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Study of the toxicity of depleted uranium on Daphnia magna life and consequences for the population dynamics in a fluctuating environment

Delphine Plaire has defended her thesis on 12th December in Cadarache.

Document type > *Mémoire/HDR/Thesis

Keywords >

Research Unit > IRSN/PRP-ENV/SERIS/LECO

Authors > PLAIRE Delphine

Publication Date > 12/12/2013

Summary

Understanding how toxicants affect species at various levels of biological organization is a major research goal in both ecotoxicology and radioecology. As part of IRSN program ENVIRHOM, which aims to assess environmental risks related to the presence of radionuclides in the environment, this PhD work explored how depleted uranium alters DNA and affects life history traits (survival, growth and reproduction) of an aquatic invertebrate, Daphnia magna. To answer to this problematic, an experimental approach and a modeling approach are conducted. An experimental study is performed to evaluate DNA accumulation and transmission during an uranium exposure (0; 2; 9.9; 22.2 et 50 µg L-1) over two successive generations (F0 and F1). Different exposures scenarios (continuous, post-hatching and embryo exposure) are achieved to test the specific sensitivity of several life stages to uranium. Genotoxic effects are estimated using random amplified DNA technique combined with PCR (PCR-RAPD). In continuous and post-hatching exposure scenarios, results highlighted an accumulation and a transmission of DNA damage across generations with an increase in effect severity. DNA alterations are reported at hatching of the F1 generation at a concentration as low as 2 µg L-1. Effects on growth and reproduction are stronger when the embryo stage is exposed and remain visible at 9.9 µg L-1 despite a return in a clean medium at hatching. Results suggest that DNA damage could be used as early indicators of future effects on life history traits. A mechanistic analysis of experimental results is conducted using a DEBtox model (dynamic energy budget applied to toxicology) to better understand the causes of the increase in effect severity across generations. A model with two stress factors (one correlated to external concentration and another correlated to a damage level) is developed. Results of fits suggest the involvement of a second mode of action to explain immediate effects of uranium on nutrition and consequences of cumulated damage across generations. The nature of the second mode of action remains to precise, DEBtox fits pointing an increase in costs for growth and maturation.


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