Mineral-mediated hyperspectral response mechanisms of soil cadmium under different contamination scenarios

Cadmium (Cd) contamination seriously threatens soil health and food security. Soil minerals critically influence Cd's behavior, governing its binding forms and speciation. However, differing mineral compositions and contamination levels between mining and farmland areas cause Cd-mineral interactions to vary, yielding distinct spectral responses that limit the generalizability of inversion models across scenarios. To address this, we investigated Cd spectral responses under two typical contamination scenarios in Hunan Province. Based on the Near-standard soil sample set (NSS group), scenario-specific modeling strategies were developed. Key Cd feature bands were extracted using the Variable Importance in Projection (VIP) method and validated on independent soils. Overlap analysis between VIP-derived Cd bands and mineral absorption features revealed strong mineralogical control: both hematite and illite contributed in farmland soils, while illite dominated in mining soils. These differences were further supported by Cd speciation analysis. The findings clarify the mineral-mediated nature of Cd spectral responses and highlight the need for mechanism-informed, scenario-specific inversion strategies.