Impact of the 2023 floods on microplastic contamination in coastal groundwater: a comparative analysis of chennai’s pre- and post-flood conditions

Over the past 70 years, the exponential rise in plastic production has led to pervasive microplastic (MP) contamination across natural ecosystems. While extensive research has focused on surface water pollution, groundwater contamination by MPs remains critically understudied despite its growing environmental and public health concerns. This study investigates MP pollution in groundwater along Chennai’s east coast, with a specific focus on pre- and post-flood variations following the 2023 flood event. Groundwater samples were collected from 49 locations along the Chennai coastline in November 2023 (pre-flood) and February 2024 (post-flood) and analyzed using a NIKON SMZ 745 binocular optic stereo microscope to assess MP physical characteristics, while ATR-FTIR spectroscopy was employed for polymer identification. To minimize confounding effects such as seasonal variation or ongoing pollution sources, sample collection was scheduled to reflect comparable hydrogeological conditions across both timeframes, with all sites located in consistent land-use zones. Comparative analysis revealed a 62% average increase in MP concentration post-flood, with some locations exhibiting an increase from 14 particles/L to over 37 particles/L, demonstrating the flood’s pivotal role in MP mobilization and infiltration. Fibers were the dominant MP type (67%), followed by fragments (28%) and film-like MPs (5%), with nylon and polystyrene (PS) identified as predominant polymers. Spatial distribution analysis revealed hotspots in highly urbanized and industrially influenced areas, especially where sewage and stormwater channels intersected with shallow aquifers. These findings highlight the compounding effect of extreme hydrological events in accelerating MP transport into groundwater systems. Given the associated risks of MP ingestion such as oxidative stress, reproductive toxicity, neurodegenerative disorders, and cancer this study underscores the need for targeted mitigation strategies. These include hydrogel-based filtration technologies, stricter plastic waste regulation, and adaptive policy frameworks to safeguard groundwater resources. The study fills a critical research gap by quantifying MP contamination dynamics and establishing the influence of disaster-driven recharge processes, offering a model applicable to flood-prone coastal regions globally.