Cerium dioxide

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 21-DEC-2007 to 27-FEB-2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations:
Triplicate samples were taken from the test media of all test concentrations (loading rate of 100 mg/L and dilutions 1:3.2, 1:10, 1:32 and 1:100) and from the control at the start of the first treatment period (Day 0), at a treatment period in the second week (Day 7), and at a treatment period in the last week (Day 16). The following samples were taken in triplicate at the end of two test medium renewal periods of 48 hours (Days 2 and 9) and at the end of one renewal period of 72 hours (Day 19):
a) Samples with food, taken from the actual test by combining the contents of the test beakers after the end of the treatment period.
b) Samples without food and test animals incubated during the renewal periods under the test conditions.
The concentrations of cerium were measured in two of the triplicate test media samples from the highest test concentration (loading rate of 100 mg/L) which was determined to be the 21-day NOELR.
- Sampling method: data not available
- Sample storage conditions before analysis: immediately after sampling, the samples were acidified with 10% (v/v) nitric acid (HNO3, 65% Suprapur, Merck) to stabilize the samples during storage. Then the samples were stored in PE flasks at ambient temperature and protected from light until analysis.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method:
Due to the low water solubility of the test item, a saturated solution of the test item with the loading rate of 100 mg/L was tested as the highest test concentration and was used as a stock solution for preparation of the test media of lower test concentrations (dilutions 1:3.2, 1:10, 1:32 and 1:100). Additionally, a control (test water without test item) was tested in parallel.
The test method is based on the OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures.
Seven days before the start of the test and seven days prior to each test medium renewal, a dispersion of the test item with the loading rate of 100 mg/L was prepared by dispersing 200 mg (effective weights: 200.0-201.4 mg) of the test item in 2000 mL of test water. The test item was mixed into the test water as homogeneously as possible using ultrasonic treatment for 15 minutes and intense stirring. No auxiliary solvent or emulsifier was used. The dispersions were stirred on magnetic stirrers at room temperature in the dark over six days. Then, the stirrers were switched off in order to allow the non-dissolved test item to deposit at the bottom of the stirring vessel. The contact time of the test item and the test water for equilibration (i.e. stirring time and deposition period) was 7 days.
The equilibrated test medium (saturated solution) was carefully separated from the non-dissolved test item. The saturated solution was used as the highest test concentration. Additionally, adequate volumes of the saturated solution were diluted with test water for the preparation of the test media with lower test item concentrations.
- Eluate: no
- Differential loading: yes
- Controls: 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):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: Water flea
- Strain: clone defined as clone 5
- Source: supplied in 1992 by University of Sheffield/UK
- Age of parental stock (mean and range, SD): < 24 hours. These daphnids originated from parental daphnids that were at least 14 days old but no older than 4 weeks, and were not first brood progeny.
- Feeding during test
- Food type: a food mixture containing a suspension of green algae of the species Scenedesmus subspicatus (freshly grown in the Harlan laboratories) and a fish food suspension.
- Amount:
The carbon contents of the algal and fish food suspensions were determined using a Shimadzu TOC 5000A Analyzer. The food amounts were based on the measured concentrations of total organic carbon (TOC) in the food suspensions and consisted of 50% algae and 50% fish food
(based on TOC). The amounts of TOC fed per test animal and day were as follows:
Day 0-4: 0.10 mg TOC / Daphnia
Day 5-13: 0.15 mg TOC / Daphnia
Day 14-20: 0.20 mg TOC / Daphnia
- Frequency: daily


ACCLIMATION
- Acclimation period: no

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

22 d

Remarks on exposure duration:

It was expected at the observation of the test animals on Day 21 that some test animals would release their offspring from brood pouch in the next hours. Therefore the test was extended for 24 hours.

Post exposure observation period:

none

Hardness:

2.5 mmol/L (= 250 mg/L as CaCO3)

Test temperature:

20°C

pH:

between 7.5 to 8.0

Dissolved oxygen:

at least 7.9 mg/L

Salinity:

not applicable

Nominal and measured concentrations:

loading rate of 100 mg/L and dilutions 1:3.2, 1:10, 1:32 and 1:100

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type : 100 mL glass beakers covered with glass plates to reduce the loss of water by evaporation and to avoid the entry of dust into the solutions
- Material, size, headspace, fill volume: vessels containing 80 mL of test medium
- Aeration: Before use, the test water was aerated until oxygen saturation. During the test, the test media were not aerated.
- Type of flow-through (e.g. peristaltic or proportional diluter): none (semi-static test)
- Renewal rate of test solution (frequency/flow rate): three times per week
- No. of organisms per vessel: Each test animal was kept individually in test vessel
- No. of vessels per concentration (replicates): 10
- No. of vessels per control (replicates): 10
- Biomass loading rate: 80 ml of medium per parental daphnid.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: reconstituted test water : analytical grade salts dissolved in purified water
- Alkalinity: 0.9 mmol/L
- Ca/Mg ratio (mol): no data
- Culture medium different from test medium: no
- Intervals of water quality measurement: At the beginning and end of each test medium renewal period, the pH and dissolved oxygen concentrations were measured in one replicate of each test concentration and the control. At the same time, the water temperature was measured in one of the control replicates. Additionally, the room temperature was continuously monitored. The appearance of the test media was recorded at the beginning and end of each test medium renewal period.
- No further data

