Particles of radioactive plutonium from nuclear testing have remained high in the stratosphere for more than 50 years, and volcanic eruptions such as Iceland’s Eyjafjallajökull in 2010 can bring those particles into the lower atmosphere, researchers report January 7 in Nature Communications. They caution, however, that the concentrations of particles in the lower atmosphere are small and do not threaten human health.
Because nuclear tests were conducted so long ago, all these radioactive stratospheric particles should mostly be gone by now, scientists had concluded.
The 2010 eruption of Eyjafjallajökull started scientists to think that those conclusions might be wrong. When the volcano erupted, researchers in Switzerland began taking aerosol samples from the troposphere, and they found elevated concentrations of radioactive particles. Levels of plutonium and cesium (another byproduct of nuclear testing) were up to three orders of magnitude higher than levels found in aerosols at ground level. These measurements contradicted the earlier aerosol studies, which had found low levels throughout the troposphere; something was up.