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Sediment toxicity

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Endpoint:
sediment toxicity: short-term
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: See 'Remarks'
Remarks:
validity not assessable; source and acclimatisation status of organisms not reported; feeding only once a week instead of daily might have enhanced sensitivity; sediment and water not specified; instar larvae status not reported
Qualifier:
no guideline followed
Principles of method if other than guideline:
The effect of fluoride on the growth and survival of Chironomus tentans exposed via the sediment was assessed in a 10-d static toxicity test.
GLP compliance:
no
Analytical monitoring:
no
Details on sampling:
However, background fluoride concentrations of laboratory dilution water and control sediment were measured. For the analysis of control sediment for fluoride, sediment was placed in a plastic jar and frozen, then freeze-dried. After drying, the sample was homogenized using a mortar and pestle.
Vehicle:
no
Details on sediment and application:
Not reported.
Test organisms (species):
Chironomus dilutus (previous name: Chironomus tentans)
Details on test organisms:
TEST ORGANISM
- Source: not reported
- Age of animals at beginning of exposure: 10-12 d; instar larvae status not described
- Feeding during test
- Food type: Hexagenia diet
- Amount: 1 ml
- Frequency: once per week

ACCLIMATION
Acclimation period and conditions are not reported.
Study type:
laboratory study
Test type:
static
Water media type:
freshwater
Type of sediment:
not specified
Limit test:
no
Duration:
10 d
Exposure phase:
total exposure duration
Test temperature:
20 °C
Temperature reduced compared to standard guideline (23 °C according to US EPA/ 600/R-99/064).
Nominal and measured concentrations:
Nominal concentrations: A geometric series of 4 concentrations was used, in the range from 175-5600 µg F-/g dry weight (not further specified).
Details on test conditions:
TEST SYSTEM
- Test container (material, size): glass jar
- Sediment volume: 325 ml
- Overlying water volume: 1300 ml

EXPOSURE REGIME
- No. of organisms per container (treatment): 15
- No. of replicates per treatment group: 3
- No. of replicates per control / vehicle control: not specified
- Feeding regime: animals were fed weekly; 1 mL Hexagenia diet

OVERLYING WATER CHARACTERISTCS
- Laboratory dilution water, not further characterized

SOURCE OF NATURAL SEDIMENT
- Sediment not specified in study

OTHER TEST CONDITIONS
- Light conditions (photoperiod, light intensity) not reported in study

EFFECT PARAMETERS MEASURED:
- Mortality, at 10 d
- Growth (difference between average final weight and average initial weight of all test organisms in each replicate), at 10 d

TEST CONCENTRATIONS
- Spacing factor for test concentrations: not specified
Reference substance (positive control):
no
Duration:
10 d
Dose descriptor:
other: IC25
Effect conc.:
661.4 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
other: fluoride ion (F-)
Basis for effect:
other: growth
Duration:
10 d
Dose descriptor:
LC50
Effect conc.:
> 5 600 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
other: fluoride ion (F-)
Basis for effect:
mortality
Duration:
10 d
Dose descriptor:
NOEC
Effect conc.:
>= 5 600 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
other: fluoride ion (F-)
Basis for effect:
mortality
Details on results:
Results of controls are not reported.
Reported statistics and error estimates:
No statistics reported.

Concentration of fluoride in sediment control was 4.62 µg F-/g dry weight. Concentration in laboratory dilution water was 0.16 mg F-/L (SD = 0.1).

Validity criteria fulfilled:
not specified
Remarks:
Validity is not assessable as control reults and oxygen concentrations are not reported
Conclusions:
The effect of sediment-associated fluoride on the growth and survival of Chironomus tentans (age: 10-12 d) was assessed in this 10-d static sediment toxicity test, following no specific guideline. For the growth of C. tentans, a 10 d IC25 of 661.4 mg F/kg sediment dw (nominal) was determined. For the mortality of C. tentans, an unbounded 10 d LC50 > 5600 mg F/kg sediment dw (nominal) and a 10 d NOEC ≥ 5600 mg F/kg sediment dw (nominal) could be derived. The feeding regime of feeding only once per week (instead of daily as recommended in US EPA/ 600/R-99/064) might have enhanced the sensitivity of test organisms.
Endpoint:
sediment toxicity: long-term
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: See 'Remarks'
Remarks:
validity not assessable; source and acclimatisation status of organisms not reported; feeding only once a week instead of daily might have enhanced sensitivity; sediment and water not specified
Qualifier:
no guideline followed
Principles of method if other than guideline:
The effect of fluoride on the growth and survival of Hexagenia limbata exposed via the sediment was assessed in a 21-d static toxicity test.
GLP compliance:
no
Analytical monitoring:
yes
Details on sampling:
Concentrations of fluoride were measured in overlying water on days 0, 12 and 21. Samples were taken from one replicate of each treatment.

