Seasonal microplastic dynamics in the Alappuzha–Changanacherry Canal, Kerala, India

Microplastic pollution has emerged as a significant environmental threat to freshwater ecosystems. This study investigated the occurrence and characteristics of microplastics in the Alappuzha-Changanacherry Canal, an artificial waterway in the Kerala, Kuttanadu region influenced by domestic, agricultural, fisheries, and municipal waste. Surface water samples were collected from three locations during the pre-monsoon and monsoon seasons. Microplastics were extracted from the samples using standardized filtration, examined under a microscope, and identified using confocal micro-Raman spectroscopy. Microplastics were detected at all sampling sites in both seasons, confirming their widespread distribution. Seasonal analysis showed significantly higher contamination during the monsoon due to increased surface runoff and hydrological transport. Statistical analysis revealed clear spatial and seasonal variations in microplastic abundance. Station 1 (Manackachira) recorded the highest mean abundance (114.0 ± 73.43 particles L⁻ 1 ), followed by Station 3 (60.67 ± 8.08 particles L⁻ 1 ), while Station 2 exhibited the lowest abundance (36.0 ± 10.58 particles L⁻ 1 ). Microplastic concentrations were substantially higher during the monsoon season, with a 48.2% increase in mean concentration and a 61.2% increase in total abundance compared with the pre-monsoon season, indicating that monsoon runoff significantly enhances microplastic transport into the canal. Fibres were the predominant morphological type, followed by fragments, films, and pellets. Analysis shows that fibres were the dominant plastic type, followed by films, fragments, and pellets. The predominant particle size range from 0.12 to 0.5 µm raises concerns about their bioavailability and ingestion by aquatic organisms. Transparent and green particles were the most abundant, indicating probable sources, such as plastic packaging and municipal waste. Confocal micro-Raman spectroscopy identified high-density polyethene, low-density polyethene, polypropylene, polystyrene, polyurethane, and polysulfone. Polyethlene and polypropylene were the dominant polymers, reflecting inputs from domestic wastewater, agricultural runoff, fisheries activities, and municipal waste. The consistent occurrence of microplastics across all sides and seasons demonstrates that the AC canal functions as both a source and a transport pathway for synthetic polymers, causing potential risk to the aquatic ecosystem, trophic transfer, and human health. This study provides the first baseline assessment of microplastic contamination in the AC canal and emphasises the need for region-specific monitoring and mitigation strategies.