Naphthenic acids, copper salts

Endpoint summary

Description of key information

Aquatic toxicity studies of copper naphthenate are not available. Thus, read-across to the assessment entities soluble copper substances and naphthenic acid is applied since the ions of copper naphthenate determine its aquatic toxicity.

Copper:

A large set of reliable aquatic toxicity data on copper ions is available from multiple studies covering all relevant trophic levels. The lowest acute and chronic Ecotoxicity Reference Values (ERVs) derived for copper at different pH bands amount to 12 µg Cu/L (acute, pH 6) and 12 µg Cu/L (chronic, pH 7). Please refer to the respective section of the assessment entity and to attached reports for further information on acute and chronic aquatic toxicity of copper:

"The environmental hazard classification of copper, Version 1.1 (European Copper Institute, 2018)"

"Derivation of acute ERVs for copper, (European Copper Institute, 2016)"

"Derivation of chronic Ecotoxicity Reference Values (ERVs) for copper, updated version (European Copper Institute, 2018)"

 

The potential of copper for toxicity to microorganisms is based on a weight-of-evidence approach of five studies, resulting in a 30-d NOEC of 0.23 mg dissolved Cu/L (inhibition of total respiration / respiration rate) for microorganisms. 

 

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.

 

Copper naphthenate:

Based on acute and chronic ERVs of copper ions of 12.1 µg Cu/L (acute, pH 6) and 12 µg Cu/L (chronic, pH 7), respectively, and acute EC/LC50 values of naphthenic acid ranging from 4.8 to 29.6 mg/L, the hazard assessment is based on the most toxic moiety, i.e. copper cations. Therefore, existing ERVs of copper are recalculated for copper naphthenate based on the maximum copper content of copper naphthenate of 12% resulting in

- an acute ERV (copper naphthenate) of 100.8 µg/L, and

- A cronic ERV (copper naphthenate) of 100 µg/L.

 

The toxic potential of copper naphthenate towards microorganisms is estimated with 1.92 mg/L based on a maximum copper content of copper naphthenate of 12% and the 30-d NOEC of 0.23 mg dissolved Cu/L.