Minerals play a key role in the biogeochemical cycling of the elements at the Earth's surface, sequestering and releasing them as they undergo precipitation, crystal growth, and dissolution in response to chemical and biological processes. Manceau's research in this field focuses on the structure of disordered minerals (clays, iron (Fe) and manganese (Mn) oxides, including ferrihydrite and birnessite), on chemical reactions at their surface in contact with aqueous solutions, and on the crystal chemistry of trace metals in these phases.
Electron image of δ-MnO2 nanoparticles viewed parallel (a) and perpendicular (b) to the layer plane.Structure of a cylindrically bent layer of δ-MnO2 nanosheet.
In 1997, he and Victor Drits led the synthesis and resolution of the structure of hexagonal and monoclinicbirnessite, and they showed in 2002 that the monoclinic form possesses a triclinic distortion.[9][10][11] The hexagonal form prevails at the Earth's surface and owes its strong chemical reactivity to the existence of heterovalent Mn4+-Mn3+-Mn2+ substitutions and Mn4+ vacancies in the MnO2 layer. The Mn4+-Mn3+ and Mn3+-Mn2+ redox couples confer to this material oxidation-reduction properties used in catalysis, electrochemistry, and in the electron transfer during the photo-dissociation of water by photosystem II,[12] while the vacancies are privileged sites for the adsorption of cations. He has characterized and modeled a number of chemical reactions occurring at the birnessite-water interface, including those of complexation of transition metals (Ni, Cu, Zn, Pb, Cd...), and oxidation of As3+ to As5+, Co2+ to Co3+,[13][14] and Tl+ to Tl3+.[15] The oxidative uptake of cobalt on birnessite leads to its billion-fold enrichment in marine ferromanganese deposits compared to seawater.[16]
From 2002 to 2012, he applied the knowledge base acquired on the crystal chemistry of trace metals and biogeochemical processes at mineral surfaces and the root-soil interface (rhizosphere) to the phytoremediation of contaminated soils and sediments, and abandoned mine sites.[17][18][19] He contributed to improving the Jardins Filtrants® (Filtering Gardens) process for treating wastewater and solid matrices by phytolixiviation, phytoextraction, and rhizofiltration developed by the Phytorestore company.
Binding site of mercury (Hg) in selenoprotein P of grebe bird.
Mercury (Hg) is a global pollutant that is generated both by natural sources, such as volcanic eruptions and wildfires, and human activities, such as coal combustion, gold mining, and the incineration of industrial waste. In aquatic and terrestrial food chains, mercury accumulates as methylmercury (MeHg), a potent toxin that affects the function of animal's and human's brain and reproductive system. Understanding the internal detoxification processes of MeHg in living organisms is essential for protecting wildlife and humans, and designing treatments against mercury poisoning.
The new Hg(Sec)4 species identified by Manceau and his collaborators was the main “missing intermediate” in the chemical reaction that helps animals to survive high levels of mercury. However, because Hg(Sec)4 has a molar ratio of selenium to mercury of 4:1, four selenium atoms are required to detoxify just one mercury atom. Thus, Hg(Sec)4 severely depletes the amount of bioavailable selenium. Selenium deficiency can affect the function of animals’ brain and reproductive system, as selenoproteins serve critical antioxidant functions in the brain and testes.[27] His works on the Hg-Se antagonism won him the ES&T 2021 Best Paper Award.
The stepwise MeHgCys → Hg(Sec)4 + HgSe demethylation reaction is accompanied by the fractionation of the 202Hg and 198Hg isotopes, denoted δ202Hg. The δ202Hg fractionation measured on whole animal tissues (δ202Hgt) is the sum of the fractionations of the MeHgCys, Hg(Sec)4, and HgSe species, weighted by their relative abundance:
δ202Hgt = f(Spi)t × δ202Spi
where δ202Spi is the fractionation of each chemical species, and f(Spi) their relative abundance, or mole fraction. Manceau and his co-authors found that δ202Spi can be obtained by mathematical inversion of macroscopic isotopic and microscopic spectroscopic data.[26][28]
The combination of isotopic and spectroscopic data on birds and cetacea revealed that dietary methylmercury and the Hg(Sec)4-SelP complex are distributed to all tissues (liver, kidney, sketetal muscle, brain) via the circulatory system with, however, a hierarchy in the tissular percentage of each species. Most of the detoxification process is carried out in the liver, whereas the brain, which is particularly sensitive to the neurotoxic effects of mercury, is distinguished from other tissues by a low mercury concentration and a high proportion of inert HgSe. These results appear to be transposable to humans.[29]
Publications
Manceau has published more than 200 scientific papers in Science Citation Index journals totalizing more than 24,000 citations and garnering an h-index over 90.[30] In 2020, he was ranked 111th out of a total of 70,197 researchers in Geochemistry/Geophysics in a bibliometric study by scientists of the Stanford University based on the Elsevier Scopus database.[31]
The chalcogens are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioactive elements polonium (Po) and livermorium (Lv). Often, oxygen is treated separately from the other chalcogens, sometimes even excluded from the scope of the term "chalcogen" altogether, due to its very different chemical behavior from sulfur, selenium, tellurium, and polonium. The word "chalcogen" is derived from a combination of the Greek word khalkόs (χαλκός) principally meaning copper, and the Latinized Greek word genēs, meaning born or produced.
Selenium is a chemical element; it has the symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elemental state or as pure ore compounds in Earth's crust. Selenium was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium.
