Most fossil groundwater resources in North Africa and the Middle East are characterized by high-quality water with low salinity. "The assumption has been that unsafe radioactive levels occur primarily in high-saline groundwater, so low-saline sources, such as water from a Nubian sandstone aquifer, are relatively safe resources just waiting to be tapped," Vengosh said.
To test that hypothesis, Vengosh and his colleagues investigated water from 37 pumping wells in the Disi aquifer's Rum Group, where low-saline groundwater is extracted from Cambro-Ordovician sandstone, and from wells in the Khreim Group, where saltier water is extracted from an aquifer containing larger amounts of clay minerals and oxides. All samples were analyzed for major and trace elements and for four radium isotopes. For comparative purposes, sandstone rocks from the Disi aquifer, along with Nubian sandstone rocks from the nearby Negev Desert in Israel, were also measured for radium.
"We found a lack of correlation between salinity and radioactivity," Vengosh said. "Instead, our findings suggest that an aquifer's geological properties may be a much more significant factor."
Vengosh and his group hypothesize that an aquifer with a higher content of clay minerals and oxides provides more adsorption sites for radium, and this results in lower radionuclide levels in the water itself. Sandstone aquifers, on the other hand, offer fewer adsorption sites, and, as a result, generate radium-rich groundwater.
"Given that most of the aquifers in the region that contain fossil water are composed of Nubian sandstone and are characterized by low-saline groundwater, similar to that in the Disi aquifer, we suggest that high-radioactive groundwater may also exist in these basins. This could pose health risks for a large population," Vengosh said. Grou
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