A Radioactive Isotope Appeared Across Europe

In January 2017, scientists at a radiation monitoring station in northern Norway detected something unusual in the air. Their instruments had picked up traces of iodine-131, a radioactive substance produced in nuclear reactors and facilities making medical isotopes.

The amount was tiny, but the discovery caught their attention. Iodine-131 loses half its radioactivity approximately every eight days, which meant the material had entered the atmosphere fairly recently.

Within weeks, monitoring stations in several other European countries began reporting the same substance. Scientists wanted to find out where it was coming from.

The Readings Kept Appearing

The first detection came during the second week of January. Soon, laboratories in Finland, Poland, Germany, France, Spain, and several other countries were finding iodine-131 in their air samples.

By the time researchers collected the reports, approximately 30 monitoring stations had detected the isotope over an eight-week period. The readings were extraordinarily small, sometimes measuring just a few millionths of a radioactive decay per second in a cubic metre of air.

These laboratories used highly sensitive instruments capable of detecting quantities far below anything that would threaten public health. Most people would never have known the material was there.

But the widespread detections attracted scientific attention. Finding fresh iodine-131 across so many countries suggested that something was releasing it into the atmosphere.

One Location Had Much Higher Readings

As researchers compared the results, one location stood out. A monitoring station in western Russia had recorded concentrations hundreds or even thousands of times higher than some of the readings farther west.

That gave investigators an important clue. At least one source might be much closer to the Russian monitoring station than to the laboratories in other countries.

Scientists began studying weather patterns to work out how the radioactive material had traveled. Winds can carry substances across national borders, transporting pollution hundreds or even thousands of kilometres from its source.

By comparing measurements with computer models of air movement, researchers could estimate where the iodine might have originated. They also examined the samples for other radioactive materials that could help identify what had produced it.

A Nuclear Accident Wasn’t the Only Possibility

Iodine-131 can be released during nuclear reactor accidents, so investigators considered whether an undisclosed incident might have occurred somewhere in Europe.

But serious reactor accidents generally release several radioactive substances together. The monitoring stations weren’t finding the mixture researchers would expect from a major reactor failure. Instead, their samples contained primarily extremely small amounts of iodine-131.

That led scientists toward industries that regularly handle the isotope. One possibility involved wastewater treatment, since radioactive material used in hospitals can eventually enter sewage systems.

Another possibility was the manufacture of radioactive medicines. Facilities producing these substances handle iodine-131 routinely, sometimes in quantities large enough that even a very small release could be detected far away.

The Search Led to Medical Laboratories

Iodine-131 is widely used in medicine, particularly for treating thyroid conditions. Specialized facilities manufacture it for hospitals, where doctors use radioactive substances to diagnose and treat certain illnesses.

During production, small quantities can escape through controlled ventilation systems. Those emissions are monitored, and facilities may be permitted to release amounts that remain within safety limits.

In 2018, an international team of scientists published an investigation in Environmental Science & Technology. The researchers examined several possible sources, including nuclear power plants, wastewater facilities, and companies manufacturing radioactive medical products.

Their calculations pointed strongly toward medical isotope production. The team found that releases from multiple facilities could account for the iodine detected across Europe. One facility in western Russia appeared to be a likely contributor to the stronger readings recorded nearby.

This introduced an interesting possibility. Instead of a single release producing one enormous cloud, several facilities might have been sending small amounts of iodine into the atmosphere around the same time.

Winter Weather Helped Trap the Material

Another clue came from the weather during January and February. Much of Europe was experiencing strong temperature inversions, conditions that can trap pollution close to the ground.

Normally, air moves vertically as well as horizontally, helping pollutants spread through the atmosphere. During an inversion, warmer air sits above colder air near the surface, making that mixing much harder.

The result can be a buildup of material that would otherwise become more diluted. Even small emissions can linger near the ground long enough for sensitive monitoring equipment to detect them.

Researchers found that these conditions had affected Europe during the iodine-131 episode. Ordinary air pollution had also risen in some areas, providing another indication that the atmosphere wasn’t dispersing substances normally.

The weather helped explain why such small releases had remained detectable over a long period. It also complicated the search for their origins, since emissions from different locations could travel and overlap.

Several Sources, One Enormous Trail

Using measurements from laboratories across Europe, the researchers reconstructed possible routes taken by the iodine-131. They compared those routes with facilities that handled the substance and estimated how much each might have released.

The results suggested that medical isotope producers were the most likely contributors. The stronger western Russian readings appeared consistent with emissions from a facility in that region, while smaller releases elsewhere could explain other detections.

The scientists also found that the estimated emissions from the suspected Russian source could have remained within authorized limits. The readings therefore didn’t necessarily point to an accident or an equipment failure.

What made the investigation difficult was the number of possible sources. Each monitoring station had collected material carried by winds that could have passed over several different facilities.

By the time scientists examined their samples, those journeys had already taken place.