Selenocysteine is the 21st proteinogenic amino acid. Selenoproteins contain selenocysteine residues. Selenocysteine is an analogue of the more common cysteine with selenium in place of the sulfur.
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to other atoms were fully ionic. It describes the degree of oxidation of an atom in a chemical compound. Conceptually, the oxidation state may be positive, negative or zero. Beside nearly-pure ionic bonding, many covalent bonds exhibit a strong ionicity, making oxidation state a useful predictor of charge.
Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust.
Methylmercury (sometimes methyl mercury) is an organometallic cation with the formula [CH3Hg]+. It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It is a bioaccumulative environmental toxicant with a 50-day half-life. Methylmercury is the causative agent of the infamous Minamata disease.
In organic chemistry, peroxyacyl nitrates are powerful respiratory and eye irritants present in photochemical smog. They are nitrates produced in the thermal equilibrium between organic peroxy radicals by the gas-phase oxidation of a variety of volatile organic compounds (VOCs), or by aldehydes and other oxygenated VOCs oxidizing in the presence of NO2.
Cerium(IV) oxide, also known as ceric oxide, ceric dioxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare-earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO2. It is an important commercial product and an intermediate in the purification of the element from the ores. The distinctive property of this material is its reversible conversion to a non-stoichiometric oxide.
Birnessite (nominally MnO2·nH2O), also known as δ-MnO2, is a hydrous manganese dioxide mineral with a chemical formula of Na0.7Ca0.3Mn7O14·2.8H2O. It is the main manganese mineral species at the Earth's surface, and commonly occurs as fine-grained, poorly crystallized aggregates in soils, sediments, grain and rock coatings (e.g., desert varnish), and marine ferromanganese nodules and crusts. It was discovered at Birness, Aberdeenshire, Scotland.
Mercury telluride (HgTe) is a binary chemical compound of mercury and tellurium. It is a semi-metal related to the II-VI group of semiconductor materials. Alternative names are mercuric telluride and mercury(II) telluride.
Mercury selenide is a chemical compound of mercury and selenium. It is a grey-black crystalline solid semi-metal with a sphalerite structure. The lattice constant is 0.608 nm.
Mercury(II) sulfate, commonly called mercuric sulfate, is the chemical compound HgSO4. It is an odorless salt that forms white granules or crystalline powder. In water, it separates into an insoluble basic sulfate with a yellow color and sulfuric acid.
Ferrihydrite (Fh) is a widespread hydrous ferric oxyhydroxide mineral at the Earth's surface, and a likely constituent in extraterrestrial materials. It forms in several types of environments, from freshwater to marine systems, aquifers to hydrothermal hot springs and scales, soils, and areas affected by mining. It can be precipitated directly from oxygenated iron-rich aqueous solutions, or by bacteria either as a result of a metabolic activity or passive sorption of dissolved iron followed by nucleation reactions. Ferrihydrite also occurs in the core of the ferritin protein from many living organisms, for the purpose of intra-cellular iron storage.
Mercury is a chemical element; it has symbol Hg and atomic number 80. It is also known as quicksilver and was formerly named hydrargyrum from the Greek words hydor'water' and argyros'silver', from which its chemical symbol is derived. A heavy, silvery d-block element, mercury is the only metallic element that is known to be liquid at standard temperature and pressure; the only other element that is liquid under these conditions is the halogen bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature.
The mercury cycle is a biogeochemical cycle influenced by natural and anthropogenic processes that transform mercury through multiple chemical forms and environments.
Photogeochemistry merges photochemistry and geochemistry into the study of light-induced chemical reactions that occur or may occur among natural components of Earth's surface. The first comprehensive review on the subject was published in 2017 by the chemist and soil scientist Timothy A Doane, but the term photogeochemistry appeared a few years earlier as a keyword in studies that described the role of light-induced mineral transformations in shaping the biogeochemistry of Earth; this indeed describes the core of photogeochemical study, although other facets may be admitted into the definition.
Buserite is a hydrated layered manganese-oxide mineral with nominal chemical formula MnO2·nH2O. It was named after Swiss chemist professor W. Buser, who first identified it in 1952 in deep-sea manganese nodules. Buser named it 10 Å manganate because the periodicity in the layer stacking direction was 10 Å. It was renamed buserite in 1970 by the nomenclature commission of the International Mineralogical Association (IMA).
Mercury methylation is the process of forming methylmercury (MeHg). The methylation of mercury can occur abiotically or biotically. Biotically, the primary methylators of mercury are sulfate-reducing and iron-reducing bacteria. Three mechanisms have been proposed for the biotic methylation of mercury by sulfate-reducing bacteria. Mercury methylation can be problematic as methylmercury is toxic and can be bio-magnified through the food web.
Elsie M. Sunderland is a Canadian toxicologist and environmental scientist and the Gordon McKay Professor of Environmental Chemistry at Harvard University. She studies processes through which human activities increase and modify pollutants in natural ecosystems and living systems.
In stable isotope geochemistry, the Urey–Bigeleisen–Mayer equation, also known as the Bigeleisen–Mayer equation or the Urey model, is a model describing the approximate equilibrium isotope fractionation in an isotope exchange reaction. While the equation itself can be written in numerous forms, it is generally presented as a ratio of partition functions of the isotopic molecules involved in a given reaction. The Urey–Bigeleisen–Mayer equation is widely applied in the fields of quantum chemistry and geochemistry and is often modified or paired with other quantum chemical modelling methods to improve accuracy and precision and reduce the computational cost of calculations.
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