Cerium dioxide

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to terrestrial plants: short-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 21-JUN-1996 to 11-DEC-1996

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 208 (Terrestrial Plants Test: Seedling Emergence and Seedling Growth Test)

Deviations:

yes

Remarks:

see details in the field: Any other information on materials and methods incl. tables. These deviations are assumed not to have affected the results of this study

GLP compliance:

yes

Analytical monitoring:

no

Details on sampling:

no data

Vehicle:

no

Details on preparation and application of test substrate:

- Method of mixing into soil: Quantities of 1829.73 (oat), 1828.92 (lettuce) and 1829.05 (mustard) mg of the test item were weighed out accurately and mixed thoroughly with 200 g of fine (grain size 0.5-1.0 mm) sand. Each portion of spiked sand and 3.03-3.04 g K2HPO4 were thoroughly mixed on a rollerbank with 1749.6 grams of adjusted damp soil/sand mixture and 120 mL of demineralized water.
- Controls: control was prepared as a similar way as above however with uncontaminated sand.

Species:

Avena sativa

Plant group:

Monocotyledonae (monocots)

Details on test organisms:

- Common name: common Oat
- Plant family: Poaceae
- Variety: Valiant
- Source of seed: CEBECO (Lelystad, The Netherlands
- Prior seed treatment/sterilization: no data
- Historical germination of seed (germination of seed lot tested): no data
- Seed storage: no data

Species:

Brassica rapa

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common names: field mustard, turnip mustard
- Plant family: Brassicaceae
- Variety: Polybra
- Source of seed: Mommersteeg (Vlijmen, The Netherlands)
- Prior seed treatment/sterilization: no data
- Historical germination of seed (germination of seed lot tested): no data
- Seed storage: no data

Species:

Lactuca sativa

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: Lettuce
- Plant family: Asteraceae
- Variety: Ravel RZ
- Source of seed: Rijk Zwaan (De Lier, The Netherlands)
- Prior seed treatment/sterilization: no data
- Historical germination of seed (germination of seed lot tested): no data
- Seed storage: no data

Test type:

other: early seedling emergence and growth toxicity test

Study type:

laboratory study

Substrate type:

other: semi-natural soil

Limit test:

yes

Total exposure duration:

18 d

Remarks:

17d for L. sativa, 17d for A. sativa, 18d for B. rapa

Post exposure observation period:

none

Test temperature:

Test temperature is recorded continuously and varied between 21.0 and 24.5°C as measured during dark and light periods respectively.

pH:

pH 7.2 at the start of the test in controls and each treated species and 7.7 to 7.8 at the end.

Moisture:

Moisture is recorded continuously and varied between 60% (light period) and 80% (dark period).
However due to a technical failure of the humidity control in the test room, the relative humidity dropped from ca. 60% to ca. 46% for a period of ca. 3 hours at t=7 days.

Details on test conditions:

TEST SYSTEM
- Testing facility: thermostatically controlled room
- Test container : circular plastic containers with a diameter of 9.3 cm and a height of 6.0 cm.
- Amount of soil: 362.7 g (320 g of soil + 42.7 g of water). Demineralized water was added till a weight of 400 g was reached.
- Method of seeding: depth of ca 1 cm (top of the seed upward) and covered with soil (A. sativa); on top of soil (L sativa) and at a depth of 0.5-1 cm and covered with soil (B rapa).
- No. of seeds per container: 10
- No. of plants (retained after thinning): 5
- No. of replicates per treatment group: 4 + 1 replicate without plant for pH control
- No. of replicates per control: 4 + 1 replicate without plant for pH control

SOURCE AND PROPERTIES OF SUBSTRATE
Substrate = mixture (1:1) of agricultural soil and coarse sand
- Geographic location: soil part sampled in an orchard in Heerewaarden (The Netherlands)
- Pesticide use history at the collection site: no data
- Collection procedures: no data
- Sampling depth (cm): no data
- Soil texture of the mixture
- % sand: 82.5% (16-2000 µm)
- % silt: 12.4% (0-16 µm)
- % clay: no data
- Soil taxonomic classification: no data
- Soil classification system: no data
- Organic carbon (%): 0.9
- Maximum water holding capacity (in % dry weigth): no data
- CEC: no data
- Pretreatment of soil: no data
- Storage (condition, duration): no data

