Thesis: This work integrates within the general framework of the European program COMET (7th Framework Programme EURATOM) and aims to assess the epigenetic responses (particularly DNA methylation), during chronic exposure to low levels of radioactive materials. During a first experiment, zebrafish (Danio rerio) were exposed in laboratory controlled conditions to environmentally relevant concentrations of depleted uranium: 2 and 20 µg L-1. This experiment allowed an impact on the genomic DNA methylation to be demonstrated, mainly in exposed males, which increased with the duration and level of exposure. In a second experiment, we observed an impact on DNA methylation patterns in the progeny of exposed parents, as well as a perturbation of transcriptomic, and histological damage in larvae skeletal muscle from exposed parents.The methods developed were applied to the second context focusing on the study of biological effects induced by radionuclides emitted following the Fukushima Daiichi nuclear power plant accident. The analyses performed on the Japanese tree frog (Hyla japonica) revealed a positive correlation between the total dose of radiation absorbed by these frogs, hypermethylation of genomic DNA as well as increasing damage to mitochondrial DNA.This work highlighted the sensitivity of epigenetic responses in different biological models exposed to low levels of radionuclides, and could be used to further characterize adaptation mechanisms and potential transgenerational effects induced by radionuclides.