Environmental assessment of heavy metal pollutants in soils and water from Ortum, Kenya.

Analysis of elemental concentration in soil and water was carried out in Ortum to ensure safe utilization of soil and water resources for agriculture, industrial, and household purposes. Elemental analysis of soil and water was done using the EDXRF spectrometer and the inductively coupled plasma - optical emission spectrometry (ICP-OES), respectively. A total of 59 soil samples from different locations and depth and 10 water samples were collected from Ortum using purposive sampling method. The results of the mean elemental composition of 13 elements Ni (ppm), Cu (ppm), Zn (ppm), Pb (ppm), K (%w), Ca (%w), Fe (%w), Ti (%w), Mn (ppm), Rb (ppm), Sr (ppm), Zr (ppm), and Nb (ppm) in soils were 58.11, 46.91, 73.49, 22.20, 3.83, 24.39, 1.72, 7.73, 1529.74, 60.98, 442.26, 410.63, and 29.36, respectively, and the mean of 19 elements Ni, Cu, Pb, Zn, Ag, Al, As, Ba, Ca, Cd, Co, Cr, Fe, K, Mg, Mn, Mo, Na, and Se in water samples in (mg/l) were 0.037, 0.0014, 0.0005, 0.0042, 0.0030, 0.021, 0.0080, 0.12, 73.81, 0.00023, 0.0036, 0.00276, 0.0040, 6.11, 38.18, 0.00023, 0.0032, 46.87, and 0.0026, respectively. The average elemental concentration in soils was within the world average range. The mean concentration of Cu, Zn, and Pb in soil reduced with increase in depth while that of Ni increased with increase in depth. The average metal pollution indices in soils, 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. According to the classification index, the results show that the soil in Ortum is moderately polluted, and the risk associated with the measured elemental concentration of Ni, Zn, Cu, and Pb in the soils is low. The elemental concentrations in water samples was lower than the recommended permissible limits except for Calcium (Ca) in borehole water with an average of 90.80 mg/l against the permissible levels of 75 mg/l (WHO, 2011). The pH for water samples was found to range from 6.60 to 7.71 with an average of 7.07 which is within the acceptable range of pH 6.5 to pH 8.5 as recommended by WHO, 2011. The study found out that elemental concentration in soil and water samples from Ortum were withing the world average values and that the soil and water in Ortum is safe for use in agriculture and domestic purposes.

NATURALLY OCCURRING RADIONUCLIDES IN SOIL SAMPLES OF BURETI SUB-COUNTY OF KERICHO COUNTY KENYA.

The activity concentration of soil samples of Bureti sub-county was measured using thallium-activated sodium iodide detector. To ascertain the level of radiation hazard to the public, gamma radiation dose rates were also estimated. The average activity concentration due to 40K, 226Ra and 232Th for soil samples are 1164 ± 70, 106 ± 8 and 79 ± 5 Bqkg-1, respectively. An average dose rate of 145 ± 10 nGyh-1 was recorded, which is about 2.5 times higher than the world average value of 60 nGyh-1(UNSCEAR). On the other hand, an average outdoor effective dose of 0.35 ± 0.02 mSvy-1 was measured, which is lower than the ICRP safety limit of 1 mSvy-1. This shows that the radiation hazards from naturally occurring terrestrial radionuclides in Bureti is low and therefore human radiation exposure is within the accepted limits.

HUMAN EXPOSURE TO BACKGROUND RADIATION IN ORTUM, KENYA.

The activity concentration of radionuclides 238U, 232Th and 40K in soil and the absorbed dose rate (ADRA) at 1 m above the ground in Ortum was determined. The activity concentration in soils ranged from 33 to 85, 20 to 67 and 148-1019 Bq kg-1, respectively with an average of 40 ± 1.43, 56 ± 1.46 and 425 ± 19.24 Bq kg-1, respectively. The activity concentration of 232Th and 238U was found to reduce with increasing depth while that of 40K increased with increasing depth. The average activity concentration in soil was higher than the world average values. The average ADRA in air at 1 m above the ground was found to be 112 ± 29.6 nGy h-1. The soil and rocks in Ortum are recommended for use because the activity concentration of the terrestrial radionuclides is lower than the recommended threshold values.

ANNUAL EFFECTIVE DOSE ASSESSMENT DUE TO RADON AND THORON PROGENIES IN DWELLINGS OF KILIMAMBOGO, KENYA.

