Magnesium zirconium oxide

Bioaccumulation: terrestrial

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Well performed and well documented study.

Remarks:

In this study Mg transfer from soil to plants was studied after soil amendment of dolomitic limestone or a combination of calcitic and dolomitic limestone. As such it is relevant to any compound releasing Mg ions into the terrestrial environment, such as magnesium zirconium oxide.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Dolomitic limestone or a combination of calcitic and dolomitic limestone were added to samples of the soils at different rates. In a greenhouse pot experiment, ryegrass (Lolium perenne cv Nui) was then sown in the treated soil. The herbage was cut five times during the experiment and analysed for Ca, Mg, K, Al, P, and S.

GLP compliance:

not specified

Radiolabelling:

no

Details on sampling:

- Samples for soil nutrient analysis were taken before and after the greenhouse experiment.
- Samples for nutrient analysis in ryegrass were taken five times. The herbage was cut when the ryegrass was approximately 250 mm high. It was cut to 25 mm above the soil surface, dried at 70°C for 48 h and weighed to measure dry matter yield.

Vehicle:

no

Details on preparation and application of test substrate:

Dolomitic and/or calcitic limestone were added to samples of the soils and, after thorough mixing, the samples were moistened to field capacity and incubated for 48 h at 60°C. The soils were then left in greenhouse conditions for 15 days before the ryegrass was sown.

Test organisms (species):

other: Lolium perenne cv Nui (perennial ryegrass)

Test temperature:

greenhouse conditions (ca. 25°C)

Details on test conditions:

TEST SYSTEM
- Test container (material, size): pots
- Amount of soil or substrate: 1 kg
- No. of replicates per treatment group: 3
- No. of replicates percontrol / vehicle control: 3

SOURCE AND PROPERTIES OF SUBSTRATE (if soil):
Faja Maisan soil: top 20 cm. Acidified Andisol from Southern Chile belonging to the Barros Arana Series. pH before addition 4.12.
Bajo Oregon soil: top 20 cm. Acidified Andisol from Southern Chile belonging to the Barros Arana Series. pH before addition 4.27.

Nominal and measured concentrations:

Control, DL2 (dolomitic limestone, 2 t/ha), DL4 (dolomitic limestone, 4 t/ha), CL1+DL1 (calcitic limestone 1 t/ha + dolomitic limestone 1 t/ha), CL2+DL2 (calcitic limestone 2 t/ha + dolomitic limestone 2 t/ha).

Type:

BSAF

Value:

53.67

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Faja Maisan soil. Control. Concentration organism: 3000 mg Mg/kg dw. Concentration soil: 55.9 mg Mg/kg dw. pH: 4.11.

Type:

BSAF

Value:

10.29

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Faja Maisan soil. DL2. Concentration organism: 3900 mg Mg/kg dw. Concentration soil: 379.2 mg Mg/kg dw. pH: 5.05.

Type:

BSAF

Value:

5.34

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Faja Maisan soil. DL4. Concentration organism: 4000 mg Mg/kg dw. Concentration soil: 748.6 mg Mg/kg dw. pH: 5.62.

Type:

BSAF

Value:

17.77

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Faja Maisan soil. CL1+DL1. Concentration organism: 3800 mg Mg/kg dw. Concentration soil: 213.9 mg Mg/kg dw. pH: 5.00.

Type:

BSAF

Value:

10.22

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Faja Maisan soil. CL2+DL2. Concentration organism: 4100 mg Mg/kg dw. Concentration soil: 401 mg Mg/kg dw. pH: 5.49.

Type:

BSAF

Value:

16

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Bajo Oregon soil. Control. Concentration organism: 2100 mg Mg/kg dw. Concentration soil: 131.2 mg Mg/kg dw. pH: 4.33.

Type:

BSAF

Value:

8.23

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Bajo Oregon soil. DL2. Concentration organism: 3300 mg Mg/kg dw. Concentration soil: 401 mg Mg/kg dw. pH: 4.89.

