Microplastic-induced alterations in water flow and solute transport dynamics in soil

The growing use of plastic-based practices in agriculture has led to a significant accumulation of plastic waste in soil. Microplastics (MPs) increasingly threaten soil health and fertility by disrupting its physical and chemical environment, and impairing essential ecological functions. We conducted laboratory column measurements combined with microfluidic experiments to assess the effects of MPs on water flow and solute transport in soil, key processes for sustaining soil water and nutrient availability and thus crop growth and yield. Changes in hydraulic conductivity and solute breakthrough curves in sandy soils were investigated in the presence of varying concentrations of polyethylene (PE) and polyvinylchloride (PVC) microplastics. Alterations in pore structure and clogging of pore throats by MPs, as further evidenced through confocal and fluorescence microscopy of synthesized porous media, led to 39% and 74% reductions in hydraulic conductivity of sand samples containing 5% PVC and 5% PE, respectively. Solute transport experiments using a brine tracer revealed broader breakthrough curves in the presence of MPs. Overall, the enhancement of pore-scale flow heterogeneity driven by the development of preferential flow paths and the formation of low-permeability zones increased hydrodynamic dispersion and resulted in both early breakthrough and delayed transport of the tracer within the soil column.