Engineered nanomaterials, massively produced for our benefits, constitute an important class of pollutants and that their fate and behaviour in aquatic systems are influenced by water chemistry as well as intrinsic nanoparticle properties. The aim of this work is to develop a mechanistic understanding of transformation processes of engineered nanomaterials in various aquatic systems. Two types of material such as metallic nanoparticles of cerium dioxide and plastic particles made of micro- and nanoplastic polystyrene latex beads were considered. The complexity of the environmental systems was reproduced by considering different water compounds, such as humic substances, polysaccharides and inorganic colloids and by using contrasting and changing water conditions including change of pH, type of electrolytes and ionic strength. Our findings demonstrated that engineered nanomaterial behaviour in aquatic systems is complex process and is highly dependent on environmental conditions and resulting electrostatic scenarios.