Naphthenic acids, cobalt salts

Toxicity to aquatic algae and cyanobacteria

Description of key information

Relevant and reliable data that could be used for classification and PNEC for freshwater algae were retrieved for two species: Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii. For Pseudokirchneriella subcapitata (the most sensitive species), reported EC50s ranged from 95 - 485 µg Co/L and the EC10s ranged from 22.0 - 296 µg Co/L; variability is attributed to differences in the characteristics of the test waters. Values used for CSA are reported as geometric means of available data.

Relevant and reliable data that could be used for classification and PNEC for marine algae were retrieved for three different species: Champia parvula (seaweed), Skeletonema costatum (marine diatom), and Dunaliella tertiolecta (marine flagellate). The EC50s ranged from 24.1 µg Co/L for seaweed to 100,000 µg Co/L for marine diatom. EC10s ranged from 1.23 µg Co/L for seaweed to 11,961 µg Co/L for marine flagellate. Test results were obtained in experiments that followed international accepted guidance and were based on measured levels of dissolved cobalt as cobalt dichloride.

Key value for chemical safety assessment

EC50 for freshwater algae:

197 µg/L

EC50 for marine water algae:

24.1 µg/L

EC10 or NOEC for freshwater algae:

66.9 µg/L

EC10 or NOEC for marine water algae:

1.23 µg/L

Additional information

Freshwater:

From the database of cobalt toxicity to freshwater algae, NOEC/EC10 high quality values are reported for the Pseudokirchneriella subcapitata algae species (Heijerick et al 2007; OSU 2015). The following table indicates those EC10 values of high quality that were used to derive the HC5 and aquatic freshwater PNEC:

 

Table 6.1.5 -1. High quality studies used for derivation of the HC₅ and freshwater PNEC

Key Study	Selected values for the most sensitive endpoints used for derivation of the freshwater HC5
	Species	Endpoint	Value (µg Co/L)
Heijerick et al, 2007	Pseudokirchneriella subcapitata (freshwater algae)	Growth	EC50: 144 EC10: 23.0
OSU 2015	Pseudokirchneriella subcapitata (freshwater algae)	Growth	EC10 (72h): 296.5 (95% CL: 248.0 - 354.3) - pH 6.0 EC50 (72h): 485.7 (95% CL: 412.5 - 571.9) - pH 6.0   EC10 (72h): 148.3 (95% CL: 109.2 - 201.5) - pH 6.4 EC50 (72h): 397.1 (95% CL: 347.3 - 454.0) - pH 6.4   EC10 (72h): 115.8 (95% CL: 92.8 - 144.6) - pH 6.6 EC50 (72h): 199.4 (95% CL: 177.7 - 223.8) - pH 6.6   EC10 (72h): 62.7 (95% CL: 18.6 - 211.3) - pH 7.2 EC50 (72h): 146.4 (95% CL: 89.8 - 238.9) - pH 7.2   EC10 (72h): 21.5 (95% CL: 16.0 - 28.9) - pH 7.4 EC50 (72h): 151.5 (95% CL: 122.8 - 186.9) - pH 7.4   EC10 (72h): 38 (95% CL: 22.6 - 63.9) - pH 8.0 EC50 (72h): 95.2 (95% CL: 77.3 - 117.3) - pH 8.0

 

Marine:

From the database of cobalt toxicity to marine algae, 10 high quality NOEC and EC10 values are reported for three species. Toxicity values (EC10) range from 1.23 μg Co/L for growth of the marine algae, Champia parvula (CDI 2010m) to 11961 μg Co/L for growth of the marine flagellate, Dunaliella tertiolecta (CDI 2010l). The table below indicates the high quality EC10 values selected for derivation of HC5 and the marine aquatic PNEC:

 

Table 6.1.5 -2. High quality studies used for derivation of the HC₅ and the marine aquatic PNEC

Key Study	Selected values for the most sensitive endpoints used for derivation of the marine aquatic HC5
	Species	Endpoint	Value (µg Co/L)
CDI, 2010k	Champia parvula (seaweed)	Cytoscarp production	EC50: 24.1 EC10: 1.23
CDI, 2010m	Skeletonema costatum (marine diatom)	Growth rate	EC50: 100000 EC10: 590.3
CDI, 2010l	Dunaliella tertiolecta (marine flagellate)	Growth rate	EC50: 71314 EC10: 11961