Furthermore, background concentrations of laboratory dilution water and control sediment were measured. For the analysis of control sediment for fluoride, sediment was placed in a plastic jar and frozen, then freeze-dried. After drying, the sample was homogenized using a mortar and pestle.
Vehicle:
no
Details on sediment and application:
Not reported.
Test organisms (species):
other: Hexagenia limbata
Details on test organisms:
TEST ORGANISM
- Common name: Giant mayfly
- Source: not reported
- Age of animals at beginning of exposure: 3-4 month
- Weight of animals at beginning of exposure: 5-25 mg
- Feeding during test
- Food type: Hexagenia diet
- Amount: 1 ml
- Frequency: once per week

ACCLIMATION
Acclimation period and conditions are not reported.
Study type:
laboratory study
Test type:
static
Water media type:
freshwater
Type of sediment:
not specified
Limit test:
no
Duration:
21 d
Exposure phase:
total exposure duration
Test temperature:
20 °C
Nominal and measured concentrations:
Nominal concentrations: Control (background: 4.62), 700, 1400, 2800, 5600 µg F-/g sediment dry weight
Measured concentrations in overlying water (day 0): 0.169 (control), 3.10, 3.26, 7.89, 17.7 mg F-/L
Measured concentrations in overlying water (day 12): 0.247 (control), 11.3, 13.7, 24.9, 56.8 mg F-/L
Measured concentrations in overlying water (day 21): < 0.03 (control), 10.4, 14.0, 26.8, 60.9 mg F-/L
Details on test conditions:
TEST SYSTEM
- Test container (material, size): glass jar
- Sediment volume: 325 ml
- Overlying water volume: 1300 ml

EXPOSURE REGIME
- No. of organisms per container (treatment): 10
- No. of replicates per treatment group: 3
- No. of replicates per control / vehicle control: 3
- Feeding regime: animals were fed weekly; 1 mL Hexagenia diet

OVERLYING WATER CHARACTERISTCS
- Laboratory dilution water, not further characterized

SOURCE OF NATURAL SEDIMENT
- Sediment not specified in study

OTHER TEST CONDITIONS
- Light conditions (photoperiod, light intensity) not reported in study

EFFECT PARAMETERS MEASURED:
- Mortality, at 21 d
- Growth (difference between average final weight and average initial weight of all test organisms in each replicate), at 21 d

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2
Reference substance (positive control):
no
Duration:
21 d
Dose descriptor:
other: IC25
Effect conc.:
1 221.3 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
other: fluoride ion (F-)
Basis for effect:
other: growth
Duration:
21 d
Dose descriptor:
LC50
Effect conc.:
1 652.2 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
other: fluoride ion (F-)
Basis for effect:
mortality
Details on results:
Results of controls are not reported.
Reported statistics and error estimates:
No statistics reported.

Concentration of fluoride in sediment control was 4.62 µg F-/g dry weight. Concentration in laboratory dilution water was 0.16 mg F-/L (SD = 0.1).

