Every glass of water carries a story, but not always a safe one. Across the world, millions of people are drinking water contaminated with invisible poisons such as lead and cadmium. These heavy metals do not degrade in the environment and accumulate in the human body, where even small amounts can cause devastating health effects. Lead exposure is linked with kidney damage, brain disorders, developmental delays in children, and cancer. Cadmium, often found in mining waste and industrial discharge, is associated with bone disease, kidney failure, and severe respiratory illnesses.
The World Health Organization (WHO) and national regulators have set strict limits for drinking water safety: just 0.01 milligrams per litre for lead and 0.003 milligrams per litre for cadmium. Yet in many parts of the world, including regions of India, China, and Africa, water sources far exceed these thresholds due to ageing infrastructure, poorly managed industrial effluents, and unsafe disposal of batteries and electronics. For rural and developing communities, high-tech solutions such as reverse osmosis and ion exchange are often out of reach. They are expensive, maintenance-heavy, and can generate environmentally harmful by-products.
Against this backdrop, scientists at the Indian Institute of Technology (IIT) Kharagpur have developed an affordable, reusable material that could change the way water is purified. Their research, recently published in Separation and Purification Technology, describes an innovative bead-based system that selectively captures lead and cadmium from contaminated water.
A breakthrough at IIT Kharagpur
The project was spearheaded by Sayak Saha Chowdhury and Devi Prasad Mishra from the Membrane Separation Laboratory, Department of Chemical Engineering, IIT Kharagpur, under the supervision of Professor Sirshendu De. Professor De is a leading scientist in the field of membrane science and water treatment in India, with a long track record of bridging fundamental research with real-world application.
At the core of the innovation is hydroxyapatite, a calcium-rich mineral naturally found in human bones and teeth. The researchers substituted some of its calcium with aluminium to create aluminium-substituted hydroxyapatite (aHAp). To enhance its affinity for toxic metals, they treated the material with thioglycolic acid (TGA), adding sulphur groups to its surface. These groups act like chemical hooks, strongly binding with heavy metals through chelation and electrostatic interactions. The resulting upgraded material, named aHAp-TGA, was then embedded into a stable polymer, polyacrylonitrile (PAN), to form easy-to-handle solid beads.
This material represents an important step towards developing cost-effective, scalable water purification systems for regions where access to advanced infrastructure is limited.
-Prof. Sirshendu De
The science behind the beads
The innovation lies in combining the strong binding capacity of modified hydroxyapatite with the mechanical robustness of polymer beads. Hydroxyapatite is already biocompatible and non-toxic, making it safe for environmental use. However, on its own, it lacks sufficient efficiency for capturing heavy metals at the levels required for drinking water treatment. By introducing sulphur groups, the researchers increased its chemical affinity for lead and cadmium, dramatically improving its performance.
Once encased in PAN, the beads are durable, simple to transport, and can be packed into filtration columns. This design makes them suitable for household filters, industrial treatment units, or community-level water purification plants. Importantly, they avoid the drawbacks of many advanced technologies, offering a low-cost solution that could be deployed in both urban and rural settings.
Laboratory validation
To test their system, the team carried out a series of laboratory experiments under controlled conditions. The results were striking. The aHAp-TGA material achieved a maximum adsorption capacity of 1131 milligrams of lead per gram and 177 milligrams of cadmium per gram. This represented around 40 per cent more lead capture and over 60 per cent more cadmium capture compared with unmodified aHAp.
Further testing of the distribution coefficient (Kd), which measures how strongly a material binds contaminants, confirmed its superior performance. For water contaminated with 5 mg/L of lead, the Kd value reached 3.66 × 10⁵ mL/g, while for cadmium it reached 1.25 × 10⁴ mL/g. These numbers indicate that the material holds onto metals much more effectively than it releases them back into the water.
When converted into PAN beads, the system still demonstrated strong performance, with maximum uptake levels of (123.5 -156) mg/g for lead and (37-51) mg/g for cadmium. This balance of efficiency and stability is what makes the technology particularly promising for real-world applications.
Performance in real conditions
The team went beyond controlled tests to explore how the beads behave under varied environmental conditions. They investigated the effect of different pH levels, temperatures, initial metal concentrations, contact times, and competing ions. The material remained highly effective across this range. Crucially, it retained its selectivity for lead and cadmium even when common ions such as calcium, magnesium, or sodium were present. This is particularly important for groundwater and wastewater, where multiple chemical species coexist.
Temperature resilience was also encouraging. The beads functioned well under fluctuating conditions, reflecting their potential use in diverse climates. In addition, the material showed robustness to repeated use. Unlike many filters that quickly lose efficiency, the aHAp-TGA PAN beads were regenerated and reused with only minimal loss in capacity. This reusability makes them both environmentally sustainable and cost-effective.
From the lab to the field
To evaluate their scalability, the researchers constructed filtration columns packed with aHAp-TGA PAN beads. Water containing lead and cadmium was passed through, and the concentration of metals was monitored until it reached prescribed discharge limits of 1 mg/L for lead and 2 mg/L for cadmium. This point, known as the breakthrough point, provided evidence that the beads could maintain their performance over extended periods. Modelling confirmed their suitability for continuous flow systems, making them adaptable for treatment plants or domestic filters.
The ability to operate in continuous systems is key for practical deployment. Communities do not need a batch treatment process; they require a reliable, ongoing supply of safe drinking water. The filter column tests showed that the IIT Kharagpur innovation could fit into such systems with relative ease.
A sustainable solution for clean water
The environmental and social implications of this research are significant. Heavy metal contamination disproportionately affects communities with limited access to advanced water treatment. For rural households near industrial zones, or for villages where groundwater is the primary source, this technology could provide a life-saving solution. The low cost of hydroxyapatite, combined with its non-toxic nature, enhances the sustainability profile of the system.
Moreover, the fact that the beads are reusable reduces both waste and expense. In a world where single-use plastics and short-lived filters dominate, a regenerative system offers a more responsible pathway towards sustainability.
Looking ahead
Although laboratory and small-scale trials have been promising, several steps remain before the technology can reach commercialization. The researchers anticipate future field trials in heavily polluted regions to assess performance under complex real-world conditions. Long-term durability testing will be required to evaluate how the beads perform over months or years of use. Scaling up manufacturing processes, while maintaining quality and affordability, will also be a challenge.
Integration into existing water treatment systems, from municipal plants to household purifiers, will require collaboration between researchers, industry partners, and policymakers. However, the potential benefits are clear. If successful, aHAp-TGA PAN beads could become an integral part of global efforts to secure safe and affordable drinking water.
Conclusion
The IIT Kharagpur team’s innovation is more than a scientific curiosity; it is a tangible step towards addressing one of the world’s most urgent challenges. By combining chemistry, engineering, and sustainability, they have developed a material that is effective, affordable, reusable, and scalable. For millions living under the shadow of toxic water, such innovations represent hope.
Access to clean water should not be a privilege but a right. Technologies like this bring us closer to that vision.
-Prof. Sirshendu De
Reference
Saha Chowdhury, S., Mishra, D.P., De, S., 2025. Synthesis of sulfonated metal-substituted hydroxyapatite and its polymeric composite for sequestration of lead and cadmium from water : Batch and column study. Sep. Purif. Technol. 362, 131822. https://doi.org/10.1016/j.seppur.2025.131822
