lambda4-cerium(4+) zirconium(4+) tetraoxidandiide

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to terrestrial plants: long-term

Data waiving:

other justification

Justification for data waiving:

other:

Reference 2

Endpoint:

toxicity to terrestrial plants: short-term

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Justification for type of information:

Read across from a study performed with cerium dioxide and zirconium dioxide (or rather zirconium tetrahydroxide, as well as two other zirconium compounds). The read across justification document is attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Remarks on result:

other: Based on the results from studies conducted with cerium dioxide, zirconium tetrahydroxide and two other zirconium compounds, it can be concluded that no effects are expected for the reaction mass of cerium dioxide and zirconium dioxide either.

Reference 3

Endpoint:

toxicity to terrestrial plants: short-term

Type of information:

experimental study

Adequacy of study:

supporting 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 was thoroughly mixed on a rollerbank with 1749.6 grams of adjusted damp soil/sand mixture and 120 mL of demineralised water.
- Controls: Control was prepared in 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/sterilisation: 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/sterilisation: 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/sterilisation: 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). Demineralised 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: demineralised 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/fertilisation: 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

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

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 was >=≥ 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 replicates 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 4

Endpoint:

toxicity to terrestrial plants: short-term

Data waiving:

other justification

Justification for data waiving:

other:

Reference 5

Endpoint:

toxicity to terrestrial plants: short-term

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well performed study of which the results of the experiments with the insoluble Zr compound are highly relevant for ZrO2. However, only unbound NOEC values were obtained because limit tests were performed.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

EPA OPPTS 850.4230 (Early Seedling Growth Toxicity Test)

Deviations:

yes

Remarks:

only 7 days of exposure

GLP compliance:

not specified

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
ZrOCl2 and Zr acetate are water soluble Zr compounds, whereas Zr(OH)4 is not.

Analytical monitoring:

yes

Details on sampling:

- Spiked soils were not sampled for analysis.
- Background Zr was determined in soil samples from both soils prior to testing.
- After 7 days of exposure, roots and aerial parts were separated for measuring weights and analyzing for Zr content.

Vehicle:

no

Details on preparation and application of test substrate:

- Method of mixing into soil (if used): soils were spiked with solutions of ZrOCl2 or Zr acetate (soluble) to increase the total soil Zr concentration by 100 mg Zr/kg dry soil - in a third experiment soils were spiked with Zr(OH)4 (insoluble) to increase the total soil Zr concentration by 286 mg Zr/kg dry soil
- Controls: in each experiment, five control replicates were used (unspiked cultivated soils)
- Background Zr concentrations in soil A and B were 417.4 and 164 mg Zr/kg dry soil. According to Kabata-Pendias and Pendias (1992) the main minerals of Zr present in soil are the low soluble zircon (ZrSiO4) and baddeleyite (ZrO2).
- In the experiments with the soluble Zr compounds total Zr concentrations were hence 517.4 and 264 mg Zr/kg dw in soil A and B, respectively.
- In the experiment with the insoluble Zr compound total Zr concentrations were hence 703.4 and 450 mg Zr/kg dw in soil A and B, respectively.

Species:

Pisum sativum

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: pea
- Plant family: Fabaceae
- Variety: cv. "Express"
- Prior seed treatment/sterilization: disinfected in a bath of 6% H2O2 and rinsed with deionized water

Species:

Lycopersicon esculentum

Plant group:

Dicotyledonae (dicots)

Details on test organisms:

- Common name: tomato
- Plant family: Solanaceae
- Variety: cv. St. Pierre
- Prior seed treatment/sterilization: disinfected in a bath of 6% H2O2 and rinsed with deionized water

Test type:

early seedling growth toxicity test

Study type:

laboratory study

Substrate type:

natural soil

Limit test:

yes

Total exposure duration:

7 d

Remarks:

Next to the soil experiments, experiments were conducted in hydroponic conditions (details of tests conditions are quite similar and not discussed here).

Test temperature:

Ambient temperature (15-32°C), greenhouse conditions

pH:

Soil A: 5.45
Soil B: 8.3
Nutrient solution: 5.5

Moisture:

Air humidity = 80%
Soil water content = 38-39% (pF = 1.5)

Details on test conditions:

TEST SYSTEM
- Testing facility: greenhouse
- Test container (type, material, size): plastic pots containing 175 g of soil
- Amount of soil: 175 g
- Method of seeding: Seeds were placed in a preculture device composed of PVC cylinders, to which a base of a 500 µm grid had been glued. The seeds were germinated in a 5L aerated nutrient solution and were protected from excess light for the first 7 days. Germinated plants were placed in contact with 5L aerated nutrient solution in the soil experiments for another 14 days prior to exposure.
- No. of seeds per container: not reported
- No. of plants (retained after thinning): not reported
- No. of replicates per treatment group: 5
- No. of replicates per control: 5

