Research on the effect of dissolved organic matter on the adsorption of oxytetracycline by high-density polyethylene

Environmental context In the soil environment, microplastics (HDPE) act as carriers to adsorb contaminants, interacting with dissolved organic matter (DOM) and antibiotics such as oxytetracycline (OTC). The results show that DOM plays a bridging role in the HDPE–OTC adsorption system, and its hydrophobic groups are complexed with OTC, resulting in the quenching of DOM ultraviolet spectrum. Rationale Dissolved organic matter (DOM) influences the migration and transformation of environmental pollutants through its diverse functional groups and properties. Microplastics, as emerging pollutants, adsorb organic contaminants, but how DOM from different sources (e.g. commercial fulvic acid v. soil-extracted DOM) affects these adsorption mechanisms remains poorly understood. Methodology This study investigated the adsorption of oxytetracycline (OTC) by high-density polyethylene (HDPE) microplastics in the presence of FA and soil DOM. Batch adsorption experiments, combined with UV-Vis and Fourier transform–infrared (FT-IR) spectroscopy, were conducted to analyse the mechanisms. Results The results showed that HDPE adsorption of FA was primarily physical. DOM addition significantly enhanced OTC adsorption by HDPE, with FA exhibiting a stronger promoting effect than soil DOM. Spectral analysis revealed that DOM acted as a bridge in the HDPE–OTC system, without altering the physical adsorption mechanism. Although FA and soil DOM exhibited similar adsorption mechanisms, their effects differed, likely due to structural and functional group variations. Discussion This study highlights the critical role of DOM in microplastic–pollutant interactions and emphasises the impact of DOM sources on adsorption behaviour. Future research should incorporate more environmentally relevant DOM sources to better simulate natural conditions and advance understanding of pollutant migration and transformation.