Cerium dioxide

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 11-SEP-2006 to 12-SEP-2007

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:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: triplicates samples from each test medium (loading rate = 100 mg/L and dilutions 1:2, 1:4, 1:8, 1:16, 1:32) and from the control were sampled just before the start of the test and after 24, 48 and 72 hours. However, the cerium concentration were determined only in control, in undiluted filtrate and dilution 1:2, as the other dilutions were below the 72h-NOELR, and thus were not relevant for interpretation.
- Sampling method: data not available
- Sample storage conditions before analysis: immediately after sampling, the samples were filtered through glass fibre microfilters and acidified with 3% (v/v) nitric acid to stabilize the test item during the storage period. Then the samples were deep-frozen and stored at about -20°C until analysis

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method:
an undiluted filtrate of a supersaturated dispersion with the loading rate of 100 mg/L and the dilutions 1:2, 1:4, 1:8, 1:16, 1:32 of the filtrate were tested . The dispersion with the loading rate of 100 mg/L was prepared by dispersing 181.1 mg of the test item in 1800 mL of test water. The test item was mixed into the test water as homogeneously as possible using ultrasonic treatment for 15 min and intense stirring. The dispersion was stirred on a magnetic stirrer at room temperature in the dark for seven days. After the stirring period, the dispersion was filtered through a membrane filter (0.45 µm). The undiluted filtrate with the maximum concentration of dissolved test item was used as the highest concentrated test medium. The test medium was prepared just before the start of the test.
- Eluate: no
- Differential loading: yes
- Controls: blank (test water without test item)
- Evidence of undissolved material (e.g. precipitate, surface film, etc): yes, on the bottom of the stirring vessel, but not in the final test solution

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Common name: Scenedesmus subspicatus CHODAT
- Strain: No. 86.81 SAG
- Source: supplied by the Collection of Algal Cultures (SAG, Institut for Plant Physiology, University of Göttingen, D-37073 Göttingen, Germany)
- Age of inoculum (at test initiation): the algal were taken from an exponentially growing pre-culture, which was set up three days prior to the test under the same conditions as in the test.
- Method of cultivation: under standardized conditions according to the test guidelines: the algae were cultivated and tested in synthetic test water (analytical grade salts dissolved in sterile purified water).


ACCLIMATION
- Acclimation period: three days
- Culturing media and conditions: same as in the test
- Any deformed or abnormal cells observed: data not available

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Post exposure observation period:

none

Hardness:

0.24 mmol/L (= 24 mg/L as CaCO3)

Test temperature:

23 to 24°C

pH:

At the start of the test, the pH values in the test media and the control ranged from 7.9 to 8.3.
At the end of the test, pH values of 8.1 to 8.5 were measured.

Dissolved oxygen:

not measured

Salinity:

not applicable

Nominal and measured concentrations:

nominal concentrations: undiluted filtrate (loading rate: 100 mg/L), dilution 1:2 (loading rate 50 mg/L), dilution 1:4 (loading rate 25 mg/L), dilution 1:8 (loading rate 12,5 mg/L), dilution 1:16 (loading rate 6.25 mg/L), dilution 1:32 (loading rate 3.125 mg/L)

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type: Erlenmeyer flasks covered with glass dishes
- Material, size, headspace, fill volume: 50 mL, filled with 15 mL of algal suspension
- Aeration: no, but algal suspensions were continuously stirred by magnetic stirrers.
- Type of flow-through (e.g. peristaltic or proportional diluter): none (static test)
- Renewal rate of test solution (frequency/flow rate): not applicable (static test)
- Initial cells density: 5000 algal cells per mL of test medium
- Control end cells density: 593000 cells/mL
- No. of vessels per concentration (replicates): three replicates
- No. of vessels per control (replicates): six replicates


GROWTH MEDIUM
- Standard medium used: yes, the algae were cultivated in synthetic test water, prepared according to the test guidelines. Analytical grade salts were dissolved in sterile purified water.


