Geogenic PAHs fractionation and mobilization driven by acid mine drainage in karst coal mining watersheds

Geogenic coal-derived polycyclic aromatic hydrocarbons (PAHs) migration and risks in karst mines remain understudied, especially acid mine drainage (AMD)-facilitated PAH transport via karst dual hydrologic systems and rapid groundwater flow. This study integrates field monitoring, multivariate statistics and laboratory leaching simulations to clarify PAH origins, AMD-controlled release mechanisms and multi-level environmental risks in karst coal basins. Surface water total PAH concentrations vary substantially with seasons and peak in dry periods. Traditional diagnostic ratios poorly distinguish coal‑PAH sources due to intrinsically overlapping fingerprints and weathering modification. Principal component analysis and molecular fingerprinting verify endogenous coal-strata leaching constitutes the primary source rather than exogenous combustion. Divergent aqueous PAH compositions stem from chromatographic fractionation during groundwater flow instead of separate pollution sources. Strong acidity below pH 3.5 breaks coal matrices and liberates low-molecular PAHs, while mild acidic conditions above pH 3.5 restrict PAH migration via adsorption onto secondary minerals in AMD. High rank coal rich in PAHs features weak mobility due to compact matrices and high-molecular PAHs mostly accumulate in the solid phase. Bituminous coal poses the highest health risk, followed by anthracite, lignite and coal gangue, with low-ring PAHs as primary non-carcinogenic risk contributors. Dry seasons witness aggravated aquatic risks, with dermal contact serving as the primary human exposure route. This study elucidates AMD-mediated PAH fractionation and mobilization in karst coal mines, remedies flaws in conventional source apportionment, identifies the neglected coal-strata leaching pathway and supports seasonal pollution control and risk management for analogous karst mining watersheds.