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
COLLECTION AND STORAGE
- Geographic location: two agricultural soils were sampled close to the underground research laboratory (Meuse/Haute Marne, France) of the National Agency for management of radioactive wastes (Andra)
- Sampling depth (cm): top soils 0-20 cm
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): air-dry soils were crushed and sieved under 2 mm
PROPERTIES
Soil A (acidic sandy clayey loamy)
- % sand: 31.9
- % silt: 48.7
- % clay: 19.4
- pH: 5.45
- Organic carbon (%): 31.8
- CEC (meq/100 g): 9.0 cmol/kg
- Background Zr content: 417.4 mg/kg dw
Soil B (clayey calcareous soil)
- % sand: 10.7
- % silt: 50.7
- % clay: 38.6
- pH: 8.3
- Organic carbon (%): 33.6
- CEC (meq/100 g): 10.02 cmol/kg- Geographic location:
- Background Zr content: 164 mg/kg dw

NUTRIENT MEDIUM (if used)
- Description: only used during preculturing (see materials and methods section for composition)

GROWTH CONDITIONS
- Photoperiod: ambient (greenhouse experiment)
- Light source: natural sunlight
- Day/night temperatures: 15-32°C temperature range
- Relative humidity (%): 80
- Watering regime and schedules: initial water content 38-39%, afterwards deionised water was added when required
- Water source/type: initially nutrient solution, afterwards deionised water

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : at the end of testing, root and shoot fresh weight was determined

Nominal and measured concentrations:

- In the experiments with the soluble Zr compounds total Zr concentrations were 517.4 and 264 mg Zr/kg dw in soil A and B, respectively (i.e., 100 mg/kg added).
- In the experiment with the insoluble Zr compound total Zr concentrations were 703.4 and 450 mg Zr/kg dw in soil A and B, respectively (i.e., 286 mg/kg added).

Species:

Lycopersicon esculentum

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

>= 517.4 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: root and shoot fresh weight

Remarks on result:

other: For soil A and 100 mg Zr/kg dw added using ZrOCl2 or Zr acetate

Species:

Lycopersicon esculentum

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

>= 264 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: root and shoot fresh weight

Remarks on result:

other: For soil B and 100 mg Zr/kg dw added using ZrOCl2 or Zr acetate

Species:

Lycopersicon esculentum

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

>= 703.4 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: root and shoot fresh weight

Remarks on result:

other: For soil A and 286 mg Zr/kg dw added using Zr(OH)4

Species:

Lycopersicon esculentum

Duration:

7 d

Dose descriptor:

NOEC

Effect conc.:

>= 450 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: root and shoot fresh weight

Remarks on result:

other: For soil B and 286 mg Zr/kg dw added using Zr(OH)4

Details on results:

- Similar unbound NOECs were observed for Pisum sativum.
- Tomato and pea roots grown on the acidic soil (soil A) spiked with ZrOCl2 or Zr acetate were slightly less developed than the other ones. This lower growth can be correlated to the higher Zr uptake for these two forms.
- In the hydroponic experiments, some chlorotic leaves were observed but this could be attributed to lack of Fe in the nutrient solution.

Reported statistics and error estimates:

ANOVA + mean comparison by LSD Fisher test

Conclusions:

In this study, tomato and pea seedlings (ca. 21 days old) were exposed for 7 days to two different soils contaminated with either a soluble Zr compound (ZrOCl2 or Zr acetate) or an insoluble Zr compound (Zr(OH)4). In none of the experiments adverse effects were observed on root or shoot fresh weight of the plants. Unbound NOEC values were obtained for all experiments. The lowest unbound NOEC was >= 264 mg Zr/kg dw for the calcareous soil (164 mg Zr/kg background) amended with 100 mg Zr/kg ZrOCl2 or Zr acetate. The highest unbound NOEC was >= 703.4 mg Zr/kg dw for the acidic soil (417.4 mg Zr/kg background) amended with 286 mg Zr/kg Zr(OH)4. Because ZrO2 is also a highly insoluble Zr compound and background Zr in soils is also assumed to be present as insoluble Zr compounds such as ZrO2 and ZrSiO4, the unbound NOECs for the experiments with Zr(OH)4 are more relevant for ZrO2.

Description of key information

There is currently no need identified to perform a short- or long-term toxicity study with terrestrial plants with the reaction mass of cerium dioxide and zirconium dioxide. The waiver is supported by short-term toxicity data available for cerium dioxide, zirconium tetrahydroxide, and two other zirconium compounds.

Additional information

No data is available for the reaction mass. A study performed with cerium dioxide and a study performed with zirconium tetrahydroxide and two other zirconium compounds were added as supporting information for the waiver.

The study performed with cerium dioxide, scored as Klimisch 1 (Hooftman and Henzen, 1996b), revealed that cerium dioxide is not harmful to terrestrial plants, as no adverse effects were observed at the highest concentration tested, i.e. 1000 mg/kg dry soil.

The study performed with zirconium tetrahydroxide (an insoluble zirconium compound related to zirconium dioxide) and the two 'water soluble' zirconium compounds zirconium dichloride oxide and zirconium acetate (Ferrand, 2006; Klimisch 2), showed that insoluble as well as 'water soluble' zirconium compounds did not cause any adverse effects in terrestrial plants up to and including at the highest concentrations tested.