1
Indoor Radon Research conducted in South Africa from 1980s – To date (2019):
A Review
*Atsile Ocwelwang
1,2
, Cynthia Sethabela
2
, Manny Mathuthu
2
, Paballo Moshupya
1
1
Centre for Nuclear Safety and Security (CNSS), National Nuclear Regulator (NNR), Eco Glades 2 Block G, 420
Witch Hazel Avenue, Highveld, Centurion. PO Box 7106 Centurion, 0046.
2
Centre for Applied Radiation Science and Technology, North-West University (NWU) – Mafikeng Campus,
Corner of Albert Luthuli and University Drive Mmabatho. Private Bag X2046 Mmabatho, 2745.
*Corresponding author’s email: [email protected]
Abstract. The history of research on radon and indoor radon measurements in South Africa (SA) dates back to
the mid-1980s and early 1990s. Small-scale studies have been performed in areas where high radon concentrations
were expected due to the geology and the mining history of the area. Most of these studies were performed in
Gauteng and Western Cape provinces. Gauteng province has a long history of gold mining and this has left behind
large amounts of waste that contain long-lived naturally occurring radionuclides such as uranium-238 (
238
U) which
decays into radium-226 (
226
Ra) from which radon-222 (
222
Rn) emanates. Radon research conducted in the Western
Cape Province was mainly due to the geology of this region, which is rich in granitic rocks. This study reviews
published journal articles and reports on indoor radon measurement studies conducted across the country to
establish a baseline data for the current study, which focuses on the development of a national radon survey and
radon mapping strategy in SA. Moreover, findings made in this desktop review will inform the development of
the national indoor radon database and the establishment of a regulatory framework for radon in dwellings and
other buildings with high occupancy by members of the public.
KEYWORDS: Radon progeny; Indoor Radon; NORM; Uranium, Mining impact; Regulatory
Framework.
1 INTRODUCTION
Radon-222 (
222
Rn) is a naturally occurring, inert radioactive gas that is produced directly from the alpha
decay of the long-lived) radium-226 (
226
Ra) along the radioactive decay chain of uranium-238 (
238
U).
This radioactive gas is colourless and odourless, it cannot be detected by human physical sense and has
a half-life of 3.82 days [1]. For many years it was believed that only underground mines have a high
level of radon and mine workers are the only individuals that have significant radon exposure [2]. Many
international studies have proven that occupants of above-ground workplaces and residences around
gold or uranium mines and geological regions with high granitic content can also be exposed to high
levels of radon that exceed the recommended levels [3].
Radon is by far one of the major contributors of radiation exposure to the public, including exposure in
homes worldwide [4]. Inhalation or ingestion of radon progenies has proven to cause damage to the
deoxyribonucleic acid (DNA) molecule of a cell and to induce lung cancer [5]. Reports by the
International Agency for Research on Cancer (IARC) have confirmed that long-term exposure to radon
and its short-lived decay products, polonium-218 (
218
Po) and polonium-214 (
214
Po) causes lung cancer
in humans [3,6]. Studies on the health effects of radon in underground workplaces began several
decades ago, the focus was extensively on uranium mineworkers. However, in the late 1970s and early
1980s, radon studies began to include measurements and surveys of radon gas concentration in private
homes and other buildings with high occupancy factors for the public [7]. It is thus very important to
conduct indoor radon measurements to assess the extent of human exposure to radon in dwellings and
other public buildings with high occupancy by the public.
South Africa (SA) has a legacy of more than 100 years of gold mining; whereby gold along with
uranium has been mined from the largest gold reefs of Witwatersrand since 1886. The Witwatersrand
(Wits) Basin includes Central Rand Basin, Eastern Basin, Western Basin, Far West Basin, the Free State
2
gold mines and the Klerksdorp goldfields comprising Klerksdorp, Orkney, Stilfontein, and
Haartebeesfontein (KOSH) region. The 2019 analysis report of the Wits goldfields and the management
of the consequent mine waste by Liefferink [8], reported that these mines have resulted in more than
270 tailings storage facilities (TSFs) with a uranium content of about 600 000 tones. As such, gold mine
tailings are expected to have high levels of radon concentration since uranium, which is a long-term
source of radon, is mined as a by-product of gold in South Africa [9, 10]. Moreover, these TSFs with
high levels of uranium contain other toxic heavy metals associated with gold mining [11]. There have
been many studies on the impact of gold mining in the country, however, indoor radon studies are still
lacking. Therefore, there is a need for indoor radon survey and continuous monitoring in residential
areas near gold and uranium mine tailings for the health assessment of community members living in
such areas.
