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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Activated sewage sludge microorganisms, OECD 209: EC50(3h) > 1000 mg/L, NOEC: 1000 mg/L  

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L
EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information

The toxicity effects of the test substance towards aquatic microorganisms were investigated according to OECD Guideline 209 under certificated GLP compliance (Wadsley, 2012). A mixed population of activated sewage sludge microorganisms, collected at the aeration stage of a predominantly domestic sewage treatment plant, were used as inoculum. This inoculum was exposed to an aqueous solution of the test substance at concentrations of 10, 100 and 1000 mg/L (3 replicates of the 1000 mg/L test concentration) for a period of 3 hours at a temperature of 20 +/- 2 °C with addition of synthetic sewage as respiratory substrate. 3,5-dichlorophenol was used as reference compound, resulting in an EC50 value of 8.8 mg/L, confirming the sustainability of the test procedure. Furthermore, 4 control replicates were run in parallel. No statistically significant toxic effects were shown at all of the test concentrations employed. Therefore, no further testing was employed and the EC50(3h) was determined to be greater than 1000 mg/L with a corresponding No Observed Effect Concentration (NOEC) of 1000 mg/L. It was considered unnecessary and unrealistic to test at concentrations in excess of this concentration. The test substance solutions appeared during the test as pale brownish dispersion, no undissolved material was visible. The validation criteria of the applied test guideline have been fulfilled.

Supporting information is given by the acute toxicity test with Pseudomonas putida ( Oláh and Kiss, 1990) according to the method of Bringmann and Kühn (1977). In this experiment the bacterial growth is quantitated by turbidimetry i.e. by measuring the extinction of both the test and the control medium. Concentrations of the test substance were 0.01, 0.02, 0.03, 0.04, 0.06, 0.09, 0.13, 0.20, 0.30, 0.44 and 0.67 g/mL. The stock culture of P. putida was kept in culture tubes containing slant agar medium. The preculture was inoculated from the stock culture and incubated for 18 +/- 2 hours at a temperature of 25 °C. The extinction of the bacterium suspension was determined at 436 nm in a cuvette of 10 mm light path with a U-3200 type HITACHI spectrometer. A formazine standard was used as blank. A control culture was prepared with the same solutions (stock solution I and II together with bacterial suspension) but distilled water was substituting the test substance solution. As result a MIC (Minimum Inhibitory Concentration) of 0.12 g/mL was determined out of the extinction values using a graphic method. Nevertheless, the result (MIC value) can neither be used for the chemical safety assessment nor for the risk assessment.