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Toxicity to terrestrial plants

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Endpoint:
toxicity to terrestrial plants: short-term
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
See attached document in section 13 "Assessment report" for justification and rationale of the analogy approach.
Original letters from the French Competent Authorities requiring the read across to be done with cerium oxide isostearate are attached below.
Reason / purpose for cross-reference:
read-across source
Key result
Species:
other: Allium cepa, Avena sativa, Beta vulgaris, Brassica napus, Cucumis sativus
Duration:
21 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
seedling emergence
Remarks on result:
other: also EC25
Key result
Species:
Glycine max (G. soja)
Duration:
21 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
seedling emergence
Remarks on result:
other: also EC25
Key result
Species:
other: Allium cepa, Avena sativa, Beta vulgaris, Brassica napus, Cucumis sativus, Glycine max
Duration:
21 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Details on results:
The study from which these data are sourced indicates that conservative establishment of the LOEC and the NOEC should be interpreted with care as, though significances were shown in single treatments, not always a continuous dose response relationship was given for all species. For this reason, it was decided to report only the EC50 values in the present target record.
Conclusions:
Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as presenting EC50 values above 1000 mg product/kg dry soil based on seedling emergence, symptoms of phytotoxicity and biomass of monocot (Allium cepa, Avena sativa) and dicot (Beta vulgaris, Brassica napus, Cucumis sativus, Glycine max) crops.
Executive summary:

The source and target substances present similar characterization (nanoparticles of very similar parameters), and similar physico-chemical and ecotoxicological properties (high melting point, low vapour pressure, very low water solubility, no expected bioaccumulation potential when considering cerium and iron elements and isostearate parts, no acute toxicity to daphnids up to and including the saturation concentration). This similarity supports the relevance of the read-across.

Thus, the toxicity to terrestrial plants is expected to be the same for the source and target substances.

Iron oxide isostearate is to be considered as cerium and iron oxide isostearate as presenting EC50 values above 1000 mg product/kg dry soil based on seedling emergence, symptoms of phytotoxicity and biomass of monocot (Allium cepa, Avena sativa) and dicot (Beta vulgaris, Brassica napus, Cucumis sativus, Glycine max) crops.

Endpoint:
toxicity to terrestrial plants: short-term
Type of information:
experimental study
Adequacy of study:
key study
Study period:
from 4 February 2008 to 1 December 2008
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 208 (Terrestrial Plants Test: Seedling Emergence and Seedling Growth Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
yes
Details on preparation and application of test substrate:
- Method of application to soil surface:
A stock solution of the highest concentration was prepared by dissolving 182.5 g test item in 500 mL carrier (cyclohexan). The lower concentrations were obtained by diluting an aliquot of the stock solution (80, 32, 12.8, 5, 2.04, 0.8, 0.32, 0.14 mL made up to 200 mL respectively) in cyclohexan.
Application was performed by distributing the total of the 200 mL prepared spray solution on 1078 g of sand with a hand atomiser. After evaporation of the carrier the treated sand was mixed with 80.3 kg of prepared soil.
- Controls: 200 mL of water and carrier control
- Chemical name of vehicle: cyclohexan (carrier)
- Evaporation of vehicle before use: yes
Species:
Beta vulgaris
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
- Common name: sugarbeet
- Plant family: chenopodiaceae
- Variety: Christella
- Source of seed: Albacete agricola
- Prior seed treatment/sterilization: none
- Historical germination of seed (germination of seed lot tested): no data
- Seed storage: no data
Species:
Brassica napus
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
- Common name: rape
- Plant family: Cruciferaceae
- Variety: Siesta
- Source of seed: Saaten Union
- Prior seed treatment/sterilization: none
- Historical germination of seed (germination of seed lot tested): no data
- Seed storage: no data
Species:
Cucumis sativus
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
- Common name: cucumber
- Plant family: Cucurbitaceae
- Variety: Supermarketer
- Source of seed: Maskarell Semillas
- Prior seed treatment/sterilization: none
- Historical germination of seed (germination of seed lot tested): no data
- Seed storage: no data
Species:
Glycine max (G. soja)
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
- Common name: soybean
- Plant family: Fabaceae
- Variety: Die Saat
- Source of seed: Saatgut Auslese
- Prior seed treatment/sterilization: none
- Historical germination of seed (germination of seed lot tested): no data
- Seed storage: no data
Species:
Allium cepa
Plant group:
Monocotyledonae (monocots)
Details on test organisms:
- Common name: onion
- Plant family: Liliaceae
- Variety: Blanca grande del pais
- Source of seed: Fito
- Prior seed treatment/sterilization: none
- Historical germination of seed (germination of seed lot tested): no data
- Seed storage: no data
Species:
Avena sativa
Plant group:
Monocotyledonae (monocots)
Details on test organisms:
- Common name: oat
- Plant family: Poaceae
- Variety: Alandra
- Source of seed: Agrusa
- Prior seed treatment/sterilization: no data
- Historical germination of seed (germination of seed lot tested): no data
- Seed storage: no data
Test type:
other: early seedling emergence and growth toxicity test
Study type:
laboratory study
Substrate type:
artificial soil
Limit test:
no
Total exposure duration:
21 d
Remarks:
following 50% emergence in the control
Post exposure observation period:
none
Test temperature:
18°C to 21°C
Moisture:
52% to 95%
Details on test conditions:
TEST SYSTEM
- Testing facility: polycarbonate greenhouse, floor area is 400 m2, located in Anna (195m above sea-level), in the province of Valencia, Spain.
- Test container: pot of non-porous material
- Amount of soil: no data
- Method of seeding: seed depth between 0.5 cm (B. vulgaris, B. napus, A. cepa) and 1cm (C. sativus, G. max, A. sativa)
- No. of seeds per container: 5 (dicotyledonae) and 7 (monocotyledonae)
- No. of plants (retained after thinning): 3 (dicotyledonae) and 5 (monocotyledonae). Pot size relative to seedlings number was sufficient to avoid overcrowding of plants.
- No. of replicates per treatment group: 10 (dicotyledonae) and 6 (monocotyledonae)
- No. of replicates per control: 10 (dicotyledonae) and 6 (monocotyledonae)
- No. of replicates per vehicle control: 10 (dicotyledonae) and 6 (monocotyledonae)

