Microplastic Interactions with Dissolved Organic Matter in Aquatic Systems

Abstract

Microplastics are now found in rivers, lakes, estuaries and oceans, where they meet dissolved organic matter, a complex mixture of humic, fulvic and protein-like compounds that is present in all natural waters. The interaction between these two components changes the surface properties, aggregation, transport, transformation and ecological effects of microplastics, and it also changes how dissolved organic matter itself behaves. This article reviews the occurrence and properties of microplastics, the composition of dissolved organic matter, the mechanisms of sorption, the formation of organic coatings known as eco-coronas, and the consequences for aggregation, settling, photochemical ageing, biological colonisation and pollutant binding. Analytical methods for studying these interactions are summarised, and research gaps are identified. A representative example shows how increasing organic matter concentration shifts the surface charge of common plastics toward similar negative values, and the numbers shown are illustrative. The article concludes that organic matter is a central factor controlling the fate and risk of microplastics in aquatic systems, and that realistic studies must include it.