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Long-term toxicity to aquatic invertebrates

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Description of key information

Given the hydrolytic instability of LiPF6, long-term toxicity to aquatic organisms 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 long-term toxicity to invertebrates: from the lowest reported fluoride 21-day Daphnia NOEC of 3.7 mg F-/l a long-term NOEC value of 4.9 mg LiPF6/l is calculated (based on the expected complete F- release).

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
4.9 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 EC50 or NOEC 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

Two different NOEC values in Daphnia 21-day reproduction studies are reported in the HF: EU Risk Assessment Report (2001): 3.7 mg F-/l and 14.1 mg F-/l. In another authoritative review of fluoride toxicity (WHO EHC 227, 2002), two further Daphnia reproduction studies are described: one reported effects on reproduction at concentrations above 26 mg F-/l, but the other presented more detailed findings. NOEC values for Daphnia growth and reproduction from the latter study were calculated to be in the range 3.7 – 7.4 mg F-/l, leading to calculation of 4.4 mg F-/l as a “safe concentration”.

 

Lithium

A series of experiments have been performed investigating the effects of lithium exposure in waters of varying sodium levels on survival and reproduction of Ceriodaphnia dubia (Kzos, Beauchamp and Stewart, 2003). In water with low sodium content (1.7 mg/l), exposure to 1 mg Li+/l proved lethal within 6 days, but with 40 mg Na/l 100% survival was seen at 4 mg Li+/l. Exposure to lithium at concentrations up to 2.55 mg Li+/l had no significant effect on reproduction (except when sodium content was increased to 700 mg/l). In a 21-day Daphnia magna reproduction study with lithium bromide, EC50 and NOEC values of 29 and 10 mg/l were determined (Japan MoE, 2001).

 

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.  Long-term measurement of daphnid populations in a major European freshwater lake (Lake Constance) showed a marked increase in population (total biomass) associated with increased phosphorus concentrations (input of phosphate): Straile and Geller, 1998. These authors noted compatibility of their findings (increased daphnid biomass with eutrophication) with those reported for several other lakes by other researchers. Later reduction of Lake Constance phosphorus levels did not clearly affect daphnid population size. Overall, only indications of a beneficial effect of phosphate input on daphnid population were reported: no evidence of adverse effects of phosphate input were seen. There is no reason to suppose that phosphate released from LiPF6 could adversely affect aquatic invertebrates.

 

Key value for assessment

The lowest long-term NOEC value reported for fluoride is 3.7 mg F-/l and the lowest NOEC for lithium is 2.55 mg/l; these values correspond to LiPF6 concentrations of 4.9 and 55.8 respectively.  Due to its low toxicity, the contribution of phosphate to LiPF6 toxicity is considered insignificant. It is therefore concluded that the fluoride released from LiPF6 in water is the “toxic marker” for long-term toxicity to invertebrates and a long-term NOEC value of 4.9 mg/l for LiPF6 is taken for use in assessment.