Hexafluorosilicic acid

Sediment toxicity

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

sediment toxicity: long-term

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

see read acros justification

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

28 d

Dose descriptor:

other: IC25

Effect conc.:

290.2 mg/kg sediment dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

F-

Basis for effect:

growth rate

Remarks on result:

other: H. azteca

Key result

Duration:

10 d

Dose descriptor:

other: IC25

Effect conc.:

661.4 mg/kg sediment dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

F-

Basis for effect:

growth rate

Remarks on result:

other: C. tentans

Key result

Duration:

21 d

Dose descriptor:

other: IC25

Effect conc.:

1 221.3 mg/kg sediment dw

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

F-

Basis for effect:

growth rate

Remarks on result:

other: H. limbata

Details on results:

Applying the conversion factor from F- to hexafluorosilicic acid, the concentrations of 290.2, 661.4 and 1221.3 mg F-/kg dw correscorresponds to 365.7, 833.4 and 1539 mg hexafluorsilicic acid/kg.

Validity criteria fulfilled:

not applicable

Conclusions:

Results of long-term (10–28-d) growth and survival tests on three species of freshwater organisms showed that H. azteca was the most sensitive species for the growth endpoint (IC25 = 290.2 mg F-/kg), followed by C. tentans (661.4 mg F-/kg), H. limbata (1,221.3 mg F-/kg).

Applying the conversion factor from F- to hexafluorosilicic acid, the concentrations of 290.2, 661.4 and 1221.3 mg F-/kg dw correscorresponds to 365.7, 833.4 and 1539 mg hexafluorsilicic acid/kg.

Executive summary:

Results of long-term (10–28-d) growth and survival tests on three species of freshwater organisms showed that H. azteca was the most sensitive species for the growth endpoint (IC25 = 290.2 mg F-/kg), followed by C. tentans (661.4 mg F-/kg), H. limbata (1,221.3 mg F-/kg).

Applying the conversion factor from F- to hexafluorosilicic acid, the concentrations of 290.2, 661.4 and 1221.3 mg F-/kg dw correscorresponds to 365.7, 833.4 and 1539 mg hexafluorsilicic acid/kg.

Reference 2

Endpoint:

sediment toxicity: long-term

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

see read across justification

Reason / purpose for cross-reference:

read-across source

Duration:

18 d

Dose descriptor:

NOEC

Effect conc.:

80 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

F-

Basis for effect:

mortality

Duration:

18 d

Dose descriptor:

NOEC

Effect conc.:

80 mg/L

Nominal / measured:

nominal

Conc. based on:

element

Remarks:

F-

Basis for effect:

behaviour

Duration:

18 d

Dose descriptor:

NOEC

Effect conc.:

> 600 mg/kg sediment dw

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Remarks:

F-

Basis for effect:

mortality

Duration:

18 d

Dose descriptor:

NOEC

Effect conc.:

> 600 mg/kg sediment dw

Nominal / measured:

meas. (not specified)

Conc. based on:

element

Remarks:

F-

Basis for effect:

behaviour

Details on results:

The influence of temperature on fluoride toxicity in B. sowerbyi was evident in the long term mortality tests: 6.67% mortality was found for all concentrations tested at 17°C, whereas mortality was higher when the test population was exposed at 22°C and increased (r2 = 0.97) with increasing fluoride concentration. At 22°C mortality increased by 1.2% for every 10 mg F-/L added (r = 0.97) and more than half the population died when exposed to the highest concentration (160 mg F-/L).
Fluoride bioaccumulation showed a statistically significant relationship (p<0.001) with increasing test concentration. The highest values were reached by test populations at 22°C; the exposure of B. sowerbyi to 160 mg F-/L resulted in accumulation at 22°C 40.25% higher than at 17°C. Sediment accumulation was directly proportional to test concentration (p<0.01), with peak values of 722 and 815 μg F-/g, for experiments at 17°C and 22°C respectively. Fluoride ion was rapidly absorbed by animals and sediment, as shown by declining fluoride concentrations in water: the highest percentage decrease (26%) was reached in 6 d at 22°C from the initial nominal concentrations.

The NOEC for mortality and behaviour is 80mg F-/L. This concentration corresponded to a measured sediment concentration of slightly above 600 mg F-/L (the sediment concentration was determined from figure 4).


Applying the conversion factor from F- to hexafluorosilicic acid, the concentrations of 80 mg F-/L and 600 mgF-/kg correscorresponds to 100.8 mg hexafluorsilicic acid/L and 756 mg hexafluorosilicic acid/kg.

Validity criteria fulfilled:

not applicable

Conclusions:

The NOEC for mortality and behaviour is 100.8 mg hexafluorsilicic acid/L and 756 mg hexafluorosilicic acid/kg.

