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Toxicity to microorganisms

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Description of key information

This information requirement is waived, on the basis of Column 2 (Annex VII) guidance indicating that testing is not needed where the substance is readily biodegradable and PEC is below the test concentration applied.  

Key value for chemical safety assessment

Additional information

Biphenyl was shown to be readily biodegradable, in an OECD 301C study employing a mixed culture of microorganisms (30 mg/L dry solids) and 100 mg/L biphenyl. As the tested concentration is well above the water solubility limit (~ 7 mg/L) of the substance, and because the undissolved test substance occurs as a solid having slightly higher density than that of water, it can be concluded that the tested concentration is well above the PEC associated with any wastewater environment. The PNECstp is derived from the concentration employed in the OECD 301C test, which according to ECHA Chapter R10 guidance (2008) is derived from an assessment factor of 10 applied to this tested concentration. PNECstp is therefore 10 mg/L.

Five studies are provided as weigth-of-evidence to show that NOEC and effect concentrations are near the solubility limit of the substance. Since none of these studies has reliability suitable for use in the chemical safety assessment, none can be used to derive PNECstp. Rogerson et al. (1983) investigated the survival of the ciliate Colpidium colpoda after 18 h of exposure in an open test system and of Tetrahymena elliotti after 24 h of exposure in a closed test system. The test with C. colpoda was conducted in a covered open test system and revealed no significant effect at the highest concentration tested, i.e., 6.3 mg/L. The test with T. elliotti was conducted in a closed test system without headspace to avoid loss of biphenyl through evaporation and – similarly – did not reveal significant effects at the highest concentration tested, i.e., 6.3 mg/L. For Colpidium campylum, a 43-h LOEC of 5.6 mg/L was determined for biphenyl based on the endpoint growth (Dive et al., 1980). The test was conducted in an open test system and some loss of biphenyl may have occurred. Finally, a 40-h TETRATOX assay with Tetrahymena pyriformis resulted in an EC50 value of 13.7 mg/L (Schultz, 1999). Biphenyl concentrations were not measured but loss of biphenyl through evaporation may be considered limited because the test vessels were closed (foam stopcock). The test vessels however contained a headspace filled with air to which biphenyl may have evaporated during the test. Schultz (1999) used a carrier solvent and the EC50 value was above the water solubility of biphenyl. Taking into consideration all available information, a weight of evidence approach resulted in a reasonable worst case LOEC of 5.6 mg/L (Dive et al., 1980). No NOEC was reported by Dive et al. (1980), however, based on the information in the publication, it can be assumed that the test concentration series 1.8 – 3.2 – 5.6 – 10.0 mg/L was used and therefore the NOEC can be assumed to be 3.2 mg/L. Based on the weight of evidence approach the endpoint requirements can be considered fulfilled in a reliable way. In case necessary, some further information e.g. from biodegradability screening tests may be added to the weight of evidence approach.