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Toxicity to microorganisms

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Description of key information

The 24-hour IC50 for inhibition of nitrification by members of the genus Nitrosomonas was 21 mg/L phenol.  

Key value for chemical safety assessment

EC50 for microorganisms:
21 mg/L

Additional information

Four toxicity studies with various components of the reaction mass of phenol and 4,4’-isopropylidenediphenol are summarized for the toxicity to microorganisms endpoint. In a valid toxicity study (Klimish = 2), inhibition of nitrification by members of the genus Nitrosomonaswas examined in response to a 24 hour exposure to phenol, and the IC50 was reported as 21 mg/L phenol. Two valid growth inhibition studies (Klimish =2) with Bisphenol A (a.k.a 4,4’-isopropylidenediphenol) were conducted with Psedomonas putida and also Pseudomonas fluorescens. In the growth inhibition study with P. putida,the 18-hour EC10 was reportedly greater than 320 mg/L Bisphenol A.  In the growth inhibition study with P. fluorescens,the 16-hour IC50 was 54.5 mg/L Bisphenol A.  A valid activated sludge respiration inhibition test (Klimish = 2) was conducted with 2-acetone, polymer with phenol (a mixture of some of the major and minor components of the reaction mass of phenol and 4,4’-isopropylidenediphenol). The 3-h EC50, based on respiration inhibition, was 4539 mg/L 2-acetone, polymer with phenol. 

 

The lowest toxicity value for this endpoint was the 24-hour IC50 of 21 mg/L phenol based on inhibition of nitrification. Therefore, this value was selected as the key parameter for this endpoint and was used in deriving the PNECSTP.