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Soil texture:
- % sand: 42%
- % silt: 26%
- % clay: 32%
- Soil taxonomic classification: clay loam
- Soil classification system: no data
- pH: 7.49
- total organic matter content: 1.07%
- Pesticide/fertiliser use history: soil, sand and clay have not been subjected to any pesticide or organic fertiliser treatment for at least 3 years prior to collection and until use within this study.
- Pretreatment of soil: sieving to a particle size of 5 mm after slight drying.
- Storage (condition, duration): no data

GROWTH CONDITIONS
- Photoperiod: 16h light, 8h dark
- Light source: natural light complemented with by high pressure sodium lamps
- Light intensity and quality: minimum 5000 lux
- Day/night temperatures: 18°C to 21°C
- Relative humidity (%): 52% to 95%
- Watering regime and schedules: The pots were irrigated with a water and nutrient source located at the bottom of each pot. A cotton strip connected soil and water source. The water consumed was controlled regularly and missing water supplemented. No plant protection measures were performed over the whole testing period.
- Water source/type: no data
- Volume applied: no data
- Interval of applications: no data
- Any pest control method/fertilization: none

ACCLIMATION PERIOD: no data

EFFECT PARAMETERS MEASURED:
Observations were made during the test to document plant conditions and growth. The condition of test plants was assessed weekly after 50% emergence in the control. Phytotoxic main adverse effects (i.e. stunted growth, wilting, discoloration, necrosis, leaf cupping) were assessed 7, 14, and 21 days after 50% of seeds in control had emerged.
At the final assessment 21 days after 50% of the seeds in the control had emerged the shoot fresh weight was determined for all plants of one replicate as a pooled sample. For each replicate the plants were clipped at soil level and each replicate was weighed immediately afterwards to avoid losses of plant fresh weight. After drying in a oven at 80°C until constant weight was reached, dry weights of replicates were determined also as a pooled sample.
- Phytotoxicity rating system: no data

VEHICLE CONTROL PERFORMED: yes (carrier)

TEST CONCENTRATIONS
- Spacing factor for test concentrations: ca. 2.5
- Range finding study: no data
Nominal and measured concentrations:
0, 0.66, 1.64, 4.10, 10.24, 25.6, 64, 160, 400 and 1000 mg/kg dry soil
Reference substance (positive control):
no
Species:
other: Allium cepa, Avena sativa, Beta vulgaris, Brassica napus, Cucumis sativus
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
seedling emergence
Species:
other: Allium cepa, Avena sativa, Beta vulgaris, Brassica napus, Cucumis sativus
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
seedling emergence
Key result
Species:
other: Allium cepa, Avena sativa, Beta vulgaris, Brassica napus, Cucumis sativus
Duration:
21 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
seedling emergence
Remarks on result:
other: also EC25
Species:
Glycine max (G. soja)
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
0.66 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: seedling emergence and biomass
Remarks on result:
other: NOEC < 0.66 mg/kg dw
Key result
Species:
Glycine max (G. soja)
Duration:
21 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
seedling emergence
Remarks on result:
other: also EC25
Species:
other: Avena sativa, Beta vulgaris
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Species:
other: Avena sativa, Beta vulgaris
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Species:
Allium cepa
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
1.64 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Species:
Allium cepa
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
4.1 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Species:
Brassica napus
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
160 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Species:
Brassica napus
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
400 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Species:
Cucumis sativus
Duration:
21 d
Dose descriptor:
NOEC
Effect conc.:
0.66 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Species:
Cucumis sativus
Duration:
21 d
Dose descriptor:
LOEC
Effect conc.:
1.64 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Key result
Species:
other: Allium cepa, Avena sativa, Beta vulgaris, Brassica napus, Cucumis sativus, Glycine max
Duration:
21 d
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Remarks:
biomass
Remarks on result:
other: also EC25
Details on results:
SEEDLING EMERGENCE
Significant effects on the emergence were noted for Glycine max from a nominal soil concentration of 0.66 to 1000 mg test item per kg dry soil with a maximum inhibition of 26.67% observed at a nominal rate of 400 mg product/kg dry soil: LOEC = 0.66 mg/kg dry soil.
Calculation of EC25 or EC50 could not be performed, as only limited inhibition and no continuous dose response relationship was found.
No significant effects were observed in the other species: NOEC ≥ 1000 mg/kg dry soil.