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: sterile purified water
- Total organic carbon, Particulate matter, Metals, Pesticides, Chlorine, Alkalinity, Ca/mg ratio, Conductivity: data not available
- Culture medium different from test medium: no
- Intervals of water quality measurement: The pH was measured and recorded in the test concentration and the control at the start and at the end of the test. The water temperature was measured and recorded daily in an Erlenmeyer flask filled with water and incubated under the same conditions as the test flasks. The appearance of the test medium was also recorded daily. The concentration of phosphate was determined in the test medium and the control at the start of the test and then daily until the end of the test using a photometric method (Merck Spectroquant phosphate test 1.14842.0001). Prior to the determination, the algal cells were removed by filtration trough glass fibre microfilters (GF/C Whatman with a maximum pore size of about 1.2 µm).


OTHER TEST CONDITIONS
- Sterile test conditions: yes
- Adjustment of pH: no
- Photoperiod: continuously illuminated
- Light intensity and quality: the measured light intensity was about 7000 Lux (mean value) and was achieved by fluorescent tubes installed about 35 cm above the test flasks.


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: small volumes of the test media and the control (1.0 mL) were taken out of all test flasks after 24, 48 and 72 hours of exposure, and were not replaced. The algal cell densities in the samples were determined by counting with an electronic particle counter (Coulter Counter, Model ZM), with at least two measurements per sample. The measurements were performed at least in duplicate. Inhibition of algal growth was determined from: (i) the area under the growth curves (AUC) (= biomass integral), (ii) the specific growth rates (µ), and (iii) the yield (Y)
- Other: in addition, after 72 hours exposure, a sample was taken from the control and from a test concentration (dilution 1:2). The shape and size of the algal cells were examined microscopically in these samples.


TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2
- Justification for using less concentrations than requested by guideline: not applicable
- Range finding study: yes
- Test concentrations: not reported
- Results used to determine the conditions for the definitive study: not reported

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Key result

Duration:

72 h

Dose descriptor:

EL50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% CL: not determined

Duration:

72 h

Dose descriptor:

LOELR

Effect conc.:

100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EL10

Effect conc.:

91 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% CL: 86-94

Key result

Duration:

72 h

Dose descriptor:

NOELR

Effect conc.:

50 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

BIOLOGICAL RESULTS & INFLUENCE OF PHOSPHATE CONCENTRATIONS
- Exponential growth in the controL: yes (in the control, the cell density increased by a factor of 119 over 72 hours)
- Observation of abnormalities: no, the shape and size of the algal cells was not affected

A statistically significant inhibitory effects was reported on the growth of Scenedesmus subspicatus after the test period of 72 h first at the loading rate of 100 mg/L. Thus, this loading rate was determined as the 72h-LOELR. The 72h-NOELR was determined to be the loading rate of 50 mg/L. The 72h-EL50 was set superior to 100 mg/L.The inhibition of algal growth in the highest test concentration was presumably caused by a secondary effect, the complexation of the essential algal nutrient phosphate by the test item. The measured concentration of phosphate in the undiluted filtrate of the dispersion stirred for seven days was much lower than in the test water. A statistically significant decrease of the phosphate concentration was determined at the loading rate of 100 mg/L. Thus, the growth inhibition determined at this loading rate, which corresponded to the maximum concentration of dissolved test item, may have been caused by depletion of phosphate in the test medium, rather than by a toxic effect of cerium dioxide. As a consequence, it seems that cerium dioxide should not have toxic effect on the algae up to its solubility limit into water.

APPEARANCE OF THE TEST MEDIUM
No remarkable observations were made concerning the appearance of test media. The test media of all test concentrations were clear solutions throughout the entire test period.

ANALYTICAL MONITORING
The analytically measured concentrations of cerium in the test media samples (dilutions 1:2 and in the undiluted filtrate) taken at the start, at days 1 and 2 and the end of the test were below the limit of quantification (LOQ = 1 µg/L).

