Journal of Environmental Protection, 2011, 2, 460-464
doi:10.4236/jep.2011.24053 Published Online June 2011 (
Copyright © 2011 SciRes. JEP
Radioactivity in Surface Soils around the
Proposed Sites for Titanium Mining Project in
M. K. Osoro1, I. V. S. Rathore2, M. J. Mangala3, A. O. Mustapha4
1Department of Physics, Kenyatta University, Nairobi, Kenya; 2Department of Physics, Northern India Engineering College, Babu
Banari Das University, Nairobi, Kenya; 3Institute of Nuclear Science and Technology, University of Nairobi, Nairobi, Kenya;
4Department of Physics, University of Agriculture, Abeokuta, Abeokuta, Nigeria.
Received March 3rd, 2010; revised March 9th, 2011; accepted April 23rd, 2011.
Radioactivity measurements were carried ou t around Maumba and Nguluku villages, two of the proposed sites for tita-
nium mining in the coastal area of Kenya. Samples of surface soils were analyzed using a HPGe gamma spectrometer.
The average activity co ncentrations for 226Ra, 232Th and 40K are 20.9 7.6, 27.6 9.1 and 69.5 16.5 Bqkg–1, respec-
tively. The absorbed dose rates in air, calculated on the basis of the measured activity concentrations, range from 9.8 to
50.0 nGyh–1, with an average of 29.2 nGyh–1. These values are below the global population-weighted mean, and they
should be considered when p lanning app ropriate mon ito ring and su rveillance programmes du ring the mining op era tion,
as well as the reclamation and restoration programmes after mining.
Keywords: Radioactivity Measurements, Titanium Mining, Absorbed Dose Rates, Natural Background Radiation
1. Introduction
The ambient natural background radiation is usually of
little or no radiological concern, and it varies from one
location to another depending partly on the local geology.
Mining and other industrial activities such as oil and gas
exploration, extraction and purification of water, etc. can
enhance the natural background radiation to levels that
are not insignificant from radiation protection point of
view [1,2]. Mining results in large volumes of materials
containing natural radionuclides – the so called naturally
occurring radioactive materials (NORM). This is not
restricted to uranium and thorium ores, it is also true for
other raw materials like heavy mineral sands, phosphate
rocks, etc.
Tiomin Resources Inc., the Canadian mining company,
discovered vast deposits of titanium in the coastal area
Kenya [3]. Earlier appraisal of the areas’ mineral poten-
tial [4] shows that most of the south coastal area of
Kenya is underlain by the Duruma group consisting of
the coarse-grained Taru and the fine-grained Maji-ya-
Chumvi formations. Two of the deposits in Kwale dis-
trict; the Central Dune at Maumba and South Dune at
Nguluku constitute the Kwale titanium mining project,
with a mineral reserve of 140.8 million tones (Figure 1).
The average ore body composition is 3.48% heavy min-
erals, and the expected annual yield is 77,000 tonnes of
rutile, 38,000 tonnes of zircon and 330,000 tonnes of
ilmenite [3]. According to the mining company, the pro-
posed operations will involve clearing the vegetation,
removing and stockpiling the topsoil for further use in
rehabilitation process, excavation of the dunes using
bucket wheel excavators or scrapers and, transportation
of the ore-bearing sand to the wet plant where the heavy
minerals will be separated from sand. The final products
will be transported from the mine sites to a ship-loading
facility that will be constructed at Likoni, in Mombasa. It
is estimated that mining activities in each of the two sites
will take seven years.
The main source of surface water in the area is the
Mukurumudzi river, a perennial river that flows from
northwest to southeast and drains into the Indian ocean
near Gazi Bay. Human population in these areas is esti-
mated to be about 3,000 [5]. The project was put on hold
because local residents and other stakeholders raised se-
rious social, economic, environmental and radiological
questions, which are still being addressed. Enhancement
Radioactivity in Surface Soils Around the Proposed Sites for Titanium Mining Project in Kenya461
Figure 1. Location of Kwale Titanium Mines (KTM) and the sampling sites.
of the natural background radiation can arise from con-
tamination of groundwater by liquid effluents and leach-
ing radionuclides, contamination of land and agricultural
produce by atmospheric releases, re-use of tailings, etc.