Validity criteria fulfilled:
not specified
Remarks:
Validity is not assessable as control reults and oxygen concentrations are not reported
Conclusions:
The effect of sediment-associated fluoride on the growth and survival of Hexagenia limbata (age: 3-4 months) was assessed in this 21-d static sediment toxicity test, following no specific guideline. For the growth and mortality of H. limbata, a 28 d IC25 of 1221.3 mg F/kg sediment dw (nominal) and a 28 d LC50 of 1652.2 mg F/kg sediment dw (nominal) could be derived, respectively. The feeding regime of feeding only once per week (instead of daily as recommended in US EPA/ 600/R-99/064) might have enhanced the sensitivity of test organisms.
Endpoint:
sediment toxicity: long-term
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: See 'Remarks'
Remarks:
exposure duration 28 instead of 42 d; no reproduction measured; validity not assessable ; source and acclimatisation status of organisms not reported; feeding only once a week instead of daily might have enhanced sensitivity; sediment and water not specified
Qualifier:
no guideline followed
Principles of method if other than guideline:
The effect of fluoride on the growth and survival of Hyalella azteca exposed via the sediment was assessed in a 28-d static toxicity test.
GLP compliance:
no
Analytical monitoring:
no
Details on sampling:
However, background fluoride concentrations of laboratory dilution water and control sediment were measured. For the analysis of control sediment for fluoride, sediment was placed in a plastic jar and frozen, then freeze-dried. After drying, the sample was homogenized using a mortar and pestle..
Vehicle:
no
Details on sediment and application:
Not reported.
Test organisms (species):
Hyalella azteca
Details on test organisms:
TEST ORGANISM
- Source: not reported
- Age of animals at beginning of exposure: 1-7 d
- Feeding during test
- Food type: not specified
- Amount: not specified
- Frequency: once per week

ACCLIMATION
Acclimation period and conditions are not reported.
Study type:
laboratory study
Test type:
static
Water media type:
freshwater
Type of sediment:
not specified
Limit test:
no
Duration:
28 d
Exposure phase:
total exposure duration
Remarks:
Exposure duration shortened to 28 d instead of 42 d according to standard guideline (US EPA/600/R-99/064)
Test temperature:
20 °C
Temperature reduced compared to standard guideline (23 °C according to US EPA/ 600/R-99/064).
Nominal and measured concentrations:
Nominal concentrations: A geometric series of 4 concentrations was used, in the range from 175-5600 µg F-/g dry weight (not further specified).
Details on test conditions:
TEST SYSTEM
- Test container (material, size): glass jar
- Sediment volume: 50 ml
- Overlying water volume: 200 ml

EXPOSURE REGIME
- No. of organisms per container (treatment): 10
- No. of replicates per treatment group: 3
- No. of replicates per control / vehicle control: not specified
- Feeding regime: animals were fed weekly; type and amount of food not reported

OVERLYING WATER CHARACTERISTCS
- Laboratory dilution water, not further characterized

SOURCE OF NATURAL SEDIMENT
- Sediment not specified in study

OTHER TEST CONDITIONS
- Light conditions (photoperiod, light intensity) not reported in study

EFFECT PARAMETERS MEASURED:
- Mortality, at 28 d
- Growth (difference between average final weight and average initial weight of all test organisms in each replicate), at 28 d

TEST CONCENTRATIONS
- Spacing factor for test concentrations: not specified
Reference substance (positive control):
no
Duration:
28 d
Dose descriptor:
other: IC25
Effect conc.:
290.2 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
other: fluoride ion (F-)
Basis for effect:
other: growth
Duration:
28 d
Dose descriptor:
LC50
Effect conc.:
1 114.6 mg/kg sediment dw
Nominal / measured:
nominal
Conc. based on:
other: fluoride ion (F-)
Basis for effect:
mortality
Details on results:
Results of controls are not reported.
Reported statistics and error estimates:
No statistics reported.

Concentration of fluoride in sediment control was 4.62 µg F-/g dry weight. Concentration in laboratory dilution water was 0.16 mg F-/L (SD = 0.1).

Validity criteria fulfilled:
not specified
Remarks:
Validity is not assessable as control reults and oxygen concentrations are not reported
Conclusions:
The effect of sediment-associated fluoride on the growth and survival of Hyalella azteca (age: 1-7 d) was assessed in this 28-d static sediment toxicity test, following no specific guideline. For the growth and mortality of H. azteca, a 28 d IC25 of 290.2 mg F/kg sediment dw (nominal) and a 28 d LC50 of 1114.6 mg F/kg sediment dw (nominal) could be derived, respectively. The feeding regime of feeding only once per week (instead of daily as recommended in US EPA/ 600/R-99/064) might have enhanced the sensitivity of test organisms.

