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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:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Recent, non-GLP published study
Qualifier:
no guideline followed
Principles of method if other than guideline:
A total amount of 8kg soil was mixed, dried, ground, sieved (2.0 mm) and filled into earthen pots lined with polythene sheet. Soil was spiked at the following concentrations: 0, 100, 200, 400, 600 and 800 mg NaF/kg, respectively, by adding sodium fluoride and thoroughly mixed. Each treatment was replicated four times. Eight seedlings of 20-days old onion (Allium cepa L.) cv. ‘‘Pusa Red” were transplanted. Five plants were maintained for the test in each pot. The irrigation was applied with de-ionised water.
All plants were harvested 90 d after transplanting. The plants were air dried for 2 d and segregated into shoots, roots and bulb. The plant material was subsequently oven-dried at 70 °C and weighed until a constant weight was achieved.

Soil samples collected from each pot after the harvest were subjected to the analysis of pH and soluble F (CaCl2 extractable).
GLP compliance:
no
Remarks:
data from a publication
Analytical monitoring:
yes
Details on sampling:
All the plants were harvested 90 d after transplanting. The plants were air-dried for 2 d and segregated into shoots, roots and bulb. The plant material was then oven dried at 70 °C and weighed until a constant weight was achieved.

Soil samples collected from each pot after the harvest were subjected to the analysis of pH and soluble F (CaCl2 extractable).
Vehicle:
no
Species:
Allium cepa
Plant group:
Monocotyledonae (monocots)
Details on test organisms:
- 20 days old seedlings were used
- cv. "Pusa Red"
Test type:
other: biomass yield
Study type:
extended laboratory study
Substrate type:
natural soil
Limit test:
no
Total exposure duration:
90 d
Post exposure observation period:
no post exposure observation period
Test temperature:
no data
pH:
no data
Moisture:
no data
Details on test conditions:
TEST SYSTEM
- Test container (type, material, size): earthen pots lined with polythene sheet
- Amount of soil: 8 kg
- Method of seeding: irrigation with de-ionised water
- No. of seeds per pot: 8
- No. of plants (retained after thinning):5
- No. of replicates per treatment group: 4

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Geographic location: Typic Natrustalfs, from the research farm of Central Soil Salinity Research Institute, Regional Research Station, Lucknow
- Sampling depth (cm): upper part of soil (0–15 cm)
- Pretreatment of soil: thoroughly mixed, dried, ground and sieved through 2.0 mm sieve.
The basic characteristics of the initial soil such as pH, EC, sand, silt, clay, organic carbon, total fluoride, and CaCl2 extractable fluoride were determined and are as follows:
Sand (%): 49.1
Silt (%): 18.5
Clay (%): 32.5
Organic carbon (%): 0.41
pH (1:2): 8.42
EC (1:2) (dS m1): 0.65
CaCl2 extractable fluoride (mg kg1): 6.01
Total fluoride (mg kg1): 311
Al2O3 (%): 1.25
Fe2O3 (%): 4.56
A mixture of nutrients was added to each pot, 1.16 g N as urea and 890 mg P as KH2PO4 H2O and 340 mg K as murette of potash. The N was applied in two splits, half as basal and other half at 60 d after plantation.
Nominal and measured concentrations:
0, 100, 200, 400, 600 and 800 mg NaF/kg
Reference substance (positive control):
no
Species:
Allium cepa
Duration:
90 d
Dose descriptor:
NOEC
Effect conc.:
200 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: biomass (yield)
Details on results:
Visible symptoms of F toxicity in terms of tip burning and plant death were noticed at concentrations ≥ 400 mg NaF/kg soil.

There was not a significant decrease in shoot, root and bulb biomass in soil treated with NaF up to 200 mg NaF/kg soil. A decrease of 20%, 59% and 70% biomass (roots, shoots and bulbs) was observed at 400, 600 and 800 mg NaF/kg soil, respectively. This suggested that plants are unable to tolerate addition of F higher than 400 mg NaF/kg soil.
Results with reference substance (positive control):
no reference substance was used
Reported statistics and error estimates:
The comparison of the treatment means were done by ANOVA and the level of significance were determined at p = 0.05 and considered as significant

Soluble F in soil

Soluble F (CaCl2 extractable) was determined in soils of different treatments. It was found that soluble F varied between 2.93 mg F/kg and 30.86 mg F/kg in the treatment range of 0–800 mg NaF/kg soil and that soluble F concentrations increased with total F levels.

Validity criteria fulfilled:
yes
Conclusions:
Visible symptoms of F toxicity in terms of tip burning and plant death were noticed at concentration ≥ 400 mg NaF/kg soil.
There was not a significant decrease in shoot, root and bulb biomass in soils treated with NaF up to 200 mg NaF/kg soil. Thus, the 90-d NOEC for biomass, i.e. yield, is 200 mg/kg NaF.

A decrease of 20 %, 59 % and 70 % biomass (roots, shoots and bulbs) was obderved at 400, 600 and 800 mg NaF/kg, respectively. This suggested that the plants are unable to tolerate additions of F that are higher than 400 mg NaF/kg soil.
Endpoint:
toxicity to terrestrial plants: long-term
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Dipotassium hexafluorotitanate is an inorganic substance which will rapidly dissociate into fluoride, potassium and titanium ions upon dissolution in the environment. However, titanium ions do not remain in solution, only fluoride ions do.
The approach follows scenario 1 of the RAAF (ECHA 2017).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source
sodium fluoride (CAS 7681-49-4)
Target
Dipotassium hexafluorotitanate (CAS 1619-27-0)

3. ANALOGUE APPROACH JUSTIFICATION
Since dipotassium hexafluorotitanate rapidly dissociates into fluoride, potassium and titanium ions upon dissolution in the environment, and only fluoride but not titanium ions will remain in solution,it can be assumed that toxicity (if any) will be driven by the fluoride anion. The NOEC of 90.49 mg F/kg derived for the decrease in biomass of onion (Allium cepa) followed by a 90-d exposure to sodium fluoride in soil was read-across to dipotassium hexafluorotitanate resulting in a NOEC of 190.6 mg/kg.

4. DATA MATRIX
see attached read-across statement in section 13.2
Reason / purpose for cross-reference:
read-across source
Species:
Allium cepa
Duration:
90 d
Dose descriptor:
NOEC
Effect conc.:
200 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: biomass (yield)
Details on results:
Visible symptoms of F toxicity in terms of tip burning and plant death were noticed at concentrations ≥ 400 mg NaF/kg soil.

There was not a significant decrease in shoot, root and bulb biomass in soil treated with NaF up to 200 mg NaF/kg soil. A decrease of 20%, 59% and 70% biomass (roots, shoots and bulbs) was observed at 400, 600 and 800 mg NaF/kg soil, respectively. This suggested that plants are unable to tolerate addition of F higher than 400 mg NaF/kg soil.
Results with reference substance (positive control):
no reference substance was used
Reported statistics and error estimates:
The comparison of the treatment means were done by ANOVA and the level of significance were determined at p = 0.05 and considered as significant

Soluble F in soil

Soluble F (CaCl2 extractable) was determined in soils of different treatments. It was found that soluble F varied between 2.93 mg F/kg and 30.86 mg F/kg in the treatment range of 0–800 mg NaF/kg soil and that soluble F concentrations increased with total F levels.

Validity criteria fulfilled:
yes
Conclusions:
Visible symptoms of F toxicity in terms of tip burning and plant death were noticed at concentration ≥ 400 mg NaF/kg soil.
There was not a significant decrease in shoot, root and bulb biomass in soils treated with NaF up to 200 mg NaF/kg soil. Thus, the 90-d NOEC for biomass, i.e. yield, is 200 mg/kg NaF.

A decrease of 20 %, 59 % and 70 % biomass (roots, shoots and bulbs) was obderved at 400, 600 and 800 mg NaF/kg, respectively. This suggested that the plants are unable to tolerate additions of F that are higher than 400 mg NaF/kg soil.

Description of key information

Since dipotassium hexafluorotitanate rapidly dissociates into fluoride, potassium and titanium ions upon dissolution in the environment, and only fluoride but not titanium ions will remain in solution, it can be assumed that toxicity (if any) will be driven by the fluoride anion. The NOEC of 90.49 mg F/kg derived for the decrease in biomass of onion (Allium cepa) followed by a 90-d exposure to sodium fluoride in soil was read-across to dipotassium hexafluorotitanate resulting in a NOEC of 190.6 mg/kg.

Key value for chemical safety assessment

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

Additional information

Since dipotassium hexafluorotitanate rapidly dissociates into fluoride, potassium and titanium ions upon dissolution in the environment, and only fluoride but not titanium ions will remain in solution,it can be assumed that toxicity (if any) will be driven by the fluoride anion. Therefore, full read-across of soil toxicity data of potassium fluoride (CAS #7789-23-3) and other fluorides based upon a molecular weight conversion is justified. However, limited reliable data are available to determine the critical value for plant toxicity of fluoride in soil. According to Jha et al. (2009), visible symptoms of F toxicity in terms of tip burning and death of onion (Allium cepa) were noticed in highly contaminated soils (>400 mg NaF/kg soil) after 90 days, and the NOEC (added) for the decrease in biomass was found to be 200 mg NaF/kg (90.49 mg F/kg).