Yttrium zirconium oxide

Bioaccumulation: terrestrial

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation: terrestrial

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

Following the read across strategy attached in section 13 of IUCLID, it is considered appropriate to cover this endpoint by data on bioaccumulation of zirconium.

Reason / purpose for cross-reference:

read-across source

Key result

Type:

BSAF

Value:

<= 0.1 dimensionless

Basis:

organ d.w.

Remarks:

for Zr (element)

Remarks on result:

other: Based on the read across data from Ferrand et al. (2006) it was concluded that there is no potential for terrestrial bioaccumulation of Zr from yttrium zirconium oxide.

Reference 2

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well performed study of which the results of the experiment with the insoluble Zr(OH)4 are the most relevant for ZrO2.

Qualifier:

no guideline available

Principles of method if other than guideline:

In this study, transfer of Zr from soil to tomato and pea plants was studied during a 7-day exposure period in two soils amended with either a soluble or an insoluble Zr compound.

GLP compliance:

not specified

Radiolabelling:

no

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.

Test organisms (species):

other: Lycopersicon esculentum and Pisum sativum

Details on test organisms:

Pisum sativum
- 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

Lycopersicon esculentum
- 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

Total exposure / uptake duration:

7 d

Test temperature:

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

pH:

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

TOC:

Soil A: 31.8% OC
Soil B: 33.6% OC

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

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).

Key result

Type:

BSAF

Value:

<= 0.005 dimensionless

Basis:

organ d.w.

Calculation basis:

other: concentrations in soil and plants after 7 days of exposure

Remarks on result:

other: aerial parts (highest value of 0.005 for pea in soil B amended with Zr acetate)

Key result

Type:

BSAF

Value:

<= 0.1 dimensionless

Basis:

organ d.w.

Calculation basis:

other: concentrations in soil and plants after 7 days of exposure

Remarks on result:

other: roots (highest value of 0.1 for tomato in soil A amended with Zr acetate

Kinetic parameters:

no data

Metabolites:

not relevant

Details on results:

Zr is mainly accumulated in the roots of both plants.
Generally a higher Zr root concentration was oberved in the acidic soil.
Translocation of Zr from roots to aerial parts was limited.
The amount of Zr bound to root cell walls was signifcantly much smaller than the amount of Zr absorbed by the roots.
The BSAF for Zr decreases according to the following sequence: Zr-acetate > ZrOCl2 > Zr(OH)4 = natural Zr forms.
Zr soluble salts were more readily available than the hydroxide.

Reported statistics:

ANOVA + mean comparison using the LSD Fisher test

Conclusions:

In this study, transfer of Zr from soil to tomato and pea plants was studied during a 7-day exposure period in two soils (an acidic and a calcareous soil) amended with either a soluble (ZrOCl2 or Zr acetate) or an insoluble Zr compound (Zr(OH)4). Zr accumulated mainly in the roots, with Zr adsorption to the root surface being of minor relevance. Translocation to aerial parts was limited. BSAF values for roots were the highest for Zr acetate and the lowest for Zr(OH)4. They were all <= 0.1. BSAF values for aerial parts were all <= 0.005 and were also generally the highest for Zr acetate and the lowest for Zr(OH)4.

Description of key information

Following the read across strategy, it is considered appropriate to cover this endpoint by data on bioaccumulation of zirconium and yttrium.
For zirconium, the study of Ferrand et al.(2006) indicates that there is no potential for bioaccumulation in terrestrial organisms, the BSAF values for roots and aerial parts of terrestrial plants being all <= 0.1 and <= 0.005, respectively. 
For yttrium, the review by Rikken (1995) reported BSAF values for food crops in the range of 0.0014 and 0.010, whereas Markert and Li (1999) reported BSAF values for rare earth elements including yttrium in the range of 0.04 to 0.09. These BSAF values being all well below 1, it can be concluded that there is no potential for bioaccumulation of yttrium in the terrestrial environment.
Because based on the low water solubility of yttrium zirconium oxide, the release of yttrium and zirconium in the environment, and hence their bioavailability, is expected to be very limited, it can be concluded that no bioaccumulation of yttrium or zirconium from yttrium zirconium oxide is to be expected in the terrestrial environment.

Additional information

1. Information on zirconium

In the study of Ferrand et al. (2006), transfer of zirconium from soil to tomato and pea plants was studied during a 7-day exposure period in two soils (an acidic and a calcareous soil) amended with either a soluble (zirconium dichloride oxide or zirconium acetate) or an insoluble zirconium compound (Zr(OH)4). Zirconium accumulated mainly in the roots, with zirconium adsorption to the root surface being of minor relevance. Translocation to aerial parts was limited. BSAF values for roots were the highest for zirconium acetate and the lowest for Zr(OH)4. They were all <= 0.1. BSAF values for aerial parts were all <= 0.005 and were also generally the highest for zirconium acetate and the lowest for Zr(OH)4. These values are however all below 1, indicating that zirconium has no potential for bioaccumulation in terrestrial organisms.

2. Information on yttrium

Because rare earth elements are being used as fertiliser to promote plant growth for certain types of crops in certain regions, a substantial amount of literature is available on the transfer of rare earths to plants in the terrestrial environment. Only a limited amount of data is included in this endpoint summary, however, this amount of information is considered sufficient for drawing conclusions on this endpoint.

Rikken (1995) summarized literature data on the accumulation of rare earth metals in plants, as a part of the investigation of data on the transfer of rare earths in the chain artificial fertilizers - soil - crops - livestock and man. The data for concentration of yttrium in different vegetables and feeding stuffs and the soil were collected and biota-to-soil accumulation factors (BSAFs) were calculated.

The concentration and accumulation of rare earths in plants differed as a consequence of plant and soil properties (e.g., species, Ca-content). The concentrations of rare earth elements in plants (dry weight) were in general low: < 0.2 mg/kg dw for root and leaf vegetables, < 0.05 mg/kg dw in most fruits and < 1 mg/kg dw in herbs/grasses. BSAFs for rare earth elements are usually within a range of 0.0001 to 0.001 for feed crops and 0.0001 to 0.01 for food crops. For yttrium specifically, BSAFs were in a range of 0.0014 - 0.010 for food crops. No data were reported for feed crops.

Further, Tyler (2004) reviewed the information about rare earth elements in soil and plant systems and arrived at the conclusion that concentrations of rare earths in plants are usually very low compared to their total concentration in soils. For example, BSAFs in forest plants of NW Germany were reported to be as low as 0.04 - 0.09 (Markert and Li, 1999).

Generally, the reviewed data indicated a low accumulation potential of yttrium and rare earth elements in general. Therefore, it can be assumed that there is no risk for accumulation in the terrestrial/sediment food chain.

Specific references:

Rikken, M.G.J., 1995. De accumulatie van zeldzamen aardmetalen. RIVM Rijksinstituut voor volksgesondheid en milieu, Bilthoven.Report nr. 601014 013.

Markert, B., De Li, Z., 1991. Natural background concentrations of rare earth elements in a forest ecosystem. Science of the Total Environment 103: 27 -35.

Tyler, G., 2004. Rare earth elements in soil and plant systems. A review. Plant and Soil 267: 191 -206.

 

3. Conclusion on yttrium zirconium oxide

Based on the available data on terrestrial bioaccumulation of zirconium and yttrium, and taking into account the low water solubility of yttrium zirconium oxide and hence the expected low bioavailability of zirconium and yttrium in the environment, it can be concluded that there is no potential for terrestrial bioaccumulation of yttrium or zirconium.