South Africa (SA) has never conducted a comprehensive national indoor radon survey and as a result,
the country does not have an indoor radon map, which highlights possible radon hotspots like most
international countries that are member states of the International Atomic Energy Agency (IAEA).
Currently, SA does not have sufficient radon data and a regulatory framework for the protection of the
public against the risk associated with radon. [12]. Thus, this paper reviews the currently available data
on indoor radon in the country as part of the initial phases to the development of a South African indoor
radon survey and mapping program. Findings made in this review serve as an indication of the possible
challenges that exist in selected regions in the country mainly due to the geological formation and
historical activities such as gold and uranium mining. Furthermore, observations made in this review
will also inform the development of the national indoor radon database and the establishment of a
regulatory framework for radon in dwellings and other buildings with high occupancy by members of
the public like schools and kindergartens, offices and other aboveground workplaces. Overall, this
review is a contribution to the long-term National Nuclear Regulator (NNR) plan to create a national
database on indoor radon levels and the development of a national radon map.
2 METHODOLOGY
Information in this paper is based on the data collected from indoor studies conducted in SA since the
1980s to date (2019). Thus far, there has never been a nationwide indoor radon survey in SA. The
available data that focuses on indoor radon measurements is from limited studies that have mostly been
conducted by independent researchers for academic purposes and a few conducted by consultants for
the then Atomic Energy Corporation (AEC), now South African Nuclear Energy Corporation (Necsa).
Indoor radon concentration levels were obtained using different measurement techniques and devices,
for varying measurement periods. No one method for indoor radon measurements has thus far been
developed and applied in SA, therefore, this paper also reviews and discusses the different radon
measurement techniques that were used and the results obtained.
3 TECHNIQUES AND DEVICES EMPLOYED IN THE REVIEWED STUDIES
Active or passive techniques are used for measurements of indoor, or both for verification purposes or
determining the radon source. Currently, the market offers different types of instruments that are used
for indoor radon measurements in both developed and developing countries. Radon tests can be
conducted over short to long periods. Short-term measurements can vary from minutes, hours to a week,
whereas long-term measurements can range from a minimum period of one month to a year. Punctual
and continuous radon measurement techniques are short-term active methods, whilst integrated
measurement techniques are long-term and passive. Outlined below are four of the radon measurement
devices and techniques that have been used in various independent studies reviewed in this paper.
3.1 Solid State Nuclear Track Detectors (SSNTD)
Solid-state nuclear track detectors (SSNTD’s) which are also referred to as “etched or alpha track
detectors” are thin plastic sheets of different materials capable of recording alpha tracks. Because of
their integral signal registration and insensitivity to low linear energy transfer (LET) radiations, they
play an important role in radon passive integrated measurements. Track detectors exist in open and
closed types and sampling is done in passive mode. The open SSNTD type can measure both radon and
its decay products while the closed SSNTD type can only measure radon because it has a filter for radon
3
progenies. This detector usually comes in two types, the LR115 (cellulose nitrate) and CR 39 (polyallyl
diglycol carbonate) which is the most popular member of the detectors.
Alpha track detectors are used to measure the energy of alpha particles emitted by radon and its
progenies (
214
Po and
218
Po). A typical alpha energy spectrum of radon and its progenies have been
reported energies of
222
Rn as 5.49 MeV,
218
Po as 6.02 MeV and that of
214
Po as 7.68 MeV [13]. When
these heavily charged particles hit and pass through the SSNTD plastic film, the material undergoes
ionization and localized damage is created on the molecular structure of the material. The damage
caused on the detector is referred to as latent tracks [14]. The plastic material is etched in NaOH and
KOH solution (ethanol can also be used) to visibly reveal latent tracks which are then viewed and
counted under an optical microscope. To obtain representative data from buildings, the exposure period
should be as long as possible [15, 16]. Generally, etched track detectors are deployed for a minimum
period of a month to a maximum of one year, this differs per country.
3.2 Alpha GUARD Radon Monitors
The Alpha GUARD is one of the commonly used portable, real-time ionization chambers used for
environmental radon measurements. It has the capability for measurement of radon in air, soil, water
and building materials. This radon monitor has high storage capacity and can be battery or net-operated.