Results with reference substance (positive control):

- Results with reference substance valid? yes
- 72-hr EC50 for the growth rate = 1.0 mg/L (acceptance range : 0.44-1.16 mg/L) (potassium dichromate)

Reported statistics and error estimates:

The EL10 and EL50 values for the different growth parameters and their 95% confidence intervals were calculated as far as possible by Probit Analysis.
For the determination of the LOELR and NOELR, the calculated mean AUC, the mean growth and the mean yield at the test concentrations were compared to the corresponding control values by multiple Dunnett-tests.

Table 1: Algal cell density during the 72-hour test period

Dilution (loading rate)	Loading rate # (mg/L)		Density of algal cells (cell number x 10,000/mL) after
			24 h	48 h	72 h
Control	-	m s n	2.7 0.2 6	10.1 1.0 6	59.3 2.7 6
Dilution 1:32	3.1	m s n	2.6 0.2 3	10.8 1.3 3	59.0 1.7 3
Dilution 1:16	6.3	m s n	2.5 0.2 3	11.6 0.9 3	59.7 1.6 3
Dilution 1:8	12.5	m s n	2.6 0.1 3	10.1 0.9 3	58.9 6.4 3
Dilution 1:4	25	m s n	2.6 0.1 3	11.4 0.3 3	63.4 1.1 3
Dilution 1:2	50	m s n	2.6 0.0 3	11.6 0.2 3	62.9 4.7 3
Undiluted filtrate	100	m s n	2.7 0.1 3	11.1 0.7 3	28.4 1.5 3

m: mean value ; s: standard deviation ; n: number of flasks

 

Table 2: Areas under the Growth Curves (AUC) and percentage inhibition of AUC (I [AUC]) during the test period

Dilution	Loading rate # (mg/L)	Areas under the growth curves AUC and % inhibition of AUC
		0 to 24 h		0 to 48 h		0 to 72 h
		AUC	I [AUC] (%)	AUC	I [AUC] (%)	AUC	I [AUC] (%)
Control	-	1.10	0.0	7.00	0.0	41.18	0.0
1:32	3.1	1.04	5.3	7.23	-3.3	41.61	-1.0
1:16	6.3	0.98	11.4	7.48	-6.7	42.61	-3.5
1:8	12	1.04	5.3	6.88	1.7	40.88	0.7
1:4	25	1.03	6.1	7.51	-7.2	44.40	-7.8
1:2	50	1.05	4.5	7.63	-9.0	44.35	-7.7
Undiluted filtrate	100	1.10	0.0	7.50	-7.1	26.76*	35.0

AUC x 5000

-% inhibition: increase in growth relative to that of control

*: mean value significantly lower than in the control (according to Dunnett’s tests, one-sided, α = 0.05)

 

Table 3: Growth rates r and percentage inhibition of r (Ir) during the test period

Dilution (loading rate)	Loading rate # (mg/L)	Growth rate r and % of inhibition of r
		0 to 24 h		0 to 48 h		0 to 72 h
		r (1/day)	lr (%)	r (1/day)	lr (%)	r (1/day)	lr (%)
Control	-	1.68	0.0	1.50	0.0	1.59	0.0
1:32	3.1	1.64	2.5	1.53	-2.2	1.59	0.1
1:16	6.3	1.59	5.7	1.57	-4.5	1.59	-0.2
1:8	12	1.64	2.5	1.50	0.0	1.59	0.2
1:4	25	1.64	2.9	1.56	-4.1	1.61	-1.4
1:2	50	1.65	2.1	1.57	-4.6	1.61	-1.2
Undiluted filtrate	100	1.69	-0.1	1.55	-3.2	1.35*	15.4

-% inhibition: increase in growth relative to that of control

*: mean value significantly lower than in control (according to Dunnett-test, one sided smaller, α = 0.05)

 