OTHER TEST CONDITIONS
- Adjustment of pH: No
- Photoperiod: a 16 hour light to 8 hour dark with a 30 minute transition period.
- Light intensity: between 500 and 630 lux

EFFECT PARAMETERS MEASURED :
Each working day, the test replicates were observed for mortality of the parental daphnids and the presence of juveniles. The offspring were counted and removed three times per week at the renewal of the test media. At the same dates, the test beakers were also checked for the presence of aborted eggs or dead offspring.
The reproduction rate was calculated as the total number of living offspring produced per parent female surviving until the end of the test.
The mean reproduction rates of the daphnids at the test concentrations were compared to the control by multiple Williams’ tests. No EL values for the inhibition of the reproduction rate could be calculated since no effect was determined on the reproduction of the daphnids up to the highest concentration tested.

RANGE-FINDING STUDY
Test concentrations / Results used to determine the conditions for the definitive study: The choice of the test concentrations was based on the results of the acute toxicity test with Daphnia magna (RCC Study Number A17493). Concentrations of the test item far above the water solubility or loading rates above 100 mg/L were not tested in accordance with the test guidelines.

Reference substance (positive control):

no

Key result

Duration:

22 d

Dose descriptor:

NOELR

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: survival and reproduction

Duration:

22 d

Dose descriptor:

LOELR

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: survival and reproduction

Details on results:

Analytical Results :
The concentration of cerium in test medium samples was below the limit of quantification of the analytical method (0.004 or 0.02 µg/L) with the exception of two samples taken at the end of the first test medium renewal period from the test medium of the actual test. In these samples concentrations of cerium of 0.2 mg/L were found.
The saturated solution used as test medium was prepared by sedimentation of the undissolved test item until the supernatant appeared to be a clear solution (24 hours). The test medium was not filtered on the request of the Sponsor. The wide range of measured concentrations of the test item was considered to be caused by very fine particles of the test item which were obviously still present in the supernatant after the deposition period. Thus, the test medium contained the maximum concentration of dissolved test item and very fine undissolved test item particles. The cerium found in the two samples was considered to originate from particles which were present in these samples.

Biological results:
In the control and at all test concentrations up to and including the loading rate of 100 mg/L, the survival of the test animals was at least 80% or higher at the end of the test. Thus, the survival of Daphnia magna over 21 days was not affected by the test item up to and including the highest test concentration (loading rate of 100 mg/L).
The first young offspring released from their parent animals were recorded in the control and at all test concentrations at observation on Day 8. Thus, the time of the first brood was not affected by the test item up to and including the loading rate of 100 mg/L.
The mean reproduction rate of the daphnids in the control was 100.4 ± 16.7 living offspring per adult (mean ± standard deviation). The mean reproduction rates of the exposed daphnids were between 104 and 121% of the reproduction in the control and no concentration-effect relationship was determined. No significant inhibitory effect of the test item on the mean reproduction rate was determined up to and including the highest test concentration (Williams’ test, one-sided, alpha = 0.05).
No visible abnormalities were observed in the test animals during the test.
No adverse effect, neither in terms of survival, nor in terms of reproduction, was observed at the highest loading rate tested (i.e. 100 mg/L), which corresponded to the maximum concentration of dissolved test item. As a result, cerium dioxide does not exhibit any chronic toxicity to daphnids up to its solubility limit into water.

General results:
No remarkable observations were made concerning the appearance of the test media. All test media were clear throughout the test medium renewal periods.

Results with reference substance (positive control):

none

Reported statistics and error estimates:

The mean reproduction rates of the daphnids at the test concentrations were compared to the control by multiple Williams'test.

