Naturally Occurring Radioactivity
Radioactivity in groundwater resources in the Middle East and Northern Africa
As part of a USAID (Middle East Research Cooperation, MERC) funded-project that included scientists from Israel, Palestine, Jordan, and the US, we investigated the occurrence of radium isotopes in groundwater from the Middle East, particularly in fossil groundwater from the Nubian Sandstone basins in Jordan and Israel. This study revealed that groundwater from the Disi sandstone aquifer in southern Jordan has high levels of radium activities (two thousands per cent relative to the US-EPA drinking water standards; paper on Ra in Jordan). In a parallel study we also found high Ra also in groundwater from the Nubian Sandstone aquifer in the Negev, Israel (paper in Geotimes; AGU abstract). These findings raise concerns about the safety of this and similar non-renewable groundwater reservoirs given the high toxicity of radium in drinking water. In Jordan, this type of groundwater is expected to substitute other water sources and will become the major drinking water source in the future. The use of short-lived (223Ra and 224Ra) and long-lived (226Ra, 228Ra) radium isotopes, combined with analysis of the overall geochemistry, suggests that radium in this groundwater is derived primarily from the balance of physical recoil of the parent nuclides in the sandstone aquifer solids and Ra retention by adsorption onto clay minerals and oxides. The relationship between uniform recoil of Ra isotopes and differential retardation is attributed to the geological properties of the aquifers; aquifer with higher content of clay minerals and oxides would provide more adsorption sites, which would enhance Ra retardation. In contrast, in highly conductive aquifers, such as the Nubian sandstone aquifers, the balance between uniform recoil contribution of Ra from the aquifer solids and limited retardation due to the relatively low adsorption sites would generate Ra-rich groundwater. We expect to conduct further research for validation of this hypothesis and expand the limited database on Ra isotopes in sandstone aquifers, particularly for the Middle East and Northern Africa where fossil groundwater is increasingly utilized due to the diminishing and contamination of the other water resources.