Naphthenic acids, nickel salts

Endpoint summary

Description of key information

Aquatic toxicity studies of naphthenic acids, nickel saltsare not available. Thus, read-across to the assessment entities soluble nickel substances and naphthenic acid is applied since the ions of naphthenic acids, nickel saltsdetermine its fate and toxicity in the environment. Reliable studies indicate that the moiety of ecotoxicological concern are nickel cations.

Nickel:

A large set of reliable aquatic toxicity data on nickel ions is available from multiple studies covering all relevant trophic levels. The lowest acute and chronic ERVs derived for nickel at different pH bands amount to 68 µg Ni/L (acute, pH 8) and 2.4 µg Ni/L (chronic). Please refer to the respective sections for further information on acute and chronic aquatic toxicity of nickel.

In addition, the potential of nickel for toxicity to microorganisms is expressed by the 30 -min EC50 of 33 mg Ni/L (Cokgor et al, 2007).

 

Naphthenate:

Acute data are available from studies for three trophic levels algae, invertebrates and fish as follows:

- 72-h NOErC and ErC50 of 7.38 and 29.6 mg/L, respectively for the algae Pseudokirchneriella subcapitata

- a 48-h LC50 of 20 mg/L represents the lowest value identified for the invertebrate species Daphnia magna. In addition, a 96-h LC50 of 4.8 mg/L (nominal) for calcium naphthenate has been determined for the marine copepod, Nitocra spinipes. 

- a 96-h LC50 of 5.62 mg/L (measured arithmetic mean) was identified for the freshwater fish species Pimephales promelas

Studies on the toxicity of a structural analoge (cyclohexane carboxylic acid) to microorganisms result in an EC50 of 13.0 mg/L for Vibrio fisheri.

In sum, naphthenic acid has some potential for acute aquatic toxicity.

 

 

Naphthenic acids, nickel salts

Based on acute and chronic ERVs of nickel ions of 68 µg Ni/L (acute, pH 8) and 2.4 µg Ni/L (chronic) and acute EC/LC50 values of naphthenic acid ranging from 4.8-29.6 mg/L, the hazard assessment is based on the most toxic moiety, i.e. nickel cations. Therefore, existing aERVs of nickel are recalculated for naphthenic acids, nickel salts based on the maximum nickel content of naphthenic acids, nickel salt of 10.8% resulting in:

Acute ERV (naphthenic acids, nickel salts): 629,6 µg/L, and

Chronic ERV (naphthenic acids, nickel salts): 22.2 µg/L.

Based on the EC50 of 13.0 mg/L for the toxicity of a structural analoge (cyclohexane carboxylic acid) to Vibrio fisheri (being lower than the 30-min EC50 of 33 mg Ni/L for the toxicity of nickel to microorganisms), the toxic potential of naphthenic acids, nickel salts towards microorganisms is conservatively estimated with 14.2 mg/L naphthenic acids, nickel salts taking into account the naphthenic acid content of naphthenic acids, nickel salts of 91.4 %.