Helmholtz European Partnering - WP2 Nanomarterials in Soil
The sensitive and selective quantification of nanoparticles (NPs) in environmental samples such as water, soil and organisms at environmentally relevant concentrations remains the overwhelming challenge for a robust risk assessment of manufactured nanomaterials (MNMs). This is especially true in the case of soil-MNM interactions. Despite soil being a major sink for MNMs released into the environment, studies on NPs reactivity in soil are still very limited and critical questions remain unanswered. A robust risk assessment needs to be based on detailed mechanistic insight on the microscopic interaction processes that determine NP fate in soils that allows upscaling and quantitative predictability of processes on the macroscale, such as overall NP mobility and retention.
Soil is composed of organic and inorganic substances as well as organisms amongst which the most active are bacteria. On the one hand, interactions of MNMs with bacteria and crystal surfaces control MNM mobility in soil, on the other hand MNMs can have significant impact on soil microorganisms by changing their community structures or physiology.
We focus on the systematic analysis of MNM mobility as modified by microbial activity and physicochemical properties of soil component surfaces. JSI provides a strong background in environmental and analytical chemistry, molecular microbial ecology, soil-microbes interaction  and weathering/dissolution of inorganic material by microbes , as well as geochemical elemental cycles and risk and environmental impact assessment . In combination with the competence of HZDR in radiolabeling of NPs for most sensitive detection in complex media [4, 5], the analysis of crystal surface reactivity , as well as analytical reactive transport analysis using radionuclide tracers  provides the necessary tools to achieve this goal of linking microscopic understanding to macroscopic outcome. Thus, the proposed work package has two main foci:
a) On the microscale, interactions of MNMs with major soil constituents (minerals, organic constituents, microbes) are to be investigated using AFM / colloidal probe techniques and X-ray spectroscopy to extract the key surface potentials driving MNM-mineral interactions. This is followed by targeted variation of these surface potentials by chemical and biological variation of the mineral substrate and surrounding medium towards increasingly complex systems, reflecting natural soils. Complementary, the impact of MNMs on microbial activity in soils, will be analyzed by using transcriptomics approaches on individual microbes as well as in biofilms and aggregated communities, thus providing a bridge to the macroscale.
b) On the macroscale this is accompanied by mobility and fate studies extracting macroscopic key parameters for MNM retention and mobility with a similar escalation of system complexity which can then be linked to the microscopic factors comprising them. Here, the use of radiolabeled MNMs enables the use of environmentally relevant concentrations. The effects on microbial communities associated with soil will be determined by using metagenomic approaches.
The combination of innovative radiolabeling strategies and state-of-the-art environmental analytical tools for mutual validation and development of robust measurement procedures for MNMs in soil will provide a significant impact to the field allowing the process validation and extraction of meaningful data from transport and extraction experiments using environmentally relevant concentrations linked to and based on a profound microscopic process understanding.
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