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Microplastics are a growing problem worldwide. They disrupt ecosystems and contribute to adverse effects, like metabolic disorders, neurotoxicity, immunotoxicity, and developmental toxicity in the bodies of various organisms as they spread upward through the food web.

This is particularly worrisome when considering species that are already endangered, like the Indus River dolphin (Platanista minor), which is listed as endangered by the . The Indus River dolphin is native to the Indus River in Pakistan, although a small population is also found in India. The Indus River is known to be one of the most polluted rivers in the world, containing high amounts of plastic waste, which is likely to be ingested by Indus River dolphins and their prey.

A group of scientists took the opportunity to analyze the gastrointestinal tract (GIT) of five deceased Indus River dolphins that had been stranded between 2019 and 2022 in order to assess the level of microplastics in their bodies. The study was recently in the journal PLOS One. No prior studies had assessed levels of microplastic contamination in the Indus River dolphin.

The team counted the extracted microplastics and characterized them by shape, size, color, and polymer type using FT-IR spectroscopy. They then determined the polymer hazard index (H), based on the toxicity of the polymers, to assess the level of risk for the dolphins.

All five dolphins showed microplastic contamination, with an average of 286.4±109.1 microplastic pieces per individual—higher averages than any previous microplastic study revealed in other cetacean species. They found that 94.76% of the microplastics were fibers, mostly blue or transparent in color, and mostly between 5 mm and 300 µm in size. Polyethylene terephthalate (PET) accounted for 58.16% of the polymers found.

The plastics found in the study reportedly represent a medium (Level III) to high (Level IV) ecological risk for the dolphins.

The study authors say, "Polymers emanate from plastic ropes, fishing nets, plastic bottles and bags, and agricultural runoff, suggesting their accumulation by intensive anthropogenic interventions. The detection of identical polymers in both prey fishes and IRD guts suggests trophic transfer and indicates that local prey species are primary vectors for IRD exposure.

"Microplastics are transferred up the food chain, and IRDs, as apex predators, accumulate them along with additives including bisphenols and phthalates, which are proven to be endocrine-disrupting chemicals. Frequent ingestion of PET, PVC, PE, and related polymers may cause digestive dysfunction, oxidative stress, immune disruption, and reproductive toxicity, collectively threatening the health, survival, and resilience of IRD populations."

The study highlights the threat of continued overuse of plastics and the growing ubiquity of microplastics in everything from freshwater to fish and higher level predators. The study authors note the urgent need for reducing plastic pollution in freshwater habitats through conservation, monitoring, and management strategies.