Seasonal Variations in Microplastic Characteristics and Distribution in Groundwater from Landfill and Non-Landfill Sites in an Urban Environment of Southern India

Groundwater is a critical resource in Udupi, Karnataka, yet its quality is increasingly threatened by anthropogenic activities. This study investigates seasonal variations in microplastic (MP) contamination in groundwater from landfill (LF) and non-landfill (NLF) sites within this urban region. During the wet season (September 2024), mean MP concentrations were 2.49 ± 6.40 MPs/L at LF sites and 1.14 ± 1.46 MPs/L at NLF sites, which declined in the dry season (February 2025) to 0.85 ± 0.28 MPs/L and 0.22 ± 0.04 MPs/L, respectively. Fragments dominated in the wet season, whereas fibers were more prevalent in the dry season. MPs in the 1000–3000 µm range were most common, comprising up to 83.63% at NLF sites. Polymer identification using Raman spectroscopy and ATR-FTIR revealed polypropylene as the dominant type (77.59%–86.37%), followed by polyethylene and polyester. SEM-EDS analysis showed weathered surfaces and the presence of toxic elements such as chromium, cadmium, and arsenic, indicating environmental exposure and potential health risks. Risk assessment revealed elevated PHI and PERI values during the dry season, particularly for polyester-rich fibers, indicating higher ecological and human health hazards. Identified MP sources included water-drawing ropes, well covers, laundry activities, and improper waste disposal. Elevated MP levels during the wet season were attributed to surface runoff introducing plastics into groundwater. These findings underscore the need for continuous monitoring and targeted management strategies to safeguard groundwater quality in Udupi, which is heavily relied upon by both residents and industries for their needs.