Seasonal variation and distribution of microplastics in surface water and sediments of Coimbatore Lakes, India

Abstract

This study quantified the abundance, distribution, and characteristics of microplastics in surface water and sediments from five lakes in the Coimbatore District: Kumaraswamy Lake, Ukkadam Lake, Kuruchi Lake, Singanallur Lake, and Sulur Lake. The highest microplastic abundance was found in the surface water of Kuruchi Lake (14.08 ± 0.63 particles/L) at site S5 during the monsoon, and in the surface sediments of Kumaraswamy Lake (13.33 ± 0.33 particles/g) at site S6 during summer. Spatial distribution patterns indicated that lakes receiving urban runoff, domestic wastewater inflow, and inputs from fishing and recreational activities exhibited higher microplastic concentrations. Seasonal variations showed elevated microplastic abundance in summer sediments and monsoon surface water samples. Microplastics were identified using Attenuated total reflectance- Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC)), revealing Linear low-density polyethylene (LLDPE), High-density polyethylene (HDPE), Polyethylene terephthalate (PET), and Polypropylene (PP). These microplastic occurred in white, transparent, black, blue, yellow, and pink colors and appeared as films, fragments, thin pieces, and fibres. Characteristic DSC melting peaks were observed 200 °C for PET, 167.98 °C for PP, 126.70 °C for LLDPE, and 130.02 °C for HDPE. The lake’s pollution load index is categorized as risk level 1, indicating a low level of microplastic pollution. The presence and distribution of these microplastics suggest potential ecological risks to freshwater organisms and possible implications for human health.