Distribution of microplastics in salt marsh habitats in the coasts of Gulf of Mannar and Palk Bay, Tamil Nadu, India.

This study offers crucial insights into the distribution of microplastics (MPs) in the salt marsh habitats of Tuticorin Coast (Gulf of Mannar) and Karankadu Estuary (Palk Bay). The mean abundance of MPs in surface sediment ranges from 4.6 ± 1.5 to 49.6 ± 6.5 items/kg on the Tuticorin coast and from 5 ± 1 to 16.3 ± 2.3 items/kg in the Karankadu Estuary. The dense landward edge of Sesuvium portulacastrum exhibits a remarkable ability to retain MPs, as its sprawling mats effectively trap larger amounts, thereby reducing their migration from inland to the shore. The trapping efficiency is closely linked to the density of vegetative zone, growth characteristics, and its specific position in the tidal flat. The abundance of MPs in core sediment declines with increasing depth. MP abundance is enhanced by sand, which allows easier infiltration and retention of MPs in the deeper sediment layers. Fiber-shaped MPs in size ranges of 0.5-1 mm and 1-2 mm with polyethylene and polypropylene were predominantly identified as the most common MP types. The study also assessed the carbon content of the MPs based on their volume, density, and theoretical carbon percentages. The microplastic-derived carbon (MPC) was found to range from 0.004 to 0.4 mg/kg (0.15 ± 0.11 mg/kg) in the study area. Although this is a small part of carbon burial, the widespread presence of MPs in the environment raises serious environmental concerns. The study highlights salt marsh sediments as sinks for MPs and emphasises the need for targeted pollution management.