Table 4: Yield (y) and percentage inhibition of y (Iy) during the test period

Dilution (loading rate)	Loading rate # (mg/L)	Yield y and inhibition of y
		0 to 24 h		0 to 48 h		0 to 72 h
		yield	ly (%)	yield	ly (%)	yield	ly (%)
Control	-	2.20	0.0	9.61	0.0	58.75	0.0
1:32	3.1	2.08	5.3	10.30	-7.2	58.45	0.5
1:16	6.3	1.95	11.4	11.05	-15.0	59.22	-0.8
1:8	12	2.08	5.3	9.60	0.1	58.38	0.6
1:4	25	2.07	6.1	10.88	-13.3	62.90	-7.1
1:2	50	2.10	4.5	11.07	-15.2	62.37	-6.2
Undiluted filtrate	100	2.20	0.0	10.60	-10.3	27.92*	52.5

y x 5000

-% inhibition: increase in growth relative to that of control

*: mean value significantly lower than in control (according to Dunnett-test, one-sided, α = 0.05)

Validity criteria fulfilled:

yes

Remarks:

In the control, the cell density increased by a factor of 119 during the test period of 72 hours (> 16), the coeff. of variation of the daily growth rates was 15.7% (<35%), and the coeff. of variation of the average specific growth rates was 1.0% (< 7%).

Conclusions:

A statistically significant inhibitory effects was reported on the growth of Scenedesmus subspicatus after the test period of 72 h first at the loading rate of 100 mg/L. Thus, this loading rate was determined as the 72h-LOELR. The 72h-NOELR was determined to be the loading rate of 50 mg/L. The 72h-EL50 was set superior to 100 mg/L. However, a significant phosphate depletion was observed at the highest tested concentration, probably due to a complexation process with the test item. As a consequence, the reduction of growth here observed was probably caused by an indirect effect of phosphate lack, rather than a toxic effect of cerium dioxide.

Executive summary:

The influence of cerium dioxide on the growth of the green algal species Scenedesmus subspicatus was investigated in a 72-hour static test according to guidelines EU C.3 (1992) and OCDE 201 (2006). The GLP were stated.

Due to the low water solubility of the test item, a supersaturated dispersion with the loading rate of 100 mg/L was prepared. Then the dispersion was filtered and the undiluted filtrate and the dilutions 1:2, 1:4, 1:8, 1:16 and 1:32 were used as test media. Additionally, a control was tested in parallel.

A statistically significant inhibitory effects was reported on the growth of Scenedesmus subspicatus after the test period of 72 h first at the loading rate of 100 mg/L. Thus, this loading rate was determined as the 72h-LOELR. The 72h-NOELR was determined to be the loading rate of 50 mg/L. The 72 h-EL50 was set superior to 100 mg/L. The inhibition of algal growth in the highest test concentration was presumably caused by a secondary effect, the complexation of the essential algal nutrient phosphate by the test item. The measured concentration of phosphate in the undiluted filtrate of the dispersion stirred for seven days was much lower than in the test water. A statistically significant decrease of the phosphate concentration was determined at the loading rate of 100 mg/L. Thus, the growth inhibition determined at this loading rate, which corresponded to the maximum concentration of dissolved test item, may have been caused by depletion of phosphate in the test medium, rather than by a toxic effect of cerium dioxide. As a consequence, it seems that cerium dioxide should not have toxic effect on the algae up to its solubility limit into water.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

From JAN 2007 to 26 APR 2007

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods with acceptable restrictions

Remarks:

The study was conducted according to an american guideline, without reference to the application of GLP and without analytical monitoring of the test substance. However, the experimental details and results were well described.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: U.S. Environmental Protection Agency. 2002b. Short-term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms. EPA-821-R-02-013. Office of Water, Washington D.C.

