Zirconium dichloride oxide

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:

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.

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.

Reference 2

Endpoint:

toxicity to terrestrial plants: long-term

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Description of key information

In the study of Ferrand et al. (2006) no adverse effects were observed when exposing tomato and pea seedlings either to soluble zirconium compounds (zirconium dichloride oxide or zirconium acetate) or insoluble zirconium compounds (zirconium hydroxide) added to soil. Only unbound NOEC values were obtained. Since the experiments only lasted for 7 days, the long-term toxicity endpoint (Annex X) is not covered. However, since there is no concern for terrestrial toxicity at the moment, the Annex X endpoint can be waived.
Since the experiments only lasted for 7 days, the long-term toxicity endpoint (Annex X) is not covered. However, since there is no concern for terrestrial toxicity at the moment, the Annex X endpoint can be waived.

Additional information

A single study was identified containig relevant and reliable information on toxicity of zirconium substances to terrestrial plants. In this study (Ferrand et al., 2006), tomato and pea seedlings (ca. 21 days old) were exposed for 7 days to two different soils contaminated with either a soluble zirconium compound (ZrOCl2 or zirconium acetate) or an insoluble zirconium 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.

Since the above experiments only lasted for 7 days, the long-term toxicity endpoint (Annex X) is not covered. However, since there is no concern for terrestrial toxicity at the moment, the Annex X endpoint can be waived.