Biphenyl

Toxicity to aquatic algae and cyanobacteria

Description of key information

Only two studies were identified reporting results of algal growth inhibition tests. One study was conducted as part of a testing program organized by the Japanese Ministry of the Environment, however, the full study report was not available and therefore the reliability of the results of this study could not be evaluated. The other study was available but was considered not reliable. Therefore, QSAR predictions were added to the available information, among with a prediction by the latest version of US EPA's ECOSAR (2009), which can be considered reliable. Further, two studies were added for read across purposes, one with diphenyl oxide, a structurally related compound, and the other with Therminol VP1, which is an eutectic mixture of diphenyl oxide and biphenyl containing 26.3% biphenyl. These studies were not reliable because test concentrations were not verified. All information mentioned above was considered sufficient for covering this REACH endpoint using a weight-of-evidence approach. The key values for the aquatic hazard assessment were the 96-h EC50 of 1.772 mg/L estimated by ECOSAR v.1.00 and a 96-h NOEC of 0.66 mg/L estimated based on the chronic value predicted by ECOSAR v.1.00.

Key value for chemical safety assessment

EC50 for freshwater algae:

1.772 mg/L

EC10 or NOEC for freshwater algae:

0.66 mg/L

Additional information

The only available experimental study (Hutchinson et al., 1980) investigated the effect of biphenyl on photosynthesis of the unicellular algae Chlorella vulgaris and Chlamydomonas angulosa and reported 3-h EC50 values of 3.86 and 1.28 mg/L, respectively. However, the study could not be considered reliable because of several reasons. The study conducted by the Japanese Ministry of the Environment was not available and therefore its reliability could not be evaluated. This study was claimed to be conducted according to OECD guideline 201 and GLP and reported a growth rate-based 72-h EC50 and NOEC of 0.78 and 0.007 mg/L, respectively. Because it is suspected that the spacing factor between the (most likely) measured concentrations was way too high, and because the NOEC is dependent on this, the NOEC was considered not reliable and should not be used in a weight of evidence approach. Instead, the EC50 value should be used. Further, non-testing data have been added to the dossier consisting of 1) predictions of a 96-h EC50 and chronic value of 2.121 and 0.587 mg/L, respectively, using an outdated version of ECOSAR (ECOWIN v.0.99e, 2000) (Escuder-Gilabert, 2001), 2) a 96-h EC50 of 1.47 mg/L predicted by a not further specified QSAR (Vighi et al., 2001), and 3) predictions of a 96-h EC50 and chronic value of 1.772 and 0.945, respectively, using the latest version of ECOSAR (v1.00, 2009) and using input values of 4.0 for log Kow, 69°C for melting point, and 7.35 mg/L for water solubility. The latter predictions were considered as the most reliable data available for biphenyl toxicity to algae and were consistent with all other non-testing and testing results. Therefore, these results were considered as key values for the chemical safety assessment. Because a chronic value represents the geometric mean of NOEC and LOEC, a NOEC was estimated of 0.66 mg/L, assuming a maximum spacing factor of 2 between adjacent test concentrations. Finally, the testing data with diphenyl oxide and Therminol VP1 (eutectic mixture of diphenyl oxide and biphenyl) yielded a 96-h EC50 and NOEC of 2.5 and 1.2 mg/L, respectively, for pure diphenyl oxide, and 1.3 and 1.0 mg/L, respectively, for the eutectic mixture containing 26.3% biphenyl. These experimental results indicate that the toxicity of biphenyl and diphenyl oxide is comparable or that biphenyl may be slightly more toxic to algae than diphenyl oxide. The EC50 and NOEC predicted by ECOSAR and used for the chemical safety assessment are in line with the outcome of this comparison and therefore additional testing for the toxicity of biphenyl to algae is considered not needed.