Type:

BSAF

Value:

4.82

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Bajo Oregon soil. DL4. Concentration organism: 3700 mg Mg/kg dw. Concentration soil: 768 mg Mg/kg dw. pH: 5.37.

Type:

BSAF

Value:

11.48

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Bajo Oregon soil. CL1+DL1. Concentration organism: 3600 mg Mg/kg dw. Concentration soil: 313.5 mg Mg/kg dw. pH: 4.83.

Type:

BSAF

Value:

9.31

Basis:

organ d.w.

Calculation basis:

steady state

Remarks on result:

other: Bajo Oregon soil. CL2+DL2. Concentration organism: 3800 mg Mg/kg dw. Concentration soil: 408.3 mg Mg/kg dw. pH: 5.29.

Conclusions:

Dolomitic limestone or a combination of calcitic and dolomitic limestone were added to two different soils using different dosing levels (as well as a control treatment). Consequently, transfer of Mg from soil to plants (Lolium perenne, ryegrass) was studied. Based on the results of these experiments BSAF factors ranging from 4.82 to 53.67 were calculated for Mg. When excluding the control treatments, the range was 4.82 to 17.77.

Reference 2

Endpoint:

bioaccumulation: terrestrial

Type of information:

experimental study

Adequacy of study:

weight of evidence

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).

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)

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.

Reference 3

Endpoint:

bioaccumulation: terrestrial

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

Read across from a study performed with zirconium dichloride oxide, zirconium acetate, and zirconium hydroxide and a study performed with dolomitic limestone or a combination of calcitic and dolomitic limestone. 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

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 magnesium zirconium oxide.

Key result

Type:

BSAF

Value:

4.82 - 53.67 dimensionless

Basis:

organ d.w.

Remarks:

for Mg (element)

Remarks on result:

other: Read across data from Mora et al. (1999) on Mg accumulation in plants.

Remarks:

Based on 1) these data, 2) the fact that Mg is an essential nutrient, and 3) the fact that only a very limited amount of magnesium is released from magnesium zirconium oxide in the environment, it was concluded that there is no terrestrial bioaccumulation hazard for magnesium from magnesium zirconium oxide.

Description of key information

Because magnesium zirconium oxide has a low water solubility, only small amounts of magnesium and zirconium may become available 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 magnesium, although BSAF values > 1 were experimentally determined, the endpoint is not considered relevant, as magnesium is an essential element and therefore internal magnesium levels are actively regulated by organisms. Based on the available information, it is concluded that there is no concern for bioaccumulation of zirconium or magnesium released from magnesium zirconium oxide. 

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 magnesium (oxide)

In the study of Mora et al. (1999), dolomitic limestone or a combination of calcitic and dolomitic limestone was added to two different soils using different dosing levels (as well as a control treatment). Consequently, transfer of Mg from soil to plants (Lolium perenne, ryegrass) was studied. Based on the results of these experiments BSAF factors ranging from 4.82 to 53.67 were calculated for Mg. When excluding the control treatments, BSAF values ranged from 4.82 to 17.77. These BSAF values are as expected, since magnesium is an essential element to plants and internal magnesium levels are actively regulated. This is also clear from the fact that the observed BSAF values increased with decreasing magnesium content of the soil. Because of the active regulation of this essential element, bioaccumulation is not considered relevant.

3. Conclusion on magnesium zirconium oxide

Magnesium zirconium oxide has a low water solubility and only small amounts of magnesium and zirconium will become available for uptake when the substance is released to the environment (Eidam, 2015, 2016; Paulus, 2010). Based on the experimental results available for zirconium, it was concluded that there is no concern for bioaccumulation of zirconium in terrestrial organisms (all BSAF values < 1). For magnesium, BSAF values > 1 were experimentally determined. However, since magnesium is an essential element to plants and internal magnesium levels are actively regulated, this should not be considered as bioaccumulation. Based on these data, it can be concluded that there is no potential for terrestrial bioaccumulation of magnesium or zirconium released from magnesium zirconium oxide.