Water pollutants: The invisible crisis

Water is vital for food security, human health and economic development. But as populations grow and climate change intensifies, pollution is increasing throughout the water cycle.

Water pollutants come in many forms, which are often invisible. Fertilizers, plastics, sewage, pharmaceuticals, hormones, industrial chemicals, petrochemicals, heavy metals and mining run-off are among the most common.

A key hurdle for countries seeking to improve water quality is the lack of data on their water resources. Nuclear and isotopic techniques can help us understand where water pollution originates and provide science-backed solutions to mitigate this challenge.

The nitrogen problem

Nitrogen is a leading source of water pollution, with potentially serious effects on human health and the environment. Major sources of nitrogen pollution include fertilizers, wastewater and industrial discharges. While nitrogen fertilizer has boosted food production over the past century, around 80% of it is lost to the environment.

“Nitrogen pollution, especially from nitrates, is a major threat to rivers, lakes, groundwater and coastal waters,” said Ioannis Matiatos, an isotope hydrologist at the Hellenic Centre for Marine Research in Greece. “Tracing where nitrate contamination comes from is essential for protecting aquatic systems and guiding efforts to clean up polluted areas.”

Nitrates are the most soluble form of nitrogen, meaning they can easily seep into groundwater, lakes and rivers. If concentrated in drinking water, nitrates can impair the blood’s ability to transport oxygen around the body. Nitrogen pollution also causes water to become overly enriched with nutrients, leading to harmful algal and plant growth in lakes and rivers. According to the United Nations Environment Programme, nitrogen pollution is the biggest driver of biodiversity loss after habitat destruction and greenhouse gas emissions.

Climate change is exacerbating the impact of nitrogen pollution. Earth’s warming climate is resulting in more wildfires, leading to increased use of fire retardants containing large quantities of nitrogen based compounds that leach into water sources. Meanwhile, lakes and rivers are warming as the planet heats, promoting the growth of types of vegetation that can harm ecosystems and the environment. Warmer lakes filled with algae can emit nitrous oxide, a greenhouse gas, while colder lakes remove nitrogen from the nitrogen cycle and store it over long periods.

Decoding nitrogen pollution through isotopic analysis

The IAEA is using isotopic techniques to help identify the sources of nitrogen pollution. As part of this research, it has worked with the University of Massachusetts to develop cheaper, safer and faster methods to trace the origin of nitrogen pollution in rivers, lakes and seas.

“Nitrate isotope techniques are a powerful tool because they help us identify nitrate pollution sources and understand how nitrogen is used and transformed in nature,” Matiatos said.

Through its technical cooperation programme, the IAEA is helping countries build capacity in isotopic techniques to study nitrogen pollution everywhere from the Italian Alps — where glacial meltwater feeds into nearby lakes — to the megacity of Kolkata, India.

The IAEA also uses isotopic and nuclear techniques to help countries use fertilizer more efficiently, enhance carbon and nitrogen capture in agro-ecosystems, and investigate how legume crops, or integrated cropping-livestock systems, can reduce the need for chemical fertilizers.

Compounds of emerging concern

Contaminants such as pharmaceuticals, hormones, industrial chemicals and personal care products are increasingly being detected in surface water systems. These contaminants usually originate in municipal, industrial and domestic wastewater. Known as ‘compounds of emerging concern’, they have only recently been identified as potential threats to the environment and are not yet widely regulated by national or international laws. Their effects in freshwater are not well understood, but it is believed that they may disrupt hormones and contribute to antibiotic resistance in humans and animals and negatively impact aquatic ecosystems.

However, compounds of emerging concern can be used to better understand sources of nitrate pollution because they occur together in polluted water systems. The IAEA is working with scientists around the world to trace the origins and pathways of nitrate pollution in surface water and groundwater by linking nitrate isotopes to these compounds.

“Compounds of emerging concern are ideal tracers for faecal contamination as they are usually linked to a specific source and are detectable in contaminated environmental samples,” said Yuliya Vystavna, an?IAEA isotope hydrologist.

