Microplastics found in guts of rare Indus River dolphins

A new investigation examined the stomach and intestines of five Indus River dolphins and found plastic in every single one. The team documented hundreds of tiny particles in each animal and identified the types of plastic involved.

These are not big bottles or bags. They are microplastics, pieces smaller than 5 millimeters, that can slip into food webs and lodge in tissues during feeding.

Ahsaan Ali of Nanjing Normal University (NNU) led the research, working with collaborators in Pakistan, Denmark, China, and the U.K.

A rare creature

The Indus River dolphin is one of the world’s rarest cetaceans, living only in the Indus system in Pakistan and a small stretch in India.

An IWC-supported abundance survey in 2017 counted about 1,987 individuals and noted that populations are split by dams and barrages.

That fragmentation makes local threats loom larger because animals cannot easily move to cleaner stretches. Plastic pollution is now part of the mix of threats.

How study was conducted

The researchers collected stranded dolphins and carefully dissected their entire gastrointestinal tract. They separated the stomach, small intestine, and large intestine, and then rinsed each section.

Next, the experts digested the organic matter, filtered the residues, and counted the remaining microplastic particles.

To confirm what the particles were made of, the team used FTIR spectroscopy, a method that matches each particle’s chemical fingerprint to known polymers. This step is essential for telling plastic from natural fibers.

Microplastics inside dolphins

Microplastics were present in all five dolphins, with a mean of about 286 particles per animal. Most particles were thin fibers, a sign that textile shedding and wastewater inputs are at play.

The dominant polymer was polyethylene terephthalate (PET). Many particles fell between roughly 0.2 and 0.012 inches (50 and 3 millimeters), a size range that is small enough to pass through the digestive system but large enough to snag along the way.

Loads tended to be higher in the small intestine, which has more length and complex folds that can temporarily retain particles. The particles were mostly clear or blue in color, which is consistent with laundry fibers and packaging.

Dolphin exposure to microplastics

Not all plastics carry equal chemical concerns. A polymer hazard framework assigns higher hazard scores to polymers with chemical building blocks that are toxic. Using this approach, the researchers rated the dolphins’ polymer mix at medium to high risk. 

“This study represents the first baseline assessment of MPs pollution caused by anthropogenic activities and offers valuable insights for the conservation of this endangered freshwater species,” wrote Ali.

The new evidence fits a broader pattern seen in Pakistan’s rivers. In the Swat River, a 2022 study measured about 192 plastic particles per liter of surface water and found plastics in fish from the same system.

For context, a 2019 paper that examined 50 stranded whales and dolphins around Britain detected microplastics in every animal, but at a much lower mean of about 5.5 particles per animal.

River dolphins feeding in polluted freshwater may therefore face a different exposure landscape than many marine mammals.

What this could mean for dolphins

Plastics are not just inert particles. They can carry additives like bisphenols and phthalates, and they can pick up other pollutants in water.

A 2023 review detailed how microplastics and their associated chemicals can disrupt hormone systems, with observed effects on reproduction and metabolism in mammals.

The Indus River dolphin already lives under stress from low flows, bycatch, and habitat fragmentation. Added chemical and particle exposure could push vulnerable animals over a physiological edge.

Microplastics that dominate in dolphins

Fibers dominate because every wash of synthetic clothing releases them. Wastewater treatment can reduce but not eliminate this load, which then travels into rivers used by people and wildlife.

PET is widespread in beverage bottles, food packaging, and textiles. This means that its prevalence is not surprising where urban and industrial effluents enter rivers. The polymer mix observed in prey fish from the Indus basin suggests a pathway for plastic to move up the food chain into dolphins.

The polymer risk results point to specific control points. Better filtration at textile mills and municipal wastewater plants can cut fibers. Stricter solid waste control upstream can reduce fragmentation into microplastics.

“Our results emphasize the need for further ecotoxicological studies to better understand the potential impacts of MPs in this endangered species,” wrote Ali. More field work should track plastic exposure alongside health markers in live dolphins and their prey. 

Protecting dolphins from microplastics

Data like these help target actions where they matter most. The dolphins’ distribution is already carved into segments, so reductions in plastic inputs near key subpopulations can pay outsized dividends.

Public reporting that includes polymer types, not just counts, will sharpen future risk assessments. That level of detail connects local waste sources to measurable risks in a species that depends on a cleaner Indus.

The study is published in the journal PLOS One.

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