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Toxicity to microorganisms

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Description of key information

The 3-h EC50 value is >1000 mg/L for microorganisms in activated sludge from a sewage treatment system receiving predominantly domestic waste water. The EC10 is 221 mg/L (determined by linear regression). 

Key value for chemical safety assessment

EC50 for microorganisms:
1 000
EC10 or NOEC for microorganisms:
221

Additional information

A GLP compliant study was performed, according to OECD guideline 209, to determine the effect of different concentrations of tetramethyl bisphenol A on sewage microorganisms by measuring the respiration rate under defined conditions. At the termination of the test, the respiration rate for the two control vessels was determined to be 17.5 and 16.9 mg O2/L/hr, which met the acceptability criterion (i.e., within 15% of each other during the test). Respiration rate in the test substance test vessels (10, 100, 1000, 1000 and 1000 mg/L) was 16.8, 16.1, 13.5, 16.7 and 14.0 mg O2/L/hr, respectively. Compared to the controls, respiratory inhibition for the test substance test vessels was 2.4, 6.7, 21.3, 2.8 and 18.8%, respectively. Based on these results, the EC50 value was empirically estimated to be > 1000 mg/L. The EC10 (equivalent to a No-Observed-Effect-Concentration, NOEC) was determined by linear regression to be 221 mg/L.

Respiration rate in the reference substance, 3,5 -dichlorophenol, test vessels (1.0, 3.0, 10 and 30 mg/L) was 12.8, 11.8, 7.7 and 2.6 mg O2/L/hr, respectively. Compared to the controls, respiratory inhibition for the 3,5-dichlorophenol test vessels was 25.9, 31.5, 55.3 and 84.8%, respectively. Based on these results, the EC50 value for 3,5-dichlorophenol was calculated to be 7.7 mg/L, which was within the acceptable limits as specified in the OECD 209 Guideline.

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