Executive summary:

In the publication from Del Piero et al (2014) an 18 day long-term test with Branchiura sowerbyi, Beddard, (Oligochaeta, Tubificidae) is described. The water was treated with sodium fluoride. The fluoride concentration in the sediment increased within 6 days to the final fluoride concentration. The long term tests were carried out both at 17±0.5°C and 22±0.5°C, for a period of 18 days. All animals were exposed to nominal fluoride concentrations of 80, 120 and 160 mg F-/L (between NOEC and LOEC) in the presence of sediment. Sediment accumulation was directly proportional to test concentration (p<0.01), with peak values of 722 and 815 μg F-/ g, for experiments at 17°C and 22°C respectively.

The influence of temperature on fluoride toxicity in B. sowerbyi was evident in the long term mortality tests: 6.67% mortality was found for all concentrations tested at 17°C, whereas mortality was higher when the test population was exposed at 22°C and increased (r2 = 0.97) with increasing fluoride concentration. At 22°C mortality increased by 1.2% for every 10 mg F-/L added (r = 0.97) and more than half the population died when exposed to the highest concentration (160 mg F-/L).

Fluoride bioaccumulation showed a statistically significant relationship (p<0.001) with increasing test concentration. The highest values were reached by test populations at 22°C; the exposure of B. sowerbyi to 160 mg F-/L resulted in accumulation at 22°C 40.25% higher than at 17°C. Sediment accumulation was directly proportional to test concentration (p<0.01), with peak values of 722 and 815 μg F-/g, for experiments at 17°C and 22°C respectively. Fluoride ion was rapidly absorbed by animals and sediment, as shown by declining fluoride concentrations in water: the highest percentage decrease (26%) was reached in 6 d at 22°C from the initial nominal concentrations.

The NOEC for mortality and behaviour is 80mg F-/L. This concentration corresponded to a measured sediment concentration of about 600 mg F-/kg.

Applying the conversion factor from F- to hexafluorosilicic acid, the concentrations of 80 mg F-/L and 600 mg F-/kg correscorresponds to 100.8 mg hexafluorsilicic acid/L and 756 mg hexafluorosilicic acid/kg.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:

366 mg/kg sediment dw

Additional information

Results of long-term (10–28-d) growth and survival tests on three species of freshwater organisms showed that H. azteca was the most sensitive species for the growth endpoint (IC25 = 290.2 mg F-/kg), followed by C. tentans (661.4 mg F-/kg), H. limbata (1,221.3 mg F-/kg). Applying the conversion factor from F- to hexafluorosilicic acid, the concentrations of 290.2, 661.4 and 1221.3 mg F-/kg dw correscorresponds to 365.7, 833.4 and 1539 mg hexafluorsilicic acid/kg.

An 18 day long-term test with Branchiura sowerbyi, Beddard, (Oligochaeta, Tubificidae). The NOEC for mortality and behaviour is 80mg F-/L. This concentration corresponded to a measured sediment concentration of about 600 mg F-/kg. Applying the conversion factor from F- to hexafluorosilicic acid, the concentrations of 80 mg F-/L and 600 mgF-/kg correscorresponds to 100.8 mg hexafluorsilicic acid/L and 756 mg hexafluorosilicic acid/kg.

In the 90 day flow-through water sediment study from Connell and Airey (1982) the toxicity of (sodium) fluoride to two amphipods Grandidierella lutosa and G. lignorum was analysed in life-cycle experiments. In one experiment (experiment 1), the perfomance of turbellarians and the harpacticoid copepod Amphiascus parvus Sars demonstrated that Grandidierella lutosa and G. lignorum were significantly more sensitive than the other groups. No explicit NOEC value is reported by Connell and Airey (1982). Based on the information provided, the NOEC is in the range of 3.90 to 4.48 mg F-/L. Applying the conversion factor from F- to hexafluorosilicic acid, the concentration of 4.1 mg F-/L corresponds to 5.17 mg hexafluorosilicic acid/L. Since the results were not reported based on mg/kg sediment, the results cannot be used directly for the sediment risk assessment. Nevertheless, by compaing the long-term results for marine sediment dwelling organisms with the long-term results from the pelagic freshwater standard test organism (D. magna), the result indicates that the sediment dwelling organisms tested in this study from Connell and Airey (1981) are less than a factor of 5 more sensitive than other aquatic invertebrates so that no extra factor is needed to cover the uncertainty from this factor. (AF factor for freshwater: 10, for marine sediment: 50). The results from this study with the two amphipods Grandidierella lutosa and G. lignorum are considered supporting for assessing the sediment toxicity.