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E N V I R O N M E N T , E A R T H A N D P L A N E T A R Y S C I E N C E S

Scientific exploration of Earth and its environment increasingly depends on techniques capable of observing matter at the atomic and nanoscale. ESRF's Extremely Brilliant Source (EBS) offers powerful insights by probing materials under extreme conditions or revealing how elements behave in complex natural systems. From tracing the fate of pollutants in coastal ecosystems to simulating the conditions deep within planetary interiors, these experiments illuminate the chemical, physical, and biological mechanisms shaping our world. Recent advances across several ESRF beamlines show how these frontiers are converging. Environmental processes and pollution dynamics

Coastal ecosystems illustrate the complexity of environmental interactions. On Guadeloupe’s beaches, Sargassum algae often become entangled with plastic debris. Using beamline ID16B, researchers applied nanoscale X-ray fluorescence (nano-XRF) and X-ray absorption spectroscopy (nano-XANES) to map arsenic in these biomasses (page 90). Arsenic can bind to plastics or accumulate in metal-rich regions, transforming plastics into vectors for contaminant transport and thereby facilitating its transfer into other environmental compartments. This highlights the combined ecological risks of plastic pollution and harmful algal proliferations.

Mining activities strongly influence environmental chemistry. Studies at BM20 found that most chromium in nickel–cobalt laterite mine tailings occurs as the less toxic Cr(III), tightly bound in stable iron oxides like haematite and thus limiting its mobility in water (page 92). Meanwhile, at BM28, the redox behaviour of arsenic in

oxygen-poor environments was examined (page 94). Green rust sulfate (GR-SO4), containing Fe(II) and Fe(III), oxidised arsenite [As(III)] to arsenate [As(V)], enhanced by citrate and accompanied by GR-SO4’s transformation into goethite, generating reactive iron sites that promote arsenic oxidation. These findings show that arsenic detoxification can occur even in anoxic wetlands or sediments. Trace metals such as nickel also interact with mineral nanoparticles. Investigations at beamline BM16 explored how nickel binds to magnetite under varying stoichiometries (page 96). At high concentrations, nickel formed surface hydroxides, while at low concentrations it incorporated into the lattice depending on the Fe(II)/ Fe(III) ratio. This behaviour explains how trace metals are stored or mobilised in soils and sediments and guides the design of functional nanomaterials. Nanotechnology also offers potential solutions for sustainable agriculture. Using ID21, researchers examined how copper-based nanoformulations interact with grapevine leaves (page 98). Compared to copper sulfate sprays, nano-Cu exhibited enhanced adhesion, greater persistence, lower phytotoxicity, and controlled release, thereby limiting environmental dispersion of copper.

Biological systems likewise rely on nanoscale protection mechanisms. At BM07, scientists studied the oxygen- sensitive molybdenum nitrogenase of Azotobacter vinelandii, which is crucial for nitrogen fixation (page 100). Single-particle cryo-electron microscopy elucidated how the ferredoxin FeSII (Shethna protein I) stabilises nitrogenase by forming a ternary complex with its catalytic subunit and reductase. This complex becomes inactive under oxidative stress but rapidly reactivates when oxygen levels decline, demonstrating a regulatory protection mechanism that may inspire the development of more robust nitrogen-fixing plant systems.