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Short-term toxicity to fish

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Description of key information

Given the hydrolytic instability of LiPF6, its toxicity to fish is best defined in terms of the toxicity of its F-, Li+ and PO4(3-) hydrolysis products.  Review of the known toxicities of these leads to a clear conclusion that the fluoride released from LiPF6 is the “toxic marker” for  toxicity to aquatic organisms: from the available data on F- toxicity to fish, a 96h LC50 value of 68 mg LiPF6/l is calculated (based on complete F- release).

Key value for chemical safety assessment

LC50 for freshwater fish:
68 mg/L

Additional information

HF

In the aquatic environment, HF will principally be present in the form of fluoride ion. For this reason, test data obtained using soluble inorganic fluorides can be used to evaluate HF toxicity and LC50 values expressed in terms of mg F-/l are appropriate for assessment of HF toxicity to aquatic organisms (HF: EU Risk Assessment Report, 2001).

 

Fluoride

In freshwater, the presence of calcium carbonate in hard water reduces F- availability and hence toxicity through precipitation of calcium fluoride (HF: EU Risk Assessment Report, 2001; WHO EHC 227, 2002). Tests performed in soft water of hardness ≤25 mg CaCO3/l reported 96h LC50 values ranging from 51-165 mg F-/l (3 studies cited, two using Oncorhynchus mykiss, one Salmo trutta: HF: EU Risk Assessment Report, 2001). Acute fish toxicity tests using waters of different hardness reviewed in EHC 227 showed a clear relationship between 96h LC50 and water hardness. At 17, 49, 182 and 385 mg CaCO3/l, reported rainbow trout LC50 values were 51, 128, 140 and 193 mg F-/l respectively; in other cited studies using the stickleback, reported LC50 values in tests using water with 78, 146 and 300 mg CaCO3/l were 340, 380 and 460 mg F-/l respectively. Toxicity tests with four different marine fish species gave 96h LC50 values in the range >100 to >225 mg F-/l (WHO EHC 227, 2002).

 

Lithium

A 96h LC50 value of 369 mg/l for lithium bromide (corresponding to 29.5 mg Li+/l) has been reported for medaka (Oryzias latipes) by the Japanese Environment Ministry (Japan NITE, 2001). In the fathead minnow, the 96h LC50 and NOEC for lithium have been reported as 42 mg/l and 13 mg/l respectively (study cited by Long, Brown and Woodburn, 1998).

 

Phosphate

Phosphate is widely present in the environment and is naturally present (and necessary) in living organisms. Control of phosphate contamination of surface waters through phosphate discharge or run-off following its use in agriculture or in detergents has been imposed to limit problems of eutrophication, with consequent increase of algal growth, rather than direct toxicity to aquatic organisms. A study of phosphorus supplementation in rainbow trout over 53 days found no evidence that addition of Na2HPO4 into low-phosphorus basal diet at levels giving up to 10.96 g P/kg dry weight (equivalent to 33.6 g PO4/kg or 50.2 g Na2HPO4/kg) adversely affected growth or survival; indeed, weight gain was increased with phosphate supplementation up to a level of approximately 5 g P/kg in diet (equivalent to 8g PO4/kg) (Rodehutscord, 1996). 

 

Key value for assessment

Given the relative quantities of F-, Li+ and PO4- entering solution after contact of LiPF6 with water (LiPF6 + 4H2O → 5HF + LiF + H3PO4 within seconds, followed by slower dissolution then dissociation of the LiF) and the low toxicity of phosphate to fish, it is appropriate to consider the lowest acute fish toxicity 96h LC50 value for fluoride (51 mg F-/l) as the key value for assessment. Conversion of this to an LiPF6 LC50 value could be based on the rapid hydrolysis equation above (i.e. 1 mole LiPF6 releases 5 moles HF which dissociate to 5 F- ions) or, as a worst-case, could also take account of the slower dissolution and ionisation of the LiF hydrolysis product (i.e. 1 mole LiPF6 releases 6 F- ions): for the purposes of assessment the latter is used, giving an LiPF6 96h LC50 value of 68 mg/l.