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1. INDOOR RADON CONCENTRATIONS AND LOCAL
GEOLOGY: A CASE STUDY FROM A UNIVERISTY
CAMPUS OF NIGERIA
Deborah Esan
(RN,RM,RPHN,BNSc,MPH)
30
th
September, 2014

2. Outline
Introduction
Project Objectives
Methodology
Result
Discussion
Conclusions

3. Introduction
Epidemiological studies have shown a clear link
between high radon levels and incidence of lung
cancer.
Testing homes/workplaces for radon levels is a
means of determining the general radon level in
order to know if mitigation action will be needed
to keep exposure levels low.
Radon is a radioactive gas produced from the
radioactive decay of radium, the progeny of
uranium

4. Introduction Contd.
It is formed as part of the normal radioactive decay chain of
Uranium which is present in small amounts in most rocks and
soil.
It slowly breaks down to other products such as radium, which
breaks down to radon.
Radon contaminates indoor air from soil and rocks by
molecular diffusion governed by Fick’s law, or gaseous
diffusion described by Darcy’s law, or by combination of both
mechanisms (Etiope and Martinelli 2002) and thereby
infiltrates foundations in houses and structures.
However, on reaching the surface, radioactive isotopes attach
rapidly to atmospheric aerosols and can enter into a human
body.

5. Introduction Contd.
Furthermore, it has been shown that radon soil–
gas found in soils overlying basement rocks are
the main source for indoor radon concentrations.
Radon exposure in buildings may arise from
certain subsurface rock formations and outcrops
(e.g. granites or granitic rocks).
greatest risk of radon exposure are from tight,
insufficiently ventilated buildings and building
that have leaks that let in soil air from the
ground into basement and dwelling rooms.

6. Introduction Contd.
US Environmental Protection Agency (EPA) estimated that
approximately 14,000 lung cancer deaths in the USA per year are
due to residential radon exposures, with an uncertainty range of
7,000–30,000 (US EPA 1993, 1994).
Ajayi and Adepelumi (2002) reported high radon concentration over
the basement fault found in the western part of the study area.
 A mountainous terrain like the study area where structures have
been built according to the landscape may be a source of high radon
emissions.
In view of potential health risks that people living in the study area
may be subjected to unknowingly due emanation of radon isotopes
from the basement environments into office spaces thus preliminary
radon measurement was conducted in office buildings underlain by
two different lithologic rock units (Granite gneiss and Grey gneiss).

7. Geology of the Study Area
The study area is mainly underlain by rocks of the
Precambrian basement Complex of Ife-Ilesha schist-belt,
gneiss complex, and unmetamorphosed intrusive
(igneous) bodies.
Rahaman (1988) classified the major lithologic rock units
of the complex into two major groups: gneisses and
schists, with minor occurrence of ultramafic rocks that
probably represent remnants of an oceanic assemblage
.

The main rock (petrologic) units in the study area are the
granite gneiss, grey gneiss and mica schist which
Adepelumi et al. (2005) recognized as unit A, unit B and
unit C respectively.

8. Geology Continued
The grey gneisses are the oldest rocks in the
study area and outcrops over about half of the
entire site and occur as low-lying outcrops.
Granite gneiss outcrops as inselbergs forming
three prominent hills (hills 1, 2 and3) and show
strong foliation of the mineral bands.
Granite is sandwiched between grey gneiss
because it intruded into the grey gneiss thus
indicating a younger age. Mica schist occurs only
in the eastern part of the study area (Adepelumi
et al.2005).

10. Methodology
The study was conducted in various office buildings of the
Obafemi Awolowo University, Ife, Osun State.
Obafemi Awolowo University (O.A.U) is a comprehensive
public institution established in 1962 as the University of Ife.
The landscape is marked by many steeply inclining hills of
granite rock formation- the inselbergs- whose slopes are
covered with dense vegetation, forming a natural green back
drop to the campus.
Its topography is hilly and there are many steep slopes,
ranging from a 6-12% incline.
The University campus is divided into 3 major zones;
academic, student residential area and staff quarters

11. Methodology Contd.
The study was conducted within the academic
core of the institution.
The study employed a cross-sectional study
design and the offices in the academic area and
their occupants were the study population.
A sample size of 87 was calculated using the
Fisher’s formula with level of confidence set at
95%; a precision of 0.05 and prevalence of
attribute at 6% which represented the
proportion of households with radon levels
exceeding 4pCi/l in the U.S (USEPA 1990).

12. Methodology Contd.
The buildings were stratified based on the
classification by Adepelumi et al., 2005 into granite
gneiss; grey gneiss and mica schist with most of the
buildings in the academic area falling within the grey
gneiss zone.
The buildings were sampled randomly in each unit
with a total of 8 buildings selected and these were
further stratified into floor levels (basement, first and
second) with equal sampling from the floor levels.
Therefore, in each building, an average of 11 offices
was selected distributed equally by floor.