Human beings are continuously exposed to ionising radiation originating from natural or artificial sources. Uranium-238 and Thorium-232 found in building materials are important sources of radon and thoron in the indoor environment. The concentration levels of radon, thoron and thoron progeny were measured in mud-walled, metallic or iron sheet-walled and stone-walled modern houses in Kilimambogo region, Kenya for 3 months. Radon and thoron concentration levels were measured using passive radon-thoron discriminative monitors (RADUET), while thoron progeny concentrations as the equilibrium equivalent thoron concentration (EETC) were measured using thoron progeny monitors. The mean radon concentration levels in mud, metallic and stone-walled dwellings were 67 ± 11, 60 ± 10 and 75 ± 10 Bq m-3, respectively. The mean thoron concentration levels in the corresponding dwellings were 195 ± 36, 71 ± 24 and 161 ± 31 Bq m-3, respectively, while EETCs were 12 ± 2, 3 ± 1 and 7 ± 1 Bq m-3, respectively. The annual effective doses for radon were 1.3 ± 0.2, 1.1 ± 0.1 and 1.4 ± 0.2 mSv y-1 in mud, metallic and stone-walled houses while those from thoron estimated from EETC were 2.4 ± 0.4, 0.5 ± 0.1 and 1.5 ± 0.2 mSv y-1 in the corresponding houses, respectively.

Analysis of internal exposure associated with consumption of crops and groundwater from the high background radiation area of Mrima Hill, Kenya.

Specific concentrations of (226)Ra, (232)Th and (40)K were measured in cassava tubers, cassava leaves and groundwater obtained from the high background radiation area of Mrima hill and used in the evaluation of the ingested dose. Cassava tubers, cassava leaves and groundwater registered average (226)Ra concentrations of 60 ± 5, 141 ± 11 and 4.3 ± 0.3 Bq kg(-1), respectively. (232)Th was not detected in cassava leaves although it was present in cassava tubers as well as in groundwater in average concentrations of 35.3±61.5 and 2.0±0.1 Bq kg(-1), respectively. (40)K was present in all samples in average concentrations of 842±539 Bq kg(-1) in cassava tubers, 1708 ± 552 Bq kg(-1) in cassava leaves and 91.4 Bq kg(-1) in groundwater. The total annual effective dose due to ingestion was found to be 7.9 mSv y(-1) of which 2.4 mSv y(-1) was due to cassava tubers, 3.8 mSv y(-1) due to cassava leaves and 1.7 mSv y(-1) due to water.

Estimation of annual effective dose due to radon and thoron concentrations in mud dwellings of Mrima Hill, Kenya.

This study presents radon and thoron concentration measurements and the corresponding effective dose rates in mud dwellings located in the high background radiation area of Mrima Hill, Kenya. Discriminative technique was used for simultaneous measurement of radon and thoron. The effective dose was evaluated based on the concentration of the isotopes and the time spent indoors. Radon concentration ranged from 16 to 56 Bq m(-3) with an average of 35±14 Bq m(-3) and a corresponding annual effective dose of 0.67 mSv y(-1), while that of thoron ranged from 132 to 1295 Bq m(-3) with an average of 652±397 Bq m(-3) and an effective dose of 13.7 mSv y(-1).

Muon-pair production by atmospheric muons in CosmoALEPH.

Data from a dedicated cosmic ray run of the ALEPH detector were used in a study of muon trident production, i.e., muon pairs produced by muons. Here the overburden and the calorimeters are the target materials while the ALEPH time projection chamber provides the momentum measurements. A theoretical estimate of the muon trident cross section is obtained by developing a Monte Carlo simulation for muon propagation in the overburden and the detector. Two muon trident candidates were found to match the expected theoretical pattern. The observed production rate implies that the nuclear form factor cannot be neglected for muon tridents.

An investigation of the repeatability of calibration factors in gamma-ray spectrometry of geological materials.

A NaI(Tl)-based gamma spectrometer for the analysis of geological materials was calibrated using the IAEA reference materials RGU-1, RGTH-1 and RGK-1. To simulate typical geological samples, two additional standards were prepared from aliquots of the three reference materials. The reproducibility of the instrument calibration factors (CFs) was tested by repeated measurements of the pure IAEA reference materials and the mixed samples in a reproducible counting geometry. The results were analysed using a two-way classification analysis of variance; it was found that the variance in the CFs is significantly higher between standards than it is between measurements. Allowance should be made for this when estimating uncertainties in measurements with the NaI(Tl) spectrometers.