Cesium fluoroaluminate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

14.21 µg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

1.421 µg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

25 mg/L

Assessment factor:

10

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

7 105 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

710.5 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

no hazard identified

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Cesium fluoroaluminate is a soluble metal salt consisting of cesium cations and fluoroaluminate anions and thus liberates cesium cations and fluoroaluminate anions upon dissolution. Fluoroaluminate ions are moderately stable but will eventually disintegrate resulting in aluminium cations and fluoride anions that participate in prevalent environmental speciation processes.The respective dissociation products behave differently in the environment and determine the fate in the environment with regard to (bio)degradation, bioaccumulation, partitioning as well as the distribution in environmental compartments (water, air, sediment and soil) and subsequently the ecotoxicological potential.

 

Aluminium:

Aluminium has a low mobility under most environmental conditions, although below pH 5.5 its solubility increases. Because of its amphoteric nature, aluminium may also be mobilised in anionic form under strongly alkaline conditions at pH > 8.

The speciation of aqueous Al is dependent on pH and the presence and nature of complexing ligands. In aqueous solutions, unhydrolyzed Al (3+) (aq) does not remain as free ion, but is surrounded by six molecules of water Al(H2O)6 (3+). As solution pH increases, protons are removed from the coordinated waters giving a series of hydrolysis products: Al(H2O)5(OH) (2+); Al(H2O)4(OH)2 (+); Al(H2O)3(OH)3; Al(H2O)2(OH)4 (-); Al(H2O)(OH)5 (2-). Thus, in the absence of significant concentrations of complexing ligands, the dominant form of dissolved Al (pH < 4.5) is Al(H2O)6 (3+). At pH > 4.5, the hydrolysed forms Al(H2O)5(OH) (2+) and Al(H2O)4(OH)2 (+) are predominant. At low pH, organic ligands, including humic and fulvic acids, and inorganic ligands, such as fluoride, readily complex with dissolved aluminium. As a result of organic complexation, particularly through chelation, a significant proportion of Al is usually in colloidal or particulate forms. Therefore, concentrations of dissolved Al are generally low in most natural waters (Salminen et al. 2015 and references therein). An European median (dissolved) concentration in streamwater and a total concentration of streamwater sediment are reported with 0.017 mg/L and 5.45 mg/kg, respectively. An European median total concentration in topsoil is reported with 5.82 mg/kg and a global with 5.92 mg/kg W (Salminen et al. 2005 and references therein).

Regarding the aquatic toxicity of aluminum, the potential is expected to be low due to its speciation, i.e. precipitation and decreased bioavailability under typical environmental conditions. This assumption is supported by the CLP classification "not hazardous to the aquatic environment" of soluble aluminium substances and ecotoxicity reference values of aluminium (http://www.meclas.eu).

 

Cesium:

Cesium is a relatively rare element. Released cesium is rapidly and strongly adsorbed by soil, especially clay, and therefore tends not to be present in the aqueous surface environment. An European median (dissolved) concentration in streamwater and a total concentration of streamwater sediment are reported with 0.01 microg/L and 3 mg/kg, respectively. An European median total concentration in topsoil is reported with 3.71 mg/kg and a global with 3 mg/kg W (Salminen et al. 2005 and references therein). Regarding the aquatic toxicity of cesium, ecotoxicity reference values of cesium are not included in MECLAS (Tool to determine the classification of inorganic materials such as ores and concentrates, alloys or UVCBs; http://www.meclas.eu). However, soluble cesium substances such as cesium chloride are not classified as hazardous to the aquatic environment.

 

Fluoride:

Fluoride is a natural element, an essential micronutrient for mammals (it strengthens the apatite matrix of skeletal tissues and teeth; Salminen et al. 2005 and references therein) and belongs to the macro/components of seawater (51% F-, 47% MgF+, 2% CaF+ and traces of HF and HF2; EU RAR, 2001 and references therein).

The natural background concentration of fluoride in water ranges from 0.01 to 0.3 mg/L but may reach higher concentrations (> 20 mg/L) in dependence of the presence of F-containing rock formations (EU RAR, 2001 and references therein).

In freshwater at environmentally relevant pH (pH > 5), the free ion is the main fluoride species. Upon dissolution, the fluoride ion forms strong complexes such as fluorapatite (Ca5[F|(PO4)3), which are mainly transferred to the bottom sediments (EU RAR, 2001 and references therein)”. Such complexes are particularly built with Ca2+, Al3+, Fe3+, PO43- and B(OH)4-. The concentration of fluoride ions in solution is often controlled by the solubility of fluoride; and the concentration inversely proportional to that of Ca2+ (EU RAR, 2001).

