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Toxicity to terrestrial plants

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Endpoint:
toxicity to terrestrial plants: long-term
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
Reliable with restrictions because effect not consistently negative amongst the different dose levels, and because it was not clearly mentioned whether IC10 and IC25 values were expressed as mg Y/kg dw or mg YCl3/kg dw.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 208 (Terrestrial Plants, Growth Test)
GLP compliance:
not specified
Analytical monitoring:
yes
Details on sampling:
- For determination of Y background levels, eight control replicates were analysed.
- To validate calculated experimental levels, two soil samples from each dose (one pre- and one post-experiment) were analysed.
- The pre-experiment soil sample was collected from the initial contaminated soil batch, while the post-experiment sample was obtained by combining and mixing the soil from 10 pots within a given dose (two pots / species) after removing plant debris.
Vehicle:
no
Details on preparation and application of test substrate:
- A 1-L stock solution of YCl3 was prepared by dissolving the appropriate amount of YCl3 in deionised water.
- Doses were prepared from the stock solution.
- To contaminate the soil, the required volume of soil for a dose was measured into large plastic containers using the total number of pots (10x10x9 cm) and converting the volume of soil to mass of soil (~300 g of dry soil per pot) in order to calculate the necessary volume of YCl3 stock solution. Working from lowest to highest dose, the YCl3 solution was poured slowly into the container and mixed thoroughly into the soil by hand using stainless steel spoons. An additional amount of water was added by rinsing the solution flask to further hydrate the soil and to ensure that all metal residues reached the soil. Once thoroughly mixed, the soil was split between the replicates in the dose treatment.
- Once prepared, all soil pots were transferred to growth chambers and allowed to settle for 24 h before seeds were sown.
Species:
other: Desmodium canadense (L.) DC.
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
- Common name: showy tricktrefoil
- Plant family: Fabaceae
- Wild, native species
- Selected based on its coefficient of conservation (see Oldham et al., 1995).
- Seed germination rates of > 70% were obtained in Petri-dish pre-trials.
Species:
other: Asclepias syriaca L.
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
- Common name: common milkweed
- Plant family: Asclepiadaceae
- Wild, native species
- Selected based on its importance to native fauna (i.e. monarch butterfly).
- Seed germination rates of > 70% were obtained in Petri-dish pre-trials.
- Due to a stratification requirement, seeds of this species were cold stratified in a 4°C refrigerator for ca. 2 months prior to the beginning of the experiment.
Species:
other: Panicum virgatum L.
Plant group:
Monocotyledonae (monocots)
Details on test organisms:
- Common name: switchgrass
- Plant family: Poaceae
- Wild, native species
- Selected based on its coefficient of conservation (see Oldham et al., 1995).
- Seed germination rates of > 70% were obtained in Petri-dish pre-trials.
Species:
Raphanus sativus
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
- Common name: radish
- Plant family: Brassicaceae
- Crop plant
Species:
other: Solanum lycopersicum L.
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
- Common name: tomato
- Plant family: Solanaceae
- Crop plant
Test type:
seedling emergence and seedling growth test
Study type:
laboratory study
Substrate type:
artificial soil
Limit test:
no
Total exposure duration:
28 d
Remarks:
28 days after seedling emergence reached 70% in the control
Test temperature:
Temperature ranged between ca. 25°C during the day and ca. 15°C at night.
pH:
6.06 ± 0.03
Moisture:
See "Details on test conditions".
Details on test conditions:
TEST SYSTEM
- Test container (type, material, size): pots, 10x10x9 cm
- No. of seeds per container: 5
- No. of plants (retained after thinning): 1 (ca. 1 week after the control pots for the species under consideration had reached 70% seed germination, all pots for that species were thinned to one plant per pot - to prevent bias, a random number generator was used to determine which seedling was left in the pot, except for D. canadense, where due to uneven germination times and sizes it was preferred to leave the largest seedling in the pot)
- No. of replicates per treatment group: 7
- No. of replicates per control: 7

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Source: Artificial soils prepared following Environment Canada (EC) protocols [EC Formulation of Artificial Soil (SOP 15.09/1.3/S)].
- Preparation procedures: To ensure proper homogenisation, soil was prepared in small batches of ca. 2.7 kg/batch that were thoroughly mixed using a commercial grade electrical mixer. 500 mL of tap water was added to each batch of soil in order to attain an initial soil moisture content of ca. 20%. Due to the acidity of the peat, CaCO3 was added to adjust the pH to the desired values (12 g CaCO3 added per batch of soil). Soil batches were allowed to settle for at least 48 h before use.
- % sand: 70% silica sand
- % silt: not reported
- % clay: 20% Kaolin clay
- % peat: 10%
- Organic carbon (%): not reported
- CEC: 7.71 +/- 0.29 mmolc/100 g soil
- Background REE concentration: 3.85 +/- 0.17 mg/kg dw

