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in water for human consumption ( EUC , 2013 ). This study aims to evaluate and supplement previous research on radon health effects in Gezira State , Sudan , and other investigations in Africa , focusing on concentration levels , effective dose rates , and age groups ( Traoré I . et al ., 2013 ; Elzain , 2014 , 2015 , 2016 , 2023 ; Isinkaye and Ajiboye , 2017 ; Elzain et al ., 2019 ). The results can help identify potential health hazards associated with water use in the region .
2 Materials and methods
2.1 The study area
Gezira State is a densely populated region located in the eastcentral part of Sudan . Its coordinates are 14.5 ° N and 33.5 ° E ( Fig . 1 ). The state ’ s capital is Wad Madani , and it shares borders with Khartoum , Sinnar , White Nile , and Gedarif States . The northern and northeastern parts of Gezira State have a semi-arid climate , while the eastern and southern parts have a dry monsoon climate with a maximum mean temperature of 47 ° C . The area is primarily flat , with clay soil and small hills , and can be divided into three major units : highlands and isolated smaller mountains , clayey and sandy soil areas , and valleys ( Wadis ). These details were reported by UNDP in 2010 , MOG in 1994 , and studies by Sami et al . ( 2014 ) and Abdelgalili et al . ( 2019 ) ( MOG , 1994 ; UNDP , 2010 ; Sami et al ., 2014 ; Abdelgalili et al ., 2019 ).
2.2 Evaluations of radon gas from water samples using the RAD7 H 2 O technique
The RAD7 radon-in-air monitor was employed to measure the levels of radon in water samples and assess their quality by using the RAD H 2 O technique . The test followed the Wat-250 protocols and began with the RAD7 ’ s internal air pump expelling radon-222 and measuring its activity concentration . The closed-loop aeration system and radon-in-air monitor completed the process within 30 min . The RAD7 was attached to 250-ml sample bottles , and a closed air loop was circulated through the water sample until the RAD-H 2 O system achieved equilibrium . The RAD7 employed a passivated implanted planar silicon detector ( PIPS ) to detect alpha-decaying radon progeny 218 Po and 214 Po . After 30 min , the RAD7 created a summary report with the average radon reading ( Durridge , 2023 ). Water samples ’ concentration levels can be determined using the following formula ( Elzain , 2017 ):
C RnW ¼ C Rn e �lt : ð1Þ
The ( C RnW ) level from water is determined by measuring the radon concentration ( C Rn ) using a RAD7 device . The time interval between sampling and testing is denoted by ( t ), while ( l ) represents the decay constant , which is equivalent to 0.181 day �1 , given that the half-life is 3.83 days .
2.3 Calculation of the annual effective dose
Home radiation exposure is primarily due to radon concentrations and the effective dose rates of water released during daily tasks like dishwashing and showering ( Nazaroff and Nero , 1988 ; Niculita-Hirzel et al ., 2021 ). The following formula can estimate the annual effective dose of radon released from water into the interior air due to regular household activities ( UNSCEAR , 2000 ):
EðmSv∙y �1 Þ¼C RnW Q f F f R D 8760 : ð2Þ
C RnW is the radon concentration in water , Q f is the indoor occupation factor with the value of 0.8 , E f is the equilibrium factor that equal to 0.4 , R : is the ratio of radon in air to water = 10 �4 , D is the conversion factor of 9 nSv . ( h . Bq . m �3 ) �1 and 8760 is the number of hours annually .
Radon in water enters the body through ingestion and inhalation , exposing the stomach and lungs . Annual effective doses can be calculated using UNSCEAR parameters ( UNSCEAR , 2000 ). The amount of water consumed impacts the annual mean exposure doses through ingestion . Additionally , radon-222 can leak into indoor air during household chores . The annual mean exposure doses of radon-222 in water for ingestion ( E wIng ) and inhalation ( E wInh ) were calculated using UNSCEAR 2000 parameters ( UNSCEAR , 2000 ):
E Ing ðmSv∙y �1 Þ¼C RnW C W D ; ð3Þ
where C W is the annual intake of water of ( 150 , 350 , and 500 ) ( l . y �1 ) for infants , children , and adults , C RnW is the concentration of radon-222 in water , and D F-Ing is the ingested dose conversion factor that equals ( 7 10 �8 , 2 10 �8 , and 1 10 �8 ) ( Sv . Bq �1 ) ICRP , 1996 .
Using the UNSCEAR parameters , the annual effective doses for inhalation of radon in water were calculated :
E Inh ðmSv∙y �1 Þ¼C RnW O E f R D ; ð4Þ
where O is the average indoor occupancy time per individual ( 7000 h . y �1 ). The ingestion dose calculated by multiplying inhalation and ingestion dose tissue weighting factors , with a tissue weighting factor of 0.12 ICRP , 1996 ; UNSCEAR , 2000 .
The total annual mean exposure doses for people may be determined by adding the annual effective doses for ingestion and inhalation .
3 Results and discussion
This study examines radon concentration levels , annual effective dose rates , ingestion and inhalation dose rates , and effective dose rates for adults , children , and infants in water samples from 26 locations in Gezira State , Sudan , as shown in Tables 1 and 2 and Figures 1 – 9 .
Table 1 and Figure 3 show how the levels of radon concentration vary from 1.55 ± 0.13Bq . l �1 to 18.38 ± 3.05Bq . l �1 with an average of 7.68 ± 1.07Bq . l �1 . The study examined water radon concentrations in various locations , revealing variations may be due to geological conditions , proximity to uranium-rich rocks , underground water , local water sources , and human activities and industrial processes . However , all measured radon concentrations were well below the recommended limits , maintaining safe domestic water standards . 23.1 % of samples exceeded the USEPA ’ s maximum contamination level , while 76.9 % were below the maximum contaminant level ( USEPA , 2022 ). 100 % of radon concentrations were below the UNSCEAR , WHO , and EU ’ s