Radioactivity assessment of radium and radon concentrations in water sources at and near selected former uranium mines in the West-Rand area of Johannesburg
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Date
2021
Authors
Tsewu, Ayabulela
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Abstract
The present work aimed at establishing the extent and distribution of the ac tivity concentration levels of 238U daughter-nuclides; 226Ra and 222Rn in the
West Rand-area of Johannesburg. The main motive was to ascertain whether
the exposure of the nearby residents to ionising radiation due to former mining
activities was within the maximum acceptable limit of 1.0 mSv/y for the pub lic. Measurements include the use of Alpha Spectroscopy system (Canberra)
with Passivated Implanted Planar Silicon (PIPS) and Solid-state Alpha De tectors for Radon measurements (RAD-7) to identify radionuclides, quantify
and analyze isotopes of interest.
A seasonal collection of 32 water samples from the mining areas was car ried out and analysed for 226Ra and 222Rn. The higher and lower radium
(
226Ra) concentration values in water samples recorded at Ezulwini inlet in
winter (June 2019) and Kloof down in Summer (December 2019) found to be
(164.42±18.47) mBq/l and (-3.38±-2.39) mBq/l, respectively. The average ra dium concentration for the water samples survey in the West-Rand area was
73,4±10,0 mBq/l, 74,6±9,6 mBq/l, 71,6±10,5 mBq/l, and 60,9±5,8 mBq/l
for June 2019, September 2019, December 2019 and March 2020, respectively.
The 226Ra activity concentration (mBq/l) of analysed samples mean values are
not significantly different (p>0.05) from June 2019 to March 2020 consecutive
seasons. The comparison of the mean values within pair of groups shows no
statistical significance. The radium values were lower than the suggested max imum contamination levels by US-EPA of 555 mBq/l [1].
The measurements show that the radon (222Rn) concentration higher and
lower values were recorded at (Bly6) Blyvooruitzicht shaft 6 discharge in Au tumn (March 2020) and (Ezul) Ezulwini Outlet discharge in Winter (June
2019) and found to be 289±272 mBq/l, and 37.1±74.1 mBq/l, respectively.
The average radon concentration for the water samples survey was 142,1±79,8
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mBq/l, 126.2±95.1 mBq/l, 134.2±108.9 mBq/l, and 140.6±123 mBq/l for
June 2019, September 2019, December 2019 and March 2020, respectively. The
obtained 222Rn concentration results in drinking water samples in the current
study are low than the approved maximum contamination level (MCL) 11.1
Bq/l as approved by US-EPA [1].
The obtained average values for radium annual effective dose (AEDRa) were
found to be 1,06E-02 mSv/y, 1,46E-02 mSv/y, 1,47E-02 mSv/y, and 1,07E+02
mSv/y from June 2019 to March 2020, respectively, while the radon annual
effective dose (AEDRn) averages were 8.53E-05 mSv/y, 7.57E-05 mSv/y, 8.05E 05 mSv/y, and 8.44E-05 mSv/y June 2019 to March 2020, respectively. The
maximum AEDRa value found at Bly4 in December 2019 (Summer) was 3.19E 02 mSv/y. Meanwhile, the maximum AEDRn effective dose value was found
in drinking water sample (Drink) in March 2020 (Autumn) as 3.38E-04 mSv/y.
The radon annual ingestion dose from the current study is lower than the
European Commission and the World Health Organization proposed concen tration of 222Rn in drinking water of 100 Bq/l [2]. The results of this study
indicate that the total annual effective doses from possible intake of 226Ra and
222Rn radionuclides in sampled water in West-Rand area are found below the
World Health Organisation (WHO) recommended limit of 0.1 mSv/y as well
as the average radiation dose of 0.29 mSv/y received per head worldwide due
to ingestion of natural radionuclides assessed by UNSCEAR (2000) [3].
Finally, the physico-chemical properties of water samples such as pH and
electrical conductivity (EC) are studied for all the surveyed seasons. The pH
averaged 1.18, 0.94, 1.13 and 1.20 for Winter (June 2019), Spring (September
2019), Summer (December 2019) and Autumn (March 2020) seasons, respec tively. Also, the EC averaged 3134, 5566, 2872, and 3086 mS/m for Winter
(June 2019), Spring (September 2019), Summer (December 2019) and Au tumn (March 2020) seasons, respectively. Above all, no significant health risk
may be posed on the population surrounding the West-Rand area from 226Ra
and 222Rn radionuclides present in the water samples as indicated in obtained
results.
Description
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, School of Physics, University of the Witwatersrand, Johannesburg, 2021