An integrated assessment of ceftazidime and photoproducts on the feeding behavior of rotifers: From exposure to post-exposure.

Compared to traditional toxicological studies, which depict the dose-effect of contaminants themselves on organisms at the given time, the exposure and post-exposure impacts of antibiotic ceftazidime and its photoproducts are carried out to systematically evaluate the environmental risk fate of ceftazidime in aquatic environments. For the exposure process, the promotion effect of ceftazidime on the feeding behavior of the rotifers decreased when the target compound was irradiated by sunlight, and the promotion effect was converted into inhibition effect, which indicated that the highest toxicity of ceftazidime on the feeding behavior of the rotifers was found after UV-B irradiation. The overcompensation occurred in the post-exposure, indicating a short - term effect of the corresponding photoproducts on the rotifer. In order to better understand the mechanism of this change, the photodegradation pathways of the target compound was analyzed and compared. The degradation degree under the UV-B irradiation had intensified greatly than that under the nature light irradiation. The reactive oxygen species (ROS) of the rotifer in exposure and post-exposure was also detected. Ceftazidime and photoproducts induced generation of ROS, indicating that oxidative damage occurred, and the decreasing of ROS levels could be viewed as the recovery of the rotifers in the post-exposure.

Electron spin resonance study of radiosterilization of antibiotics: ceftazidime.

Fundamental information on radiosterilization of ceftazidime was obtained by electron spin resonance (ESR) measurement of free radicals produced in gamma-ray-irradiated ceftazidime at 4.2-295 K. Three types of free radicals are produced by gamma-irradiation. The first one shows septet lines in an ESR spectrum and decays at 230 K: it is assigned as a .C(CH3)2COOH radical. The second one shows triplet lines and decays at 293 K: it is assigned as iminoxyl radicals (> C = N-O.). The third one shows a broad singlet line and survives even at 295 K. The plausible assignment of this spectrum is discussed. It is concluded that an O-C bond of the gamma-irradiated ceftazidime is ruptured, producing the iminoxyl radicals and .C(CH3)2COOH radicals. The yields of free radicals increase linearly with the increasing dose of gamma-irradiation up to 10 kGy at 295 K as well as 77 K. Half of the radicals that show a broad singlet line survive at 295 K upon storage of the irradiated ceftazidime for 159 days. It is concluded that the ESR measurement of free radicals gives a good method for discrimination of irradiated antibiotics from non-irradiated ones and an estimation of an irradiation dose.