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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The toxicity to algae was assessed according to EU method C.3. In this 72-hour toxicity test with freshwater algal species Desmodesmus subspicatus, the EbC50 and ErC50 values were determined to be 29 mg/L and 43 mg/L (nominal concentrations, WAF), respectively. The no-observed-effect concentration (NOEC) and lowest-oberved-effect-concentration was determined to be 12.5 mg/L and 25 mg/L (both nominal concentrations, WAF), respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:
43 mg/L
EC10 or NOEC for freshwater algae:
12.5 mg/L

Additional information

A study was performed to assess adverse effects of the test item on the growth (= increase in cell density) and the growth rate (=rate of increase of cell density with time) of the planktonic freshwater algal species Desmodesmus subspicatus over several generations. The study was conducted in accordance with EEC methods for Determination of Ecotoxicity Annex to directive 92/69/EEC Part c, Method 3 which is in most parts equivalent o the OECD guideline for testing of chemicals no. 201.

Exponentially growing algal cells were exposed for a period of 72 h to a range of concentrations, nominally 6.25, 12.5, 25, 50 and 100 mg/L of the test item dissolved in water. Auxiliaries used to prepare the test media were an ultra turrax, a magnetic stirrer and folded flters. The cell densities were measured at 24 h intervals. Inhibition of the algal population was measured as reduction in growth (index b) and growth rate (index r) relative to control cultures grown under identical conditions. Growth and growth rates were used to calculate a No Observed Effect Concentration and a Lowest Observed Effect Concentration according to Dunnett (1994, 1995). The following values were determined: EbC50 (72 h)=29 mg/L; ErC50 (72 h)=43 mg/L; NOEC (b)=12.5mg/L; LOEC (b)= 25 mg/L; NOEC (r)= 12.5 mg/L and LOEC (r)=25 mg/L. The results were expressed in terms of effective loadings. Considering the heterogeneous composition of the test item, Water Acomodated Fractions (WAF) were tested. The results of DOC determinations reflect a rough impression only of exposure conditions over time. Not informations are available on a molecular weight of the test item and on a potential correlation between effective loadings and measured DOC values.