13. Methodology Contd.
The office owners were given explanation about
the study and their consent sought and obtained.
Pro3 Series Radon detector device was used for
the measurement of radon concentration in
these office buildings and point source
measurements were obtained inside the
buildings.
Instrument was calibrated to measure radon
activity between values 0.0 to 999.9 pCi/L.
Readings were taken after 48 hours and recorded
on proforma data sheet.

14. Methodology Contd.
Precision/reliability of the device was done by
setting up 2 of the devices, in the same location
and mode and readings were taken at the end of
48 hours.

It was found that the two instruments produced
the same result(0.5 pCi/L)

15. Results and Discussion
Radon-222 measurements in various buildings constructed on two
lithologic units vary from 0.5 to 3.2 pCi/L for granite gneiss, and 0.0
to 5.3 pCi/L for the grey gneiss respectively (Table 1).
However, there is some degree of overlap of values for different rock
types.
These concentration values averaged 1.05 pCi/L (arithmetic mean)
for granite gneiss, and 0.99 pCi/L (arithmetic mean).
The soil overlying the granite gneiss showed the highest radon-222
concentration, followed by grey gneiss.
Radon concentrations were not taken inside buildings over mica
schist because of inaccessibility to few structures situated on this
rock type.
Radon-222 indoor concentrations of the various buildings underlain
by the two rock types exhibit distinct different characteristics.

16. Table 1: Radon Classification based on Geology
Geology N Mean SD SE Minimum
pCi/L
(Bq/m
3
)
Maximum
pCi/L
(Bq/m
3
)
Statistical
Value
Granite
gneiss
area(un
it A)
131.050.74900.2077 0.5
(19.0)
3.2
(118.4)
 
T-
test=0.2
17
 
α=0.05
Grey
gneiss
area(un
it B)
490.9940.84500.1206 0.0
(0.0)
5.3
(196.1)
Total 62 1.007 0.8266 100.0    

17. Results and Discussion
Throughout the period of survey, radon level
obtained from sampled buildings within the
study area ranged from 0.00 to 5.30 pCi/L with
the mean of 1.0 pCi/L.
Most of the sampled buildings (95%), fell within
the ‘permissible reference level’ recommended
by WHO as a standard for countries to adopt.
This is presented in table 2.

18. Table 2: Radon levels obtained of sampled
offices in pCi/L
Radon
level/Concentration
(pCi/L)
Number of offices %
≤2.7 *
(Permissible level)
59 95.1
>2.7 ** (Risky level)2 3.2
≥4 ***(Critical
Threshold)
1 1.6
Total 62 100
Mean = 1.005 (0.819)


 

19. Results and Discussion
The result of one-way analysis of variance that
was done to compare the mean of the dependent
variable (radon level) and the independent
variable (office location - basement floor, ground
floor and first floor) is revealed in table 3.
There is a significant difference in the means of
Radon levels obtained from these 3 different
strata (p=0.00).

20.  
Basemen
t
Ground floorFirst floorF  P
Mean±SD
1.54±1.3180.99±0.556 0.63±0.409 5.77
 
<0.001
Table 3: Statistical Analyses of the Radon levels

21. Results and Discussion Cont….
The values obtained from basement stratum
ranged from 0.4 - 5.3pCi/L, values obtained from
the ground floor stratum ranged from 0.0 -
3.2pCi/L and the values obtained from the First
floor stratum ranged from 0.0 - 1.5pCi/L.
This result shows a decreasing trend of radon
concentration with height.
This is consistent with literatures which reveal
that the higher the elevation in a building, the
lower the radon level (Shirav and Vulcan 1997)

22. Results and Discussion……..
Of particular interest was a building (Yellow house) in the study
area .
It was observed in a particular building (Yellow house), four offices
were sampled in this building and the radon concentrations was
observed to return null values.
This reading was repeated to ascertain the validity of the
recordings since the building was located on a grey gneiss
environment.
The building was observed to be the youngest in the environment
and the zero radon concentrations can be ascertain to absence of
cracks, due to age (recent) of the building.
This shows that age of buildings may play an important role in the
emanation of radon into such structures; inspite of geological
composition of subsoil in which buildings are sited

23. Conclusions
My research findings established that radon concentration
exhibits a very strong dependence on local geology of an area.
It was important to relate radon level with local geology on
which each buildings are sited because the main source of
indoor radon is its immediate parent radium-226 in the
ground of the site and in the building materials (European
Commission et al.1995).
However, age of building may play an important role in
influencing indoor radon concentration levels found in office
spaces/residential setting.

24. Recommendations
Further studies needs to be conducted on age of buildings
(new versus old building) viz-a-viz Geological composition
of subsoils in relation indoor radon levels.
More studies should be undertaken especially in
habitation underlain by rocks in other to understand how
widespread the risk of radon is in Nigeria.
EIA undertaken for developmental projects should
include radon studies
Unless more studies are undertaken to understand how
widespread the risk of radon is, the threat from radon
exposure may remain an undisclosed health hazards for a
long time to come.

25. Thank you for the kind attention.