Crystallinity to Cleanup: a Mechanistic Guide to Emerging Contaminants in Landfill Leachate

Abstract

Landfill leachate is a reservoir of emerging contaminants (ECs), yet persistence is often reported without connecting it to underlying chemical structure. This review addresses this gap by linking molecular determinants of recalcitrance such as type of bond, functional groups, and polymer architecture to the mechanism governing sorption, transport, and transformation under dynamic leachate conditions. The scope integrates chemical principles with environmental determinants of leachate composition across landfill age, providing a perspective on contaminant behaviour. The review also highlights how structural features dictate interactions with complex leachate matrices by focusing on key contaminant classes; microplastics, antibiotic residues and associated antibiotic resistance genes (ARGs), and heavy metals. In particular, microplastics are examined as vectors that sorb and transport metals and ARGs, increasing mobility, persistence and contributing to resistome development in leachate. Advances in analytical techniques including liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) techniques, spectroscopic tools such as nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) and aptamer-based biosensors are discussed in the context of resolving speciation and detection challenges. The review further aims to provide insights into sustainable and cost-effective treatment strategies and discuss their effectiveness in relation to contaminant structure and leachate chemistry. Overall, the present review concludes that persistence in landfill leachate can be systematically understood through measurable structural determinants, enabling more targeted monitoring and treatment strategies. Key challenges and future research directions are also addressed to advance management of ECs in leachate system.