Deviations:

no

GLP compliance:

not specified

Analytical monitoring:

no

Details on sampling:

none

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Test solution was prepared by combining Cerium oxide with moderately hard reconstituted lab water. Cerium oxide was insoluble, which resulted in highly turbid solution. As a result, in order to eliminate any toxic effects due to high suspended solids, the solids were allowed to settle before using the solution in the test. The stock solution was prepared and allowed to mix for 24 hours. After 24 hours of mixing, it was removed from the stir plate and the suspended solid was allowed to settle for an additional 24 hours. The stock solution (50 g/L) was then decanted and used to prepare the tests solutions.
- Controls: yes, reconstituted water without test item
- Evidence of undissolved material (e.g. precipitate, surface film, etc): no data
- No further data

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

TEST ORGANISM
- Common name: Selenastrum capricornutum
- Strain: no data
- Source: S. capricornutum were obtained from Aquatic BioSystems, Inc. (Fort Collins, CO).
- Age of inoculum at study initiation : 4, 6, or 7 days old (no age variation within the same test)
- Method of cultivation: no data

ACCLIMATION
- Acclimation period: no data

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Hardness:

80-110 mg CaCO3/L

Test temperature:

25°C

pH:

8.16-9.67

Dissolved oxygen:

6.8-7.3 mg O2/L at the test initiation

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 2500, 5000, 12500, 25000, 50000 mg/L

Details on test conditions:

TEST SYSTEM
The test was performed twice on the same day.
- Test vessel: 250 ml autoclaved glass Erlenmeyer flasks filled with 50 ml test solution
- Aeration: no data
- Type of flow-through (e.g. peristaltic or proportional diluter): none (static test)
- Renewal rate of test solution (frequency/flow rate): not applicable (static test)
- Initial cells density: 10000 cells/ml
- Control end cells density: test A: 4.4 x 10exp6 cells/ml and test B: 4.6 x 10exp6 cells/ml
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: The reconstituted lab water was prepared using ultra-pure deionized water combined with reagent grade chemicals and followed the standard EPA recipe, with a slight modification to increase the hardness to approximately 100 mg/L.
- Alkalinity: 44-64 mg CaCO3/L
- Conductivity: 324-349 µmho/cm
- Total dissolved solids: 155-167 mg/L
- Ammonia: 0.12-0.32 mg NH3/L
- Intervals of water quality measurement: Total hardness (as mg CaCO3/L), pH, alkalinity (as mg CaCO3/L), conductivity, total dissolved solids, ammonia, and dissolved oxygen were measured in all concentrations at test initiation. Temperature, conductivity, pH, and dissolved oxygen were measured daily in each concentration.
- No further data

OTHER TEST CONDITIONS
- Photoperiod: constant illumination
- Light intensity: 400 ft-c light intensity
- No further data

EFFECT PARAMETERS MEASURED : In this test, growth measured and replication of the algae cells (cells/ml) is the endpoint used to determine the 25% Inhibition Concentration for the compound, referred to as the IC25.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2
- Justification for using less concentrations than requested by guideline: no data
- Range finding study: yes
- Test concentrations: 1000, 2500, 5000, 10000 mg/L
- Results used to determine the conditions for the definitive study: no data

Reference substance (positive control):

not specified

Remarks:

Reference toxicity tests were conducted monthly to ensure consistent organism quality. No further information.

Duration:

96 h

Dose descriptor:

other: IC25

Effect conc.:

33 631 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: growth

Remarks on result:

other: test A

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

5 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: growth

Remarks on result:

other: test A

Duration:

96 h

Dose descriptor:

other: IC25

Effect conc.:

36 607 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: growth

Remarks on result:

other: test B

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

< 2 500 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: growth

Remarks on result:

other: test B

Details on results:

The IC25 and NOEC values were based on growth, and not on growth rate (i.e. change in cell densities over time). Growth was calculated by subtracting initial cell density from final cell density.

The discrepancy between the IC25 and the NOEC values appeared to be anomalous. The IC25 effect levels are more representative of the correct toxicity value.

