Mercury (Hg) is an important pollutant distributed all over the world, in the atmosphere, onto continents and inside oceans. It can be accumulated and bioamplificated in aquatic food chains where concentrations of its main toxic form, monomethylmercury (MMHg), reach level potentially dangerous for human health. The main goal of the RIMNES-Project is to propose innovative geochemical and biological tools at the link between Environment and Health. Recent interest leads us to develop a new tracer tool which might characterize the different types of Hg exposure, not only in developed countries but also in emerging regions. The first objective is to understand Hg processes and transformation in the environment. Very recently, stable isotope signatures have been recognized as a powerful tool to trace processes and sources of Hg. We propose to use this method to analyze environmental samples in two contrasted regions impacted by Hg polluting activities: 1) in French Guiana, along the Oyapock R. where numerous artisanal gold-mining activities lead to recurrent environmental, social and economic pressure; and 2) in the Guizhou Province known as the “mercury capital” of China. High Hg concentrations in human hair of populations living in the selected areas have already been evidenced and attributed to food exposure (fish diet in French Guiana and rice consumption in China). Our recent studies have demonstrated that Hg isotope signatures in human hair provide qualitative and quantitative information on MMHg sources related to human exposure via diet. A focus on the trophic chain, through bedrock, sediments, biofilms, fish and rice analyses, will permit to understand Hg isotopes fractionation before absorption of MMHg by human. Additionally, an experimental study, consisting in feeding adult male zebrafish with contaminated food (MMHg and inorganic Hg), will allow us to highlight Hg isotopes fractionation in their organs (brain, liver and muscle) by metabolic processes. The second objective is to better understand the mechanisms of action of Hg species in fish and in human cells. MMHg contamination will be analyzed from aquarium and Oyapock river fish through genomic and cell biology approaches. The study will first focus on gene cluster expression relevant to metabolic pathways such as detoxification, oxidative stress, apoptosis and newly identified Notch pathway. This genomic study will be accompanied by the setting up of human cell lines dedicated to the analysis of the newly identified MMHg-dependent Notch pathway. Identified biomarkers will allow designing new informative genomic and biomarker-based cell assays. It is important to notice that the genomic and cell based studies dealing with MMHg-dependent Notch pathway activation will provide the very first data available on both fish and human models. At the end of the project, biomarker assays will be delivered in high throughput format in order to provide biomonitoring tools for in situ MMHg toxicity measurement. The strengths of this project are related to 1) its methodology combining experimental studies with natural environment sampling, 2) its originality by coupling geochemical with biological innovating methods to trace Hg sources and effects on living organisms in contaminated environments and 3) its exclusivity as we are the unique research group in the world working on the Hg isotope fractionation in human tissue.

Carbon nanotubes (CNTs) represent an emerging nanomaterial for a wide range of applications both in materials science and biomedicine. The increasing production of CNTs, their processing and eventual incorporation into new types of composites and/or into biological systems has raised fundamental issues on the impact of CNTs on health and environment. In the context of studies on the environmental release of CNTs, accumulation and degradation of CNTs are very limited. Potential exposure routes are multiple. Depending on the life cycles of the products and their fate, CNTs may cause different environmental health effects. Indeed, the CNTs can reach the environment and eventually accumulate along the food chain. The study of the destiny of the types of CNTs released in the environment is important to avoid possible risks of contamination, pollution and damages to the living systems. As CNTs will be disseminated in the environment at some concentration, terrestrial and aquatic microorganisms coming in contact with the CNTs will integrate such materials and eventually try to eliminate using their metabolic capacities of degradation. In this context, the main objective of the DECANO project is to study the interactions between functionalized CNTs and bacteria. We will explore the possibility that these bacteria, possessing high enzymatic activities (i.e. oxidative action), could carry out the degradation of CNTs. Recent studies by the group of Star showed the capacity of peroxidases to degrade CNTs in the presence of low concentrations of hydrogen peroxide. We will perform in silico studies to identify new oxidative enzymes into the available genomic and metagenomic data banks capable of degrading CNTs. We will also assess the potential toxicity of products arising from the degradation of CNTs. Pristine CNTs are extremely difficult to manipulate due to solubilization/dispersibility problems and manufactured products often incorporate nanotubes that have been previously modified. As a consequence, we have chosen to study functionalized CNTs rather than pristine material. Thus, carboxylated double- and multi-walled carbon nanotubes and further modified CNTs will be investigated in DECANO for the identification and selection of enzymes capable of biodegradation. We will identify the fragments derived from the degradation of CNTs and their potential use as carbon source by bacteria. For this purpose, 13C-labeled CNTs will be used and 13C-enriched biomolecules potentially integrated into the microorganisms will be identified. In parallel, we will analyze the impact of CNTs and their biodegradation products on the bacterial populations and the ecotoxicity on an amphibian model. The ultimate goal of the DECANO project is the development of bioremediation processes of CNTs involving naturally occurring bacterial systems. It is highly important as the production of CNTs and the integration of CNTs in products available on the market are exponentially growing, along with the risk of contamination of the environment with CNTs. The results gathered in the DECANO project could lead to a natural route to reduce the potential contamination risk of CNTs in the environment.