On a sunny spring morning, Stephen Wangari joins other young scientists from the IAEA’s Isotope Hydrology Laboratory carrying pumps, vials, plastic containers and tubes to a quiet backwater of the Danube River near the IAEA Headquarters in Vienna. On the grassy bank they connect the equipment, submerge a tube in the water and turn on a pump. Water starts circulating through the set-up, which the scientists closely monitor. 

“This is a test run to improve water sampling,” says Astrid Harjung, a researcher in the laboratory. “It doesn’t look very fancy, does it?” she laughs, pointing at the items spread out on the grass. “But field tests like this give us a chance to test and fine-tune the equipment under real conditions so that sampling can be done as efficiently as possible.”

Astrid and her team are developing a new method that utilizes sulphur-35 to track how surface water — and any contaminants it may carry — migrate into groundwater.

“Sulphur-35 has a short half-life of 87 days and occurs naturally in precipitation,” Astrid explains. “Tracing it helps us quickly assess whether groundwater in a specific location is vulnerable to contamination. This could be especially useful, for example, in refugee camps without proper sanitation or in areas affected by natural disasters.”

Stephen assisted in the initial development of sulphur-35 analysis while an intern in the laboratory. After a stint at a laboratory in his home country of Kenya, he is now back at the IAEA as a technician in the Isotope Hydrology Laboratory, where the focus of his work has shifted from sulphur-35 to tritium.

Tritium is an isotope of hydrogen with a half-life of 12.3 years, providing water cycle information over a timeframe of around 50 years. This information helps hydrologists and water managers understand longer term changes in groundwater recharge, how well aquifers are connected to surface water systems, and what this means for groundwater sustainability.

Supporting Member States with tritium analysis has been a core function of the Isotope Hydrology Laboratory for over 60 years.

As Stephen’s colleagues continue their work on the riverbank, he says a quick goodbye and heads off to the laboratory to process water samples for the Global Network of Isotopes in Precipitation.

He checks for new water samples from Member States and finds that several have arrived. His day will be spent purifying, enriching and measuring them.

Stephen puts each sample in a water purification system. He connects tubes that will guide the water through tiny columns filled with ion exchange resins — special materials that act like magnets on salts and other charged particles, removing them from the water. The process takes about an hour, and Stephen uses the time to update the laboratory’s sample database. 

Once the water purification is done, the samples are ready for the next step: enrichment. Stephen inserts them into the electrolytic enrichment system, a two-metre-long, steel framed machine lined with cables, digital displays and rows of tubes. Electricity begins to flow through the system.

Unlike sulphur-35, which floats freely in water, tritium is part of the water molecule itself, so it cannot simply be filtered out for measurement. Electrolysis gradually splits water molecules into hydrogen and oxygen gases, reducing the water’s volume and consequently concentrating the tritium.

Stephen regularly checks and maintains the machines and oversees the enrichment process, which can take up to two weeks to complete. He ensures that the electricity running through the samples is gradually increased as required.

“We are always striving to improve the enrichment process,” he says. “The concentration of tritium is very low and hard to measure. Effective enrichment is essential in getting reliable information out of the samples.”

Although tritium is highly concentrated after the enrichment process, it is still barely detectable in water samples. Even the faintest contamination from atmospheric radiation could distort the measurements of the samples. That is why Stephen takes the enriched samples to a room located several stories underground and lined with thick concrete, shielding it from environmental radiation. Here, he carefully mixes each sample with a chemical solution and puts them into machines that will measure their radioactive signature over the next 24 hours.

Back upstairs, the day is drawing to a close. Astrid has returned from the field and she and Stephen catch up on each other’s day. They are happy with the progress they have made and discuss their tasks for the following day.

“Our work here connects us with many regions of the world,” Stephen says, as he hangs up his lab coat and prepares to head home. “What we do supports so many areas — agriculture, climate change, public health and more. I am proud to be part of it.”