PHYTOTOXICITY:
Visual phytotoxicity in all tested concentrations did not occur for tested species.

BIOMASS:
Increasing concentration rates of the test item exhibited significant effects for Allium cepa, Brassica napus, Cucumis sativus and Glycine max. The most sensitive species was Cucumis sativus showing a maximum biomass inhibition of 21.69% at a nominal rate of 64 mg product/kg dry soil. Calculation of EC25 or EC50 could not be performed, as only limited inhibition was found.

It is important to notice that no difference was found between water and carrier controls, regardless the considered endpoint.
Validity criteria fulfilled:
yes
Remarks:
In control: seedling emergence > 70%; no visible phytotoxicity, mean control survival > 90%
Conclusions:
The critical value for the establishment of an EC50 must be found beyond the maximum tested rate of 1000 mg product/ kg dry soil concerning seedling and biomass inhibition for all the tested species.
The conservative establishment of the LOEC and the NOEC should be interpreted with care as, though significances were shown in single treatments, not always a continuous dose response relationship was given for all species.
Executive summary:

The effect of cerium and iron oxide isostearate on the seedling emergence and growth of monocot (Allium cepa, Avena sativa) and dicot (Beta vulgaris, Brassica napus, Cucumis sativus, Glycine max) crops was studied at nominal concentrations of 0, 0.66, 1.64, 4.10, 10.24, 25.6, 64, 160, 400 and 1000 mg/kg dry soil (according to OECD guideline 207 and GLP). The growth medium used in the seedling emergence and growth test was artificial soil (sand 42%, silt 26%, clay 32%, pH 7.49, total organic matter content 1.07%). The endpoints assessed were seedling emergence, phytotoxicity at days 7, 14 and 21, and biomass at the end of the test (i. e. 21 days after 50 % emergence in the control).

 

SEEDLING EMERGENCE

Significant effects on the emergence were noted for Glycine max from a nominal soil concentration of 0.66 to 1000 mg test item per kg dry soil with a maximum inhibition of 26.67% observed at a nominal rate of 400 mg product/kg dry soil: LOEC = 0.66 mg/kg dry soil.

Calculation of EC25 or EC50 could not be performed, as only limited inhibition and no continuous dose response relationship was found.

No significant effects were observed in the other species: NOEC 1000 mg/kg dry soil.

 

PHYTOTOXICITY:

Visual phytotoxicity in all tested concentrations did not occur for tested species.

 

BIOMASS:

Increasing concentration rates of the test item exhibited significant effects for Allium cepa, Brassica napus, Cucumis sativus and Glycine max. The most sensitive species was Cucumis sativus showing a maximum biomass inhibition of 21.69% at a nominal rate of 64 mg product/kg dry soil. Calculation of EC25 or EC50 could not be performed, as only limited inhibition was found.

 

The critical value for the establishment of an EC50 must be found beyond the maximum tested rate of 1000 mg product/ kg dry soil concerning seedling and biomass inhibition for all the tested species.

The conservative establishment of the LOEC and the NOEC should be interpreted with care as, though significances were shown in single treatments, not always a continuous dose response relationship was given for all species.

Description of key information

By analogy with cerium and iron oxide isostearate (active matter of DPX10), iron oxide isostearate (active matter of DPX13) should present EC50 values above 1000 mg product/kg dry soil based on seedling emergence, symptoms of phytotoxicity and biomass of monocot (Allium cepa, Avena sativa) and dicot (Beta vulgaris, Brassica napus, Cucumis sativus, Glycine max) crops.

Key value for chemical safety assessment

Additional information

One GLP-compliant study performed according to OECD guideline 208 is available on the analogue, cerium and iron oxide isostearate (active matter of DPX10). It is quoted as reliability 1 according to Klimisch criteria and flagged as a key study.