It has an inbuilt rechargeable battery which can last for 10 to 15 days and this allows for operation
independent of a power supply [17]. Due to its high sensitivity and long-time stable calibration, the
Alpha GUARD is the reference instrument for professional radon monitoring and accurate measurement
on site. It can be used for short as well as long-term radon measurements. In addition to the radon
concentration in air, this device can simultaneously measure and record ambient temperature, relative
humidity and atmospheric pressure with integrated sensors [18]. By combining the monitoring of radon
with these associated environmental parameters it is possible to draw valid conclusions regarding the
temporal and spatial distribution of the radon gas. This is of significant benefit initial radon screening
and investigations during radon mitigation stage. These are continuous active radon detectors that
contain an ionization chamber and uses alpha spectrometry for the detection of radon [19]. The device
identifies the common radon isotopes (
220
Rn and
222
Rn) by their different energies from the alpha decays.
The generated signal from the detection of alpha particles is converted to a digital output. This output
can be read on the Alpha GUARD, data saver or a computer [20].
3.3 Electret Ion Chambers EIC)
These passive devices are the electrostatic equivalent of permanent magnets, due to the permanent
surface charge, the surface potential may be several kilovolts (kV). It functions as an interoperating
detector for measuring the average indoor radon concentration during the measurement period [6]. It
contains an electret which functions as a sensor in the ion chamber as well as a source of an electric
field. A Teflon electret is placed at the bottom of a conducting plastic chamber called an electret ion
chamber (EIC). Radon gas enters the chamber volume by passive diffusion through the inlet, this results
in electret losing charge due to the general ionization of air produced by radon and its progenies in the
chamber volume [15].
The positively charged electret at the bottom of the chamber collects the negative ions and the energy
given off by the electret over a certain time interval is a measure of time integrated ionization during
the interval. The energy given off by the electret in volts is measured by a noncontact battery-operated
electret reader, this value in alliance with the calibration factor and the duration, are used to obtain the
radon concentration. The EICs can be employed for short-term and long-term measurements. EICs
designed for short term measurements can measure up to 15 days at a concentration of 50 Bq/m
3
, and
the long-term detectors are designed to measure from 3 to 12 months at a concentration of 150 Bq/m
3
[6]. These devices have proven to be a good measure of radon exposure; however, they have a limited
dynamic range. They are sensitive to gamma rays, thus, compensation for this has to be applied. To
obtain precise measurements, correction for the elevation must be made to compensate for the variation
of atmospheric pressure effects [16].
3.4 Charcoal detectors
4
Activated charcoal devices are passive detectors that have a canister that holds granular-activated
`1carbon and they do not require power [15]. These devices are used to measure indoor radon for 1-7
days [6, 21]. The charcoal absorbs the radon gas that gets into the canister through a screened opening,
the absorbed radon will then decay and its progenies will be retained. After the set exposure period, the
canister is sealed allowing the radon progeny gamma decay in the charcoal to be collected directly by
the high purity germanium (HPGe) gamma spectrometry of the emissions from Lead-214 (
214
Pb) and
Bismuth-214 (
214
Bi). Alternatively, it can be collected by liquid scintillation counting technique which
uses 20 ml liquid scintillation vials that contain about 2-3 g of activated carbon [6]. The device is highly
affected by humidity; therefore, it must be calibrated at different humidity levels. In high humidity the
charcoal can become saturated, however, a diffusion barrier is used to reduce this humidity effects. The
device must also be calibrated over the same duration of exposure and the temperature of the area it will
be exposed at [6, 22]. The good thing about this method is that, since charcoal allows accumulation and
desorption of radon, this method gives a very good estimation of the average of radon concentration
over the exposure period if there’s a small change in the radon concentration. Considering the half-life
of
222
Rn which is 3.82 days, the device should be returned soon after the exposure period for analysis
[22].
4 RESULTS AND DISCUSSION OF INDOOR RADON DATA FROM VARIOUS
STUDIES IN SA
Table 1 presents the minimum and maximum range of the measurements that were obtained and the
average concentration starting with the earliest available studies since 1980 to the latest study in 2019.
The measurements were conducted indoors, in private dwellings and public buildings, most of the
studies have limited or no data on specific procedures that were followed to obtain the results. The
detector exposure periods followed in these studies also differed; they ranged from hours to months for
both passive and active measurement devices. Specific characteristics of the buildings and habits of the
inhabitants were not reported.
5
Table 4.1. Indoor radon concentrations from various studies conducted in SA from 1989-2019.
