Paired water-sediment DOM optical fingerprints reveal sediment-side signals of apparent potentially toxic element partitioning in coal-mining subsidence lakes.

Coal-mining subsidence lakes contain active sediment-water interfaces, where surface sediments can influence the apparent partitioning and potential secondary mobilization of potentially toxic elements (PTEs). Dissolved organic matter (DOM) influences metal speciation and transport, but sediment-side organic-matter signals remain underrepresented in monitoring based on overlying-water chemistry or bulk sediment inventories. Here, we evaluated a paired water-sediment DOM optical screening approach integrating ultraviolet-visible absorbance, fluorescence indices, EEM-PARAFAC components, sediment water-extractable organic matter (WEOM), cross-phase optical fingerprint indicators, and apparent log Kd values for As, Cd, Cr, Cu, Ni, Pb, and Zn. We applied the approach to 24 water-sediment sample pairs from coal-mining subsidence lakes in the Linhuan mining area, China. Overlying-water DOM exhibited fresher and more autochthonous features, whereas sediment WEOM showed greater aromaticity, higher humification, and larger apparent molecular size. Type-aligned PARAFAC components showed component-level resemblance and systematic phase-specific deviations between the two organic-matter pools. All target PTEs had positive apparent log Kd values, with mean apparent partitioning strength following Pb > Cu ≈ Ni > Zn ≈ Cr > As > Cd. Sediment WEOM properties showed clearer element-specific statistical associations with apparent PTE partitioning than instantaneous overlying-water DOM descriptors, whereas selected cross-phase optical fingerprint indicators primarily characterized phase-specific DOM organization. Cu provided a representative example of an association between apparent PTE partitioning and sediment WEOM molecular-size-related and humification-related characteristics. These findings suggest that paired water-sediment DOM optical fingerprints, particularly sediment WEOM descriptors, may complement concentration-based monitoring and help prioritize further sediment-oriented investigation in mining-impacted lake systems.