Lithium hexafluorophosphate(1-)

Endpoint summary

Additional information

Biodegradation

Waiver: lithium hexafluorophosphate is inorganic and thus no biodegradation can be expected: in accordance with REACH Annex VII Column 2, no test of ready biodegradability is required.

 

Abiotic degradation (hydrolysis)

Lithium hexafluorophosphate is reactive and unstable in water and air. Reaction in contact with water proceeds rapidly, with release of hydrogen fluoride (forming hydrofluoric acid). Under ambient conditions, the substance LiPF6 may even be represented as an equilibrium state: 

LiPF6 ↔ LiF + PF5

The following rapid hydrolysis reaction sequences can therefore occur:

LiPF6 → LiF + PF5, followed by PF5 + 4H2O → 5HF + H3PO4

or LiPF6 + H2O → LiF + 2HF + POF3, followed by POF3 + 3H2O → 3HF + H3PO4

Both of these can be summarised as:

LiPF6 + 4H2O → 5HF + LiF + H3PO4

(Xu, 2004; Unpublished stability and degradation report, 2011).

 

The kinetics of the hydrolysis reaction have been tested by monitoring of pH and pF values (Unpublished stability and degradation report, 2011). After initial investigations of temperature- and concentration- dependence of the reaction, hydrolysis rate was determined measuring pH and pF for up to 49 seconds after addition of 30g LiPF6 to 500 ml water at 20°C. In a series of experiments, the rapid reaction phase (considered to be release of HF, LiF and H3PO4 as shown above) was effectively complete within 3 seconds. The rate at which subsequent ionisation of LiF occurs will be limited primarily by the rate of LiF dissolution in water. 

Hydrolysis in air:

A subsequent investigation of reaction time in moist air indicated a two-stage reaction, starting after 10 -20 minutes according to LiPF6 particle size and progressing slowly over 1 or 2 hours.

 

Adsorption/desorption

Waiver: in case of environmental release of LiPF6, the speed of its reaction with water and the subsequent dissociation of the soluble hydrolysis products will be such that only the adsorptive behaviour of the resultant ions has relevance for environmental mobility. In accordance with section 2 of REACH Annex XI, adsorption testing of LiPF6 is not technically possible due to its high reactivity and instability: further, in accordance with REACH Annex XI section 1 testing is not scientifically necessary since it is the products of rapid LiPF6 hydrolysis which could enter the environment and existing information is available on the adsorptive properties of these.

 

HF

In the soil compartment, HF itself is not expected to be present: any fluoride introduced via unexpected release of LiPF6 will principally be present in the form of fluoride ion. For this reason, separate assessment of HF mobility is not meaningful or necessary.

 

Fluoride

A soil column of ferruginous lateritic clay was efficient at removing fluoride from aqueous solution: 10 mg F-/l reduced to 0.019 mg/l after 120 minutes: Chidambaram, Ramanathan and Vasudevan, 2003). Wang et al (2002) reported that clay and acid soils can strongly adsorb dissolved fluoride, leading to local accumulation of fluoride in soil; however in alkaline and quartz-sandy soils fluoride is not retained and leaches extensively into groundwater. However a more extensive review of fluoride mobility in soil (WHO EHC 227, 2002) notes that the principal determinants of fluoride mobility in soil are pH and availability of aluminium and calcium for complex formation and cites extreme immobility of fluoride in soil in lysimeter experiments. However the introduction of fluoride into the soil compartment through weathering of minerals means that fluoride is often found in groundwater: partitioning of fluoride entering the soil via pollution between soil solids and ground/pore water will depend on the local background concentration in groundwater as well as other soil characteristics.

 

Lithium

Lithium is selectively adsorbed in preference to other cations by certain clays, the extent of its retention in secondary clays is related to the local presence of magnesium (Li+ substituting for Mg2+); however it appears to be only poorly adsorbed onto river sediments (Aral and Vecchio-Sadus, 2008). Lithium also adsorbs slightly to humic soils, but in general lithium compounds are not expected to adsorb strongly to soils or sediments (Webwiser – US NLM, 2012).

 

Phosphate

Concerns arising from phosphate in runoff form agricultural lands indicate high soil mobility in some cases, and addition of inorganic phosphates have been shown to raise water-soluble phosphorus levels. Soil organic content affects phosphorus/phosphate mobility (Tarkalson and Leytem, 2009).

 

Bioaccumulation

Waiver:following rapid hydrolysis of LiPF6 on contact with water, HF and subsequently the ionised hydrolysis products F-, Li+ and PO4- are present in solution. In accordance with section 2 of REACH Annex XI, bioaccumulation testing of LiPF6 is not technically possible due to its high reactivity and instability: further, in accordance with REACH Annex XI section 1 testing is not scientifically necessary since existing information is available to assess bioaccumulative properties of the dissolved hydrolysis products.

