Influence of Microplastics on the Hydraulic Conductivity of Riverbed System

Microplastics (MPs) are anthropogenetic pollutants, with particle sizes between 5 mm and 1 μm. These particles enter riverine ecosystem through sources like discharge from wastewater treatment plants, surface runoff from landfills and plastic recycling plants. Movement of the MP particles in the water column is influenced by changes in river flow, leading to deposition and re-suspension from the riverbed. These dynamic actions have considerable impact on the benthic ecosystem. The present study aims to understand how the deposited MP particles affect the hydraulic conductivity of the riverbed. For this, experiments were conducted using the constant head permeability test setup with gravels (mean particle size, d50 = 14 mm) and pebbles (d50 = 13 mm). The MPs used in the present study were collected from PVC recycling plant in Karaikal, Puducherry, India. The collected sample predominantly constituted of fragment (82%) and fibre (18%) shaped particles, with a d50 of 2 mm. The intrusion effect was analysed by altering the concentration of MPs and the unit weight of the aggregate. Results show that the hydraulic conductivity is inversely proportional to the concentration of MPs and positively correlated with a decrease in aggregate unit weight. Consequently, the hydraulic conductivity of gravels and pebbles is significantly due to the presence of MPs, with a more marked effect observed for gravels than pebbles. Moreover, the particle shape and texture properties also influenced the hydraulic conductivity. These findings are crucial to environmental managers and decision-makers seeking to understand MPs’ impact on riverbed and groundwater quality.