Results with reference substance (positive control):

no data

Reported statistics and error estimates:

no data

Results of Selenastrum capricornutum toxicity cerium oxide

Nominal concentration (mg/L)	0	2500	5000	12500	25000	50000
Test A: Initial cell density (cells/mL) Final cell density (cells/mL) Mean growth (cells/mL)	1 x 10E4 4.4 x 10E6 4.4 x 10E6	1 x 10E4 4.4 x 10E6 4.4 x 10E6	1 x 10E4 4.4 x 10E6 4.4 x 10E6	1 x 10E4 4.2 x 10E6 4.2 x 10E6	1 x 10E4 3.5 x 10E6 3.5 x 10E6	1 x 10E4 3.0 x 10E6 3.0 x 10E6
Test B: Initial cell density (cells/mL) Final cell density (cells/mL) Mean growth (cells/mL)	1 x 10E4 4.6 x 10E6 4.6 x 10E6	1 x 10E4 4.3 x 10E6 4.3 x 10E6	1 x 10E4 4.2 x 10E6 4.2 x 10E6	1 x 10E4 4.2 x 10E6 4.2 x 10E6	1 x 10E4 3.7 x 10E6 3.7 x 10E6	1 x 10E4 3.2 x 10E6 3.2 x 10E6

Validity criteria fulfilled:

not specified

Conclusions:

Cerium oxide had low toxicity to algae up to a concentration of 50000 mg/L.

Executive summary:

The 96hr-acute toxicity of cerium oxide to Selenastrum capricornutum was studied according to the US EPA method EPA/600/4 -91/002 (2002). Selenastrum capricornutum were exposed to control and test chemical at 2500, 5000, 12500, 25000 and 50000mg/L for 96 hr. Growth were observed during the test and 96-hour IC25 of 33631 mg/L (test A) and 36607 mg/L (test B) were calculated; implying a low toxicity of cerium oxide to algae.

Reference 3

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: :

Remarks:

Some tables and figures of the publication report results on bulk cerium dioxide. However, the article primarily deals with the nanoparticle form, and no experimental detail is given concerning the experiment with the micrometric ones. Therefore, a reliability 4 was attributed to this data.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

No data are available on the bulk form. As results are presented concomittantly with those on nanoparticles, one can expected that the same experimental protocol was applied (i.e. OECD method 201).

GLP compliance:

not specified

Analytical monitoring:

not specified

Details on sampling:

No data on the analytical monitoring of concentrations of the bulk cerium dioxide during the test.

Vehicle:

not specified

Details on test solutions:

No data are available on the bulk form.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

No data are available concerning the organisms tested during the experiment on the bulk form.

Test type:

not specified

Water media type:

freshwater

Total exposure duration:

72 h

Hardness:

No data

Test temperature:

No data

pH:

No data

Dissolved oxygen:

No data

Salinity:

Not applicable

Nominal and measured concentrations:

No data are available on the bulk form.

Details on test conditions:

No data are available on the bulk form.

Reference substance (positive control):

not specified

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Validity criteria fulfilled:

not specified

Conclusions:

Based on the limited details provide, cerium dioxide does not present algal toxicity.

Executive summary:

In this publication primarily dealing with nanoparticulate cerium dioxide, some results are given concerning the bulk form. A 48 -hour NOEC superior to 1000 mg/L based on growth was reported; implying that bulk cerium dioxide does not present toxicity for the algae Pseudokirchneriella subcapitata.

Description of key information

The 72-hour EL50 (Fresh water algae: Scenedesmus subspicatus) of the bulk form of cerium dioxide was > 100 mg/L based on the growth rate. Hence, the bulk form of cerium dioxide is not harmful for the algal species tested.

Additional information

Three experimental studies were available (RCC, 2007; Lambert, 2007; Van Hoecke et al., 2009a). The first of them, scored as Klimisch 1, was selected as a key study, and the other ones of a reliability 2 (Lambert, 2007) and 4 (Van Hoecke et al. 2009a) gave consistent results and were flagged as supporting studies. All the data concluded that the bulk form of cerium dioxide was not harmful to algae.