 

Regarding the aquatic toxicity of fluoride, a read-across approach from hydrogen fluoride to soluble fluoride compounds was applied in the 2001 EU Risk Assessment on "hydrogen fluoride (Cas 7664-39-3), and relevant effect concentrations of fluoride were derived in tests with soluble sodium fluoride (NaF). Because HF occurs in the aquatic compartment mainly as fluoride ion, the effect concentrations of NaF are read-across to determine the potential hazard of HF to aquatic organisms (EU RAR, 2001). Short- and long-term toxicity data of fluoride are available for freshwater organisms covering three trophic levels (fish, invertebrate, algae). Acute effect concentrations range from 51 - 340 mg/L, 97 - 352 mg/L and 43 - 122 mg/L for fish, daphnia and algae, respectively, and are thus well above the acute aquatic hazard criteria. All tests were performed in soft water, thus reflecting worst-case conditions (since fluoride precipitation increases with increasing water hardness).

Regarding long-term toxicity, the 21-d LC5 for fish is reported with 4 mg/L, NOEC values for daphnids range from 3.7 to 14.1 mg/L and for algae from 50 - 249 mg/L, respectively, and are thus well above the long-term aquatic hazard criteria. Hardness information is lacking for all algae endpoints and it remains unclarified if test conditions represent realistic conditions or caused experimental artifacts such as indirect effects such a phosphate depletion e.g. by precipitating fluorapatite (Ca5[F|(PO4)3).

Available effect concentrations of fluoride and cesium tetrafluoroaluminate are summarized in the Table below.

 

Table: Aquatic toxicity data for cesium fluoroaluminate and fluoride to three trophic levels (i.e. fish, invertebrate, algae) of the aquatic environment as well as microorganisms:                                                                                                  

Species	Trophic level Endpoint for CsAlF4 (based on measured Cs conc)	Range of endpoints for fluoride as reviewed by EU RAR, 2001
Fish	96-h LC50; G. rarus; > 120 mg/L (measured, TWA) (Jing, 2013)	96-h LC50 51 to 340 mg/L
Daphnia	48h-EC50 (mobility); D. magna; 50 mg/L (geometric mean) (Brüggemann, 2018)	48-h EC50 97 to 352 mg/L
Algae	72-h ErC50 R. subcapitata; 14.21 mg/L (arithmetic mean) (Schlich, 2018) 96-h EbC50	43 to 122 mg/L
Microorganisms	Activated sludge OECD 209 Test; 3 h-NOEC = 250 mg/L	Activated sludge OECD 209 Test; 3 h-NOEC = 510 mg/L *
Chronic toxicity
Fish	not required according to Annex VIII.	21-d LC5 4.0 mg/L
Daphnia	not required according to Annex VIII.	21-d NOEC (reproduction) 3.7 to 14.1 mg/L
Algae	not required according to Annex VIII.	7-d NOEbC 50 to 249 mg/L

* Endpoints (n=7) listed in EU RAR, 2001 actually range from 7.1 to 510 mg/L, most of the studies focussed on bacteria species such as E. coli and P. putida that are not relevant for the environmental hazard assessment. The NOEC of 510 mg/L was derived in the available guideline study and is thus most relevant.

 

The comparison of effect concentrations in the table indicates that the potential for aquatic toxicity of fluoride is even lower than that of cesium fluoroaluminate and effect concentrations are well above criteria of acute and long-term hazard to the aquatic environment under Regulation (EC) No 1272/2008.

References:

European Union Risk Assessment Report (EU RAR) (2001) on hydrogen fluoride, CAS No.: 7664-39-3; EINECS No.: 231-634-8; European Commission, Joint Research Centre.

Conclusion on classification

Cesium tetrafluoroaluminate is a soluble metal salt consisting of cesium cations and tetrafluoroaluminate anions and thus liberates cesium cations and tetrafluoroaluminate anions upon dissolution. Tetrafluoroaluminate ions are moderately stable but will eventually disintegrate resulting in aluminium cations and fluoride anions that participate in prevalent environmental speciation processes.The respective dissociation products behave differently in the environment and determine the fate in the environment with regard to (bio)degradation, bioaccumulation, partitioning as well as the distribution in environmental compartments (water, air, sediment and soil) and subsequently the ecotoxicological potential.

 

Acute (short-term) toxicity: Acute EC/LC50 values of cesium tetrafluoroaluminate available for three trophic levels of aquatic organisms (fish, crustacea and algae) amount to > 120, 50 and 14.21 mg/L respectively. All acute effect concentrations are well above classification criteria of acute (short-term) hazard to the aquatic environment under Regulation (EC) No 1272/2008.

 

Long-term (chronic) toxicity: A 72-h EC10 of 7.69 mg/L cesium tetrafluoroaluminate is available for algae and well above classification criteria of long-term hazard to the aquatic environment under Regulation (EC) No 1272/2008. Since the EC50 value for algae is lower than EC/LC50 values for crustacea and fish, algae appear to be most sensitive. The lack of a hazard potential of cesium tetrafluoroaluminate is supported by the lack of a hazard potential for long-term toxicity of its dissociation products aluminium, cesium and fluoride (Please refer to additional information). Thus, cesium tetrafluoroaluminate does not meet criteria of a long-term hazard to the aquatic environment under Regulation (EC) No 1272/2008.

In sum, cesium tetrafluoroaluminate does not meet acute and long-term aquatic hazard criteria of Regulation (EC) No 1272/2008.