GROWTH CONDITIONS
- Photoperiod: 16L:8D
- Light source: artificial
- Light intensity and quality: average photosynthetic active radiation of 309 +/- 9 µmol photons/m2/s
- Day/night temperatures: ca. 25°C during the day and ca. 15°C at night
- Watering regime and schedules: Water was supplemented daily, as needed (but usually twice a day), from the top in order to maintain consistent moisture in the growth medium according to the method described by Environment Canada (2005).
- Nutrients: To supplement the low nutrient artificial soil, fertiliser (Plant-Prod 20-20-20 All Purpose Fertiliser) was added to all pots on approximately day 17 after planting the seeds. Fertiliser was prepared by dissolving 7.8 g of the soluble fertiliser in 1 L of water to make a stock solution. From the stock solution, 8.30 mL (ca. 65 mg of fertiliser) was added to each pot by pipette (equivalent to 13 mg N, 13 mg P, 13 mg K).
- All plants were rotated within the growth chamber on a weekly basis to exclude confounding environmental factors.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable):
- seed germination (recorded daily for ca. 31 days)
- All plants were harvested 28 days after their respective controls had reached 70% germination. On the day of harvest, all aboveground biomass was collected by cutting the plant at the base of the soil, and placing it in a paper bag. For R. sativus, the belowground bulb was also harvested and bagged along with the aboveground section. All plant material was then dried in a drying oven at ca. 70°C for at least 48 h prior to biomass measurements.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: geometric progression of doses by a factor of 1.9
- Range finding study: not reported
Nominal and measured concentrations:
Nominal concentrations: control + 22.4, 42.5, 80.8, 153.5, 291.6, 554.0, 1052.0, and 2000.0 mg YCl3/kg dw (equivalent to control + 10.2, 19.4, 36.8, 69.6, 132.8, 252.2, 479.0 and 910.6 mg Y/kg dw)
Measured concentrations were not reported, but the results of the study (IC10 and IC25) were calculated using average measured concentrations (pre- and post-experiment samples).
Reference substance (positive control):
no
Species:
other: Asclepias syriaca
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
95.8 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether expressed as mg Y/kg dw or mg YCl3/kg dw + not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Species:
other: Desmodium canadense
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
33.7 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether expressed as mg Y/kg dw or mg YCl3/kg dw + not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Species:
other: Panicum virgatum
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
329.6 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether expressed as mg Y/kg dw or mg YCl3/kg dw + not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Species:
Raphanus sativus
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
> 910.6 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Species:
other: Solanum lycopersicum
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
> 910.6 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Details on results:
Other effect concentrations for growth (biomass):
- EC25 for Asclepias syriaca = 257 mg Y/kg dw
- EC25 for Desmodium canadense = 109.4 mg Y/kg dw
- EC25 for Panicum virgatum = 591.6 mg Y/kg dw
Not entirely clear whether expressed as mg Y/kg dw or mg YCl3/kg dw + not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Further, it was reported that the adverse effects on biomass observed in the three native species were not consistently negative amongst the different dose levels. Therefore, the results of this study should be considered reliable with restrictions and in the absence of any other studies on terrestrial plants should only be considered as supporting information.

