Microplastic Pollution in a Tropical River–Mangrove System of the Brahmani River in Bhitarkanika Wildlife Sanctuary, Odisha (India)

Abstract Microplastics (MPs), recognised as emerging contaminants, are increasingly prevalent in riverine ecosystems due to escalating anthropogenic activities. River deltas, which typically serve as ecologically rich and pristine habitats, are now under threat from solid and liquid waste inputs, particularly in rivers flowing through urban and agricultural landscapes. This research investigates MP contamination in sediments of the Brahmani River within the Bhitarkanika Wildlife Sanctuary, Odisha (India), encompassing both mangrove and non-mangrove sites. The highest recorded abundance was 50.4 items/kg dry weight (dw) and 25 items/kg wet weight (ww), with fibers, fragments, and films as the dominant morphotypes. Across most sites, fibers in the 0.1–5 mm size range were predominant. Polymer identification by ATR-FTIR revealed a predominance of polyamide (PA), followed by low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP). SEM–EDS analyses revealed that MPs had surface-adsorbed heavy metals (HMs), including chromium, copper, zinc, arsenic, cadmium, barium, and lead, which were sourced from the surrounding riverine environment. Risk assessment indices, including contamination factor (CF), polymer hazard index (PHI), potential ecological risk index (PERI), and pollution load index (PLI), indicated high ecological risk at several sites. High ecological risk indices were observed, raising serious concerns for elephants that depend on the river for drinking water. Ecological functioning in the Brahmani River in Bhitarkanika Wildlife Sanctuary supports saltwater crocodiles, Olive Ridley turtles, and other native and migratory birds. Mangrove sediments were identified as significant sinks for MPs, with the potential to disrupt benthic communities and impair mangrove productivity. This research will help ecologists, policymakers, NGOs, and state and federal governments develop policies and regulations to protect the Brahmani River, which supports the ecological functions of Bhitarkanika Wildlife Sanctuary and Bhitarkanika National Park. Graphical Abstract