Transcript INDOOR RADON CONCENTRATIONS AND LOCAL GEOLOGY: A …

INDOOR RADON CONCENTRATIONS AND LOCAL
GEOLOGY: A CASE STUDY FROM A UNIVERISTY CAMPUS
OF NIGERIA
Deborah Esan
(RN,RM,RPHN,BNSc,MPH)
30th September, 2014
Outline
 Introduction
 Project Objectives
 Methodology
 Result
 Discussion
 Conclusions
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
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.
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.
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).
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.
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).
Methodology
 The study was conducted in various office buildings of the
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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
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).
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.
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.
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)
Results and Discussion
 Radon-222 measurements in various buildings constructed on two
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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.
Table 1: Radon Classification based on Geology
Geology
Granite
N
13
Mean
1.05
SD
0.7490
SE
0.2077
gneiss
Minimum
Maximum
Statistical
pCi/L
pCi/L
Value
(Bq/m3)
(Bq/m3)
0.5
3.2
(19.0)
(118.4)
T-
area(uni
test=0.2
t A)
17
Grey
49
0.994
0.8450
0.1206
gneiss
area(uni
t B)
Total
62
1.007
0.8266
100.0
0.0
5.3
(0.0)
(196.1)
α=0.05
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.
Table 2: Radon levels obtained of
sampled offices in pCi/L
Radon
Number of offices
%
level/Concentration
(pCi/L)
≤2.7
* (Permissible 59
95.1
level)
>2.7 ** (Risky level)
≥4
2
3.2
***(Critical 1
1.6
Threshold)
Total
62
Mean =
1.005 (0.819)
100
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).
Table 3: Statistical Analyses of the Radon levels
Mean±SD
Basement Ground floor
First floor
F
P
1.54±1.318 0.99±0.556
0.63±0.409
5.77
<0.001
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)
Results and Discussion……..
 Of particular interest was a building (Yellow house) in the study
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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
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.
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.
Thank you for the kind attention.