Region
Location
Researchers
Year
Method of measurement
Time and room
measured in
Average
concentration
(Bq/m
3
)
Gauteng
Western cape
Gauteng
Witwatersrand
Cape town
Pretoria
A H Leuschner, D
van As, Grundling, A
Steyn
[23].
1989
Track etch samplers and
charcoal canisters
Day time (average)
Early morning
40
20
300
600
Western Cape
Paarl region near the
Berg River
(west)
(East)
R. Lindsay, R.T.
Newman, W.J.
Speelman
[26].
2008
Electret ion Chambers(E-
PERM)
(Passive technique)
Living room
132
37
North West
province
Midvaal Water,
Klerksdorp
Botshabelo,
Klerksdorp
Nnenesi A Kgabi
[24].
2009
Radon Electret Chambers (S
chamber, E-PERM type).
(Passive technique)
Day time
30.16 ±2.52 pCi/L
(1115.92 Bq/m
3
)
46.06 ± 5.21 pCi/L
(1704.220 Bq/m
3
)
Western Cape
Gauteng
Aardoom, Beaufort
West
Tshepisong, Soweto
NNR Position Paper
(PP-0011), [27].
(n.d)
Electret ion Chambers (L –
Chamber)
Radon Gas Monitors (RGM)
Pantry & living
room
(n.a.)
478
211.9
Gauteng,
Johannesburg
Ezulweni mine West
Rand
Ava Nourian
Dehkordi
[19].
2011
Alpha Guard active detector
RGMs Passive (SSNTND)
technique
winter at night and
early morning
store-room,
bedroom and living
room
Winter 44.67;
Summer 33.17
Winter 38.58;
Summer 30.83
Average 38
Gauteng,
Johannesburg
Carletonville
Kamunda C,
Mathuthu M,
Madhuku M
[17].
2017
Alpha Guard Professional
Radon Monitor
(active technique)
(n.a.)
119.5
Gauteng,
Johannesburg
Krugersdorp
West rand region
Paballo Moshupya
[31].
2017-2018
Solid-state nuclear track
device (RGMs)
(n.a.)
105
Western Cape
Baviaansberg
Jacques
Bezuidenhout
[30].
2018
sodium iodide
(NaI (Tl)) scintillation
Summer
400
Western Cape,
Peninsula
Vredenburg
Saldanha
R. R. Le Roux,
J. Bezuidenhout,
H. A. P. Smit
[29].
2019
Electret ion chamber
(Passive technique)
(n.a.)
58.7
38.6
6
4.1 Studies conducted: 1980 – 89:
Before the 1980s, there are no reported studies or existing data on indoor radon measurements in SA dwellings
and public buildings such as offices, schools and similar types of workplaces. Table 2 below present summarized
indoor radon data from the biggest study conducted by Leuschner and co-workers in 1988 - 1989. This study
covered 2000 houses in 27 regions across the country. However, there was no information on the houses built
around mine tailings. The highest indoor concentration was recorded at Paarl region in the Western Cape Province,
the area is known to have a large number of granite rocks, which contain a high content of uranium. In 1989, the
study was repeated at a house that recorded concentrations higher than 450 Bq/m
3
[2, 23]. The indoor radon
concentration from all these regions was calculated to be 63 Bq/m
3
from measurements conducted during winter
seasons of three consecutive years. Wooden floors and radium content in soil has also been reported to influence
the high levels of indoor radon concentration. This was observed in a study done in the Witwatersrand region of
Gauteng province, where high radon concentration levels were recorded in wooden floor houses compared to
houses with other floor types. Measurements were taken from 100 houses and all the houses with wooden floor
had concentrations higher than 80 Bq/m
3
[23]. In one house in Pretoria where measurements were taken in the
basement, radon concentration levels of an excess amount of 1400 Bq/m
3
was recorded. This concentration was
higher than the bedroom and living room concentration, however, measurements were also taken below the floor
and the measured concentration was an excess amount of 1400 Bq/m
3
which was higher than concentrations in
both the bedroom and living room [23].
Table 4.2. Summary of Indoor radon concentrations (Bq/m
3
) from a study conducted in 1988-1989 [23].
7
4.2 Studies conducted: 1990 – 1999
Studies conducted in the period between 1990 – 1990 could not be found and some could not be accessed.
