Lead Lα ₁ High Energy Resolution Fluorescence Detected X-ray Absorption Spectroscopy: A Powerful Tool for Chemical Speciation of Lead

Lead exposure remains a major global health concern, contributing to an estimated 1.5% of annual deaths worldwide and causing widespread, irreversible neurodevelopmental and cardiovascular damage, particularly in children. A central challenge in understanding and mitigating lead toxicity is the determination of its chemical speciation in complex biological and environmental systems, where conventional Pb LIII-edge X-ray absorption spectroscopy (XAS) is fundamentally limited by severe core-hole lifetime broadening. Here we show that Pb Lα1 high-energy-resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) provides a practical and experimentally accessible route to overcoming this limitation. Pb Lα1 HERFD-XAS yields an approximately 2-fold improvement in spectral resolution relative to conventional XAS, enabling enhanced sensitivity for quantitative speciation in heterogeneous and dilute systems. The method shows negligible chemical shifts (<0.06 eV) in the emission energy, simplifying implementation, distinguishes holodirected and hemidirected Pb(II) coordination environments, resolves biologically relevant Pb binding modes in zinc-finger model peptides, and identifies hemidirected Pb-substitution in hydroxyapatite, a key long-term reservoir of lead in humans. These results establish Pb Lα1 HERFD-XAS as a sensitive and experimentally accessible tool for determining Pb speciation in environmental and biological systems.