All living organisms are daily exposed to ionizing radiation coming from natural sources. However, due to anthropogenic activities exposure to radionuclides and radiation can be locally increased. For example the nuclear accident of Chernobyl in 1986 has led to a vast area contaminated with different radionuclides leading to increased radiation exposure of this ecosystem. Lab-based studies as well as improved dosimetry have reduced the uncertainties related to impacts on individual organisms. However, further refinement is needed as in field situations organisms are usually (i) chronically exposed within or even over generations, (ii) in a multiple stressor context (iii) and live in communities in which they interact and compete with other species. It is the aim of this PhD to study the long-term effects (over multiple generations) at different levels of biological complexity (from molecular to population and community level) in a duckweed species (Lemna minor) exposed to environmental relevant concentrations of different genotoxic radionuclides linked to possible nuclear accidental scenario’s (137Cs, 90Sr). Lemna minor was chosen as it is a model organisms within ecotoxicology and the only freshwater plant for regulatory toxicity testing for chemicals. In addition we have extensive experience studying the toxicity and molecular responses in this organisms to different radionuclides or to gamma radiation. This PhD will take the results of previous studies further by testing the response of a set of potential biomarker genes as well as changes in (epi)genetic marks in exposure scenarios relevant for studying the long term effects of a nuclear accident on the environment. Uniquely to this PhD will be that for the first time the response of Lemna minor plants collected alongside a gradient of contamination will be compared and studied at different levels of biological complexity including in a small food chain. We hypothesise that (i) long-term exposure to low levels of nuclear accident related radionuclides will lead to profound changes in growth and metabolisms in Lemna minor (ii) Key changes in epigenetic marks or molecular endpoints occur and that these can be linked to higher population relevant endpoints. (iii) that Lemna plants with a radiation history or challenged by other stressors (U, Cd or herbivory) show a different sensitivity towards radiation potentially indicating radiation-induced adaptive responses. In order to test these hypotheses both lab and field experiments will be set up in which endpoints at different levels of biological complexity (from (epi)genetic to population/community level) are followed in naive and field collected Lemna plants and in different environmental relevant scenario’s. Field experiments will be performed in the Chernobyl exclusion zone in Ukraine. Ultimately bi-species foodchain model (Lemna-Gammarus) will be used to test the response of Lemna at community level.
The outcome of this PhD will lead to a better understanding of the long-term impact of ionising radiation in plants and will be used to build more robust environmental radiation protection approaches.
The availability of this topic depends on the outcome of the evaluation of the HARP project proposal.