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Due to intensive activities in agriculture, forestry and transport sectors, certain active components of pesticides that are prone to leaching become emergent chemicals in aquatic systems. Terbuthylazine (TBA), as one of widely used broad-spectrum herbicides, has been recognized as relatively (e.g. vs atrazine) more hydrophobic and resistant to biodegradation, dissipates much more slowly in aquatic ecosystems and often exceeds the EU limit for drinking water (0.1 μg/L). The in-depth characterisation of fly ash (FA, from a cogeneration plant facility fuelled by deciduous hardwood chips) using advanced in situ approaches (scanning electron microscopy, X-ray diffraction) raised the hypotheses that developed nano-to-micro-structure and alkaline Ca/Mg/Si-enriched mineralogy of FA could be effectively exploited for removal of TBA from watercourses. Thus, the aim of study was to investigate dissipation dynamic and adsorption mechanism of TBA in aquatic media amended with FA. The results show that 48 h after addition of FA (1% w/v) to watercourse, TBA was completely removed from its initial level (250-fold higher than the EU limit for drinking water), while in the Control (without FA) treatment, TBA remained nearly 80% of its initial amount. The X-ray photoelectron spectral footprint of FA after 48-h exposure to TBA revealed a shift in peak position and intensity among O, Ca, K, Mg and Si, suggesting that their active sites likely participated in adsorption of TBA and its removal from the watercourse. Adsorption kinetics were clearly described by the pseudo-second order model (R2= 0.9997), assuming single-layer chemisorption as a rate-controlling mechanism, but multilayer physisorption and intra-pore diffusion could also be present. The equilibrium adsorption data fitted the best to the Langmuir isotherm model, confirming the spontaneous monolayer TBA-FA interaction with a mean maximum adsorption capacity of 84 mg/g FA (1% w/v) after 24-h contact time at 25 °C and pH 12. These results will contribute to formulation and development of novel FA-based polymers, targeted for purification of aquatic ecosystems loaded with TBA and similar compounds that represent threat to environmental and human health.