Harnessing invasive weed species for fly ash-polluted site remediation: Comparative assessment of organic contaminant degradation and bacterial shifts using GC-MS and 16S rRNA amplicon sequencing.

Phytoremediation of coal fly ash disposal sites is challenging due to the complex mixtures of persistent pollutants in alkaline, nutrient-depleted substrates. A multi-platform evaluation (physicochemical analysis, BCF/TF, GC-MS Van Krevelen type classification, 16S rRNA amplicon sequencing and functional networks) was conducted to assess two natural colonizers, Cannabis sativa L. and Parthenium hysterophorus L., at the NTPC ash disposal site. Weed colonization reduced pH from 9 (NS) to 7.49 (CS) and 7.08 (PS). The large surface depletion of zinc, iron, and manganese caused by these reductions was reflected in the mass balance calculations as <0.02% due to direct plant uptake, with the main drivers being solubilization from rhizosphere acidification and vertical leaching (no data on leachate or deep soil profile were collected). The levels of arsenic, lead, chromium, nickel, cadmium, mercury, copper, and radionuclides decreased by 20-67% due to combined leaching effects and low uptake (BCF < 1). GC-MS showed decreases of 42.1% (CS) and 22.95% (PS) in organic compounds, with Van Krevelen shifts from aliphatic-dominated to oxygen-enriched, humic-like residues, suggesting oxidative biotransformation. Rhizosphere enrichment of plant-specific genera was observed by 16S rRNA sequencing, whereas predicted genera involved in the degradation of aromatic compounds (Pseudomonas, Lysobacter) and predicted genes for the degradation of carbazole (carAa/Ac in silico) were enriched. The network (hypothesis-generating) was constructed using curated literature-based functional annotations (linking metals, compound classes, and genera to KEGG pathways). These findings show that invasive plants, with high ecological adaptability, are effective models for decreasing surface toxicity in fly ash-tainted sites while modifying the rhizosphere.