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EC number: 604-086-6
CAS number: 138577-01-2
Cesium fluoroaluminate is a soluble
metal salt consisting of cesium cations and fluoroaluminate anions and
thus liberates cesium cations and fluoroaluminate anions upon
dissolution. Since cesium and fluoroaluminate ions behave differently in
the environment, their fate is assessed separately. Fluoroaluminate ions
are moderately stable but will eventually disintegrate resulting in
aluminium cations and fluoride anions that participate in prevalent
geochemical speciation processes.
The assessment of the partitioning of
aluminium and cesium between freshwater and sediments is based on Kp
values derived from monitoring data for elemental Al and Cs
concentrations in water and corresponding sediments provided by the
FOREGS Geochemical Baseline Mapping Programme that aimed to provide high
quality, multi-purpose homogeneous environmental geochemical baseline
data for Europe. Paired samples, i.e. samples with the same coordinates
for the sampling location of stream water (filtered to < 0.45 µm) and
sediment (wet sieved in the field to <0.15 mm) were processed (Salminen
et al. 2005) and results correspond to steady-state conditions,
independent of environmental speciation. Sampled stream water and
sediments cover a wide range of environmental conditions. Water
parameters such as pH, hardness and organic carbon concentrations cover
several magnitudes. Since FOREGS sampled on a grid aiming to equally
represent geochemical baseline concentrations across Europe, the
European median values are selected as representative sediment-water
partition coefficients of Europe.Sediment-water partition coefficients
of fluoride cannot be calculated
since the FOREGS dadabase does only contain streamwater but not sediment
concentrations. A conservative estimate is applied based on
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 below about pH 4.5
is Al(H2O)6 (3+). Above 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.
Concentrations of dissolved Al are generally low in most natural waters
(Salminen et al. 2015 and references therein). Median aluminium
concentrations across Europe amount to 5.45 mg/kg sediment and 0.017
mg/L stream water, respectively. Regarding the partitioning of aluminium
in the water column, a European median log Kp value of 2.39 L/kg is
derived for sediment-water partitioning.
Cesium is a relatively rare element.
Released cesium is rapidly and strongly adsorbed by soil, especially
clay, and therefore does not tend to be present in the aqueous surface
environment. 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). Median cesium concentrations across Europe
amount to 3 mg/kg sediment and 0.01 microg/L stream water, respectively.
Regarding the partitioning of cesium in the water column, a European
median log Kp value of 5.70 L/kg is derived for sediment-water
partitioning. Regarding the partitioning of cesium in the water column,
a European median log Kp value of 1.95 L/kg is derived for
Fluoride ions in solution form strong
complexes with other ions, particularly 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+. Fluoride also adsorbs to mineral
surfaces such as gibbsite, kaolinite, halloysite, and freshly
precipitated amorphous Al(OH)3. Sorption to these solid phases may be
favoured at lower pH (Salminen et al. 2005 and references therein). The
transport, distribution and transformation of fluoride in soil are
influenced by pH and the formation of predominantly aluminium and
calcium complexes. Adsorption to the soil solid phase is stronger at
slightly acidic pH (5.5–6.5). Fluoride is not readily leached from
soils. Median fluoride concentrations across Europe amount to 0.1 mg/L
stream water. According to a review conducted by SCHER (2011), the
electronegativity of the fluoride ion results in little partitioning to
solids and thus, sewage sludge and soils are unlikely to become
contaminated (SCHER, 2011). Further, for a substance produced at 100,000
- 1 000,000 tpa, soil levels of fluoride were found to be „negligible
compared to background concentrations“ (EU RAR, 2001). Consequently,
due to the electronegativity of the fluoride ion, it may be assumed that
there is little partitioning to solids in soils, sediment and suspended
matter. Conservatively, an estimate of 0.01 for the solids-water
partition coefficient soil, solids-water partition coefficient sediment
(freshwater) and solids-water partition coefficient suspended matter
(freshwater) is applied.
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.
SCHER, 2009: Scientific Committee on
Health and Environmental Risks (SCHER). Critical review of any new
evidence on the hazard profile, health effects, and human exposure to
fluoride and the fluoridating agents of drinking water.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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