Impact of flooding events on microplastic distribution from rivers to coastal areas: a case study from Tuticorin, Southeast India

Extreme weather events driven by climate change may significantly impact the fate and transport of particulate pollutants in the environment. This study investigates the impact of the 2023 flood event on microplastic (MP) distributions in the Thamirabarani River, through the Punnakayal estuary and into the coastal waters of the Bay of Bengal. The flood significantly increased MP abundance and diversity, indicating that such events mobilize MPs from sediments to surface waters and transport terrestrial MPs into aquatic systems. The mean abundance of MPs across all water samples was 28.29 ± 12.29 items/L before the flood and 95.14 ± 21.13 items/L after the flood, a 3-fold increase. In sediments, it was 36.14 ± 16.78 items/kg before the flood and 54.71 ± 27.74 items/kg after the flood, a 1.5-fold increase. The abundance of smaller MPs (<0.5 mm, 0.5-1 mm, and 1-2 mm) increased significantly in post-flood water samples at all sites, while no clear pattern emerged for sediments. Post-flood, there was a significant increase in the number of fiber (ca. 425 %), fragment (230 %), foam (450 %) and film-type MPs (650 %) in water samples from most sites, with a significant increase in foam (530 %) and film-type MPs (450 %) in sediments at most sites. FTIR-ATR analysis revealed 7 polymer types pre-flood and 16 post-flood, which included an additional 9 not previously identified. Mangroves can trap MP flowing through estuarine regions, while hydrodynamic factors impact MP retention in the coastal area. This study aids in understanding flood-related MP redistribution, helping to improve pollution management.