Saturated hydraulic conductivity in microplastics incorporated soils: Effects of soil texture, polymer type, particle size, and concentration

The present study investigated the saturated hydraulic conductivity (Ks) of two distinct textured soils (loam and sandy loam) in the presence of three different types of plastic polymers [polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polyethylene (PE)] of two different sizes (0.5 to < 1 mm and < 0.5 mm). The Ks was measured in this experiment using the constant-head approach, which follows the concept of Darcy's law. In sandy loam soils (sand 62%), PET particles ranging from 0.5 mm to < 1 mm had the highest Ks (2.1 cm/h). Since PET particles are more hydrophobic than PVC, as seen in prior investigations, the highest Ks in the presence of PET reflects the impact of the hydrophobicity of the resulting particles on water repellency. Additionally, the average trend of Ks is PET > PVC > PE. The effect of increased pore dimensions might represent the mechanism underlying the greater Ks in sandy loam soils than in loamy soils. Two mechanisms, pore dimension increase, and pore-clogging influence the Ks value at low and high concentrations, respectively. However, significant variations in the effects of MP size on Ks were not detected. In this investigation, regardless of particle size, the pore dimension mechanism often increased the Ks at low concentrations. In contrast, the pore-clogging effects prevailed at higher concentrations, affecting and decreasing the Ks value. In addition, the Ks value in the presence of PE particles in loam and sandy loam soils decreased as the concentration increased, and the Ks value was higher for smaller PE particles than for larger PE particles. Due to the limited data on the effects of MP polymer type and size on the Ks of soil within a narrow range of contamination inputs, it might reveal substantial implications for nutrient and pollutant transport in soil. The authors designed to examine the paucities in MP investigation in this unlikely polluted condition of soil environments.