Low Dose Rate Irradiation Facility: initial study on chronic exposures to medaka.

Uncertainties associated with the effects from chronic low-level exposures to radiation prompted us to construct a Low Dose Rate Irradiation Facility (LoDIF). The facility was designed specifically to test the appropriateness of the 10 mGy d(-1) guideline often espoused as acceptable for protection of aquatic biota from ionizing radiation. Scientists at the 0.4 ha facility use 40 outdoor mesocosms and 137Cs irradiators of three different source strengths to research the effects of chronic low-level irradiation at different levels of biological organization. A description of the facility is included along with results from a pilot study in which Japanese medaka (a small fish native to Asia) were chronically irradiated at the highest dose rate possible within the facility (350+/-150 mGy d(-1)). Irradiated fish produced fewer eggs per day (p=0.03); had a lower percentage of viable eggs (p=0.04), and produced a lower percentage of hatchlings (p=0.05). Although these data are not surprising based on the relatively high dose rates, they are important to future work at the LoDIF because they confirm the utility of our chosen model organism for detecting population-level responses, and they illustrate the statistical power achieved from using replicated mesocosms, in that statistical significance was achieved with few replicates per treatment. Future directions for the LoDIF are presented, as well as an invitation for interested researchers to participate in our studies.