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Toxicity to microorganisms

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Description of key information

The effect of DTDM on the respiration rate of activated sludge was assessed by the methods detailed in EC Directive 440/2008, Method C.11, ‘Biodegradation - Activated Sludge Respiration Inhibition Test’ and OECD Test Guideline 209, ‘Activated Sludge, Respiration Inhibition Test’. The three-hour EC50 for DTDM was calculated to be 759 mg/L (95% confidence limits, 384 to 1780 mg/L). The EC20 was calculated to be 40.5 mg/L (95% confidence limits, 8.1 to 134.0 mg/L); the EC80 could not be calculated.

Key value for chemical safety assessment

EC50 for microorganisms:
759 mg/L

Additional information

The effect of DTDM on the respiration rate of activated sludge was assessed by the methods detailed in EC Directive 440/2008, Method C.11, ‘Biodegradation - Activated Sludge Respiration Inhibition Test’ and OECD Test Guideline 209, ‘Activated Sludge, Respiration Inhibition Test’.

Samples of activated sludge (suspended solids 1.6 g/L), fed with synthetic sewage, were exposed to dilutions of the test substance for three hours. Their rates of oxygen consumption were determined using an oxygen electrode and were compared with those of controls that contained activated sludge and synthetic sewage alone and were established at the beginning and end of the test.

The specific respiration rate of the control culture established at the end of the test (Control 2,30.0 mgO2/g/h) was 106% of the rate established at the start (Control 1, 28.3 mgO2/g/h). The three-hour 50% effect concentration (EC50) for 3,5-DCP was calculated to be 9.9 mg/L (95% confidence limits, 6.7 to 14.7 mg/L). These results show that the sample of activated sludge employed was sensitive to inhibition.

Inhibition of respiration rates were observed at DTDM concentrations between 100 mg/L and 1000 mg/L with the highest concentration (1000 mg/L) showing 48 to 52% inhibition (mean 50%).

The three-hour EC50 for DTDM was calculated to be 759 mg/L (95% confidence limits, 384 to 1780 mg/L). The EC20 was calculated to be 40.5 mg/L (95% confidence limits, 8.1 to 134.0 mg/L); the EC80 could not be calculated.