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Toxicity to aquatic algae and cyanobacteria

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Description of key information

An algae study with Pseudokirchneriella subcapitata according to OECD TG 201 showed an ErC50 > 0.854 mg/l and NOEC = 0.201 mg/l using mean measured concentrations. Only EC10 is presented as key value for risk assessment.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
0.201 mg/L

Additional information

Two algae studies are available both according to OECD TG 201, the van Dijk (1997) study has the lowest NOEC and is used as key study. The Kos-Durjava et al. (2012) is used as supporting. An invalid study by Ding et al., (2020) is summarised too. 

Key study, Van Dijk (2007; RCC 380632), Freshwater, Pseudokirchneriella subcapitata, Kl. 1

The toxicity to algae was studied in a static test according to OECD Test Guideline 201 with Pseudokirchneriella subcapitata. The test was carried out under GLP and the validity criteria were fulfilled. Algae were exposed to solutions of the test material at nominal concentrations in the range of 6.25-1000 μg/L (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24°C. Concentrations were measured at the start and end of the test. Results: Maintenance of the concentrations proved to be difficult and in some cases pH-values rose to above 10. The loss of test material in the algal test was studied for a related polycyclic musk and it was shown that sorption to algal cells was the most relevant ‘sink’, whereas sorption to glass and volatilisation might have played a role as well. The results were expressed as the mean concentration over the exposure time. The inhibition based on Area Under the Curve was 35% and 56% at the highest two concentrations. Both biomass production and growth rate were not significantly inhibited up to and including 0.201 mg/l. Growth rate was inhibited by 9 and 20% (both statistically significant) at 0.466 and 0.854 mg/l. The ErC50 is therefore > 0.854 mg/l, the NOEC = 0.201 mg/l.

Supporting study, Kos Durjava et al., (2012; Cadaster project deliverable 2.5, Public Health Institute Maribor, Solvenia), Freshwater, Pseudokirchneriella subcapitata, Kl 2

The acute toxicity towards Pseudokirchneriella subcapitata was investigated according to OECD guideline 201. Algae were exposed to five concentrations of the test material arranged in a geometric series for 72 hours at 20°C ± 2°C. The 72h-EC50 and 72h-NOEC were found to be >0.7 and 0.23 mg/l respectively, based on measured concentrations.

Invalid study, Ding et. al. (2020), Navicula sp. and Scenedesmus quadricauda, Journal of Hazardous Materials 384: 121360, Kl 3

The study is a non-GLP and non-guideline test. It has been disregarded due to missing essential information on measured concentrations, preparation of the algae culture, pH and raw data to derive the experimental results or assess validity. An EC10 is not provided. Biomass in the control cultures did not increase exponentially by a factor of at least 16 within the 72-hour test period (only a factor of 2).

A study was performed to assess the effect of the test material on the growth of freshwater algae (Navicula sp. and Scenedesmus quadricauda). This study was conducted to provide more information on the aquatic risk assessment of the substance and investigate the effectiveness of freshwater algae in removing the substance in water. Algae were exposed to the substance at nominal concentrations of 0, 0.1, 0.2, 0.5, 1.0, 1.5, and 2.0 mg/l (three replicates per concentration), and incubated for 16 d at 23 ± 1 °C in the dark or under a 12 h photoperiod of 4000 lx provided by fluorescent lamps. The 72h-EC50 for Navicula sp. and Scenedesmus quadricauda were reported as 0.012 and 0.336 mg/l respectively.