 

HF

In fresh or marine waters, HF will principally be present in the form of fluoride ion. For this reason, test data relevant to soluble inorganic fluorides can be used to evaluate the bioaccumulative potential of HF. 

 

Fluoride

In freshwater, fluoride BCF values (based on dry weight) of 53 – 58 and <1 have been reported for fish and crustaceans respectively; a BCF value (based on wet weight) of 3.2 has been reported for molluscs (and 7.5 in aquatic macrophytes). As in mammals, fluoride is retained in fish bones and the exoskeleton of crustaceans: no such accumulation has been reported in edible fish tissue (HF: EU Risk Assessment Report, 2001).

 

Lithium

In a 28-day test, carp exposed to lithium bromide showed or no indication of lithium bioaccumulation. BCF values at two test concentrations being <31 (Japan NITE, 2001). A review of lithium toxicity concluded that lithium is not expected to bioaccumulate (Aral and Vecchio-Sadus, 2008) and in man and animals most of an absorbed dose of lithium is rapidly removed from the circulating blood (Hunter, 1998) and excreted via the kidneys (Nordic Expert Group for Criteria Documentation of Health Risks from Chemicals 131, 2002). There is some evidence of retention or accumulation of lithium in certain marine species: analysis of the lithium content of >30 different marine species (including mammals, fish, crustaceans and other types) collected from offshore European, American and Japanese locations using a sensitive secondary ion mass spectrometry method found lithium in most cases (Chassard-Boucheau et al, 1984). The investigators reported measured ion intensity ratios (7Li/40Ca) recorded in processed samples from various tissues and/or organs. Among dolphins and fish, the highest lithium concentrations were found in samples of muscle tissue (that of the flounder showing the greatest value) while in crustaceans of commercial importance little or no lithium retention was seen in edible tissues. No measurements of seawater Li+ levels are presented, although a report of 173 µgLi/l in ocean surface waters is cited and no BCF values are calculable. Even the findings in dolphins and fish do not provide evidence of marked bioaccumulation.

 

Phosphate/phosphorus

 Uptake of phosphorus present in water as dissolved phosphate is believed to be a minor contributor to accumulated phosphorus in fish, with phosphorus intake in food being estimated to be some 40,000 times greater (Smith, Bowes and Cailes, 2011). An overall Concentration Factor for the stable form of phosphorus in the edible portion (muscle) of larger freshwater fish can be calculated from the data of these authors to have an approximate range of 1,222-36,666, but most of the accumulated phosphorus is likely to have been taken up from feeding and not by absorption from water.

 

Transport and distribution

Following rapid hydrolysis of LiPF6, only the reaction products F-, Li+ and PO4- could persist for any significant time following an environmental release.

 

Fluoride

The HF: EU Risk Assessment Report (2001) notes the natural occurrence of fluoride in surface waters, seawater and soil. In surface waters, fluoride concentrations are dependent on the local geology: concentrations of 0.01 – 0.03 mgF-/l have been reported in areas without fluoride-containing rock and concentrations of 4.7 - >20 mgF-/l in areas with such rock formations. Naturally occurring levels in seawater are higher than those in freshwater (average 1.4 mgF-/l). Fluoride enters the soil through the natural processes of rock weathering and atmospheric deposition and is found at levels in the range 80 – 700 mg/kg dry weight.

 

Lithium

Lithium occurs widely in the earth’s crust. In surface freshwaters, concentrations of 1 – 10 µg/l and in seawater 170 – 190 µg/l have been reported, although in areas with high local rock lithium rock mineral levels much higher river concentrations (e.g. 5 mg/l) are known in sediment and soil concentrations of 56 and 3 – 350 mg/kg have been reported. Lithium is found in all soils, primarily in the clay component: soil concentrations vary widely according to local geology with levels from 7 to 500 mg/kg being reported (Aral and Vecchio-Sadus, 2008).

 

Phosphorus/phosphate

Inorganic phosphate is an essential cellular component, necessary for biological processes in plants and animals. Phosphate rock formations contribute to the ubiquitous presence of phosphorus/phosphate in surface waters seawater and soil, but in many European areas with high agricultural activity dissolved phosphate in rivers or lakes have been significantly affected by phosphate in run-off or leachate from soil treated with inorganic fertilisers or manure. If unrestricted, this leads to eutrophication: total phosphorus concentrations as high as 87 – 525 µg/l have been reported in Swiss lakes, falling to well below 20 µg/l after control of the nutrient (phosphate) inputs (Swiss Federal Institute of Aquatic Science and Technology, 2010).

 

No foreseeable environmental release of LiPF6 could add significantly to these levels, except at the immediate point of a substantial discharge into static or slow-moving water.