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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

- A 30 min EC50 of 33 mg Ni/L (Cokgor et al 2007) was the only study carried forward for PNEC-STP derivation. 

Key value for chemical safety assessment

Additional information

Toxicity to microorganisms (STP)

Only a few internationally accepted test methods for microorganisms exist, such as the OECD N° 209 (inhibition of respiration of activated sludge) and ISO N° 9509 (inhibition of nitrification). Generally, short-term measurements (in terms of hours) are preferred, generally corresponding with typical retention times in biological STPs. The TGD (EC, 2003) suggests 10 h as a preferable test duration. Furthermore, the information available has to be relevant for the processes that are potentially at risk of disruption, e. g. microbial degradation activity in an STP. To assess risks to these processes, microbial endpoints such as respiration and nitrification inhibition are considered to be the most relevant. Testing using a mixed microbial inoculum is considered more relevant than using single-species inoculum. Thus information reported on individual bacterial species like Microtox (with Vibrio fisherias test organism), Pseudomonas putida, Pseudomonas fluorescens and even Escherichia coli are therefore considered as less relevant than those from mixed inoculum.

It should be noted that, unlike for some other environmental compartments (e.g., water and terrestrial compartment) there are currently no tools available for correcting the PNECmicro-organism for bioavailability. Therefore the effects assessment and risk characterisation for nickel in this compartment are based on non-normalised dissolved nickel concentrations.

Studies assessing the effects of nickel on ciliated protozoa (preferably T. pyriformis) and respiration/nitrification using bacteria originating from sewage treatment plants were regarded as directly relevant for the derivation of a PNEC STP. The key publication selected for Ni-PNEC STP derivation is Cokgor et al (2007). No other PNEC relevant studies that investigated the effects of Ni on bacterial populations were identified. However, the other studies in the database not deemed directly relevant, supported the relevancy and the conservative nature of an EC50 of 33 mg/L.