Date of Award

Summer 5-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology

First Advisor

Dr. Ahmed Murad

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, ICP-MS, 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 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.

Arabic Abstract

ﺗﺤﺘﻮي اﻟﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ ﻋﻠﻰ ﺑﻌﺾ الﻧﺸﺎط اﻹﺷﻌﺎﻋﻲ اﻟﻨﺎﺗﺞ ﻋﻦ اﻧﺤﻼل الﻧﻈﺎﺋﺮ اﻟﻤﺸﻌﺔ ﻟﻌﻨﺎﺻﺮ الﯾﻮراﻧﯿﻮم واﻟﺜﻮرﯾﻮم واﻟﺒﻮﺗﺎﺳﯿﻮم. إن اﻟﺪراﺳﺔ اﻟﻤﻔﺼﻠﺔ ﻟﮭﺬه اﻹﺷﻌﺎﻋﺎت وﺧﻮاﺻﮭﺎ وﺗﻮزﯾﻌﮭﺎ اﻟﻤﻜﺎﻧﻲ وﻣﺼﺎدرھﺎ ﺗﻌﺪ ﺿﺮورﯾﺔ ﻟﻠﻤﺢاﻓﻈﺔ ﻋﻠﻰ اﺳﺘﺪاﻣﺔ وﺟﻮدة ﻣﻮارد اﻟﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ ﻓﻲ دوﻟﺔ اﻹﻣﺎرات اﻟﻌﺮﺑﯿﺔ اﻟﻤﺘﺤﺪة. ﺗﮭﺪف ھﺬه الدراﺳﺔ إﻟﻰ اﺳﺘﻜﺸﺎف اﻟﺘﻮزﯾﻊ اﻟﻤﻜﺎﻧﻲ و اﻟﺘﺄﺛﯿﺮ اﻟﺒﯿﺌﻲ ﻟﻠﻨﺸﺎط اﻹﺷﻌﺎﻋﻲ اﻟﻄﺒﯿﻌﻲ ﻓﻲ اﻟﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ، و اﻟﻤﻨﺒﻌﺚ ﺗﺤﺪﯾﺪا ﻣﻦ ﻧﻈﯿﺮ اﻟﯿﻮراﻧﯿﻮم-238، وﻧﻈﯿﺮ اﻟﯿﻮراﻧﯿﻮم-235 وﻧﻈﯿﺮ اﻟﺜﻮرﯾﻮم-232، إﺿﺎﻓﺔ إﻟﻰ ﻗﯿﺎﺳﺎت اﻧﺒﻌﺎﺛﺎت إﺷﻌﺎﻋﺎت أﻟﻔﺎ وﺑﯿﺘﺎ ﻓﻲ اﻟﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ ﻓﻲ ﺑﻌﺾ ﻣﻨﺎطﻖ دوﻟﺔ اﻹمارات. وﻟﻮﺟﻮدھﺎ ﻓﻲ ﻧﻔﺲ اﻟﻤﻨﻄﻘﺔ اﻟﺠﻐﺮاﻓﯿﺔ واﻟﻈﺮوف اﻟﻤﻨﺎﺧﯿﺔ اﻟﺠﺎﻓﺔ، ﺗﻢ أﺧﺬ ﻋﯿﻨﺎت ﻣﯿﺎه ﺟﻮﻓﯿﺔ ﻣﻦ ﺳﻠﻄﻨﺔ ﻋﻤﺎن ﻟﺪراﺳﺘﮭﺎ وﻣﻘﺎرﻧﺘﮭﺎ بالﻣﯿﺎه اﻟﺠﻮﻓﯿﺔ ﻓﻲ اﻹﻣﺎرات. ﻛﻤﺎ ﺗﻢ أﺧﺬ ﻋﯿﻨﺎت ﻣﻦ ﺻﺨﻮر أﺣﺪ اﻟﺨﺰاﻧﺎت اﻟﻤﺎﺋﯿﺔ ﻟﻠﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ ودراﺳﺔ اﻟﻌﻼﻗﺔ ﺑﯿﻦ ﻧﺴﺒﺔ اﻟﻌﻨﺎﺻﺮ اﻟﻤﺸﻌﺔ في ﻣﯿﺎه اﻟﺨﺰان الﺟﻮﻓﻲ وﺻﺨﻮره واﻟﺘﺮﺑﺔ اﻟﺰراﻋﯿﺔ اﻟﺘﻲ ﺗﺮوى ﺑﮭﺬه اﻟﻤﯿﺎه. اﺳﺘﺨﺪﻣﺖ ﻣﺠﻤﻮﻋﺔ ﻣﻦ اﻷﺟﮭﺰة اﻟﺘﺤﻠﯿﻠﯿﺔ اﻟﻜﺘﻠﯿﺔ ﻓﻲ ﻗﯿﺎﺳﺎت اﻟﻨﺸﺎطﺎت اﻹﺷﻌﺎﻋﯿﺔ اﻟﻤﺘﻨﻮﻋﺔ ﻓﻲ اﻟﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ، ﻛﻞ ﻋﻨﺼﺮ ﺣﺴﺐ ﻣﺎ ﯾﺘﻨﺎﺳﺐ ﻣﻊ ﺧﺼﺎﺋﺼﮫ، ﻟﻠﺤﺼﻮل ﻋﻠﻰ ﻧﺘﺎﺋﺞ دﻗﯿﻘﺔ. أظﮭﺮت ﻧﺘﺎﺋﺞ اﻟﺘﺤﺎﻟﯿﻞ ﺗﺮاﻛﯿﺰ ﻣﺘﻔﺎوﺗﺔ ﻟﻺﺷﻌﺎع ﻣﻦ ﻧﺎﺣﯿﺔ اﻟﺘﻮزﯾﻊ اﻟﻤﻜﺎﻧﻲ، وﻗﺪ أﻛﺪت اﻟﺪراﺳﺔ أن أﺳﺒﺎب ھﺬه اﻻﺧﺘﻼﻓﺎت ﯾﻌﻮد إﻟﻰ ﻣﺠﻤﻮﻋﺔ ﻣﻦ الﻋﻮاﻣﻞ اﻟﺘﺎﻟﯿﺔ: اﻟﻔﺘﺮة اﻟﺰﻣﻨﯿﺔ اﻟﻄﻮﯾﻠﺔ ﻟﻠﺘﻔﺎﻋﻞ ﺑﯿﻦ اﻟﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ و ﺻﺨﻮر اﻟﺨﺰان الﺟﻮﻓﻲ، وارﺗﻔﺎع ﻣﻠﻮﺣﺔ ﺻﺨﻮر اﻟﺨﺰان، وﻏﺰو ﻣﻲاه البﺣﺮ ﻟﺨﺰاﻧﺎت اﻟﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ اﻟﻘﺮﯾﺒﺔ ﻣﻦ اﻟﺴﺎﺣﻞ، إﺿﺎﻓﺔ إﻟﻰ ﺗﺴﺮب اﻟﻤﻜﻮﻧﺎت اﻟﻔﻮﺳﻔﺎﺗﯿﺔ ﻟﻸﺳﻤﺪة ﺧﻼل اﻟﺘﺮﺑﺔ اﻟﺰراﻋﯿﺔ و ﻣﻨﮭﺎ إﻟﻰ اﻟﺨﺰاﻧﺎت الﺟﻮﻓﯿﺔ اﻟﻀﺤﻠﺔ. وﯾﻌﺘﺒﺮ ﻣﺎ ذﻛﺮ ﻣﻦ أﺳﺒﺎب ﻣﺮﺗﺒﻄﺎً ﺑﻨﺴﺐ اﻟﯿﻮراﻧﯿﻮم، أﻣﺎ اﻟﺜﻮرﯾﻮم ﻓﺘﺮاﻛﯿﺰه ﻣﻨﺨﻔﻀﺔ ﻧﺴﺒﯿﺎ ﻓﻲ اﻟﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ ﺑﺲﺑﺐ ﻗﻠﺔ ذوﺑﺎﻧﮫ ﻓﻲ اﻟﻤﯿﺎه. وﺑﺎﻟﻤﻘﺎرﻧﺔ ﻣﻊ ﺗﻮﺻﯿﺎت ﻣﻨﻈﻤﺔ اﻟﺼﺤﺔ اﻟﻌﺎﻟﻤﯿﺔ، وﺟﺪﻧﺎ أن ﻣﻌﻈﻢ ﻋﯿﻨﺎت اﻟﻤﯿﺎه اﻟﺠﻮﻓﯿﺔ ﺗﺤﺘﻮى ﻋﻠﻰ ﺗﺮاﻛﯿﺰ الﯾﻮراﻧﯿﻮم والﺛﻮرﯾﻮم أﻗﻞ ﻣﻦ اﻟﺤﺪ اﻷﻋﻠﻰ اﻟﻤﺴﻤﻮح ﺑﮫ ﻓﻲ ﻣﯿﺎه اﻟﺸﺮب، أﻣﺎ ﺑﺎﻟﻨﺴﺒﺔ إﻟﻰ اﻧﺒﻌﺎﺛﺎت أﻟﻔﺎ و ﺑﯿﺘﺎ ﻓﻘﺪ ﺗﺠﺎوز ﻋﺪد ﻛﺒﯿﺮ ﻣﻨﮭﺎ اﻟﺤﺪ اﻟﻢﺳﻤﻮح ﺑﮫ، وﻧﻌﺘﻘﺪ أن ذﻟﻚ ﯾﻌﻮد إﻟﻰ اﻟﻨﻈﺎﺋﺮ اﻟﻤﺸﻌﺔ اﻷﺧﺮى اﻟﺘﻲ ﻟﻢ ﯾﺘﻢ ﻗﯿﺎﺳﮭﺎ ﺗﻔﺼﯿﻠﯿﺎ ﻣﺜﻞ اﻟﺮادﯾﻮم و اﻟﺮادون واﻟﺒﻮﺗﺎﺳﯿﻮم. أﻣﺎ ﺑﺎﻟﻨﺴﺒﺔ ﻟﺴﻠﻄﻨﺔ ﻋﻤﺎن، ﻓﺠﻤﯿﻊ ﻋﯿﻨﺎﺗﮭﺎ ﺗﺤﺘﻮى ﻋﻠﻰ ﻧﺸﺎط إﺷﻌﺎﻋﻲ أﻗﻞ ﺑﻜﺜﯿﺮ ﻣﻦ اﻟﺤﺪ اﻷﻋﻠﻰ اﻟﺬي أﻗﺮﺗﮫ ﻣﻨﻈﻤﺔ اﻟﺼﺤﺔ اﻟﻌﺎﻟﻤﯿﺔ ﻓﻲ ﻋﺎم 2011، و ﯾﻌﻮد ذﻟﻚ إﻟﻰ زﯾﺎدة ﻣﻌﺪل اﻷﻣﻄﺎر اﻟﺴﻨﻮي في اﻟﺴﻠﻄﻨﺔ، واﻟﺬي ﯾﻘﻮم ﺑﺪوره ﺑﺖﻗﻠﯿﻞ ﺗﺮاﻛﯿﺰ اﻟﻨﺸﺎط اﻹﺷﻌﺎﻋﻲ ﻓﻲ اﻟﻤﯿﺎه. وﻗﺪ ﺗﻢ ﺗﺄﻛﯿﺪ ھﺬا اﻻﺳﺘﻨﺘﺎج بﻣﻘﺎرﻧﺔ ﺑﯿﻦ ﻣﺠﻤﻮﻋﺔ دول ﻣﻦ ﻣﻨﺎطﻖ ﻣﻨﺎﺧﯿﺔ ﻣﺨﺘﻠﻔﺔ ﺣﻮل اﻟﻌﺎﻟﻢ، ﺣﯿﺚ ﺗﺒﯿﻦ أن اﻟﺪول ذات اﻟﻤﻨﺎخ اﻟﻤﻄﯿﺮ ﺗﺤﻮي ﺗﺮاﻛﯿﺰ أﻗﻞ ﻣﻦ ﻧﻈﺎﺋﺮ اﻟﯿﻮراﻧﯿﻮم اﻟﻤﺸﻊ ﻓﻲ ﻣﯿﺎھﮭﺎ، ﺑﺎﺳﺘﺜﺎء ﺗﻠﻚ اﻟﺪول اﻟﺘﻲ ﯾﻄﻐﻰ ﻓﯿﮭﺎ اﻟﺘﻜﻮﯾﻦ اﻟﺼﺨﺮي اﻟﻐﻨﻲ ﺑﺎﻟﯿﻮراﻧﯿﻮم واﻟﻔﻮﺳﻔﺎت.

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