Description of key information

Fluoride has a low toxic potential towards sediment freshwater organisms, as indicated by IC25 values for growth ranging from 290.2-1221.3 mg F/kg and LC50 values for mortality ranging from 1114.6 to > 5600 mg F/kg.

Key value for chemical safety assessment

EC50 or LC50 for freshwater sediment:
1 114.6 mg/kg sediment dw

Additional information

Three sediment toxicity studies of limited reliability (RL3), in which the validity was not assessable, but which are well reported and conducted, are assessed in a weight of evidence approach to conclude on the sediment toxicity of fluoride:

 

The effect of sediment-associated fluoride on the growth and survival of Hyalella azteca (age: 1-7 d) was assessed in this 28-d static sediment toxicity test, following no specific guideline. For the growth and mortality of H. azteca, a 28 d IC25 of 290.2 mg F/kg sediment dw (nominal) and a 28 d LC50 of 1114.6 mg F/kg sediment dw (nominal) could be derived, respectively. The feeding regime of feeding only once per week (instead of daily as recommended in US EPA/ 600/R-99/064) might have enhanced the sensitivity of test organisms (Metcalfe-Smith et al. 2003).

 

The effect of sediment-associated fluoride on the growth and survival of Chironomus tentans (age: 10-12 d) was assessed in this 10-d static sediment toxicity test, following no specific guideline. For the growth of C. tentans, a 10 d IC25 of 661.4 mg F/kg sediment dw (nominal) was determined. For the mortality of C. tentans, an unbounded 10 d LC50 of > 5600 mg F/kg sediment dw (nominal) and a 10 d NOEC 5600 mg F/kg sediment dw (nominal) could be derived. The feeding regime of feeding only once per week (instead of daily as recommended in US EPA/ 600/R-99/064) might have enhanced the sensitivity of test organisms (Metcalfe-Smith et al. 2003).

 

The effect of sediment-associated fluoride on the growth and survival of Hexagenia limbata (age: 3-4 months) was assessed in this 21-d static sediment toxicity test, following no specific guideline. For the growth and mortality of H. limbata, a 28 d IC25 of 1221.3 mg F/kg sediment dw (nominal) and a 28 d LC50 of 1652.2 mg F/kg sediment dw (nominal) could be derived, respectively. The feeding regime of feeding only once per week (instead of daily as recommended in US EPA/ 600/R-99/064) might have enhanced the sensitivity of test organisms (Metcalfe-Smith et al. 2003). 

 

Data on marine sediment organisms is not available.

 

Finally, it is concluded that fluoride has a low toxic potential towards sediment freshwater organisms, as indicated by IC25 values for growth ranging from 290.2-1221.3 mg F/kg and LC50 values for mortality ranging from > 5600 to 1642.2 mg F/kg.

Read across justification:

Tin difluoride is an inorganic solid at room temperature and consists of the tin cation and fluoride anions. Based on the solubility of tin difluoride in water (300-428 g/L according to handbook data (Merck, 2006; Gestis, 2015)), a complete dissociation of tin difluoride resulting in tin and fluoride ions may be assumed under environmental conditions. The respective dissociation is reversible and the ratio of the salt /dissociated ions is dependent on the metal-ligand dissociation constant of the salt, the composition of the solution and its pH. The metal-ligand equilibrium constant for the formation of tin difluoride is reported as follows (Japan Nuclear Cycle Development Institute, 1999):

 

Sn2++ 2F- SnF20(log K =7.74)

 

Thus, it may reasonably be assumed that based on the tin-difluoride formation constant, the respective behaviour of the dissociated tin cations and fluoride anions in the environment determine the fate of tin difluoride upon dissolution with regard to (bio)degradation, bioaccumulation, partitioning resulting in a different relative distribution in environmental compartments (water, air, sediment and soil) and subsequently determine its ecotoxicological potential.

Therefore, in the assessment of the ecotoxicity of tin difluoride, read-across to data for fluoride and soluble tin substances is applied since only the ions of tin difluoride are available in an aqueous environment and determine the environmental fate and toxicity. Read-across to environmental fate and toxicity studies of soluble fluoride salts (predominantly sodium fluoride) is therefore appropriate and scientifically justified. This read-across approach was already applied in the 2001 EU Risk Assessment of hydrogen fluoride.