The principal exposure pathways will be inhalation of
airborne radionuclides, ingestions of radionuclides with
food, water, etc., and external exposures to gamma radia-
tion from tailings, surface deposition, and submersion in
airborne r ad ionucli d es .
In order to assess the net radiological impact of the
mining operations, it is necessary to establish baseline
concentrations of the naturally occurring radionuclides in
relevant environmental matrices prior to the commence-
ment of the mining operation. Soil is th e ultimate sin k fo r
various kinds of contaminants and it could be an impor-
tant indicator of environmental pollution [6]. This is the
report of an independent study carried out to establish the
baseline concentrations of radionucides in the surface
soil around the proposed mining sites.
2. Materials and Methods
2.1. Soil sampling and Preparations
Soil sampling was carried out in an area of about 20 km2
and 10 km long surrounding the two mine sites (Figure
1). The area was divided into large grids around the two
villages and along the adjoining path, but the sampling
points within each grid were chosen randomly provided
they are free from large stones or roots and relatively in
the open. This is similar to the systemic/stratified random
sampling technique described in the IAEA technical
document [6]. The distance between neighbouring grid
centers is about 500 m. At each sampling point, dirt and
other extraneous (non-soil) materials were first removed
to expose the soil. Soil was then collected with hand
trowels down to 5 - 10 cm depth within a 30 × 30 cm2
area. The soil was homogenized and three samples, each
of about 1000 cm3, were packed in clean polythene bags
and labeled accordingly. Altogether 78 samples of sandy
soil were collected from 26 sa mpling points. Th e sample
preparation involve oven-drying at 110˚C, pulverizing to
fine powder, and sealing aliquots in 450 ml bottles for a
minimum of 4 weeks to establish secular equilibrium
between 226Ra and the short-lived decay products of
222Rn before gamma-ray spectrometric analysis.
2.2. Gamma-Ray Spectrometric Analysis
The samples were analyzed using a high purity germa-
nium (HPGe) detector of 30% efficiency relative to the
standard 3” × 3” NaI(Tl) detector and energy resolution
of 1.8 keV (FWHM) at the 1.33 MeV gamma line of
60Co. Detailed description of the gamma-ray spectrome-
ter setup as well as the detector calibration procedures
using the IAEA reference materials (RGU-1, RGTh-1,
and RGK-1) are presented in ea r l i e r reports [ 7-9].
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Radioactivity in Surface Soils Around the Proposed Sites for Titanium Mining Project in Kenya
3. Results and Discussions
3.1. Activity Concentrations of Radionuclides in
Soil Samples
Figure 2 shows a typical gamma-ray spectrum of the
soils. Concentrations of 226Ra and 232Th were derived
from the gamma-lines of their respective decay products,
namely: 238 keV of 212Pb, 583 of 208Tl, and 911 keV of
228Ac for 232Th; 295 keV and 352 keV of 214Pb and 609
keV of 214Bi for 226Ra, while concentration of 40K was
derived from its 1460 keV gamma-line. There is no sig-
nificant difference between the ranges of activity con-
centrations in the soils from Nguluku and those from
Maumba (Table 1). A summary of the distributions of
the concentrations is presented in Figure 3. They are
lower than the global averages [10], and also lower than
those reported by Mustapha et al [7] for soils in other
parts of Kenya. Generally, soils derived from sedimen-
tary rocks, such as in the areas where the present study
was carried out, are expected to contain less radioactivity
compared to those derived from igneous rocks. In par-
ticular, the surface soils from the mine sites appear de-
pleted of 40K - the highest concentration recorded (114
Bqkg–1) is less than 30% of the global average (Table 1 ).
These values are comparable to some of the lowest val-
ues so far reported, e.g. from Cyprus, Egypt, Iceland, etc.
[10], and from Gazi [8] near the area being surveyed in
the present study (Figure 1).
3.2. Absorbed Dose Rate in Air
Absorbed dose rate conversion factors: 0.047, 0.462,
0.604 nGyh–1 per Bq·kg–1 of 40K, 226Ra, and 232Th, respec-
tively [10], were used to convert the concentrations of
radionuclides in the soils to absorbed dose rates,
D(nGyh–1), in air at 1m above the ground according to
the relation:
40 226232
0.047K 0.462Ra 0.604ThDA AA 
where A(40K), A(226Ra) and A(232Th) are the specific ac-
tivities (in Bq·kg–1) of 40K, 226Ra, and 232Th, respectively.
