Low-dose neutron dose response of zebrafish embryos obtained from the Neutron exposure Accelerator System for Biological Effect Experiments (NASBEE) facility

The dose response of embryos of the zebrafish, Danio rerio, irradiated at 5h post fertilization (hpf) by 2-MeV neutrons with ≤100mGy was determined. The neutron irradiations were made at the Neutron exposure Accelerator System for Biological Effect Experiments (NASBEE) facility in the National Institute of Radiological Sciences (NIRS), Chiba, Japan. A total of 10 neutron doses ranging from 0.6 to 100mGy were employed (with a gamma-ray contribution of 14% to the total dose), and the biological effects were studied through quantification of apoptosis at 25hpf. The responses for neutron doses of 10, 20, 25, and 50mGy approximately fitted on a straight line, while those for neutron doses of 0.6, 1 and 2.5mGy exhibited neutron hormetic effects. As such, hormetic responses were generically developed by different kinds of ionizing radiations with different linear energy transfer (LET) values. The responses for neutron doses of 70 and 100mGy were significantly below the lower 95% confidence band of the best-fit line, which strongly suggested the presence of gamma-ray hormesis. •Neutron dose response was determined for embryos of the zebrafish, Danio rerio.•Neutron doses of 0.6, 1 and 2.5mGy led to neutron hormetic effects.•Neutron doses of 70 and 100mGy accompanied by gamma rays led to gamma-ray hormesis.