Antibiotics don’t just drift through rivers and lakes untouched. Dissolved organic matter (DOM), one of the most common natural substances in aquatic systems, latches onto these compounds and changes how they move, degrade, and interact with living organisms. Humic acid is a major part of DOM. It carries a dense set of functional groups that let it complex, adsorb, and participate in redox reactions with all sorts of contaminants. Oxytetracycline (OTC) is a tetracycline-class antibiotic used in human medicine, aquaculture, and livestock farming. Wastewater carries it into natural water bodies, where it can persist long enough to cause ecological and health problems. How OTC binds to humic acid is a…