Spatial dynamics of microplastics in Mula- Mutha River: A compehensive assessment of distribution, concentration, pollution load, and associated risks in the Pune Metropolitan Region

The emergence of plastic pollution over the last few decades has led to the dumping of > 590 million tons of plastic into the natural system. This plastic undergoes recycling and degradation transforming into micro and nano-plastics, thereby generating a substantial volume of micro- and nanoparticles to the extent suggested as the plasticene epoch. Sediment samples were collected from specified sites, and microplastics were extracted using explicit methods including density separation using high-density solution, filtration, and organic matter oxidation, followed by identification via microscopy or spectroscopy. Studies were conducted to comprehend degradation rates based on scanning electron microscopy (SEM) analysis of microplastic surfaces marked by roughness and porosity. Fourier transform infrared (FTIR) spectrometer with a spectral range of 4000–400 cm-1 and a resolution of 4 cm-1 was used to identify specific polymer types. This study highlights the crucial role of sediment texture in influencing the concentration and retention of microplastic particles, with a pronounced presence in fine to medium-grained sediment matrices in river basins based on the example of the Pune Metropolitan Region as part of the Mutha river sub-basins. A quadripartite first-order characterization has been inferred here with: i) particles greater than 1 mm; ii) particles ranging from 1 mm to 0.25 mm; iii) particles 0.25 to 0.062 mm; and iv) particles less than 0.062 mm. Prevalence of categories ‘iii’ and ‘iv’ suggests a potential higher degradation rate governed by rapid fluvial transport. Fragments followed by fibers, films, beads/pellets, lines, and granules are some of the most common plastic types recorded. Polymer types were identified using FTIR peaks are polyethylene, polyethylene terephthalate, polyamide, polypropylene, polystyrene, acrylonitrile butadiene styrene. The findings imply that a significant proportion of plastic products are breaking down into smaller particles, increasing the distribution rate over a larger surface area. The risk assessment of microplastic contamination is marked by a high to very high Microplastic Hazard Index (MHI) indicating substantial pollution, emphasizing the severity of microplastic presence.