Dangerous levels of microplastics and toxic heavy metals have accumulated in the sediments of the Bhairab and Rupsa rivers in southwestern Bangladesh, posing a serious threat to aquatic life, public health, and the fragile ecosystem of the Sundarbans, according to a recent scientific study.
The research, conducted by the Department of Environmental Science and Technology at Jessore University of Science and Technology (JUST) and published in the international journal Emerging Contaminants in January, found widespread contamination in river sediments collected from nine locations along the Bhairab and Rupsa rivers.
The study was carried out by researchers Nishat Salsabil, Md. Touhiduzzaman, Tapas Kumar Chakraborty and Gopal Chandra Ghosh. Sediment samples were collected from depths of up to 30 centimetres at locations stretching from Rupdia in Jessore to Batiaghata in Khulna.
Researchers detected a maximum of 5,700 microplastic particles per kilogram of sediment in the upper sediment layer, with an average concentration of 3,600 particles per kilogram. The average concentration declined to 2,744 particles in the middle layer and 1,177 particles in the lower layer. Notably, microplastics were found as deep as 10 to 30 centimetres below the riverbed, indicating long-term accumulation.
Among the detected microplastics, fragments accounted for 51 per cent, followed by fibres (26 per cent) and films (18 per cent). Polyethylene was the most common polymer, making up 23 percent of the samples, followed by polystyrene (21 per cent) and polypropylene (18 per cent).
The researchers also detected elevated concentrations of toxic heavy metals, including cadmium, lead, chromium, nickel and copper, in the river sediments. They warned that fish and other aquatic organisms ingest microplastics, allowing these toxic substances to enter the food chain and potentially increasing the risk of serious health conditions, including cancer, in humans.
The study identified untreated municipal and industrial waste as the principal sources of pollution. More than 22 drainage outlets connected to canals and stormwater drains in Khulna city discharge waste directly into the Bhairab and Rupsa rivers. Industrial facilities and tanneries in the Nawapara area also release untreated chemical effluents into the Bhairab River, contributing to the accumulation of toxic metals in river sediments.
According to the 2021 Waste Wise City Tool survey conducted with support from the United Nations, Khulna generates approximately 732 tonnes of waste daily, of which the city corporation collects 461 tonnes. The remainder is dumped into drains, canals and rivers. Private-sector estimates suggest the city's daily waste generation may be as high as 1,000 to 1,200 tonnes.
Researchers said the pollution level falls into the very high (Class V) category under the Potential Ecological Risk Index (PERI). They warned that excessive concentrations of cadmium and nickel are severely threatening river biodiversity and that continued plastic pollution and untreated sewage discharge could make ecological restoration increasingly difficult.
Local fishermen say the environmental degradation is already affecting their livelihoods. Md. Javed, who has fished in the Rupsa, Atharobeki and Bhairab rivers for more than two decades, said fish populations have declined sharply as water quality has deteriorated.
"The river no longer supports fishing the way it once did. Fish have become scarce, and earning a living has become increasingly difficult," he said.
Dr. Md. Mujibur Rahman, a professor of Environmental Science at Khulna University, warned that pollutants carried by tidal currents from the Bhairab and Rupsa rivers are reaching the Sundarbans, threatening the world's largest mangrove forest.
"The presence of lead, cadmium and other toxic metals in river sediments is deeply concerning. Unless industrial discharge and urban waste are effectively managed, the ecological balance of the Sundarbans and the wider coastal environment will face growing risks," he said.
Sundarbans East Division Divisional Forest Officer (DFO) Md. Rezaul Karim Chowdhury echoed the concern, saying toxic pollutants transported by tidal flows could spread throughout the coastal region, endangering biodiversity and environmental health.
He urged authorities to immediately stop the direct discharge of domestic and industrial waste into rivers, strengthen industrial waste recycling, enforce environmental regulations and expand public awareness programmes.
The Forest Department, together with local communities and tour operators, continues weekly operations to remove plastic waste from the Sundarbans. However, experts stressed that preventing pollution at its source remains essential to protecting Bangladesh's rivers, coastal ecosystems and the Sundarbans from irreversible damage.