4.3 Studies conducted: 2000-2009
A study conducted by Kgabi and co-authors (2009) in the North West province around the Klerksdorp regions
recorded an average of 30.16±2.52 pCi/L (1115.92 Bq/m
3
) and 46.06±5.21 pCi/L (1704.22 Bq/m
3
) in the Midvaal
water and Botshabelo sites respectively [24]. Results in this study were compared to indoor radon concentrations
from other southern African countries such as Swaziland, where a study by Mahlobo and co-workers (1995)
showed that radon concentrations were higher in winter than in summer due to the ventilation system. The highest
measured radon concentration in the Swaziland study was 87 Bq/m
3
, which is lower than the concentration
recorded in the in Klerksdorp study [25]. It was observed that radon concentrations build-up and exposure in
Klerksdorp region was higher and probably the highest in the Southern African region. The variation of the indoor
concentrations in the two regions were justified by the direction of the wind, which was determined in the two
study sites. The wind direction values (2500° - 3600° from the North to West) were associated with high indoor
radon concentrations in Botshabelo. It was further concluded that the wind blowing from the west and south-west
in the Klerksdorp mining region elevates the exposure levels for the communities around Midvaal and Botshabelo.
It was also concluded that the Klerksdorp gold mine region has the highest radon concentration, build-up and
exposure in South Africa [24].
Other studies have also reported that the level of radium content in the soil that underlies the foundation of a
building or house and the type of material used for floors can also influence the level of indoor radon concentration.
In the Paarl region, measurements were taken from houses in the east and west side of the Berg River and Paarl
mountain. Two-thirds of the houses in the west recorded concentration above 100 Bq/m
3
and these were all wooden
floor houses. The main source of these high indoor radon concentration levels was reported to be due to the high
level of radium in the soil [26].
The results presented in the NNR Position Paper PP-0011 showed that in Aardoom area in Beaufort West, the
highest average radon concentration detected was 478 Bq/m
3
. Radon measurements conducted in informal
dwellings at Tshepisong in Soweto showed a range between 93.1 Bq/m
3
and 1728.5 Bq/m
3
, with an average of
211.9 Bq/m
3
. The concentration levels in this region were found to be associated with the Bird Reef Formation of
the Witwatersrand Supergroup [27].
4.4 Studies conducted: 2010-2019
Studies have proven that granite rocks are the main source of elevated radon concentration levels [4, 28]. This is
shown in a study conducted in the Vredenburg, Western Cape Province, where indoor radon concentration ranging
between 190 Bq/m
3
and 200 Bq/m
3
with an average of 58.7 Bq/m
3
were recorded [29]. The study also reported
that the other factor that contributed to these levels of indoor concentrations was the lifestyle of the occupants of
the homes in the area. It was reported that the occupants live a ‘closed’ lifestyle, meaning there is limited airflow
in their houses to diffuse indoor radon and minimize its build-up. Indoor radon concentration in Saldanha house
located in an area with mild microclimate was calculated to be approximately 2.5 Bq/m
3
. Residents in this house
had an open lifestyle, meaning there is enough airflow to reduce the build-up of indoor radon. The low level of
indoor concentration in this house confirms that the lifestyle of house occupants plays a role in the build-up of
indoor radon.
Another factor that affects the indoor radon build-up and emanation is the type of building materials. In Saldanha,
8
the highest measured concentration of 86 Bq/m
3
was in a confined flat on the ground floor with few windows and
a concrete ceiling. This house did not have enough airflow, resulting in high radon concentration [29]. In one of
the studies where measurements were taken from the living room, bedroom and storeroom, the highest
concentrations were measured during the winter season in the store-room using both the Alpha Guard (short-term)
and the radon gas monitors (RGMs) (long-term measurements). The highest concentrations were 62 Bq/m
3
and 48
Bq/m
3
respectively. Since this house was the farthest from the slimes dam, it can be concluded that the recorded
radon concentration was due to the lack of ventilation and the material used to build the house [19].
An excess indoor radon concentration of 400 Bq/m
3
was estimated through measurements of uranium
concentration in the Western region, Saldanha Bay in Western Cape Province. The area is dominated by granite
bedrock, which generally contains a high level of uranium. The presence of radon in this area was estimated by
linking the measured uranium concentration to the indoor concentrations in Paarl since the two areas are
geologically similar. The measured indoor radon concentration in the Paarl area was greater than 300 Bq/m
3
in
about 6% of the houses. This confirms the predictions that 5.7% of the points would exceed 300 Bq/m
3
radon
potential in Baviaansberg [30].
