Surface water in and around industrial areas along the Turag and the Shitalakkhya contains high concentrations of four harmful heavy metals, including lead, which was detected at up to 45 times the safe limit set by the World Health Organization, according to a new study.
Laboratory tests of water samples collected from industrial discharge points along the two rivers in Gazipur and Narayanganj also found excessive levels of iron, mercury and manganese.
While lead and mercury are classified as highly toxic pollutants, iron and manganese fall in the category of moderate pollutants.
The concentration of iron was found to be almost eight times the WHO safe limit, mercury nearly six times the limit, and manganese twice the limit, highlighting the extent of industrial pollution that poses risks to both human health and the environment.
In one of the samples, arsenic was detected at 10.56 ppb (parts per billion), slightly above the safe limit of 10 ppb.
“The concentration and widespread presence of lead were the highest among all these heavy metals. Once water is polluted with heavy metals, it is very hard to treat that,” said Prof Sharmind Neelotpol, chairman of the School of Pharmacy at BRAC University and the principal investigator of the study.
Her fellow researcher and BRAC University lecturer Asef Raj co-authored the study.
The study, titled “Heavy Metal Pollution and Health Risk Assessment in Surface Waters Impacted by Pharmaceutical Effluents in Gazipur and Narayanganj, Bangladesh,” was published in Nature, a British weekly scientific journal, in March.
Asked whether conventional treatment plants can remove heavy metals from water, Sharmind replied in the negative.
She further said that exposure to lead and other heavy metals causes various health problems. “Once lead enters our body, it is deposited in bones.”
Referring to WHO health advisories, Dr Tareq Salahuddin, a public health professional, said that no level of lead exposure is known to be without harmful effects. Children are particularly vulnerable because lead can permanently affect the developing brain. Chronic exposure in adults is associated with hypertension, heart disease and kidney problems.
Noting that mercury poses a particular risk to human health through fish consumption, he said that in rivers, microorganisms can convert mercury into methylmercury, a highly toxic form that accumulates in fish. As a result, larger predatory fish can contain much higher levels of methylmercury than the surrounding water.
“For communities that regularly consume contaminated fish, this can become a major exposure pathway. Pregnant women, foetuses, and young children are of particular concern because methylmercury can interfere with neurological development.”
He also pointed out that iron and manganese are essential for the human body but excessive exposure to either metal is harmful. High levels of manganese may affect the nervous system, while too much iron can damage organs, though neither is as strongly linked to cancer as heavy metals like arsenic or cadmium.
SAMPLE COLLECTION AND LAB TESTS
Samples were collected from 12 key locations across two major industrial zones — Gazipur (the Turag) and Narayanganj (the Shitalakkhya) — between late November 2024 and early January 2025. These rivers receive effluents from textile, dyeing, chemical and pharmaceutical factories.
Two samples were collected from each location, within 100-250 metres of industrial discharge points.
The samples were tested at Bangladesh Council of Scientific and Industrial Research (BCSIR) to determine the levels of 10 heavy metals. Lead and iron exceeded the WHO safe limit in 10 samples, mercury in six samples, manganese in four samples and arsenic in one sample.
Analysing the sampling locations, the study said the findings “confirm that untreated pharmaceutical and mixed industrial effluents are the principal sources of heavy metal pollution in the studied regions”.
It said the predominance of lead, iron, mercury and manganese in surface water is commonly associated with residues from pharmaceutical and chemical manufacturing units.
Industrial emissions, leather tanning, battery waste, smelting operations and effluents from metal-processing plants are also major sources of heavy metal pollution.
The study recommended regular monitoring of heavy metals in surface water and stronger regulatory measures to curb pollution.
WHAT OFFICIALS, EXPERTS SAY
According to officials of the Department of Environment (DoE), more than a thousand industrial units, especially textile, dyeing, and pharmaceutical units, have been polluting the two rivers in Gazipur and Narayanganj. Though the majority of them have effluent treatment plants (ETPs) to treat liquid waste, these ETPs don’t function properly in most cases.
They also pointed to a severe workforce shortage that is hampering their monitoring. In its two district offices, the department has only 10 officials, including field inspectors, to monitor several thousand industrial units.
“Even if we recruit 50 inspectors, that number will not be enough to monitor all these industries,” said one of the DoE officials on the condition of anonymity.
When contacted, Arefin Badal, deputy director of the DoE, said, “In Gazipur, 688 industrial units discharge liquid waste. All of them have effluent treatment plants.”
Asked about the industrial units polluting the Shitalakkhya, AHM Rashed, deputy director of the DoE, said, “At least 420 industrial units in Narayanganj generate and discharge liquid waste. Of them, 360 have effluent treatment plants.”
Some of the units without ETPs are operating after securing court orders in their favour, he added.
Experts said the rapid pace of urbanisation, industrial growth and population increase in Bangladesh has intensified pollution in water bodies, especially in cities.
Industrial units have mushroomed in Gazipur and Narayanganj over the last few decades, and most of them discharge untreated waste into nearby canals and the Turag and the Shitalakkhya amid inadequate oversight by the regulatory authorities.
Mujibur Rahman, a professor at the civil engineering department of Bangladesh University of Engineering and Technology (BUET), who has been working on river pollution in Dhaka for over three decades, said that when a river is polluted with heavy metals, it is certain that untreated industrial waste is causing the pollution.
“The regulatory authorities have to monitor the industrial units and make sure they treat their effluents before discharging them.”
When his attention was drawn to the DoE’s manpower shortage, Mujibur said that many advanced monitoring technologies are available now.
“For tracking pollution by industrial units, they could install devices at effluent treatment plants and monitor from their offices whether a particular industry is violating the rules,” he added.