Table 2 shows the range and mean of the absorbed
dose-rate in air around the miming sites. The mean value
(29.2 nGyh–1) is less than 50% of the global popula-
tion-weighted average [10] and it is likely to be less than
the country (Kenya) average, judging from results of
similar surveys carried out in other parts of Kenya, e.g.
Mustapha et al. [7]. According to the 2000 UNSCEAR
report [10], the lowest cases of outdoor absorbed dose
rates were reported in Cyprus (18 nGyh–1), Iceland (28
nGyh–1), Egypt (32 nGyh–1), th e Netherlands (32 nGyh –1),
Brunei (33 nGyh–1) and UK (34 nGyh–1). It therefore
implies that prior to the commencement of mining opera-
tions in the proposed sites the external exposure rates due
to the natural background radiation are among the
world’s lowest. It is therefore imperative that future as-
sessment of radiological impact of the mining operations,
as well as the effectiveness of the post-mining restoration
programs should be based on the area-specific average as
documented in this report, rather than on country or
global averages. It is also recognized that distribution of
radionuclides in surface soil alone will not provide com-
plete assessment of the radiological impact of large-scale
mining operations. The pre-operational survey should be
extended to measurements of distribution of radionuclides
in other relevant media, e.g. air, water, sediments and
biota, etc. in the areas of interest. Finally, it is conceivable
that mining operations and other NORM generating hu-
man activities will continue for the foreseeable future in
different parts of Kenya. Therefore a well planned na-
tionwide environmental radioactivity survey is desirable.
Figure 2. A typical gamma-ray spectrum of the soil samples.
Copyright © 2011 SciRes. JEP
Radioactivity in Surface Soils Around the Proposed Sites for Titanium Mining Project in Kenya463
Table 1. Comparison of mean activity concentrations of radionuclides in soils around the titanium mining sites to other ar e as.
Activity concentration (Bq·kg–1)
Location 40K 226Ra 232Th
Nguluku 61.1 ± 13.0 21.2 ± 9.7 27.0 ± 11.8
Maumba 77.0 ± 15.0 20.6 ± 4.8 28.3 ± 5.8
Overall mean (and ranges) 69.5 ± 16.5
(31.9 - 114.1) 20.9 ± 7.6
(7.4 - 40.6) 27.6 ± 9.1
(8.4 - 43.6)
Kenya (differe nt parts) a 255.7 ± 38.5 28.7 ± 3.6 73.3 ± 9.1
Gazib 206.1 ± 26.7  11.9 ± 1.4 10.8 ± 1.0
Global average for soilc 420 33 45
a[7], b[8], c[10]
Figure 3. Distribution of activity concentrations of radionuclides in soil samples.
Table 2. Absorbed dose-rate in air estimated from activity
concentrat ions of 40K, 226Ra and 232Th in soil.
Absorbed dose-rate in air (nGyh–1)
Location Range Mean
Proposed mi ni n g sites 9.8 - 50.0 29.2
Kenya (different parts)a 9.9 - 176.5 68.2
Global averagesb 18 - 93 59
a[7], b[10].
4. Conclusions
Pre-operational environmental radioactivity measure-
ments carried out around the proposed sites for Kwale
titanium mining project in the coastal area of Kenya re-
vealed that activity concentrations of naturally occurring
radionuclides are low in the area’s surface soils: means
of 61.1, 21.2 and 27.0 (in Bq·kg–1) for 40K, 226Ra and
232Th, respectively. The absorbed dose rates in air due to
the observed radionucides concentrations in soils are also
low, with a mean of 29.2 nGyh–1. These values are the
baseline on which the assessment of the impact of the
mining operations should be based, instead of country or
global averages. They will also be used in evaluating the
effectiveness of the land restoration program.
5. Acknowledgements
The authors than the following: Kenyatta University and
Institute of Nuclear Science and Technology (University
of Nairobi) for availing field and laboratory equipment;
the government of Kenya (through the ministries of edu-
cation and the office of the President) for authorising the
study; and the United Nations Environmental Programme
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Radioactivity in Surface Soils Around the Proposed Sites for Titanium Mining Project in Kenya
(UNEP) – Nairobi for granting access to their library.
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