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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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In a short term respiration test, performed similar to OECD guideline 209 and using ammonium chloride (CAS: 12125 -02 -9) as test substance, an EC50 of 1936 mg/L was determined (values refer to ammonium hydrogencarbonate, BASF AG 1988). Furthermore, in a single species test, using Pseudomonas putida as test organism and Ammonium hydrogencarbonate as test substance, an EC10 of 1347 mg/L was determined. Therefore, inhibition of degradation activity of activated sludge is not anticipated when introduced in appropriate low concentrations.

Suwa et al. (1994) investigated 14 strains of Nitrobacter spp. (ammonium oxidising bacteria) isolated from 25 different sludges including three sludges from primary sewage treatment plants and two sludges from nightsoil treatment plants. Nitrite production kinetic studies showed that insensitive strains (those which grew well at 4700 mg/l ammonium sulfate) showed Monod growth, while sensitive strains (those which grew at 94 mg/l but not at 4700 mg/l) followed Haldane kinetics. The results suggested that ammonium sulfate sensitive strains had a growth advantage in lower ammonium sulfate concentrations, while insensitive strains had a growth advantage at higher ammonium sulfate concentrations. Both sensitive and insensitive strains were found in the primary and night soil sludges, with the sensitive strains predominating. This explained the operational observations in several sewage treatment plants concerning the efficacy of nitrifying bacteria.