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Ecotoxicological information

Toxicity to terrestrial plants

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Reference
Endpoint:
toxicity to terrestrial plants: long-term
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: No guidelines used, but well documented and well performed according to scientific standards. Unbounded NOEC as supporting information. Nominal concentrations used.
Qualifier:
no guideline followed
Principles of method if other than guideline:
In this study, sorgrass (Sorghum vulgare var. sudanense Hitchc.) was sown in natural soil either with or without added Se and shoot dry and fresh weight was recorded after 6 weeks. Two different soils were used (Blanton and Orangeburg), either limed or unlimed.
GLP compliance:
not specified
Analytical monitoring:
no
Vehicle:
no
Details on preparation and application of test substrate:
see test conditions
Species:
Sorghum vulgare
Plant group:
Monocotyledonae (monocots)
Details on test organisms:
- Common name: sorgrass
- Plant family: Poaceae
- Variety: sorghum-sudangrass hybrid (var. sudanense Hitchc.)
Test type:
seedling emergence toxicity / vegetative vigour test
Study type:
laboratory study
Substrate type:
natural soil
Limit test:
no
Total exposure duration:
6 wk
Test temperature:
No data
pH:
Blanton sand:
- limed: pH 6.5
- unlimed: pH 4.9

Orangeburg loamy sand
- limed: pH 6.0
- unlimed: pH 5.5
Moisture:
No data
Details on test conditions:
TEST SYSTEM
- Testing facility: Greenhouse experiment
- Test container (type, material, size): 7-kg polyethylene pot, bottom lined with gravel
- Amount of soil: 6 kg
- No. of seeds per container: 10
- No. of plants (retained after thinning): 4 (low Se treatments) to 6 (high Se treatments)
- No. of replicates per treatment group: 5
- No. of replicates per control: 5

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographic location: Savannah River Site, Aiken, SC
- Sampling depth (cm): Ap horizon
- Two soils were used: Blanton sand (loamy, siliceous, thermic Grossarenic Paleudult) and Orangeburg loamy sand (loamy, siliceous, thermic Typic Paleudult)
- % sand: 91.9% (Blanton), 87.4% (Orangeburg)
- % silt: 6.2% (Blanton), 7.9% (Orangeburg)
- % clay: 1.9% (Balnton), 4.7% (Orangeburg)
- Soil taxonomic classification: Grossarenic Paleudult (Blanton) and Typic Paleudult (Orangeburg)
- Organic carbon (%): 11.0% (Blanton), 18.5% (Orangeburg)
- CEC: 3.23 cmolc/kg (Blanton), 3.93 cmolc/kg (Orangeburg)
- Pretreatment of soil: The soils were air dried and passed through a 2-mm sieve to remove gravel and coarse debris.
- Macronutrient and micronutrient fertilizers were added (B, Cu, Fe, K, Mn, Mo, N, P, Zn)

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): shoot dry and fresh weight
Nominal and measured concentrations:
Nominal: 0, 1, 2, 4 mg Se/kg
Reference substance (positive control):
not specified
Species:
Sorghum vulgare
Duration:
6 wk
Dose descriptor:
NOEC
Effect conc.:
1 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
Se
Basis for effect:
growth
Remarks:
shoot dry weight
Remarks on result:
other: Blanton sand, unlimed
Species:
Sorghum vulgare
Duration:
6 wk
Dose descriptor:
NOEC
Effect conc.:
>= 4 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
Se
Basis for effect:
growth
Remarks:
shoot dry weight
Remarks on result:
other: Blanton sand, limed
Species:
Sorghum vulgare
Duration:
6 wk
Dose descriptor:
NOEC
Effect conc.:
>= 4 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
Se
Basis for effect:
growth
Remarks:
shoot dry weight
Remarks on result:
other: Orangeburg loamy sand, unlimed
Species:
Sorghum vulgare
Duration:
6 wk
Dose descriptor:
NOEC
Effect conc.:
>= 4 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
Se
Basis for effect:
growth
Remarks:
shoot dry weight
Remarks on result:
other: Orangeburg loamy sand, limed
Reported statistics and error estimates:
multiple comparison tests (p<0.05)

 Additional Results

Test substance

Test organism

Soil

pH

Organic matter (%)

Clay (%)

Background conc. (mg Se/kg)

