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Toxicity to terrestrial plants

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Reference
Endpoint:
toxicity to terrestrial plants: long-term
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Study period:
From September 18, 2002 to October 08, 2002
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
KL2 due to RA
Justification for type of information:
Refer to Section 13 of IUCLID for details on the category justification.
Qualifier:
according to guideline
Guideline:
OECD Guideline 208 (Terrestrial Plants, Growth Test)
Version / remarks:
partially adapted to the Draft Updated Guideline "Terrestrial (Non-target)-Plant Test: 208A: Seedling Emergence and Seedling Growth Test" (July 2000).
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
yes
Remarks:
acetone
Details on preparation and application of test substrate:
- Preparation of the application mixtures:
Due to its low solubilty in water, the test substance was dissolved in acetone, applied to quartz sand and mixed with the soil.
A stock solution of nominal 50 mg/mL was prepared by dissolving 500 mg of the test substance completely in 10 mL of acetone. This stock solution was used as the application solution for the highest test concentration and for the preparation of the lower concentrated application solutions of nominal 5 and 0.5 mL.
An aliquot of 3 mL of the respective application mixture was homogeneously distributed onto 15g of sans (particle size0.1-0.3 mm). After complete evaporation of the acetone under a stream of nitrogen gas, each application mixture was mixed homogeneously using a Vortex mixer. Control sand was treated in the same way but with acetone only.
- Incorporation of the test substance into the soil:
Aliquots of 10g of each sand mixture were incorporated uniformly into 990g of soil (dry weight basis) using a planetary mixer. In this way, for each concentration to be tested, the whole lot of soil needed for all plants was treated as one batch. The soil was continuously mixed during application. The ratio of sand was 1% (w/w, dry weight) for all treatments including the control.
- Preparation of the bioassay:
Immediately after incorporation of the test substance, the soil was weighed into the bioassay pots at an amount corresponding to 70 dry soil (+/- maximum 0.8g). The test seeds were sowed not longer than 2h after filling of the pots to avoid drying of the soil surface. All seeds of each species were of the same size class. The seeds were not imbibed. Per replicate, 10 seeds were sown. After sowing the seeds, the soil surface was carefully sprayed with deionized water. The water reservoirs were filled not before emergence of the seedlings. A surplus of seeds was sown to increase the statistical significance of the emergence rates. After emergence, the seedlings were reduced to five plants per pot to obtain representativeand healthy plants. This was done at the earliest possible date after emergence.
Species:
Avena sativa
Plant group:
Monocotyledonae (monocots)
Details on test organisms:
from Landi Landesprodukte, CH-4460 Gelterkinden, Switerland (oat)
Species:
Brassica rapa
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
from H. Nebiker AG, CH-4450 Sissach, Switerland (turnip)
Species:
Lepidum sativum
Plant group:
Dicotyledonae (dicots)
Details on test organisms:
from Landesprodukte , CH-4410 Liestal (cress)
Test type:
other: emergence of seedlings and early stages of growth after a single application
Study type:
laboratory study
Substrate type:
natural soil
Limit test:
no
Total exposure duration:
14 d
Test temperature:
19-25°C
pH:
6.5 +/- 0.1
Moisture:
The soil was stored slightly moist (about 21% of the maximum water holding capacity (MWC))
(The MWC was 38 +/- 1 g/ 100g dry soil)
Details on test conditions:
- Bioassay pots: plastic pots (8 cm in diameter), glued to the middle of a petri-dish lid (9 cm in diameter). The lids were painted black to avoid algae growth in the water. A hole for a glass fiber wick was punched through the bottom of the pot and the lid. The wick had a length of about 8 cm and served for the transport of the water to the soil. This unit (pot, lid and wick) was placed on a plastic box which served as water supply.
Soil: Standart Soil Speyer 2.3
- Growth conditions:
Oat: after sowing and spraying of the soil surface with water, the pots were incubated for 2 days at room temperature in the dark. Thereafter, the pots were incubated at room temperature under diffuse light (300-400 Lux) for one further day. The reservoirs were filled with deionized water and the pots were placed in a temperature controlled room in a randomized design.
Turnip and cress: after sowing and spraying of the soil surface with water, the pots were incubated for 1 (cress) or 2 (turnip) days at room temperature in the dark. Thereafter, the reservoirs were filled with deionized water and the pots were placed in a climatic chamber in a randomized design.
All plants were illuminated for 16h per day (fluorescent tubes, Philips TLD 36W/840, about 7000 Lux measured at the soil surface at study start). The temperature were between 19-25°C during the test period.
-Time schedule:
The test was started when >50% of the control seedlings had emerged (5 days after sowing = Day 0) and was finished 14 days after this date. The total number of seeds sown per species was 40. The number of control seeds emerged up to Day 0 was between 36-38 for the 3 species. The emergence rate was determined to be between 90 and 95%. The assessment of the symptoms were performed on Days 2, 9 and 14. The determination of fresh weight was made on Day 14.
- Experimental evaluation: number of plants emerged per replicate and phytotoxic symptoms (stunted growth, chlorosis/discoloration, necrosis). The determination of shoot fresh weight was carried out at the end of the test for all plants of one pot as one replicate. The plants were cut directly between root and shoot with a pair of scissors. For that purpose, each plant was pulled slightly out of the soil to uncover the site of cutting. Immediately after cutting the plants were weighed to avoid as fas as possible losses in fresh weight by evaporation from the plants.
Nominal and measured concentrations:
0 (untreated control), 1, 10 and 10 mg/kg soil (dry weight) (nominal)
(four replicates per test concentration and plant species)
Reference substance (positive control):
no
Key result
Species:
other: oat, turnip and cress
Duration:
14 d
Dose descriptor:
EC50
Effect conc.:
> 100 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
seedling emergence
Key result
Species:
other: oat, turnip and cress
Duration:
14 d
Dose descriptor:
NOEC
Effect conc.:
>= 100 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
seedling emergence
Key result
Species:
other: oat, turnip and cress
Duration:
14 d
Dose descriptor:
EC50
Effect conc.:
> 100 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Key result
Species:
other: oat and turnip
Duration:
14 d
Dose descriptor:
NOEC
Effect conc.:
>= 100 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Key result
Species:
other: cress
Duration:
14 d
Dose descriptor:
NOEC
Effect conc.:
10 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth
Details on results:
1. Oat
No effects were observed on the emergence rate of oat seeds (97% relative to untreated control) for all concentrations. The 14d day NOEC for emergence was at least 100 mg/kg dry soil and the 14d LOEC and LC50 for emergence were higher than 100 mg/kg soil. No visual phytotoxic symptoms were recorded up to and including 100 mg/kg dry soil. The fresh weight of plant grown in 1, 10 and 100 mg/kg dry soil was 114, 107 and 109% of untreated controls. Even if the the value for the group 1 mg/kg dry soil was statistically different from the controls, the increase of the fresh weight was clearly lower than 25%. Therefore, the 14d day NOEC for growth was at least 100 mg/kg dry soil and the 14d LOEC and LC50 for growth were higher than 100 mg/kg soil.
2. Turnip
No effects were observed on the emergence rate of oat seeds (97-103% relative to untreated control) for all concentrations. The 14d day NOEC was at least 100 mg/kg dry soil and the 14d LOEC and LC50 were higher than 100 mg/kg soil. No visual phytotoxic symptoms were recorded up to and including 100 mg/kg dry soil. The fresh weight of plant grown in 1, 10 and 100 mg/kg dry soil was 115, 108 and 93% of untreated controls. Even if the the value for the group 1 mg/kg dry soil was statistically different from the controls, the increase of the fresh weight was clearly lower than 25%. Therefore, the 14d day NOEC for growth was at least 100 mg/kg dry soil and the 14d LOEC and LC50 for growth were higher than 100 mg/kg soil.
3. Cress
No effects were observed on the emergence rate of oat seeds (100-105% relative to untreated control) for all concentrations. The 14d day NOEC was at least 100 mg/kg dry soil and the 14d LOEC and LC50 were higher than 100 mg/kg soil. No visual phytotoxic symptoms were recorded up to and including 100 mg/kg dry soil. The fresh weight of plant grown in 1, 10 and 100 mg/kg dry soil was 97, 102 and 77% of untreated controls. Therefore, the 14d day NOEC and LOEC for growth were determined to be 10 and 100 mg/kg dry soil, respectively and the 14d EC25 for growth was ca. 100 mg/kg soil.
Results with reference substance (positive control):
-
Reported statistics and error estimates:
For data evaluation, the fresh weight per plant at the different concentrations was calculated as percentage of untreated plants. Additionally, the mean value (x), the standard deviation (s) and the coefficient of variation (CV%) were calculated.
The LC50 and EC50 and their 95% confidence limits could not be calculated since the test substance had no adverse effect on the growth of the plants up to the highest test concentration (and therefore were determined directly from the raw data). For the determination of the LOEC and NOEC, the number of emerged seeds and the mean shoot fresh weight per plant at the tested concentrations were tested on statistically significant differences to the control values by a Dunntt-test (alpha = 0.05, one-sided).
Dose-response curves were obtained by plotting the fresh weight (percent of untreated against the logarithmic concentration.
Validity criteria fulfilled:
yes
Conclusions:
Under the study conditons, the 14 d NOEC of the test substance for emergence in oat, turnip and cress was determined to be 100 mg/kg dry soil (nominal). The 14 d NOEC for growth was 100 mg/kg dry soil for oat and turnip and 10 mg/kg dry soil for cress (nominal).
Executive summary:

