours – number of cells and calculation of specific growth rate at each loading rate

Nominal loading rate (mg/L)

Rep.

Total no. of cells at 72hrs (104/mL)

Ln No. of cells

Mean Ln No. of cells

Specific growth rate

% inhibition of growth rate

0

1

2

3

4

5

6

29.0

24.0

26.5

27.5

29.0

30.0

12.58

12.39

12.49

12.52

12.58

12.61

12.53

0.14

 

1

1

2

30.0

28.5

12.61

12.56

12.59

0.14

-1.75

10

1

2

117.0

94.0

13.97

13.75

13.86

0.19

-40.25

100

1

2

3

123.0

112.0

115.0

14.02

13.93

13.95

13.97

0.20

-43.44

 

Table 2: T96 hours – number of cells and calculation of specific growth rate at each loading rate

Nominal loading rate (mg/L)

Rep.

Total no. of cells at 72hrs (104/mL)

Ln No. of cells

Mean Ln No. of cells

Specific growth rate

% inhibition of growth rate

0

1

2

3

4

5

6

160.0

141.5

130.0

150.0

128.0

138.5

14.29

14.16

14.08

14.22

14.06

14.14

14.16

 0.21

 

1

1

2

146.0

152.0

14.19

14.23

14.21

0.21

-1.12

10

1

2

314.0

179.0

14.96

14.40

14.68

0.23

-10.52

100

1

2

3

355.0

320.0

343.0

15.08

14.98

15.05

15.04

0.24

-17.74

Validity criteria fulfilled:
yes
Conclusions:
Cerium and iron oxide isostearate had no toxic effects on Pseudokirchnerella subcapitata up to its solubility limit in the test water at the loading rate of 100 mg/L (100% saturated solution) under the present test conditions.
Executive summary:

The influence of cerium and iron oxide isostearate on the growth of the green algal species Pseudokirchnerella subcapitata was investigated in a 96-hour static test according to OCDE guideline 201. The GLP were stated. The algae were exposed to control and test chemical at a nominal loading rate of 100 mg/L. The water-soluble fraction (WSF) procedure was applied to prepare the test solutions.

Measurements of cell numbers were performed daily to calculate specific growth rate and biomass.

At T72 and T96 hours, inhibitions of the growth rate and growth at 100 mg/L were 0% relative to control. The same results were observed in the range-finding test at 1 and 10 mg/L at T72 and T96 hours. In fact the growth rate and the growth increased with the test item loading rate at each measurement time (T24, T48, T72 and T96 hours) for the growth rate, and at T72 and T96 hours for the growth. It was statistically significant at 10 and 100 mg/L and probably due to iron coming from the test item, a metal which is known for its stimulating action on the growth of unicellular green algae in water.

Thus, the 96-hour and 72-hour NOEC is ≥ 100% saturated solution, while the 96-hour and 72-hour EC50 is > 100% saturated solution. As no adverse effect was observed at the highest loading rate tested (i.e. 100 mg/L), which corresponded to the maximum concentration of dissolved test item, cerium and iron oxide isostearate is not toxic for algae up to its solubility limit into water.

Description of key information

By analogy with cerium and iron oxide isostearate (active matter of DPX10), iron oxide isostearate (active matter of DPX13) is not considered as harmful for the algal species tested.

Key value for chemical safety assessment

Additional information

One GLP-compliant study performed according to OECD guideline 201 is available on the analogue, cerium and iron oxide isostearate (active matter of DPX10). It is quoted as reliability 1 according to Klimisch criteria and flagged as a key study.