Temperature (°C)

Equilibration

Exposure period

Endpoint

Effect parameter

Value (mg Se/kg dw)

Na2SeO3

Sorghum vulgare

Blanton limed loamy sand

6.5

11

1.9

NR

NR

NR

6 weeks

total plant dry yield

NOEC (unbounded)

≥4 (4% inhibition)

Na2SeO3

Sorghum vulgare

Blanton unlimed loamy sand

4.9

11

1.9

NR

NR

NR

6 weeks

total plant dry yield

NOEC

1 (-27% inhibition)

Na2SeO3

Sorghum vulgare

Orangeburg limed loamy sand

6

18.5

4.7

NR

NR

NR

6 weeks

total plant dry yield

NOEC (unbounded)

≥4 (15% inhibition)

Na2SeO3

Sorghum vulgare

Orangeburg unlimed loamy sand

5.5

18.5

4.7

NR

NR

NR

6 weeks

total plant dry yield

NOEC (unbounded)

≥4 (-7% inhibition)

Conclusions:
In this Klimisch 2 study, sorgrass (Sorghum vulgare var. sudanense Hitchc.) was sown in natural soil either with or without added Se and shoot dry and fresh weight was recorded after 6 weeks. Two different soils were used (Blanton and Orangeburg), either limed or unlimed. In unlimed Blanton sand, the 6-wk NOEC was 1 mg Se/kg soil dw. In limed Blanton Sand and both limed and unlimed Orangeburg loamy sand, the 6-wk NOEC was >= 4 mg Se/kg soil dw.

Description of key information

The lowest reported NOEC value for Na2SeO3 is 1.0 mg Se/kg soil for yield of Sorghum vulgare after 6 weeks exposure in a loamy sand soil (Carlson et al., 1991; Klimisch 2).

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for terrestrial plants:
1 mg/kg soil dw

Additional information

Reliable results are available on toxicity of Na2SeO3 and Na2SeO4 to terrestrial plants. Two studies compare the toxicity of selenite and selenate to yield of Lolium perenne and Sorghum vulgare (Cartes et al., 2005; Carlson et al., 1991). Both studies confirm the higher toxicity of selenate compared to selenite, which is consistent with toxicity data to other terrestrial organisms and the difference in sorption to soil between selenite and selenate. Therefore, only the available reliable results for selenite are taken into account for the hazard assessment of tetravalent inorganic selenium substances.

Reliable chronic NOEC values for selenite vary between 1 and ≥10 mg Se/kg dw (added concentrations). The lowest reported NOEC value for Na2SeO3 of 1.0 mg Se/kg soil was observed for yield of Sorghum vulgare after 6 weeks exposure in a loamy sand soil (Carlson et al., 1991). Three unbounded NOEC values of ≥4.0 mg Se/kg soil were obtained for the same endpoint and species in 3 other soils differing in pH, organic matter and clay content. Additionally, field data are available for the effect of initial Na2SeO3 applications on yield of maize, carrots, potato and pea in subsequent cropping seasons, with NOEC values of 29, 81, 29 and 7 mg Se/kg dw (Kadar, 1995; Biacs et al., 1995; Kadar et al., 1994; Nyarai-Horvath et al., 1997). These field data confirm the conservative nature of the selected 1 mg Se/kg threshold value for the toxicity of selenite to terrestrial plants.

Also reliable chronic toxicity data for Na2SeO4 are available for the monocotyledon plants (Lolium perenne, Triticum aestivum, Sorghum vulgare and Hordeum vulgare) and dicotyledon plants (Medicago sativa, Beta vulgaris, Lycopersicon escultentum and a Prunus species) and vary between 0.39 and ≥3 mg Se/kg dw (added concentrations). Two reliable studies (Soltanpour and Workman, 1980 and Wan et al., 1988; both Klimisch 2) reported a total of 14 NOEC values for the effect of Na2SeO4 to Medicago sativa on several endpoints (total plant dry yield, shoot yield and root yield) in 10 different soils. The geometric mean of the lowest NOEC value reported in each study (0.39 and 0.50 mg Se/kg soil, both for root and shoot yield), 0.44 mg Se/kg soil, is the lowest bounded NOEC reported for the toxicity of selenate to terrestrial plants.

All results are based on nominal added or background corrected measured Se concentrations.