Naphthenic acids, copper salts

Toxicity to aquatic algae and cyanobacteria

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 fate and toxicity in the environment. Reliable studies indicate that the moiety of ecotoxicological concern are copper cations. Based on copper toxicity to freshwater algae, species mean NOEC values of 43 µg/L Cu for Pseudokirchernella subcapitata and 138 µg/L Cu for Chlorella vulgaris were reported. In addition, with copper being an essential element to algae and cyanobacteria, a concentration of 1-35 µg/L Cu was determined as optimal concentration range for algal growth. Individual NOECs available for marine diatom species Phaeodactylum tricornutum and macroalgae Macrocystis pyrifera range from 2.9 µg Cu/L to 50 µg Cu/L, respectively with species-mean NOEC values ranging from 2.9 µg/L Cu (Phaeodactylum tricornutum) to 11 µg/L Cu (Fucus vesiculosis). Data for naphthenic acid point to a low toxic potential to freshwater algae with 72-h NOErC and ErC50 values of 7.38 and 29.6 mg/L (measured dissolved), respectively, for the inhibition of growth rate of Pseudokirchneriella subcapitata.