Natural Radioactivity in Groundwater, Rocks and Sediments from Some Areas in the UAE: Distribution, Sources and Environmental Impacts
Abstract
Groundwater contains a certain amount of natural radioactivity that generally results from the decay of uranium, thorium and 40K isotopes. Knowledge of concentration levels, spatial distribution and sources of these isotopes in groundwater is crucial for environmentally safe and sustainable groundwater resources in the United Arab Emirates (UAE). This dissertation focuses on investigating the distribution, environmental impact and sources of 235U, 238U, 232Th, as well as the activity of gross β and α in groundwater in some locations in the UAE. Additionally, groundwater samples from Oman and selected aquifer rocks and sediments from the UAE were analyzed for comparison. A variety of techniques including liquid scintillation counter, ICPMS, ICP-OES and ICP-SFMS, were used for the analyses. The results reveal considerable differences in radioactivity in terms of spatial and local variability and show relatively high concentrations of 238U in some locations. Most of the 238U concentrations in the groundwater are below the World Health Organization permissible limit for drinking water. The relatively high uranium concentrations in some aquifers suggest a long period of geochemical interactions between rocks, sediments and water as well as possible contribution from fertilizers. In coastal aquifers, however, seawater intrusion is expected to be an additional source of uranium. The 232Th concentrations were generally comparable and relatively low in all groundwater samples due to the low solubility of thorium in water. Results of the uranium distribution in the rocks and sediments indicate higher concentration in the sediments and further support the possible effect of fertilizers vii as an additional source of uranium. The activity of gross β and gross α were found to exceed the WHO permissible limits for drinking water in 77% and 13% of the groundwater samples, respectively. The most likely reason for this phenomenon is occurrence of 40K, 228Ra and 226Ra in the aquifer body. The results of groundwater samples from Oman indicate low levels of 235U, 238U and 232Th, and the activity of 222Rn and 226 Ra were lower than the WHO permissible limits for drinking water. Dilution of groundwater by relatively high rainfall can be a possible cause of the relatively low activity of the radionuclides in Oman and other regions in the world