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Toxicity to aquatic algae and cyanobacteria

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Description of key information

For dilithium adipate, the EC50 (72h) based on growth rate was 23 mg/L and the NOEC was 3.2 mg/L.
For dilithium azelate, the EC50 (72h) based on growth rate was > 100 mg/L and the NOEC (72h) was 100 mg/L
For dilithium sebacate, the EC50 (72h) based on growth rate was > 100 mg/L and the NOEC (72h) was 10 mg/L .

Key value for chemical safety assessment

EC50 for freshwater algae:
23 mg/L
EC10 or NOEC for freshwater algae:
3.2 mg/L

Additional information

The toxicities to algal growth were determined in GLP-compliant, static, freshwater tests (Tobor-Kaplon 2015) following OECD guideline 201. In all studies the chemical confirmation of the test substance was based on analysis of the appropriate fatty acid, lithium and the total organic carbon (TOC). The algal growth inhibition test on dilithium adipate was conducted at 1.0, 3.2, 10, 32 and 100 mg/L. The chemical analysis confirmed nominal concentrations of test substance. Based on growth rate the 72 h NOEC was 3.2 mg/L and the ErC50 was 23 mg/L dilithium adipate.

  

The results of the algae study for dilithium azelate were based on a second definitive study because the first study was not valid. The test concentrations were 1.0, 3.2, 10, 32 and 100 mg/L dilithium azelate. There were significant effects based on growth rate at 32 and 100 mg/L dilithium azelate but as these resulted in <10% inhibition of the algae compared with the control they were not considered to be biologically significant. The 72 h NOEC for growth rate was 100 mg/L and the ErC50 was ≥ 100 mg/L dilithium azelate based on nominal concentrations.

  

The dilithium sebacate study was conducted at 0.10, 0.32, 1.0, 3.2, 10, 32 and 100 mg/L. Statistically significant inhibition of growth was observed at nominal concentrations of 10 mg/L dilithium sebacate based on growth rate, however the effect was < 10% inhibition of the algae compared with the control so was considered to be biologically not significant. The 72 h NOEC based on growth rate was 10 mg/L and the ErC50 was ≥ 100 mg/L dilithium sebacate based on nominal concentrations.

  

In the dilithium azelate and the dilthium sebacate studies the lithium concentration was confirmed to be stable throughout the test. The concentration of the appropriate fatty acid was confirmed as stable for up to 24 hours but after 72 hours measured fatty acid concentrations were much lower (often below the limit of quantification). In both studies the fatty acid concentration was maintained in the blank test vessel without algae throughout the exposure period. It is considered that as the algal cell density is increasing in the test vessels the fatty acid is becoming associated with the algal material. The algae are therefore still exposed to the test substance throughout the test period and all endpoints are reported based on nominal test concentrations.

  

Overall, the three test substances show low toxicity to algae. The most sensitive results are based on the dilithium adipate study and these are used as the basis of the risk assessment.  

 

In addition to the long-term toxicity data on category members, assessments of metal salts should consider the inorganic moiety if the substances dissociate rapidly or both the inorganic moiety and the substances themselves if the dissociation rate is unknown. As there is currently no experimental data on the rate of dissociation of the substances in the lithium salts of dicarboxylic acids C6-C10 category, data are presented here on the lithium ion for completeness.

 

In aqueous environments, the substances in the lithium salts of dicarboxylic acids C6-C10 category would dissociate into acids and lithium ions. The acids used for the formation of the salts in this category are readily biodegradable. Data on the lithium component of the salts are available in the dossiers for soluble lithium salts such as lithium carbonate and lithium hydroxide. In a toxicity test with lithium hydroxide on algae, an EC50 of 87.57 mg/L and a NOEC of 5.71 mg/L for lithium hydroxide anhydrous (equivalent to 153.44 mg/L and 10.0 mg/L for lithium hydroxide monohydrate) were determined, which are equivalent to 288.9 and 18.8 mg/L for dilithium adipate. In a toxicity test with lithium carbonate on algae, an EC50 of 400 mg/L, an EC10 of 90 mg/L and a NOEC of 50 mg/L for lithium carbonate were determined, which are equivalent to an EC50 of 855.3 mg/L, an EC10 of 192.5 mg/L and a NOEC of 106.9 mg/L for dilithium adipate. The lowest result of a NOEC of 18.8 mg/L for dilithium adipate has been read across to all substances in the lithium salts of dicarboxylic acids C6 – C10 category, following a worst-case approach as dilithium adipate is the shortest chain length substance in the category and contains the highest proportion of lithium, calculated as 8.79% lithium.

 

The lowest result of a NOEC of 18.8 mg/L calculated for dilithium adipate based on lithium toxicity to algae is higher than the experimental value of 3.2 mg/L for dilithium adipate so the experimental value for the substance will be used in the conclusion on aquatic toxicity.

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