The joint study, led by Jahangirnagar University’s departments of Zoology and Environmental Science, documents the presence of microplastics not only in river water but across the river ecosystem – even inside insect bodies.

A new scientific investigation has revealed alarming levels of microplastic contamination throughout the Dhaleshwari River ecosystem, including in six species of aquatic insects – raising worries that plastic pollution is already infiltrating the food chain and threatening human health in Bangladesh.

The joint study, led by Jahangirnagar University’s departments of Zoology and Environmental Science, documents the presence of microplastics not only in river water and sediments but also inside insect bodies. The work marks the first time such measurements have been made for aquatic insects in Bangladesh, and underscores the urgency of tackling plastic-pollution at the policy level.

Researchers collected 100 samples in all, including 30 water samples, 30 sediment samples, and insect specimens across six species. Sampling sites were chosen by random selection, with special attention paid to pollution “hotspots” – such as areas near urban settlements, industrial discharge points, dumping sites, and agricultural runoff zones.

In water samples, they found an average of 143 microplastics per litre. In river sediments, microplastic concentrations reached 30,153 particles per kilogram.

Among the insects studied, the three aquatic Heteroptera species were Diplonychus annulatus, Diplonychus rusticus, and Ranatra sp. The other three belonged to the Odonata group: Brachythemis contaminata, Crocothemis servilia, and Orthetrum sabina. Notably, this study confirmed for the first time in Bangladesh the presence of D. annulatus and D. rusticus.

The average microplastic load (particles per gram of insect tissue) varied:

• D. rusticus recorded the highest concentration of 57.82 MPs/g,
• B. contaminata at 38.53,
• Ranatra sp at 34.05,
• C. servilia at 26.99,
• D. annulatus at 16.44,
• O. sabina at 14.13.

The researchers also identified eight types of plastic polymers in the river ecosystem. The microplastic particles present in insects were almost identical (in size, colour, and shape) to those found in water and sediment samples – strongly suggesting that the insects ingest these particles from their surroundings and thus act as transporters across compartments of the ecosystem.

Ecological and human health implications

According to lead researcher, Md. Mostafizur Rahman, the findings point to a growing spread of plastic pollution into the environment – and show how insects may play a pivotal role in transferring microplastics within aquatic systems. “The presence of microplastics in small insects proves that they play an important role in transferring microplastics within the aquatic ecosystem,” he remarked.

He warned that the risk of these plastic particles eventually entering the human food chain is extremely high. Fish and birds that feed on these insects may accumulate microplastics, which could then pass to humans consuming fish or other aquatic animals.

To quantify ecological risk, the researchers applied indices such as the contamination factor, Nemerow pollution index, pollution load index, and polymer hazard index. The results showed varying degrees of risk across different river segments and compartments (water, sediment, biota).

Because freshwater-based microplastic studies are still scarce relative to marine research, this new evidence from the Dhaleshwari River is particularly significant. It highlights that rivers –  often the link between inland human activity and downstream marine systems – are also being burdened by plastic pollution.

Expert Calls; Next Steps

Rahman emphasised the need for wider, more systematic studies across Bangladesh’s river systems to map the scale and distribution of microplastic contamination. He urged that policy makers take the findings seriously and incorporate microplastic monitoring into environmental management plans.

He also noted that insect species’ microplastic burden can vary depending on their size, weight, feeding habitat, and behaviours. This heterogeneity must be accounted for in future ecological risk assessments.

Given that aquatic insects are foundational to many food webs, their contamination raises concern for biodiversity, food security, and public health alike. The researchers hope their findings will catalyse greater awareness among scientists, government agencies, industries, and civil society about the hidden but insidious menace of microplastic pollution.

Broader Relevance

Microplastics – defined as particles smaller than 5 millimetres – are increasingly recognized worldwide as a contaminant of serious concern. While much attention has focused on oceans, especially in coastal plastic pollution, the new study underlines that freshwater systems are also absorbing and transporting plastic residues, which can reach humans either directly or through trophic transfer.

In Bangladesh, where rivers are lifelines for transport, agriculture, fisheries, and daily livelihood, the infiltration of microplastics into freshwater ecosystems may pose new and underappreciated threats – not only to aquatic species but also to those who rely on riverine food sources.

As the first study of its kind in Bangladesh linking insect contamination to water and sediment microplastics, the research sets a precedent. But it is only a first step: comprehensive baselines, long-term monitoring, and regulatory integration will be essential if Bangladesh is to protect its rivers, its biodiversity, and its people from the creeping dangers of plastic pollution.