Nickel difluoride

Toxicity to microorganisms

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

EC50 for microorganisms:

54 mg/L

Additional information

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.

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. Data reported on individual bacterial species like Microtox (with Vibrio fisherias test organism), Pseudomonas putida, Pseudomonas fluorescens and even Escherichia coli are considered as less relevant than those from mixed inoculum.

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 EC₅₀of 33 mg/L.

CONCLUSION EC50 33 mg/L Ni = 54 mg/L

FOR AN EXTENSIVE DISCUSSION, REFER TO THE NICKEL SULFATE DOSSIER WHICH IS BASED ON THE CONCLUSIONS EXPLAINED IN THE 2008/2009 EUROPEAN UNION EXISITING SUBSTANCE RISK ASSESSMENT OF NICKEL (EU RAR) (EEC 793/93)