The threat to the environment posed by uranium left over from the Cold War may be less severe than feared, according to a field study led by Liverpool John Moores University.
Uranium has emerged as a global threat to human health and ecosystems due to elevated concentrations in groundwater from historical uranium mining and processing, nuclear weapons testing and waste disposal.
But the level of hazard posed by uranium leaching into rivers habitats is hitherto unknown.
Now a study of a major US river system has found that, although the toxic concentration in the groundwater was up to 70 times greater than safe levels for drinking water, the impact on river water quality was limited due to hydrological and geochemical attenuation processes in the riverbed sediments.
“Considering the potential toxicity of uranium to river organisms, it’s relatively good news, as we found that most of the uranium existed in a chemical form, which essentially makes it inert to organisms,” explained Dr Patrick Byrne, lead author of the study and an expert in enviromental pollution in the School of Biological and Environmental Science at LJMU.
Decades of leaching
In the USA, the ‘uranium rush’ of the 1950s, spurred on by the Cold War saw tonnes of waste ‘yellowcake’ deposited in storage reservoirs termed ‘tailings ponds’, many of which had no underground liners.
Decades of leaching has caused a very serious issue for millions of Americans as groundwater and groundwater-fed rivers are an increasingly important source of drinking and irrigation water.
In order to understand how uranium passes between groundwater and surface water, Byrne and his collaborators set out to map the precise locations where uranium-rich groundwater emerges into river systems and to establish the impact of this uranium on river water quality and ecosystems.
They focussed investigations on the former Riverton uranium ore processing site in Wyoming, where a uranium-rich groundwater plume threatens the Little Wind River, and used riverbed temperature surveys, groundwater and surface water sampling, and geochemical modelling to establish the impact of the plume on the river’s ecosystem.
Battle for clean water
Using temperature surveys of the riverbed, the researchers were able to map in great detail the cold water signature of groundwater moving up through the riverbed sediment and into the river. The precise location and magnitude of the uranium-rich plume was then established using passive pore water samplers.
“With many global regions demonstrating a climate shift towards aridity, groundwater will become an increasingly more important source of water for humans, and have a greater influence on river water quality,” added Dr Byrne.
“Our research has shed light for the first time on the hydrological and geochemical processes that control the transport of uranium between groundwater and river systems. And we have also established some of the constraints on uranium toxicity in river ecosystems.”
The research was funded by the U.S. Department of Energy and the U.S. Geological Survey and is published in the journal Science of the Total Environment.