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Toxicity to microorganisms

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Description of key information

A nitrification inhibition test with Zn sulfate on activated slugde originating from a municipal wastewater treatment plant was performed leading to a NOEC of  100 µg Zn/L.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
100 µg/L

Additional information

Several data were available for this endpoint. Formerly (ECB 2008), and in the REACH-registrations of a number of zinc substances of November 2010, a PNEC of 52 µg/L for STP was derived, based on the lowest EC50 of 5.2 mg Zn/L observed in a sludge respiration inhibition test (Dutka et al. 1983). According to the guidance (ECHA 7.8.17.1) preference should be given to nitrification inhibition because respiration inhibition is a less sensitive endpoint. A study conducted by Juliastuti et al. (2003) reported a NOEC of 0.1 mg Zn/L in an ISO 9509 nitrification inhibition test. Applying the rules for PNEC setting (ECHA R.10, table R.10.6) this result yields a PNEC STP of 100 µg Zn/L (AF of 1).