Number of surviving test animals:

Exposure day	Treatment / Dilution
	Control	Dilution 1:100	Dilution 1:32	Dilution 1:10	Dilution 1:3.2	Saturated solution (loading rate 100 mg/L)
0 1 2 5 6 7 8 9 12 13 14 15 16 19 20 21 22	10 10 10 10 10 10 10 10 9 9 9 9 9 9 9 8 8	10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10	10 10 10 10 10 10 10 10 10 10 9 9 9 9 9 9 9	10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10	10 10 10 10 10 10 9 9 9 9 9 9 9 9 9 9 9	10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
% surviving on Day 22	80	100	90	100	90	100

 

Total number of living young daphnids produced by all adults (cumulative values):

Exposure day	Treatment / Dilution
	Control	Dilution 1:100	Dilution 1:32	Dilution 1:10	Dilution 1:3.2	Saturated solution (loading rate 100 mg/L)
0 1 2 5 6 7 8 9 12 13 14 15 16 19 20 21 22	0 0 0 0 0 0 172 172 428 475 475 615 618 719 719 789 884	0 0 0 0 0 0 160 160 422 479 480 666 670 842 842 915 1047	0 0 0 0 0 0 182 182 482 614 614 761 762 925 925 1056 1139	0 0 0 0 0 0 170 170 456 607 607 739 742 910 910 1053 1152	0 0 0 0 0 0 185 185 446 586 586 676 676 837 837 1012 1079	0 0 0 0 0 0 169 169 382 485 487 589 647 837 837 973 1094
% of control(1)	100.0	118.4	128.8	130.3	122.1	123.8

(1): based on the value of the last exposure day

 

Number of living offspring produced per surviving adult after 22 days of exposure:

Replicate No.	Treatment / Dilution
	Control	Dilution 1:100	Dilution 1:32	Dilution 1:10	Dilution 1:3.2	Saturated solution (loading rate 100 mg/L)
1 2 3 4 5 6 7 8 9 10	110 * 75 110 111 119 * 75 104 99	100 105 137 112 103 126 105 110 114 35	130 137 100 129 137 122 * 108 113 114	125 121 81 115 133 135 135 106 97 104	123 125 121 120 108 94 118 113 * 135	119 106 96 119 124 126 101 86 112 105
Mean SD n	100.4 16.7 8	104.7 27.0 10	121.1 13.1 9	115.2 18.1 10	117.4 11.6 9	109.4 12.9 10
CV %	16.6	25.8	10.8	15.7	9.9	11.8
% of control	100.0	104.3	120.7	114.8	117.0	109.0
STAT	-	n.s.	n.s.	n.s.	n.s.	n.s.

SD: standard deviation

n: number of replicates (surviving adults)

CV %: coefficient of variation in %: (SDx/meanx)x100%

*: test animal died during the test period

STAT: results of a Williams’ test with the mean values of living offspring

(one-sided, alpha = 0.05)

n.s.: mean value not significantly lower than in the control

Validity criteria fulfilled:

yes

Remarks:

Control's survival rate = 80%, and control's mean reproduction rate > 60

Conclusions:

The test item Cerium dioxide had no toxic effect on survival and reproduction of Daphnia magna after the exposure period of 22 days up to the loading rate of 100 mg/L. Thus, the NOELR of the test item was determined to be at least the loading rate of 100 mg/L . The LOELR was above the loading rate of 100 mg/L.

Executive summary:

The effect of the test item Cerium dioxide on the survival and reproduction of Daphnia magna was investigated in a semi-static test over 22 days following the OECD Guidelines for Testing of Chemicals, No. 211 (1998) and the EU Commission Directive 92/69/EEC, C.20 (2001). Daphnids were exposed to control, and test chemical at nominal concentration of 100 mg of dry substance /L (loading rate) and the dilutions 1:3.2, 1:10, 1:32 and 1:100 of the saturated solution. The mortality and reproduction of the daphnids were compared with the corresponding parameters in the control and symptoms of toxicity were recorded.

 

The test item Cerium dioxide had no toxic effect on survival and reproduction of Daphnia magna after the exposure period of 22 days up to the loading rate of 100 mg/L. Thus, the NOELR of the test item was determined to be at least the loading rate of 100 mg/L. The LOELR was above the loading rate of 100 mg/L. As no adverse effect, neither in terms of survival, nor in terms of reproduction, was observed at the highest loading rate tested (i.e. 100 mg/L), which corresponded to the maximum concentration of dissolved test item, cerium dioxide does not exhibit any chronic toxicity to daphnids up to its solubility limit into water.

 

This study is classified as acceptable and satisfies the guideline requirements for a chronic toxicity study with freshwater invertebrates.

Description of key information

The 22-day NOELR (Daphnia magna) of the bulk form of cerium dioxide is ≥ 100 mg/L based on the survival and the reproduction. Hence, the bulk form of cerium dioxide has no adverse chronic effect on survival and reproduction of Daphnids.

Additional information

One experimental study (Harlan, 2009), scored as Klimisch 1, was available and selected as a key study. It concluded on the absence of chronic adverse effects of the bulk form of cerium dioxide on the survival and the reproduction of the daphnids. Another study of reliability 4 was available (Van Hoecke et al., 2009a) giving same results in terms of survival, but not in terms of reproduction (21d-NOEC = 32 mg/L versus 22d-NOEC ≥ 100 mg/L in the Harlan study). However, due to the lack of experimental details provided in this study, it is not possible to conclude on its reliability.