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Toxicity to microorganisms

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Description of key information

Activated sewage sludge respiration inhibition.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
15 mg/L

Additional information

The effect of the test substance on activated sludge microorganisms was assessed by the Activated Sludge Respiration Inhibition Test Method (OECD Guideline 209) under conditions of Good Laboratory Practice.

The test contained control, reference and treatment groups. The control group was used to determine the background respiration rate of the sludge and was not dosed with TBBPA or the reference substance. The reference group was dosed with 3,5-dichlorophenol, a known inhibitor of respiration, at nominal concentrations of 3, 15, and 50 mg/L. TBBPA was dosed at a limit concentration of 15 mg/L in triplicate. After an exposure period of approximately three hours, the respiration rates of the test solutions were measured using a dissolved oxygen meter.

The individual respiration rates of the two controls were 15.3 and 17.1 mg O2/L/hr. The difference between the two control respiration rates was 10.5% and was within the 15% difference limit established for the test. The validity of the test was further supported by the results from the 3,5-dichlorophenol reference group, which resulted in an EC50 of 9.6 mg/L. This EC50 value for the reference substance was within the 5 to 30 mg/L range considered acceptable for the test.

Minimal inhibitory effects upon respiration were observed at a TBBPA concentration of 15 mg/L. The average respiration rate for the treatment group was 15.9 ± 0.0 O2/L/hr and was slightly lower than the average respiration rate of the control (16.2 ± 1.3 mg/L/hr).The average percent inhibition observed was approximately 1.9%. The EC50 was therefore >15 mg/L.

With there only being 1.9% difference between the control and test samples, it is considered that there is no significant difference; the dose level of 15 mg/L can therefore be considered to be a NOEC as the level of respiration observed in the test vessels is within the range of the controls.