A study was conducted to determine the short-term toxicity of the test substance, isoC18 MIPA (96% active), to terrestrial plants according to OECD Guideline 208, in compliance with GLP. One monocotyledonous plant species (Avena sativa, oat) and two dicotyledonous plant species (Brassica rapa, turnip and Lepidium sativum, cress) were exposed to 0, 1, 10 and 100 mg test substance/kg dry soil for 14 d. the emergence of seedlings and early stages of growth after a single application were measured. Except for reduction in fresh plant weight at 100 mg/kg dry weight in cress, there were no treatment-related effects on emergence and growth in any of the plant species. Under the study conditions, the 14 d NOEC of the test substance for emergence in oat, turnip and cress was determined to be 100 mg/kg dry soil (nominal). The 14 d NOEC for growth was 100 mg/kg dry soil for oat and turnip and 10 mg/kg dry soil for cress (nominal) (Seyfried, 2002).

Description of key information

Key value for chemical safety assessment

Short-term EC50 or LC50 for terrestrial plants:
100 mg/kg soil dw

Additional information

A study was conducted to determine the short-term toxicity of the read across substance, isoC18 MIPA (96% active), to terrestrial plants according to OECD Guideline 208, in compliance with GLP. One monocotyledonous plant species (Avena sativa, oat) and two dicotyledonous plant species (Brassica rapa, turnip and Lepidium sativum, cress) were exposed to 0, 1, 10 and 100 mg test substance/kg dry soil for 14 d. the emergence of seedlings and early stages of growth after a single application were measured. Except for reduction in fresh plant weight at 100 mg/kg dry weight in cress, there were no treatment-related effects on emergence and growth in any of the plant species. Under the study conditions, the 14 d NOEC of the test substance for emergence in oat, turnip and cress was determined to be 100 mg/kg dry soil (nominal). The 14 d NOEC for growth was 100 mg/kg dry soil for oat and turnip and 10 mg/kg dry soil for cress (nominal) (Seyfried, 2002).