Sodium hydrogendifluoride

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.9 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

no data: aquatic toxicity unlikely

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

51 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

3.52 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

no hazard identified

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

11 mg/kg soil dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Available studies were performed with sodium fluoride (NaF); read-across is appropriate as both NaF and sodium hydrogen difluoride are highly water soluble and therefore will dissociate into their constituent ions in the aquatic environment. The same is true for hydrogen fluoride (HF) for which data is available from the HF EU RAR. The toxicity of these substances is essentially due to the fluoride ion. The EU RAR notes a clear relationship between the aquatic toxicity of sodium fluoride (and therefore its dissociated 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 are expressed in terms of concentrations of the fluoride ion (F-).

As such all PNECs above are derived in terms of the fluoride ion in a read across approach HF and to NaF. This is considered valid in all cases for sodium hydrogendifluoride.

The derived sodium fluoride/fluoride ion PNECs are presented below:

 

PNEC Aqua (freshwater) - The aquatic PNEC is derived from the arithmetic mean NOEC of 8.9 mg/L from the long-term studies in Daphnia; the lowest EC50 value for Scenedesmus of 43 mg/L is also taken into consideration. However it is noted that the natural background levels of fluoride in water are variable, therefore the PNEC is not directly applicable to those areas with high natural background levels. The EU RAR suggests that the background concentration should be added to the PNEC for the purposes of risk characterisation. Although a lower NOEC of 4 mg/L is available from a fish study, this is not considered appropriate for the PNEC derivation as the test was performed in very soft water. Based on an assessment factor of 10, the PNEC is 0.9 mg/L.

 

PNEC Aqua (marine water) - A separate PNEC for marine waters is not derived; the freshwater PNEC is considered to be adequately protective. Background levels of fluoride are higher in seawater than in freshwater and are higher that the PNEC of 0.9 mg/L.

 

PNEC Aqua (intermittent releases) - A separate PNEC for intermittent release is not derived.

PNEC Sediment -   In the absence of any ecotoxicological data for freshwater sediment dwelling organisms, a provisional PNECsediment is derived by calculation with the equilibrium partitioning method (EPM) on the basis of the outcome of the aquatic toxicity data according to the calculations specified in the REACH guidance document chapter R 10. For PNEC derivation the physicochemical properties of hydrogen fluoride are taken into account. As discussed in section 4 the behaviour of hydrogen fluoride in the environment is complex and as such the EPM PNEC values have been calculated based on the estimated Kow and Koc values as used in environmental modelling. A PNECsediment of 0.766 mg/kg wwt is obtained. This value may be converted from wet-weight to dry weight using a conversion factor for sediment concentrations of 4.6.

PNEC terrestrial - PNEC soil is based on the lowest NOEC of 106 mg/kg for nitrification; a factor of 10 is used as data are available for three trophic levels.

PNEC STP - The PNEC STP is based on the NOEC of 510 mg/L from a guideline-compliant activated sludge test.

No PNECs for other compartments (for example air) are considered necessary.

Conclusion on classification

No classification is triggered based on available data, according to EEC Council Directive 79/831/EEC Annex VI, Part II (D) as described in Commission Directive 93/21/EEC or Regulation (EC) No 1272/2008. No hazards for the environment have been identified.