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Toxicity to microorganisms

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Description of key information

The inhibition of the degradation activity of activated sludge is not anticipated when introduced in appropriate low concentrations.

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Additional information

In a GLP study, the inhibition of oxygen consumption by activated sludge was investigated according to OECD 209 (BASF SE 2010). Activated sludge was obtained from a municipal wastewater treatment plant, test concentrations ranged from 62.5 to 1000 mg/L (nominal). After 180 minutes incubation at 20 °C the respiration rates were recorded. An EC10 of 210 mg/l was determined. At 510 mg/L 50% inihibition was observed (EC 50), at 940 mg/L 80% inhibition. The PNECmico-organismswas derived from the EC10 using an assessment factor of 10.

Nalecz-Jawecki and Sawicki (1998) studied the effect of sodium nitrite on deformation (morphological changes such as shortening, bending of the cell, etc.) and mortality of Spirostomun ambiguum (protozoa). The 48 hour EC50 and LC50 were 421 and 533 mg/L (expressed as NaNO2), respectively. In addition, a poorly documented guideline study on the toxicity towards microorganisms from an industrial sewage treatment plant showed no effect on the respiration rate at the highest test concentration.

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