Benzophenone

Phototransformation in water

Description of key information

After irradiation of aqueous solutions of benzophenone with artificial UV or sunlight 4 -hydroxy and 3 -hydroxybenzophenone were identified as photoproducts. The photodegradation of benzophenone at low concentrations in pure water, East Lake water, and Changjiang River water was examined. The wavelength-averaged (250 -350 nm) quantum yields of benzophenone were determined to be 0.0013 +/- 0.001. Half-life times (1/2) of 16.23, 10.62, and 8.672 h were determined for the photlytic degradation of benzophenone in pure water, East Lake water, and Changjiang water. It could be shown that the presence of Cl(-), Fe(3 +), and humic acids, the initial benzophenone concentration, a continuous benzophenone input, the presence of benzophenone analogues influenced the degradation rate.

Key value for chemical safety assessment

Half-life in water:

10.62 h

Additional information

After exposure of aqueous solutions of benzophenone to artificial UV light or sunlight 4 -hydroxy and 3 -hydroxybenzophenone were identified as phototransformation products via HPLC/MS. It could be shown that reactive oxygen species were involved in the ring hydroxylation of benzophenone. The benzophenone concentration-dependent H2O2 generation indicates that benzophenone can act as a photosensitizer.

Benzophenone was shown to be photodegraded at low concentrations in pure water as well as in non-polluted surface water from East Lake and Changjiang River (Wuhan, China). Dark controls were performed. The wavelength-averaged (250 -350 nm) quantum yields of benzophenone were determined to be 0.0013 +/- 0.001. Based on the different medium compositions different kinetic parameters were observed: Half-life times (1/2) of 16.23, 10.62, and 8.672 h were determined for the photlytic degradation of benzophenone in pure water, East Lake water, and Changjiang water. The removal of benzophenone was faster obviously in the presence of Cl(-), Fe(3 +), and humic acids. The effect of the initial benzophenone on the photodegradation was also studied. The photodegradation rate of benzophenone decreased as the initial benzophenone concentration in water was increased. The decay of the photodegration rate with increasing benzophenone concentrations followed approximately an exponential function. The continuous input of benzophenone resulting in an equal initial benzophenone concentration resulted in an obvious decrease in degradation rate of benzophenone. The half-life t1/2 for benzophenone dissolved in pure water increased from 16.23 h to 36.46 h after four times of concentration recovery. In tests simulating the natural conditions, the presence of benzophenone analogues could reduce the photodegradation rate of benzophenone while the presence of benzophenone non-analogue did not influence the degradation rate significantly.