PHD-Department of Physics

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Browsing PHD-Department of Physics by Subject "Human Exposure"

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    Effects of Human Exposure and Associated Risks Due to Natural Radioactivity and Heavy Metals in Bureti, Kericho County, Kenya
    (Kenyatta University, 2022) Kipngeno, Rotich Charles; Margaret W. Chege; Nadir O. Hashim
    The knowledge of distribution of natural radiation sources as well as radiation levels in the environment is important for evaluating the risk associated with natural radiation exposure. The activity concentration of selected primordial radionuclides in soil, earthen building materials, maize and kales together with heavy metal concentration as well as 222Rn concentration in underground water samples from Butreti region was determined in this study. The choice of Bureti Sub County in this research was informed by the dominance of granitic rocks in the region which are known for high levels of radiation. The activity concentration of 226Ra, 232Th and 40K in soil, earthen building materials, maize and kales was determined using Thallium activated Sodium Iodide NaI (TL) detector. Soil samples recorded mean activity concentrations of 1164±70 Bqkg-1, 106±23 Bqkg-1 and 79±5 Bqkg-1 for 40K, 226Ra and 232Th respectively which are above the world average range. On the other hand, Bureti earthen building materials recorded mean activities of 1019±59 Bqkg-1, 98±7 Bqkg-1 and 79±5 Bqkg-1 for the same radionuclides respectively. The strong positive correlation due to 226Ra, 232Th and 40K for Bureti soil and earthen building materials implies that Bureti residents source their earthen building materials from the local soil. kales samples registered average activities of 651±33Bqkg-1, 68±4 Bqkg-1 and 77±5 Bqkg-1 while 827±45 Bqkg-1, 62±5 Bqkg-1 and 57±4 Bqkg-1are the activity concentrations in maize samples for the same radionuclides respectively. A mean outdoor absorbed dose rate in air at a height of 1m above the ground level was recorded as 145±10 nGyh-1 which is about 2.5 times the global mean value of 60 nGyh-1. Bureti earthen building materials recorded an indoor Annual Effective Dose of 0.6954 mSvy-1 which is below the International Commission on Radiological Protection (ICRP) limit of 1 mSvy-1. This value shows that the radiological risks associated with exposure from soil in Bureti is low hence the latter can be used for building houses. Maize and kales consumption contributed 3.68 mSvy-1 and 0.89 mSvy-1 respectively to the total absorbed dose rate. The activity concentration due to 222Rn in ground water was determined using Liquid Scintillating Counter detector and a mean concentration of 12.41 Bql-1 was reported. A Total Effective Dose (TED) of 33.23 𝜇Svy-1 due to inhalation and ingestion of waterborne radon was recorded and this is lower than the United States Environmental Protection Agency (USEPA) recommended limit of 100 𝜇Svy-1 for drinking water. Atomic Absorption Spectrophotometer was used to determine the concentration of selected heavy metals in ground water. Manganese, arsenic, copper, zinc and lead recorded mean metal concentrations of 97±11 𝜇gl-1, 7.11±0.11 𝜇gl-1, 31±5 𝜇gl-1, 373±15 𝜇gl-1 and 24±5 𝜇gl-1 respectively which are lower than the WHO permissible limits for drinking water. Incremental Life Time Cancer Risk (LTCRMP) due to heavy metal pollution in ground water and (LTCRRC) due to radionuclides concentration in soil was found to be 5.61×10-5 and 1.23×10-3 respectively and are within the recommended safe limits. In terms of dose contribution by waterborne radon and heavy metal concentration levels, Bureti ground water is considered safe for human consumption. Residual Radiations (RESRAD) code was adapted for a 100 - year extrapolation period to simulate annual effective dose due to concentration of 40K, 238U and 232Th in Bureti soil for inhalation, ingestion and external radiation exposure pathways. The results revealed that ingestion (food i.e., plants, meat and milk) pathways contributed the highest percentage of about 64.61 % to the Total Effective Dose Equivalent (TEDE) compared to 35.06 %, 0.06 % and 0.25 % contribution from ground, inhalation (excludes radon) and soil/rocks respectively. The simulated values of TEDE throughout a 100 - year extrapolation period is lower than ICRP 2007 recommended dose limit of 2.4 mSvy-1.
