Transformation and Mobility of Al Nanomaterials in the Environment
Engineered aluminum nanoparticles have become a part of our everyday life. Aluminum (Al) oxides and (oxy)hydroxides are used in a wide range of industrial applications (pharmaceuticals, cosmetics, food, water treatment…) either in the form of the particle core or in the form of coating of other nano-sized objects. While a rapid library search reveals that synthesis and reactivity of nano-sized Al species are popular research fields, their environmental fate and/or potentially adverse effects have received only marginal attention. Just like any other chemical, the environmental reactivity, mobility and toxicity of nano-sized Al phases are controlled by their speciation, and especially their surface chemistry. Al is a known toxicant for over a century, but its toxicity is usually attributed to soluble species, and in particular the Al3+ monomer. In the early 1990s, it was demonstrated that a ca. 2 nm Al nanoparticle (i.e. aka Al13) exhibits toxic effects 60 times more severe than Al3+.1 In more recent years, it has been reported than Al oxides and (oxy)hydroxides, which are usually considered as non toxic, have detrimental effects when their size falls within the nano range.2
In a time where regulators must address concerns against nano-enabled products in general, it is important to provide a sound knowledge basis to be used by mechanism-driven predictive tools. In this vast endeavor, the present project aims at determining the mechanisms controlling the fate of Al based nanomaterials after their intended use. In this end-of-life stage, the aim is to characterize the fate of selected Al nano-phases in a wastewater treatment plant (WWTP) and the downstream natural environment. This project has been selected in the 2016 DOC2AMU call, but the chosen candidate did not respond to the invitation for the interview.
To reach this goal, it is necessary to monitor the speciation of these Al compounds but also their spatial distribution, including in the food chain (algae, unicellular and higher organisms). Given the affinity between Al and organics, which are ubiquitous, the analytical tools used in this project need to be able to determine the Al and C speciation with the least amount of sample preparation. Nuclear magnetic resonance (NMR) is an element specific probe that is extremely valuable to provide a detailed speciation for both Al and C, and is perfectly suited to analyze nanoparticles and their coatings. In the present case, however, several challenges need to be met, mainly because it is conceptually necessary to monitor the Al nanophase in realistic environments. Besides standardized physical and chemical aging tests, the bio-physical-chemical alteration will be addressed using bio-reactors to simulate a WWTP situation, and mesocosm testing to simulate environmental aging, both of which are available. The analytical challenges are just as demanding owing to low concentration issues (which result in low sensitivity). In fact, while the "chemical resolution" of NMR is unparalleled, especially for low Z elements, its application to the speciation of environmentally relevant systems typically suffers from its inherent lack of sensitivity. This limitation is being lifted by recent advances in the so-called dynamic nuclear polarization (DNP) technique, which enhances nuclear magnetization through the microwave-driven transfer of electron spin polarization to nuclei via exogenous paramagnetic centers. DNP is currently revolutionizing NMR by providing huge sensitivity enhancements (up to 100-fold), hereby reducing the duration of NMR experiments from several years down to a few hours. As such, DNP NMR has become particularly efficient for unraveling the structure of surface species and core-shell particles.3 In addition, characterizing the fate and mobility of Al-nanomaterials also requires mapping their distribution within the different compartments of the system, including living organisms. While 3D X-ray imaging has the necessary spatial resolution, this absorption technique cannot unequivocally identify the underlying element. In this context, magnetic resonance imaging (MRI) could prove highly complementary because it is an element specific technique (i.e. 27Al imaging) with a resolution in the µm3 range that makes it ideal for investigating the aggregation state of Al nanomaterials. Therefore, an important outcome of the project will be the development DNP NMR and MRI methodologies to study the speciation and mapping of Al-nanomaterials in an environmentally significant context.
The work to be accomplished within this project consist of two main phases: application of the DNP NMR and MRI to model system to determine detection limits, examine specific spectral features and develop adequate data acquisition sequences. The materials will be commercial aluminum nanophases used in industry (nanoboehmite, nanobayerite, PCBA…) included in simple abiotic (e.g. sand, polysaccharide gels) and biotic matrices (e.g.model organisms such E. Coli, P. Brassicacaerum, Aribidopsis roots). The PhD candidate will also use this phase to familiarize himself/herself with the DNP and MRI techniques that are usually not part of a typical university curriculum.
The second phase will examine the aging of actual products during and after the use phase of these products and the furhter development of Al DNP NMR and MRI to take into account the specificity of natural samples. At this point, the nano-enabled materials will be chosen among off-the-shelf cosmetics and water treament coagulation agents. This phase is subdivided into two parts: abiotic and biotic monitoring of the aging and (bio)distribution of the Al nanophases. Abiotic aging includes abrasion and weathering of the products using standardized protocols when avaible; bio-physico-chemical aging includes bio-reactor and mesocosm testing to simulate environmental aging. All these tests are long term experimentation (as an example, to complete a mesocosm testing with its data treament a minimum of 4 months is necessary) and consequently will represent the majority of the time.
Main supervisor for this PhD project is Armand MASION (CNRS research director) from the InterFast (Interfaces and Transfer) research group at the CEREGE (UM 34 AMU/CNRS/IRD/Collège de France). The group has ca. 10 permanent staff involved in research regarding the environmental impacts of nanotechnolgies. Intrumentation to determined particle size, charge, and chemistry is available on-site, as well as as 2D XRF and micro- and nano- Xray tomography equipment and a complete mesocosm facility. Additionally the group has access to synchrotron based tools (EXAFS, XANES, SAXS) and bio-reactors.
Co-supervisor is Stéphane VIEL (AMU Professor, Junior Member of the Institut Universitaire de France). He leads the NMR group of the Institut de Chimie Radicalaire (UMR 7273 AMU/CNRS, Director: Dr. Didier GIGMES) within the SACS research team managed by Pr. Laurence CHARLES. The NMR group is composed of 4 permanent staff members and develops research activities at the interface of analytical chemistry and molecular spectroscopy. In particular, this group develops and applies novel nuclear magnetic resonance (NMR) methodologies, both in the liquid and in the solid state, to investigate the structure and dynamics of complex molecules and materials. The group has access to a full range of on-site NMR spectrometers, from 400 to 600 MHz (1H nuclear Larmor frequency), and benefits from a privileged access to state-of-the-art dynamic nuclear polarisation (DNP) solid-state NMR instrumentation via the Bruker Biospin R&D centre located in Wissemborug (France).
Use of the on-site instrumentation and lab supplies are funded by other current research proposals Additional funding is applied for at the Amidex foundation and at the Labex Serenade.
The candidate should have a strong background in physical-chemistry and chemistry and a working knowledge in environmental science and/or geosciences. Experience in NMR spectroscopy is strongly desired. He/she needs to have excellent English communication skills (oral and written) and the ability to work as an active member of in a multi-site, multi-disciplinary team. Basic knowledge in the French language is not required but would be appreciated.
This is a Marie Curie grant (grant agreement No 713750) with specific eligilibity criteria. Please check the requirements at : http://doc2amu.univ-amu.fr/en/transformation-and-mobility-of-al-nanomaterials-in-the-environment-0
Application must be submitted online on this website by April 10th 2017.
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