Radiation technology for wastewater treatment

Removing micropollutants such as microplastics, persistent organic contaminants and pharmaceuticals from wastewater is critical to achieving and maintaining clean water. Radiation technology, including electron beams (e-beams) and gamma irradiation, plays a significant role in addressing a wide range of organic pollutants in wastewater and sewage sludge by breaking down these complex molecules into less harmful or more easily removable forms.

Microplastics pose a particularly stubborn challenge because they resist biodegradation and tend to fragment into even smaller particles.

Microplastics have been found in tap and bottled water, the air we breathe, river sediments and soil. They contaminate groundwater and surface water and end up in the ocean. Plastic pollution monitoring carried out under the IAEA’s Nuclear Technology for Controlling Plastic Pollution (NUTEC Plastics) initiative has found microplastics even in the most pristine and protected areas of the planet, including the Galapagos Islands and Antarctica.

Treating wastewater with e-beam technology offers a promising solution. It aggregates microplastics into clumps that can be easily removed from wastewater. Recent experiments at Poland’s Institute of Nuclear Chemistry and Technology, an IAEA collaborating centre for radiation technology, show that between 85% and 95% of microplastics can be separated from wastewater following treatment with e-beam technology.

“Microplastics are challenging to remove using conventional water and wastewater treatment methods,” said Bumsoo Han, a radiation expert and chief consultant at Bright Future Technologies in the Republic of Korea. “Although research is still in its early stages, ongoing studies are expected to contribute significantly to addressing microplastic pollution in our environment.”

NUTEC Plastics: Addressing plastic pollution

The IAEA’s flagship NUTEC Plastics initiative brings together countries and partners worldwide to address plastic pollution by leveraging nuclear technologies to improve the detection and identification of microplastics and nanoplastics in the marine environment, and to develop effective plastic recycling techniques that reduce reliance on fossil fuel-based plastics. Radiation can be used to make biobased plastics, which are a more sustainable alternative to conventional plastics because they are biodegradable and/or easily recyclable by design.

Many countries are keen to move towards a more sustainable plastics economy. At the 2025 United Nations Ocean Conference, where participants focused on the ongoing negotiations towards an international legally binding agreement on plastic pollution, the IAEA highlighted the role of nuclear science in tackling this challenge.

“Nuclear science helps protect our ocean and support life below water,” IAEA Director General Rafael Mariano Grossi said at the conference. “Through our marine laboratories in Monaco and NUTEC Plastics, we are helping countries tackle marine pollution by equipping 100+ labs worldwide to monitor microplastics.”

Around 80% of marine plastic pollution originates on land, so intensifying efforts to improve recycling and treatment of plastic waste before it ends up in landfill sites and water systems would help to address this growing global challenge. ?

Constructed wetlands to remediate mining wastewater

Natural wetlands — in which freshwater filtering occurs as a result of physical, geochemical and biological processes in soil, sediment and plants — have proved to be effective in sequestering pollutants from contaminated water. Constructed wetlands — engineered systems that use these same natural processes — are already used around the world to treat wastewater. They are typically less expensive and require less energy to operate and maintain than conventional waste treatment systems.

Constructed wetlands are increasingly being used to remediate water contaminated by mining by-products such as heavy metals and other toxic elements. These can persist for decades after mining has ceased, with potentially serious implications for human health and surrounding ecosystems.

When uranium is mined, naturally occurring radioactive contaminants such as radon and radium are often present in wastewater. According to Hannah Affum, an IAEA industrial technologist, “there is a research gap in how effectively plants and sediments can remove radioactive contaminants in constructed wetlands.”

To help bridge this gap, the IAEA recently launched a coordinated research project that uses radiotracers to investigate how the soil, gravel and plants in constructed wetlands remove and transform contaminants in wastewater produced by uranium, copper and gold mining. As the capacity of constructed wetlands to do this may decrease over time, the project will also investigate flow hydrodynamics and collect data to optimize future wetland designs.

“Focused research can give us critical insights to guide the sustainable design of these systems and improve long term contaminant sequestration,” said Affum.

From nitrogen to compounds of emerging concern, microplastics and heavy metals, the world’s water systems are coming under increasing strain. Nuclear science is providing solutions to meet this challenge.