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

OutlineIntroduction Project ObjectivesMethodology ResultDiscussionConclusions

IntroductionEpidemiological 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 AreaThe 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 ContinuedThe 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).

MethodologyThe 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

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 DiscussionRadon-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.

Table 1: Radon Classification based on GeologyGeology N Mean SD SE Minimum

pCi/L

(Bq/m3)

Maximum

pCi/L

(Bq/m3)

Statistic

al Value

Granit

e

gneiss

area(u

nit A)

13 1.05 0.749

0

0.207

7

0.5

(19.0)

3.2

(118.4)

 

T-

test=0

.217

 

α=0.0

5

Grey

gneiss

area(u

nit B)

49 0.994 0.845

0

0.120

6

0.0

(0.0)

5.3

(196.1)

Total 62 1.007 0.8266 100.0    

Results and DiscussionThroughout 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/LRadon

level/Concentratio

n (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)

 

Results and DiscussionThe 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).

  Baseme

nt

Ground

floor

First floor F   P

Mean±S

D

1.54±1.318 0.99±0.556 0.63±0.409 5.77   <0.001

Table 3: Statistical Analyses of the Radon levels

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

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

ConclusionsMy 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.

RecommendationsFurther 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.