Long distance transport of plutonium by colloids
Actinides – a group of radioactive elements such as thorium, uranium and plutonium – are generally considered to be poorly soluble in water. Nevertheless, they contaminate bodies of water over long distances by binding to small particles called colloids and being transported with them, as researchers led by Rodney Ewing from the University of Michigan in Ann Arbor have now demonstrated.
The researchers found plutonium in the groundwater three to four kilometers away from the Mayak nuclear production facility in the Urals, which seeped underground with the liquid within 55 years. The plutonium activity at this point is still 0.16 becquerels per liter, while at the source - the Mayak reprocessing plant - it is 1000 becquerels per liter. Seventy to ninety percent of the plutonium found by the scientists outside the plant area was bound to colloids, which were therefore mainly responsible for large-scale distribution. Ion mass spectroscopy of these tiny soil particles revealed that they were primarily amorphous iron oxide colloids that add plutonium-4 hydroxides or carbonates and also uranium carbonates.
Ewing and his colleagues therefore urgently advise considering this transport route for future final storage sites for nuclear waste - for example the highly controversial storage in the Yucca Mountains in Nevada - since there, too, the geochemical and hydrological conditions for the formation of the dangerous Colloids are given.
