The effects of waterborne uranium on the hatching success, development, and survival of early life stages of zebrafish (Danio rerio)

In this study, we investigated the effects of the radioactive metal uranium (U) on the embryonic development, hatching success, growth rate, and survival of juvenile zebrafish (Danio rerio). We studied the effects of depleted uranium (20-500 μg L−1 of DU), inducing mainly chemical toxicity due to its low specific activity, and the combined effects of chemical and radiological toxicity by using a higher specific activity uranium isotope (20 and 100 μg L−1 of 233U). Results showed that early life stages are significantly affected by uranium exposure through both chemical and combined (chemical and radiological) toxicity. Experiments showed significant effects of U on hatching success starting at the concentration of 250 μg L−1 of DU, causing a 42% delay in median hatching times relative to control. Furthermore, a reduction of growth (decrease in body length and weight) was observed followed by a high mortality of pro-larvae stage (up to 100% at DU concentrations of 250 μg L−1 upon a 15 day exposure). Bioaccumulation measurements highlighted that U was mainly localised in the chorion but penetrated in the embryo inside eggs at a higher concentration. The effects differed depending on the isotopic composition of the uranium: sublethal defects in the tail detachment process were more pronounced for 233U than DU exposure, while the presence of 233U specifically affected embryo development and led to higher mortality rates of the prolarvae. The results from this study showed that the early life stages of zebrafish seems to be more sensitive to uranium contamination than more mature stages, and underline the importance of including pro-larval stages into toxicity tests in order to improve the relevancy for environmental risk assessments.