Environmental factors-mediated behavior of microplastics and nanoplastics in water: A review

The release of plastics in nature is an increasing global concern due to their degradation from microplastics (MPs) and even to nanoplastics (NPs), which are being recognized as a potential global threat to humans and environment. This paper summarizes the current knowledge on the effect of different environmental factors on the aggregation of MPs and NPs in aquatic environment. Stability (or extent of aggregation) of MPs and NPs varies with pH, ionic strength, ion type (monovalent, divalent, and trivalent), kind of minerals, and natural organic matter (NOM) of the aquatic environment. Electrostatic interactions between particles at different pH and ionic strength caused by salts of different valents govern the aggregation. In the presence of minerals (or inorganic colloids), net surface charge of mineral and surface potential of MPs and NPs (i.e., positive or negative surface functionality) play important roles in the heteroaggregation of MPs and NPs. In the presence of NOM, additional complex interactions including hydrophobic interactions and bridging are also involved in the aggregation of particles. Understanding the interactions of MPs and NPs of different surface charge with diverse environmental factors at a wide range of environmental conditions is pivotal to assess the mobility and the fate of degraded plastic particles and their risk to human health and ecological systems.