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Toxicity to aquatic algae and cyanobacteria

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Description of key information

72-hour ErC50 = 32 mg/L, NOEC = 3.2 mg/L, LOEC = 10 mg/L, US EPA OCSPP 850.4500 and OPPTS 850.1000

Key value for chemical safety assessment

EC50 for freshwater algae:
32 mg/L

Additional information

A study was performed to assess the effect of the test material on the growth of the green alga Pseudokirchneriella subcapitata.The study was conducted in accordance with the standardised guidelines US EPA OCSPP 850.4500 and the US EPA OPPTS 850.1000 under GLP conditions. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

Following preliminary range-finding tests, Pseudokirchneriella subcapitata was exposed to an aqueous solution of the test material at concentrations of 1.0, 3.2, 10, 32 and 100 mg/L (four replicate flasks per concentration) for 96 hours, under constant illumination and shaking at a temperature of 24 ± 1 °C.

Due to the highly alkaline nature of the test material, the pH of the test preparations was adjusted to pH 7.5 prior to inoculation with algal cells at the beginning of the test in order to determine the true toxic effect of the test material.

Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter® Multisizer Particle Counter.

Analysis of the test preparations at 0, 72 and 96 hours showed measured test concentrations to range from 99 to 123 % of nominal and so the results are based on nominal test concentrations only.

The growth rate (r), yield (y) and biomass integral (b) were affected by the presence of the test material over the 96-hour exposure period.

Under the conditions of this study, the 72 hour ErC50 was 32 mg/L (95 % Confidence Limits 27 - 39 mg/L). The NOEC and LOEC were 3.2 and 10 mg/L, respectively. A re-growth test was performed which showed the test material to be algistatic in effect.