Comparative study on the status of microplastics in different functional areas of Tuticorin, Southeast coast of India

Microplastics (MPs) and the pollutants associated with them pose a significant risk to the aquatic ecosystems. This study analysed the spatial and seasonal differences in MPs in terms of diversity, inventory and associated heavy metals, and assessed the risk carried by MPs in different functional areas of Tuticorin, southeast coast of India. The mean MPs abundance varies from 5.67 ± 3.1 to 94.66 ± 6.5 items/L in water and 6 ± 1.73 to 147 ± 18.6 items/kg in sediment. More MPs are found in monsoon water and post-monsoon sediment. Fibre-shaped polyethylene (PE) and polypropylene (PP) MPs have a dominant presence in all seasons. They might derive from synthetic clothing, derelict fishing gear and improper dumping of plastic waste in this region. The carbonyl index (CI) of PE varies from 0.01 to 1.2 and that of PP from 0.03 to 0.98. The high surface oxidation rate (with CI ≥ 0.31) indicates the weathering level of MPs. The high microplastics diversity index (MPDII) of the Fishing Harbour points to the diverse pollution sources. The inventory of MPs is expressed in terms of their weight-based accumulation. Higher inventory of MPs is detected in the water (0.018 ton/km²) and sediment (2.03 ton/km²) of Fishing Harbour. The scanning electron microscope (SEM) images of MPs reveal various surface morphologic features like cracks, protrusion, void space, and adsorbed microorganisms. Energy dispersive X-ray spectroscopy (EDAX) shows the presence of metals (Mn, Cu, Zn, Ni, K, Ca, Cr, Mg, Ti, Cd, As, Se, Fe, Al, and Si) on the MPs surfaces. The polymer hazard index (PHI) indicates a III to IV chemical risk level. All the information obtained from the analysis presents a clear image of the nature and distribution of MPs in this region.