Hexafluorosilicic acid

Endpoint summary

Description of key information

Freshwater:

Lowest EC50 (short-term study): 32.8 mg/L (Trichoptera)

Lowest NOEC (long-term study): 18 mg/L (Daphnia magna)

Marine:

Lowest EC50 (short-term study): 13.23 mg/L (marine invertebrates)

Lowest NOEC (long-term study): 5.17 mg/L (G. lutosa and G. lignorum)

Additional information

 Most available studies were performed with sodium fluoride (NaF); read-across is appropriate as both NaF and HF are highly water soluble and will dissociate into their constituent ions in the aquatic environment. The toxicity of both substances is essentially due to the fluoride ion. The EU RAR notes a clear relationship between the aquatic toxicity of sodium fluoride (and therefore hydrogen fluoride) and water hardness. Tests performed in soft water (<50 mg CaCO3/L) showed greater toxicity than those performed in hard water (>50 mg CaCO3/L) due to the precipitation of fluoride as CaF2.

 

All endpoints presented below are expressed in terms of concentrations of hexafluorosilicic acid.

 

Short-term toxicity to fish

The lowest 96 -h LC50 for Hexafluorosilicic acid of 50 mg/l (Lepomis macrochirus, freshwater species). For marine species, the key study result (LC50) was 123 mg hexafluorosilicic acid /L.

An LC50 value corresponding to 107.5 mg hexafluorosilicic acid /L at 96h are reported for rainbow tout (Camargo & Tarazona, 1991). The same authors report LC50 value for brown trout corresponding to 207.3 mg hexafluorosilicic acid /L after 96h. The EU RAR for hydrogen fluoride reports additional LC50 values corresponding to 376.74 mg hexafluorosilicic acid /L (48h in Leuciscus idus); 64.26 mg hexafluorosilicic acid /L in (96h in Onchorynkus mykiss) and 428.4 mg hexafluorosilicic acid /L (96h in Gasterosteus aculeatus). The RIVM Integrated Criteria Document reports additional data, with LC50 values ranging from 64.3 - 428.4 mg hexafluorosilicic acid /L (Sloof et al, 1988).

 

Long-term toxicity to fish

The key study for long-term toxicity to fish is covered by an ELS-study (OECD 210) to Pimephales promelas. The NOEC of that study corresponded to a value of 83.9 mg hexafluorosilicic acid /L. Long-term data for marine fish species are not available/not reliable.

 

Short-term toxicity to aquatic invertebrates

Camargo & Tarazona (1991) report that benthic larvae are sensitive to the concentration of fluoride, with corresponding EC50 values ranging from 32.8 to 60.5 mg hexafluorosilicic acid /L (freshwater). The study with D. magna from Fieser et al. (1986) resulted in an EC50 corresponding to 311.2 mg/L. The EU RAR reviews and summarises the available data on short-term toxicity to aquatic invertebrates. The reported EC50 values for Daphnia sp. range from corresponding to 122.22 -443.52 mg hexafluorosilicic acid /L and are based on nominal concentrations. Further data for aquatic worms, snails and midges (Advent Group, 2000) indicate that the organisms investigated by Camargo & Tarazona (1991) were more sensitive under the tested conditions. Hence, their EC50 values can be considered to be worst case for freshwater short -term toxicity to aquatic invertebrates for the risk assessment.

For marine invertebrates EC50 values corresponding to 13.23 to 49.14 mg hexafluorosilicic acid /L were reported.

 

Long-term toxicity to aquatic invertebrates

There are two reliable reproduction studies on Daphnia magna. The two studies report NOEC values corresponding to 18 and 32.9 mg hexafluorosilicic acid /L. For two marine species, the NOEC was corresponding to 5.17 mg hexafluorosilicic acid /L.

 

Toxicity to algae

The EU RAR reviews and summarises the available data on the toxicity of sodium fluoride to freshwater and marine algae species. The EC50 values for freshwater algae correspond to concentrations from 54.2 to 153.7 mg hexafluorosilicic acid /L. For marine algae (Skeletonema costatum) the EC50 values correspond to 102 mg hexafluorosilicic acid /L. NOEC values corresponding to 63 - 314 mg hexafluorosilicic acid /L and 63 -252 mg hexafluorosilicic acid /L are reported for freshwater and marine algae, respectively.

 

Toxicity to microorganisms

For activated sludge an OECD 209 guideline-compliant study reports a 3 -hour NOEC corresponding to 642.4 mg hexafluorosilicic acid /L.