Registration Dossier

Environmental fate & pathways

Bioaccumulation: terrestrial

Currently viewing:

Administrative data

Link to relevant study record(s)

Referenceopen allclose all

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:
Read across from a study performed with zirconium dichloride oxide, zirconium acetate, and zirconium hydroxide. The read across justification document is attached to IUCLID Section 13.
Reason / purpose:
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 tungsten zirconium oxide.
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

Because tungsten zirconium oxide has an extremely low water solubility, only small amounts of tungsten and zirconium may become bioavailable for uptake when the substance is released to the environment. Experimental data for zirconium confirm that there is no concern for bioaccumulation of this element in terrestrial organisms (all BSAF values well < 1). For tungsten, no data have been included in the dossier. However, since zirconium is the most dominant element in tungsten zirconium oxide on a weight by weight basis, and because tungsten is expected to be released only to a very limited extent in environmental media, it was considered sufficient to cover the endpoint by data on zirconium alone. Based on the available information, it can be concluded that there is no concern for bioaccumulation resulting from environmental exposure to tungsten zirconium oxide.

Key value for chemical safety assessment

Additional information

1. Information on zirconium (dioxide)

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, covered by the ZrO2 registration dossier). 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 a very limited potential for bioaccumulation in terrestrial organisms.

2. Information on tungsten (oxide)

There are no data on the terrestrial bioaccumulation of tungsten used.

3. Conclusion on tungsten zirconium oxide

Tungsten zirconium oxide has an extremely low water solubility and only small amounts of tungsten and zirconium may become available for uptake when the substance is released to the environment (Buchholz, 2018; Ablitt, 2018; Vryenhoef, 2018). For zirconium, experimental data confirm that there is no concern for bioaccumulation. For tungsten, no data are included in the dossier. However, since zirconium is the most dominant element in tungsten zirconium oxide on a weight by weight basis, and because tungsten is expected to be released only to a very limited extent in environmental media, it was considered sufficient to cover the endpoint by data on zirconium alone. Based on the available information, it can be concluded that there is no concern for bioaccumulation resulting from environmental exposure to tungsten zirconium oxide.