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Toxicity to aquatic algae and cyanobacteria

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Description of key information

In order to predict effects of chemicals in an aquatic environment, the toxicity to freshwater algae was assessed. The algal toxicity was determined in the Algal Growth Inhibition test in accordance with OECD 201, EEC and ISO 8692 test guidelines and with the OECD Principles of Good Laboratory Practice. The guidelines were slightly modified to ensure good growth and pH control of the cultures.

The green algae Pseudokirchneriella subcapitata (formerly known as Se/enastrum capricomutum) was exposed to the following nominal concentrations: 0, 4.3, 9.4, 20.7, 45.5 and 100 mg/L prepared from the 0.1 g/L stock solution of Witconate P-1460. The toxicity of Witconate P-1460 to an exponentially growing culture of P. subcapitata was determined over an exposure period of 72 hours. The EbC50 and ErC50 (0 - 72 h) are 46.3 (95% confidence limits: 26.4 - 89.1) and >100 mg/L, respectively. The NOEC and LOEC are 9.4 mg/I and 20.7 mg/I, respectively. The test was conducted in a mineral salts medium in a climatized illuminated orbital incubator. The maximum variation in pH in the test media was 1.0 pH unit.

The definitive test is valid as shown by the increase of the extinction of the control over 72 h by a factor of 134.

The results of the chemical analyses show that the initial concentrations in the test solutions are close to the nominal (expected) concentrations. A decrease of >70% of test substance concentration during the 72 hours of testing is observed at 4.6 and 20.7 mg/L. No decrease is observed at 100 mg/L. Degradation and sorption to glassware of the test substance are both unlikely reasons for the decrease because at 100 mg/L no significant decrease of the test concentration is observed. For chemical analyses, the samples were filtered to remove the algae. The most obvious reason for the observed decrease is therefore adsorption of the test substance to the algae. If no degradation or sorption to glassware occurred, the algae in the test vessels were fully exposed to the test substance. Therefore the nominal test concentrations were used to calculate the effects.

Key value for chemical safety assessment

EC50 for freshwater algae:
46.3 mg/L

Additional information