Combined effects of depleted uranium and ionising radiation on zebrafish embryos

In the environment, living organisms are exposed to a mixture of stressors, and the combined effects are deemed as multiple stressor effects. In the present work, the authors studied the multiple stressor effect in embryos of the zebrafish (Danio rerio) from simultaneous exposure to alpha particles and depleted uranium (DU) through quantification of apoptotic signals at 24 h post-fertilisation (hpf) revealed by vital dye acridine orange staining. In each set of experiments, dechorionated zebrafish embryos were divided into 4 groups, each having 10 embryos: Group (C) in which the embryos did not receive any further treatment; Group (IU) in which the embryos received an alpha-particle dose of 0.44 mGy at 5 hpf and were then exposed to 100 µg l(-1) of DU from 5 to 6 hpf; Group (I) in which the embryos received an alpha-particle dose of 0.44 mGy at 5 hpf and Group (U) in which the dechorionated embryos were exposed to 100 µg l(-1) of DU from 5 to 6 hpf. The authors confirmed that an alpha-particle dose of 0.44 mGy and a DU exposure for 1 h separately led to hormetic and toxic effects assessed by counting apoptotic signals, respectively, in the zebrafish. Interestingly, the combined exposure led to an effect more toxic than that caused by the DU exposure alone, so effectively DU changed the beneficial effect (hormesis) brought about by alpha-particle irradiation into an apparently toxic effect. This could be explained in terms of the promotion of early death of cells predisposed to spontaneous transformation by the small alpha-particle dose (i.e. hormetic effect) and the postponement of cell death upon DU exposure.