GROWTH CONDITIONS
- Photoperiod: 16 h light and 8 h dark
- Light source: no data
- Light intensity and quality: measured above test containers on days 4 and 11 : from 6300 to 6980 lux
- Day/night temperatures: see above
- Relative humidity (%): see above
- Wind velocity: not applicable (indoor test)
- Air exchange rate: no data
- Watering regime and schedules:
- Water source/type: demineralized water
- Volume applied: the daily weight loss (in comparison with the initial weight : 400 g) of each container was made up
- Interval of applications: daily weighed of each container, compensation if necessary
- Method of application: no data
- Any pest control method/fertilization : addition of K2HPO4 added at the preparation step of the substrate

ACCLIMATION PERIOD: no data

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
All emergence of seedlings was recorded. The visual appearance of the plants and the number of surviving plants were recorded once or twice a week. At the end of the test all surviving plants were harvested and immediately weighed individually.
- Phytotoxicity rating system : no data

TEST CONCENTRATIONS
1000 mg/kg dry weight
- Justification for using less concentrations than requested by guideline: no adverse effect were to be expected so a limit test at 1000 mg/kg dry weight was performed.
- Range finding study : no data

Nominal and measured concentrations:

0 and 1000 mg/kg dry weight nominal

Reference substance (positive control):

no

Key result

Species:

other: A sativa, L sativa

Duration:

17 d

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: seedling emergence + growth + survival

Key result

Species:

Brassica rapa

Duration:

18 d

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: seedling emergence + growth + survival

Details on results:

SEEDLING EMERGENCE
- Percent seedling emergence: the emergence of control turnip mustard was less than 80% at 7 days but 2 seedlings emerged later. So the total emergence was 31/40 (77.5%). In the treated turnip mustards, the emergence was 30/40 (75%).
For oat, the control and treated emergence were 40/40 (100%) and 39/40 (97.5%) respectively.
For lettuce : 40/40 (100%) in the control and treated groups.
- Abnormal seed development or appearance: none

VEGETATIVE VIGOUR
- Wet weight and survival of the seedlings (see the tables 1 to 3)
- Abnormal seed development or appearance: none

INJURY RATING SYSTEM: no data , visually estimated

Results with reference substance (positive control):

none

Reported statistics and error estimates:

The LC50 is not determined because no effect was observed at the single concentration tested.
To determine the NOEC for emergence and survival, the data on emergence and survival of each concentration were compared pair-wise with those of the control using a binomial test (at 5% of significance).
To determine the NOEC for wet weight; multiple comparison was made between the wet weight of each plant at each concentration and the wet weight of the plants in the control using a two-tailed Dunnett-test. It was assumed that the plants in each container were growing independently of each other. A significance level of 1 and 5% were used.
The NOEC for appearance and behaviour was not determined statistically.

Number of seeds sown, number of seedlings emerged, number of seedlings removed, plant survival, plant condition and mean wet-weight of the plants at the end of the test after exposure to several concentrations of the test substance (mg/kg dry soil)

S: number of seeds sown on day 0

E: cumulative number of seedlings merged (only given if at least one seedling had emerged since last observation day)

R: number of plants removed

A: number of plants after removing

M: cumulative number of plant mortality

X: number of seedlings found during harvest under other plants

 

Table 1: Data on emergence, condition, survival and wet-weight of A. sativa (oat) exposed to cerium oxide. A, B, C and D are replicate test containers

Day	Container	S	E	E	R	A	A	A	A	A	M	Weight			Average weight (g) ± s.d.
		0	3	4	4	4	7	11	14	17	17	mean	s.d.	n
Concentration (mg/kg) 0 0 0 0	A B C D	10 10 10 10	10 10 9 10	10 10 10 10	5 5 5 5	5 5 5 5	5a 5a 5a 5a	5a 5a 5a 5a	5a 5a 5a 5a	5a 5a 5a 5a	0 0 0 0	1.098 1.196 1.176 1.147	0.133 0.283 0.099 0.114	5 5 5 5	1.154 ± 0.164
1000 1000 1000 1000	A B C D	10 10 10 10	10 10 10 9	10 10 10 9	5 5 5 4	5 5 5 5	5b 5b 5b 5b	5b 5b 5b 5b	5b 5b 5b 5b	5b 5b 5b 5b	0 0 0 0	1.224 1.168 1.209 1.191	0.274 0.095 0.179 0.067	5 5 5 5	1.198 ± 0.161

 

Table 2: Data on emergence, condition, survival and wet-weight of L. sativa (lettuce) exposed to cerium oxide. A, B, C and D are replicate test containers