Recently, a study conducted by Moshupya and co-workers in 2018-2019 recorded indoor radon concentration
levels with a maximum of 174 Bq/m
3
and an average of 105 Bq/m
3
. This study was done in Kagiso Township in
Krugersdorp, which is located west of Johannesburg city in Gauteng province. Johannesburg is the city which
dominates the whole of SA with gold and uranium mines [28]. Solid-state nuclear track devices monitors (RGMs)
with CR-39 polyallyl diglycol carbonate (PADC) which is highly sensitive to alpha particles were installed in
dwellings to measure the levels of indoor radon. Outdoor radon measurements were also conducted in areas
dominated by mine tailings and dams and the recorded radon concentrations levels ranged between 32 Bq/m
3
and
1069 Bq/m
3
. The effective dose received by the public from outdoor exposure showed a maximum of 16 mSv/y,
which is above the recommended level of 1 mSv/y proposed for public radiation exposure. This high levels of
outdoor radon concentrations could be the source of indoor radon concentration [31].
Kamunda [32] also conducted a radon measurement study in Gauteng province, south-west of Johannesburg near
the Carletonville mining area which also forms part of the renowned Witwatersrand basin. An alpha Guard
Professional Radon Monitor was employed for indoor radon measurements. Indoor radon concentrations were
measured overnight for about 24 hours in 6 houses in the east and west villages from the mine settlements and 2
houses from the control area. The average indoor radon concentration was 119.6 Bq/m
3
and the maximum value
obtained was 472.0 Bq/m
3
, which was said to be due to the high content of Uranium-238 in this region. The
calculated annual effective doses ranged between 0.03 -11.89 mSv with an average value of 3.01 mSv, thus
indicating a potential health hazard to the population residing in the area.
4.5 Indoor radon spatial map
Spatial distribution of indoor radon data obtained from studies conducted in various regions in South Africa is
presented in Figure 1. It can be observed that there are areas with high indoor radon concentrations. It is also
evident that there is limited data available on existing radon exposures indoors. The presented data indicate that it
is important to conduct further investigations on a national scale to have a quantitative representation of existing
radon exposure situations.
9
Figure 1: Indoor radon results obtained from various studies conducted in South Africa.
5 CONCLUSION
This paper reviewed the limited experimental studies and reports relating to indoor radon measurements in South
Africa for the past four decades. The studies have revealed indoor radon concentrations vary due to factors such
as geology (types of rocks), wind speed and direction, type of house, building material and floor type. Gold and
uranium mine waste, mine tailings and granite rocks with high uranium content were found to be major sources
of indoor radon in most of the conducted studies. The possible entry mechanism of radon in dwellings near mine
tailings is due to the infiltration of radon bearing air released from tailings and soil that contain a high concentration
of
226
Ra leached from tailings. It is observed from the studies conducted in the Paarl region in the Western Cape
and the Witwatersrand in the Gauteng Province, that floor type influences indoor radon concentration levels. These
studies reported elevated indoor radon concentrations in homes that had wooden floors compared to houses with
other floors types.
Currently, the available data only serves as an indication that there might be an indoor radon challenge in the
country, especially in regions with a history of gold mining activities and areas that have a geological formation
10
with high uranium or granitic content. It is thus necessary for SA to conduct an indoor national radon survey and
radon map, this will help with the identification of possible radon hotspots and public exposure areas. Moreover,
this will enable the development of policies and building codes to prohibit development of radon hotspots into
residential areas. Radon mapping will increase awareness about the health hazards of exposure to radon over a
long period.
One of the objectives of this paper was to find a trend in the studies reviewed. From the data presented in Table 1
and Figure 1, there is still a wide data gap that needs to be filled by further research and integrated, long-term
indoor radon measurements to collect quality data especially in potential radon hotspots such as residential areas
around the gold or uranium mining areas and mine dumps. With sufficient data, it will be possible to establish a
trend between parameters that influence indoor radon accumulation as well as the development of a national radon
database, and ultimately a national radon map. Moreover, this will assist in determining the sources of indoor
radon in different regions and further guide in future epidemiological and environmental impacts studies. From
this review paper, it is concluded that further research and data collection is required to inform the development
of regulation o manage conditions in existing exposure situations.
6 ACKNOWLEDGEMENTS
The authors would like to thank Subject Matter Experts (SMEs) at NNR for their guidance and valuable inputs, as
well as the CNSS and NWU Research Support Office for financial support.
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