Biphenyl

Endpoint summary

Additional information

From the available information it was clear that hydrolysis and direct phototransformation in air and/or water will not contribute much to the degradation of biphenyl in the environment. The only relevant abiotic process is indirect phototransformation in air through reaction with photochemically-generated hydroxyl radicals, which is estimated to occur at a half-life of 16 h at hydroxyl radical concentration of 1.5 million OH molecules/cm3. Overall, biodegradation is the most important degradation process affecting fate and lifetime in aquatic and terrestrial compartments. Biphenyl has been demonstrated to be readily biodegradable. Additionally, simulation studies in water and water/sediment systems yielded half-lives of 2-3 days in water and 2-10 days in water/sediment (at 20 and 22°C, respectively).

Relevant processes which influence the distribution of biphenyl in the environment are volatilization, advection, adsorption, and bioaccumulation. No experimental data have been identified on the partitioning between air and water. EUSES calculates a Henry's Law constant for biphenyl of 25 Pa/m3/mol (at 25°C), indicating that the molecule may undergo volatilization from aqueous solutions. A major process determining the distribution of biphenyl in the environment is adsorption. Based on measured adsorption of the subsance in several different soils, an average log Koc of the substance was determined to be 3.19, whereas strong binding to soil is generally indicated by log Koc > 4. It is noteworthy that biodegradation studies in sewage sludge and natural soils indicate that biphenyl remains available for microorganisms and can still be degraded in the partly adsorbed form. Finally biphenyl is easily taken up by organisms but does not tend to be highly bioaccumulative. Studies investigating both total bioaccumulation (total 14C-based) as well as the distribution of accumulated 14C-activity between parent and metabolites indicated that when based on concentrations of parent biphenyl the BCF factors are much lower. A conservative BCF value of 1900 L/kg (wet weight, based on total accumulated biphenyl and metabolites) in fish will be used in the chemical safety and PBT assessments.