Envirhom-Eco reflects the radioecological research priorities and aims defined by the European Radioecology Alliance as described in the Strategic Research Agenda (SRA). One of the three aims of this research agenda is to mechanistic understanding of the processes inducing radiation effects at different levels of biological organisation, including the consequences on ecosystem integrity, and be able to accurately predict effects under the realistic conditions in which organisms are actually exposed. Understanding the aforementioned effects also involves putting forward and justifying the methods and knowledge required to build the environment's radiation protection system. The main aims of Envirhom-Eco are therefore to help answer several questions:
What are the exposure levels at which the protection of ecosystems is guaranteed? Protection criteria, which are essential to assess and manage the risk to ecosystems, are determined on the basis of the relationships between the level of exposure (expressed as a dose or dose rate) and the responses of the physiological functions of species that are representative of the structure of the ecosystems.
Can the responses of these species observed on a macroscopic level be linked to indicators (biomarkers of exposure and effect) of the toxic modes of action of the stressors studied (taking account for the type of radiation, the exposure pathway, etc.)?
While the basic mode of action of ionising radiation is relatively well known on a molecular level, the harmful consequences on higher levels of biological organisation (cell, tissue, organ, individual, population, community, ecosystem) remain complex and hard to predict over the long term and under real exposure conditions in situ. High-throughput screening tools and advanced methods which use specific biomarkers to qualify and quantify damage to the genome and epigenome now let us follow new lines of research to understand the mechanisms governing the propagation of responses at several levels of organisation within living organisms and multi-generational responses of populations of animal and plant species chronically exposed (maternal effect, hereditary effects, adaptive responses, genomic instability). The knowledge acquired and the methods and models developed within Envirhom-Eco supplement environmental expertise which is used to assess and manage the risk to ecosystems which are subject to chronic exposure situations (Risque-Eco programme).
The Envirhom-Eco programme (and its operational application through the Risque-Eco programme) therefore aims to better understand the processes by which organisms are exposed to radionuclides, to identify the mechanisms responsible for the biological effects and to link disorders observed among individuals with effects on higher ecological organisation levels (populations, communities, ecosystems). The approach suggested goes beyond the traditional approach used in ecotoxicology (establishing a dose-effect relationship) by focusing on an innovative approach that aims to understand (and model) the relationship between the responses of the molecular targets and the various higher organisation levels of the living organism.
Five main lines of research have been defined:
- study of interactions between living organisms and their environment: the aim is to understand and quantify the influence of environmental factors on the bioavailability of radionuclides and their bioaccumulation in animals and plants;
- identification of the effects of radionuclides on the reproduction and, more generally, on the 'life cycle' of organisms: depends on the proposal of effect criteria specific to the ecosystems' different animal and plant groups and validated through laboratory or in situ experimental observations;
- identification of the molecular mechanisms of ecotoxic responses: the aim is to understand the modes of action and cascade reactions, characterise damage and repair to DNA, identify molecular targets, understand the effects on the individual and uncover radio-sensitivity differences within a species (e.g. difference in sensitivity between different organs and tissues, one stage of life and another) and between species;
- identification and understanding of interaction processes between contaminants in a mixture (stable metals, organic substances, radioactive substances): depends on understanding and modelling interactions at the time of exposure (accumulation and elimination dynamic) and interactions related to the effects (e.g. synergy, antagonism);
- determination of the ecological consequences and the capacity to adapt to chronic exposure: strengthened since 2010 in particular thanks to cooperation with Ineris and Université du Québec à Montréal, this line of research aims to carry out experimental tests on various types of animals (for example, Caenorhabditis elegans, a nematode), the transmission of genetic and phenotypic characteristics to offspring (natural selection phenomenon).
The developments are based on compared ecotoxicology studies for various types of ionising radiation (α,β,γ) and/or radionuclides (i.e. tritium, uranium, caesium). These studies are carried out on a collection of laboratory plant and animal models (bacteria, micro algae, higher plants, crustaceans, molluscs, insects, fish) and rely on the Ecoritme platform. Ecoritme is an integrated technical platform (analytical equipment, breeding of organisms, exposure laboratories) which allows experiments to be carried out under controlled conditions for several biological models with, or without, radioactive tracers, ionising radiation and chemical elements such as metals.
This knowledge, which is acquired under controlled conditions, is supplemented by work in natura, particularly in Chernobyl's exclusion zone, the 100-km site around the stricken Fukushima Daiichi power plant and in areas affected by uranium-bearing mining sites.