Nano–Nitrogen Nexus: Linking Soil, Plants, Animals, and Human Health

Nitrogen (N) links the soil–plant–animal–food–environment continuum to human nutrition through protein and to health through biomarkers, yet cross-continuum methods remain limited and fragmented. Using N as a model element, this review evaluated how nano-enabled measure-ments integrate with reference methods and models to connect N sources with biological transfer, nutrition, exposure, and health. A structured integrative evidence-mapping review synthesized 152 studies to develop the Nano–Nitrogen Nexus (N³), a source-to-endpoint framework. The Nitrogen Nutrition–Exposure Continuum (NNEC) tracked N from soil–root processes through plant uptake, animal forage selection, and ruminal metabolism. NNEC links a nutrition route, where milk and meat N indicate protein quality, with an exposure route in which animal-excreted N products, food-safety markers, microbial metabolites, and pathogen and disease biomarkers support human health-risk interpretation. When combined within N³, NanoSIMS-based N localization, nanosensor detection of N-related target analytes, source attribution, validation, cross-compartment synthesis, and modeling (e.g., hierarchical, machine-learning, and risk-assessment models) convert meas-urements into source-to-endpoint evidence, identifying where N originates, moves, is used, retained, lost, or expressed as nutritional value or exposure risk. Therefore, N³ provides a nano-enabled source-to-endpoint framework that can also be applied to other elements, bioactive compounds, chemicals, and disease-relevant exposures to develop continuum-specific intervention targets for food quality, environmental protection, human nutrition, and health.