Effects of Human Exposure and Associated Risks Due to Natural Radioactivity and Heavy Metals in Bureti, Kericho County, Kenya
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Date
2022
Authors
Kipngeno, Rotich Charles
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
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.
Description
A Thesis Submitted in Fulfillment of the Requirement for the Award of the Degree of Doctor of Philosophy in (Physics) In the School of Pure and Applied Science of Kenyatta University
Keywords
Effects, Human Exposure, Risks, Natural Radioactivity, Heavy Metals, Bureti, Kericho County, Kenya