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Toxicity to microorganisms

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Description of key information

The lowest valid value for toxicity to aquatic microorganisms is a NOEC of 2.55 mg Sb/L and an EC50 of 27 mg Sb/L for inhibition of nitrification (EPAS, 2005).

Key value for chemical safety assessment

Additional information

One study that provided reliable data for toxicity to aquatic microorganisms has been identified. In this study (EPAS, 2005) the effect of SbCl3 on nitrification inhibition in activated sludge was assessed according to the ISO 9509 protocol (Water quality – Method for assessing the inhibition of nitrification of activated sludge micro-organisms by chemicals and waste waters). The protocol was slightly modified as the NH4-N concentration in the prescribed medium had an inhibitory effect on nitrification. The test was performed by aerating a nitrifying sludge in the presence and absence of Sb. The nominal Sb concentrations used ranged from 1.1 mg Sb/L to 1200 mg Sb/L. The protocol was modified by washing the sludge with tap water instead of demineralised water and medium because the proposed buffer was not sufficient to ensure a stable pH. By modifying the protocol this way, an activity in the sludge of 4.5 mg N/(g. h) could be calculated, which lies within the proposed interval of 2 to 6.5 mg N/(g. h). Each test solution was set up in duplicate. The flasks were incubated for 4 hours at a constant temperature and aerated in the dark. No inhibitory effects could be observed at a measured concentration of 2.55 mg Sb/L. Based on measured Sb concentrations an EC50 of 27 mg Sb/L was derived (confidence interval of 14-52 mg/L).