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Toxicity to microorganisms

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Description of key information

In an activated sludge respiration inhibition test according to OECD TG 209 the 3-hour EC50 and EC10 for the test item were determined to be > 1000 mg teflubenzuron/L (nominal).

Key value for chemical safety assessment

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

Additional information

One guideline study on the toxic effect to aquatic microorganisms is available and was peer-reviewed during the assessment of teflubenzuron according to Council Directive 91/414/EEC (2007).

teflubenzuron = active substance (a.s.)

Key information

ECT (2003): A Study on the Respiration Inhibition of Activated Sludge by BAS309 I (Teflubenzuron). Unpublished report, report No. G3XA, according to Draft Assessment Report (2007) according to Council Directive 91/414/EEC, crossreference: MCA 8.7.1/01

To assess the effect of the test item to microorganisms a GLP-compliant Activated Sludge, Respiration Inhibition Test according to OECD TG 209 was carried out. Activated sludge from the aeration tank of municipal sewage treatment plant treating predominantly domestic sewage was exposed to the test item at six different nominal concentrations of 62.5, 125, 250, 500 and 1,000 mg a.s./L, based on the results of a non-GLP range finding test. These concentrations above the water solubility limit of the test substance were prepared by direct addition of the respective amount of the test item to the test solutions. In addition, the nominal concentration of 0.028 mg/L was tested, which is in the range of the water solubility (approx. 0.01 mg/L). 3,5-dichlorophenol was used as reference substance. After a 3 hours incubation period, the respiration rate of the activated sludge was determined and the percent of inhibition of respiration rate was calculated in comparison to a test solution without any test substance.

Under the test conditions, the highest test concentration, with 1000 mg a.s./L exhibited no inhibition of the respiration rate. In conclusion no adverse effect towards the respiration activity of the activated sludge was observed. The EC50 (3 hours) was determined to be > 1000 mg/L (nominal).

The sensitivity of the activated sludge to 3,5-Dichlorophenol was in the accepted range of 5 - 30 mg (EC50 for 3 hours incubation time). The test temperature was in the required range of 20 +/- 2 °C. Hence, the validity criteria required by the guideline were fulfilled.



The experimental results indicate that the test item has no adverse effects towards the respiration activity of the activated sludge for concentrations of up to 1000 mg/L. The EC50 and EC10 (3 hour) for the test item were greater than 1000 mg a.s./L.