Current understanding of subsurface transport of micro‐ and nanoplastics in soil

Abstract Environmental problems caused by plastic pollution in terrestrial systems have received increasing attention, especially the issues related to micro‐ and nanoplastics. Soils are a major receptacle and reservoir of plastics, and accumulated plastics can negatively affect soil health. In this short review, we discuss the current state of knowledge of subsurface transport of micro‐ and nanoplastics in soils. We discuss the fundamental transport mechanisms for micro‐ and nanoplastics and highlight the peculiarities of environmentally relevant micro‐ and nanoplastics. Plastic particles >10 μm are generally filtered out in soil, but smaller plastic particles have the potential to move through soil. Larger plastics in soil will break down into micro‐ and nanoplastics over time due to environmental weathering reactions, making the plastics more prone to subsurface transport. Moreover, interactions with microorganisms and dissolved organic matter may render micro‐ and nanoplastics more hydrophilic, thereby facilitating subsurface transport. Further, soil organisms can move plastic particles by bioturbation, and plastics themselves can affect soil hydraulic properties. Although much of the past research has focused on transport of pristine plastic particles, focus should be given to environmentally relevant plastics, considering the complexities of irregular shape, polydisperse size, and heterogenous surface properties, as well as the temporal changes of these properties caused by continuous environmental modifications.