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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

3-Hour EC50 = 928 mg/L based on calculation.  EC50 > 1000 mg/L based on actual percentage inhibition (41% at 1000 mg/L).

3-Hour NOEC = 30 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:
928 mg/L
EC10 or NOEC for microorganisms:
30 mg/L

Additional information

An Activated Sludge Respiration Inhibition Test (ASRIT) was performed (Huntingdon Life Science, 2013) to assess the effect of MTF on sewage microorganisms. The study was conducted according to OECD test guideline 209 and in compliance with GLP.

Samples of activated sluge taken from a supply which treats predominantly domestic waste were exposed to nominal MTF concentrations 10, 30, 100, 300, and 1000 mg/L. The rate of oxygen consumption of these solutions over three hours were compared to that of a concurrent control solution; four replicate samples were used for each concentration including the control.

The mean respiration rates of the sludge exposed to MTF was significantly decreased by 21% at 100 mg/L, 37% at 300 mg/L and 41% at 1000 mg/L. Based on these data, an EC20 value of 105 mg/L (95% confidence limits of 28.5 and 388 mg/L) was calculated and the EC50 value was estimated to be 928 mg/L (95% confidence limits of 453 and 1904 mg/L) although based on percentage inhibition, the EC50 was >1000 mg/L (41% inhibition).

The no observed effect concentration (NOEC) for MTF was 30 mg/L (p>0.999).