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    Human Exposure and Associated Risks Due to Natural Radioactivity and Heavy Metals In Ortum, West Pokot County, Kenya
    (Kenyatta University, 2021) Felix Omonya, Wanjala; Nadir Hashim; Otwoma David
    The background radiation in air, the activity concentration of selected radionuclides in soil and rock samples, the radon and thoron concentration in selected mud houses and elemental concentration of heavy metals in soil and water samples from Ortum, West Pokot County in Kenya was determined in this study. Ortum was chosen due to the presence of granitic and silicon rocks which are associated with high levels of background radiation. The activity concentration of 238U, 232Th and 40K in soil was determined using the High Purity Germanium detector (HPGe) and the average values were 40 ± 3 Bq/kg, 56 ± 4 Bq/kg and 425 ± 19 Bq/kg respectively which is within the world average range. The activity concentration of 238U and 232Th in soil samples reduced with increasing depth while that of 40K increased slightly with increase in depth. The average activity concentration of 238U, 232Th, and 40K in soil samples was higher than in the rock samples implying that the soils originate from other regions. The average outdoor absorbed dose rate in air at 1 m above the ground was found to be 112 ± 30 nGy/h which is almost double the world average value of 60 nGy/h. The average Raeq was 153 ± 49 Bq/kg which is less than the limit of 300 Bq/kg and the external hazard indices (Hex) and the internal hazard index (Hin) were 0.41 ± 0.13 and 0.52 ± 0.16 respectively which is below the limit values of unity (>1). This implies that soil and rocks in Ortum poses low radiological risk and they can therefore, be used for construction of houses, industrial and agricultural purposes. The average radon and thoron concentration in mud houses was determined using RADUET detector and found to be 40 ± 19 Bq/m3 and 54 ± 30 Bq/m3 respectively which is below the ICRP recommended lower and upper limit of 100 Bq/m3 and 300 Bq/m3 respectively. The elemental concentration of Ni, Cu, Zn, Pb, K, Ca, Fe, Ti, Mn, Rb, Sr, Zr and Nb in soil was determined using the Energy dispersive X-Ray Fluorescence Spectrometer (EDXRF) and found to be below the WHO recommended limits. The mean concentration of trace elements Pb, Zn and Cu in soil samples reduced with increasing depth while that of Ni increased with increasing depth. The Geoaccumulation Index (Igeo), Potential Ecological Risk Index (Ei) and synthesized potential ecological risk index (Er) were evaluated and found to be -0.40, 4.92 and 19.69 respectively. The results show that soil from Ortum is moderately polluted and the risk associated with exposure to heavy metals in soil is low. The concentration of Ni, Cu, Pb, Zn, Ag, Al, As, Ba, Ca, Cd, Co, Cr, Fe, K, Mg, Mn, Mo, Na and Se in water samples was determine using Agilent-5100 Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The elemental concentrations in water samples from the two rivers was found to be lower than the WHO permissible limits, except for calcium (Ca) which was higher than the permissible levels in borehole water. Hence, water from rivers in Ortum is unpolluted and fit for use except for borehole water which has high calcium levels. The lifetime cancer risk due to background radiation (LTCRBR) and elemental pollution in water (LTCREP) was found to be 1.47 x 10-3 and 1.92 x 10-6 respectively which is within the recommended safe limits. The lifetime cancer risk due to exposure to background radiation evaluated using RESRAD programme for a resident farmer in Ortum was found to be 0.011 or 1.1%. This implies that cancer risk due to exposure to background radiation in Ortum is low.