Diammonium [[N,N'-ethylenebis[N-(carboxymethyl)glycinato]](4-)-N,N',O,O',ON,ON']cobaltate(2-)

Toxicity to aquatic algae and cyanobacteria

Description of key information

ErC50 > 400 mg/l (based on nominal concentration)

Additional information

The toxicity of the test item to the unicellular freshwater green alga Pseudokirchneriella subcapitata was determined according to the principles of OECD guideline 201.

The aim of the study was the determination of the effects on growth rate and yield over a period of 72 hours. 

The study was conducted under static conditions with an initial cell density of 6442 cells/mL. A stock solution with a nominal loading of 400 mg test item/L was freshly prepared with dilution water. This dispersion was agitated until the solution was visually clear. The stock solution was diluted to obtain the required test item concentrations. Five concentrations were tested in a geometrical series with a spacing factor of 2.5: 10.2 - 25.6 - 64.0 - 160 - 400 mg/L, corresponding to the geometric mean measured cobalt concentration of 0.0171 – 0.0617 – 0.157 – 0.140 – 0.220 mg/L.

Three replicates were tested for each test item concentration and six replicates for the control. The environmental conditionswere within the acceptable limits.

 

The concentrations of the test item were analytically verified via spectrophotometric analysis at the start (0 hours) and at the end of the exposure (72 hours).

The measured concentrations of Cobaltat the start of the exposure (0 hours) were between 0 and 1% of the nominal concentration. At the end of the exposure (72 hours), the Cobalt concentration was detected in the range of 1 and 8 % of the nominal concentration

The EC₅₀-values for inhibition of growth rate (E_rC₅₀) and yield (E_yC₅₀) after 72 hours were > 400 mg/L [0.220 mg Co²⁺/L] and 235 (138 - 363) mg/L [0.190 (0.158 - > 0.220) mg Co²⁺/L], respectively. The NOEC for both growth rate and yield was 160 mg/L [0.140 mg Co²⁺/L].