Effects on germination:
No effects of yttrium (trichloride) on seed germination were found in Asclepias syriaca, Panicum virgatum, and Raphanus sativus.
A significantly negative effect starting at the first affected dose was noted for Desmodium canadense.
For Solanum lycopersicum, a significantly negative effect was documented, but occasionally some intermediate higher doses were not significantly different.
The concentrations at which effects were observed were not clearly reported.
Reported statistics and error estimates:
Inhibition concentrations (IC25 and IC10) causing 25% or 10% reductions in plant biomass respectively, as compared to the controls, were calculated using non-linear regression model analyses (Environment Canada, 2005). These were performed in the cases where the model assumptions of homogeneity of variance (Levene's test) and normality of residuals (Shapiro-Wilk test) were met. In cases where the assumptions could not be met even after transformation of the data, the IC25 and IC10 values were calculated using the non-parametric ICPIN program (Norberg-King, 1993).
Non-parametric Kruskal-Wallis tests or parametric ANOVAs were used to determine if any statistically significant difference existed in the different treated and control plant parameters.
Validity criteria fulfilled:
yes
Conclusions:
In this study, the effect of yttrium (administered as yttrium trichloride) on seed germination and seedling growth was investigated in three native plant species and two crop plant species. Some effects on seed germination were reported for the native species Desmodium canadense and the crop plant species Solanum lycopersicum. No effects were observed in the other three species tested. Based on biomass measurements of the seedlings (28 days after the control reached 70% germination), 10 and 25% inhibitory concentrations were reported. In the two crop plant species Raphanus sativus and Solanum lycopersicum, no effects were observed up to and including the highest concentration tested, i.e. the IC10 and IC25 were > 910.7 mg Y/kg dw. The IC10 values for the native species Desmodium canadense, Asclepias syriaca and Panicum virgatum were reported to be 33.7, 95.8 and 329.6 mg/kg dw, respectively. It was however not clearly reported whether these concentrations represent yttrium or yttrium trichloride concentrations (assumed yttrium). Moreover, it was reported that the effects were not consistently negative amongst the different concentrations tested. Therefore, the results of this study are considered reliable with restrictions and should, in the absence of other information on toxicity of yttrium (trichloride) to terrestrial plants, only be used as supporting information.
Endpoint:
toxicity to terrestrial plants: long-term
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
Supporting information on the toxicity of yttrium trichloride to terrestrial plants (Thomas et al., 2014) was considered relevant for yttrium trinitrate too, as both compounds are water-soluble yttrium compounds and any observed toxicity in studies performed with these compounds is attributed to exposure to bioavailable yttrium. The read across justification document is attached to IUCLID Section 13.
Reason / purpose:
read-across source
Species:
other: Asclepias syriaca
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
95.8 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether expressed as mg Y/kg dw or mg YCl3/kg dw + not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Remarks:
Effect concentration obtained in the read across study of Thomas et al. (2014) performed with yttrium trichloride, and considered relevant for yttrium trinitrate as well.
Species:
other: Desmodium canadense
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
33.7 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether expressed as mg Y/kg dw or mg YCl3/kg dw + not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Remarks:
Effect concentration obtained in the read across study of Thomas et al. (2014) performed with yttrium trichloride, and considered relevant for yttrium trinitrate as well.
Species:
other: Panicum virgatum
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
329.6 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether expressed as mg Y/kg dw or mg YCl3/kg dw + not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Remarks:
Effect concentration obtained in the read across study of Thomas et al. (2014) performed with yttrium trichloride, and considered relevant for yttrium trinitrate as well.
Species:
Raphanus sativus
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
> 910.6 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Remarks:
Effect concentration obtained in the read across study of Thomas et al. (2014) performed with yttrium trichloride, and considered relevant for yttrium trinitrate as well.
Species:
other: Solanum lycopersicum
Duration:
28 d
Dose descriptor:
EC10
Effect conc.:
> 910.6 mg/kg soil dw
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: Not entirely clear whether arithmetic mean or geometric mean of analysed concentrations was used.
Remarks:
Effect concentration obtained in the read across study of Thomas et al. (2014) performed with yttrium trichloride, and considered relevant for yttrium trinitrate as well.

Description of key information

Only supporting information has been identified on the toxicity of yttrium (obtained with the read across substance yttrium trichloride) to terrestrial plants.

Key value for chemical safety assessment

Additional information

No useful information was identified on the toxicity of yttrium trinitrate to terrestrial plants. Supporting information, obtained with the read across substance yttrium trichloride, i.e. a similar water-soluble yttrium compound as yttrium trinitrate, was however considered useful and therefore added to this dossier. The read across justification document is attached to IUCLID Section 13.

In the study of Thomas et al. (2014), the effect of yttrium (administered as yttrium trichloride) on seed germination and seedling growth was investigated in three native plant species and two crop plant species. Some effects on seed germination were reported for the native species Desmodium canadense and the crop plant species Solanum lycopersicum. No effects were observed in the other three species tested. Based on biomass measurements of the seedlings (28 days after the control reached 70% germination), 10 and 25% inhibitory concentrations were reported. In the two crop plant species Raphanus sativus and Solanum lycopersicum, no effects were observed up to and including the highest concentration tested, i.e. the IC10 and IC25 were > 910.7 mg Y/kg dw. The IC10 values for the native species Desmodium canadense, Asclepias syriaca and Panicum virgatum were reported to be 33.7, 95.8 and 329.6 mg/kg dw, respectively. It was however not clearly reported whether these concentrations represent yttrium or yttrium trichloride concentrations (assumed yttrium). Moreover, it was reported that the effects were not consistently negative amongst the different concentrations tested. Therefore, the results of this study are considered reliable with restrictions and should, in the absence of other information on toxicity of yttrium (trichloride) to terrestrial plants, only be used as supporting information.