Day	Container	S	E	E	E	E	R	A	A	A	A	A	M	Weight			Average weight (g) ± s.d.
		0	1	2	3	4	4	4	7	11	14	17	17	mean	s.d.	n
Concentration (mg/kg) 0 0 0 0	A B C D	10 10 10 10	9 10 9 8	10 10 10 9	10 10 10 10	10 10 10 10	5 5 5 5	5 5 5 5	5a 5a 5a 5a	5a 5a 5a 5a	5a 5a 5a 5a	5a 5a 5a 5a	0 0 0 0	1.274 1.495 1.423 1.520	0.088 0.079 0.210 0.128	5 5 5 5	1.428 ± 0.159
1000 1000 1000 1000	A B C D	10 10 10 10	9 9 10 8	10 10 10 10	10 10 10 10	10 10 10 10	5 5 5 5	5 5 5 5	5b 5b 5b 5b	5b 5b 5b 5b	5b 5b 5b 5b	5b 5b 5b 5b	0 0 0 0	1.362 1.347 1.423 1.316	0.147 0.140 0.263 0.170	5 5 5 5	1.362 ± 0.176

a: appearance of the plants normal (control, visually estimated)

b: appearance of the plants equal to that of the control plants

 

Table 3: Data on emergence, condition, survival and wet-weight of B. rapa (mustard) exposed to cerium oxide. A, B, C and D are replicate test containers

Day	Container	S	E	E	E	R	A	A	R	A	A	M	X	Weight			Average weight (g) ± s.d.
		0	3	4	7	7	7	11	11	14	18	18	18	mean	s.d.	n
Concentration (mg/kg) 0 0 0 0	A B C D	10 10 10 10	2 2 2 2	6 5 5 4	8 6 8 7	3 1 3 2	5 5 5 5	6a 6a 5a 5a	1 1 0 0	5a 5a 5a 5a	5a 5a 5a 5a	0 0 2 0	0 0 2 0	1.321 1.352 1.344 1.267	0.297 0.541 0.471 0.540	5 5 5 5	1.321 ± 0.435
1000 1000 1000 1000	A B C D	10 10 10 10	3 1 3 1	4 5 5 4	6 9 5 7	1 4 0 2	5 5 5 5	5b 5b 5b 5b	0 0 0 0	5b 5b 5b 5b	5b 5b 5b 5b	1 0 2 0	1 0 2 0	1.302 1.227 1.274 1.195	0.350 0.451 0.308 0.266	5 5 5 5	1.249 ± 0.324

a: appearance of the plants normal (control, visually estimated)

b: appearance of the plants equal to that of the control plants

Validity criteria fulfilled:

yes

Remarks:

The validity criteria in the guideline is: at least 80% of the seeds in the control must emerge. Their growth should be normal throughout the study.

Conclusions:

The NOEC for emergence, survival of seedlings and growth were ≥ 1000 mg/kg dry soil for all species. Cerium dioxide is not considered as harmful to the tested plant species.

Executive summary:

Cerium dioxide has been tested for its toxicity to plant species Avena sativa, Lactuca sativa and Brassica rapa. The study was carried out according to the OECD Guideline 208 and in compliance with the principles of Good Laboratory Practices.

 

4 replicate of 5 plants were grown in a mixture of agricultural soil and coarse sand, supplemented with potassium and phosphorus. Cerium dioxide was tested at the limit concentration of 1000 mg/kg dry soil for the three plant species, in parallel to a control.

 

Cerium dioxide did not cause reduction of emergence for any of the plant species tested. Leaf damage or reduction of growth was not observed in any of the plant species tested. The NOEC is equal or higher than 1000 mg/kg. Cerium dioxide is not considered as harmful to the tested plant species.

Reference 2

Endpoint:

toxicity to terrestrial plants: long-term

Data waiving:

other justification

Justification for data waiving:

other:

Description of key information

The 17-day NOEC (Avena sativa and Lactuca sativa) and the 18-day NOEC (Brassica rapa) of the bulk form of cerium dioxide was ≥ 100 mg/kg dry soil based on the seedling emergence, the growth and the survival. Hence, the bulk form of cerium dioxide is not considered as harmful to the tested plant species.

Additional information

One experimental study, scored as Klimisch 1, was available and selected as a key study (TNO, 1996). It revealed that the bulk form of cerium dioxide was not harmful to terrestrial plants.