Analysis of the radionuclides and heavy metals concentrations of the Vaal River, South Africa.

Introduction

The issue of river water pollution due to various anthropogenic activities in South Africa is of major concern (Claassens et al., 2016; Zhou et al., 2020). Water pollution refers to the contamination of water bodies, such as rivers or lakes, by human activity, which has a negative impact on water users (Ajibade et al., 2021). Toxins from sewage discharge, industrial operations, mining, agriculture, and urban or storm-water runoff interact with water bodies to cause contamination (Zhou et al., 2020; Khan et al., 2022). When humans use contaminated water for various activities such as drinking or irrigation, it can cause ecosystem destruction and spread water-borne diseases (Zhou et al., 2020; Moloi et al., 2020; Mokarram et al., 2020; Mararakanye et al., 2022). The more polluted the water bodies, the worse the water quality becomes (du Plessis, 2021). According to numerous studies, the main causes of poor water quality in South Africa are mining, urbanization, and other anthropogenic causes (Durand, 2012; Manyatshe et al., 2017; van Rensburg et al., 2016; Winde et al., 2017).

South Africa has many aspects of water challenges that can affect its economic growth, especially when the levels of water scarcity, droughts, and increasing and deteriorating water resources are not well addressed (Plessl et al., 2019; van Rensburg et al., 2016; Wepener et al., 2011). Potable water is essential for life. Therefore, it is important to ensure that its quality is maintained through careful monitoring activities (du Plessis, 2021).

South Africa is known for its mining industry, which plays an important economic role (Winde et al., 2017; Worlanyo and Jiangfeng, 2021). South Africa is also considered to be the largest gold producer (Winde and de Villiers, 2002). The Gauteng province within the Witwatersrand Basin of South Africa has more uranium than gold, which was mined as a byproduct. The mining of uranium within the Gauteng province is mainly on the outskirts of Johannesburg near Randfontein and west of Witwatersrand (Winde and de Villiers, 2002). Uranium waste recovered from gold mining operations was deposited in Witwatersrand mud dams. Over the years, waste piles have grown and have intensified radionuclides in the environment (Winde et al., 2017; Worlanyo and Jiangfeng, 2021).

According to Du Plessis (2021), the sustainability of South Africa’s freshwater resources is critical. South African water bodies require attention and status to ensure that the quality of water is at the desired state for users (Makubalo and Diamond, 2020). Within Gauteng and North - West Province of South Africa, the deterioration of rivers due to mining activities is noticeable (Durand, 2012). Mines are allegedly the major environmental sources of radionuclides and heavy metals (Durand, 2012; Manyatshe et al., 2017; van Rensburg et al., 2016, Winde et al., 2017).

The radionuclides and heavy metals are normally released during surface mining operations (Manyatshe et al., 2017; van Rensburg et al., 2016; Winde et al., 2017). They are found everywhere in the environment and can accumulate easily in soil and water (Manyatshe et al., 2017; van Rensburg et al., 2016; Winde et al., 2017). The activity concentrations of radioactive materials and heavy metals produced during mining processes can pose serious risks to people and the environment when exposed to persistent levels (Groffen et al., 2018; Marara and Palamuleni, 2019; Moloi et al., 2020).

Furthermore, mines are considered liable for a series of environmental issues and human health problems (Plessl et al., 2019; van Rensburg et al., 2016; Wepener et al., 2011) and can potentially cause severe risks to the environment and people (Plessl et al., 2019; van Rensburg et al., 2016). Some of these risks may cause damage to water bodies, biodiversity loss, and lifestyle changes as well as affect food security and potentially cause pollution (Plessl et al., 2019; van Rensburg et al., 2016). These risks can be due to the decay series of long-lived natural uranium (U) and thorium (Th) (Madzunya et al., 2020). The radionuclides can enter into the environment and cause various health effects when ingested or inhaled in high concentrations resulting in sicknesses such as cancer and eye problems (Davies and Mundalamo, 2010).

According to Durand (2012), the Gauteng and North - West mine effluents contain thorium, uranium, radium, and polonium, which are considered radioactive. These pollutants accumulate in river sediments and soil, posing a severe threat to the water, environment, and people (Durand, 2012). The presence of toxic pollutants tends to affect people through ingestion, inhalation, and absorption (Davies and Mundalamo, 2010). Exposure to these pollutants may cause damage to the kidneys, blindness, paralysis, cancer, tissue diseases, and changes in the immune system (Durand, 2012; Jibiri and Okeyode, 2012; Moloi et al., 2020).

The permissible limit of uranium in drinking water is 30 mg/l as to the recommendations of the World Health Organization (WHO) (Burritt and Christ, 2018). The level is based on epidemiological studies of consumption of 2 litres of drinking water by a 70 kg adult per day, with 80% tolerable daily intake (Ma et al., 2020).

Problem statement

The Vaal River provides potable water to various industries in the Gauteng, North - West, Northern Cape, Free State, and Mpumalanga provinces of South Africa (Davies and Mundalamo, 2010; Durand, 2012; Manyatshe et al., 2017). However, these industries tend to discharge polluted water back into the river system and affect the state of the river economically, environmentally, and ecologically (Atangana and Oberholster, 2021; Marara and Palamuleni, 2019; Moloi et al., 2020).

The river flows through gold mines and is potentially contaminated with substantial amounts of radionuclides, heavy metals, and other toxic chemicals (Manyatshe et al., 2017). Furthermore, the Vaal River is argued to be a dumping site for radiotoxic and heavy metals from various industries, including mining. The state of the river showed no signs of improvement (Chokwe and Okonkwo, 2019; Wepener et al., 2011). At this rate, the continued pollution of the river will potentially have serious impacts on human health, food production, and the environment (Chokwe and Okonkwo, 2019; Plessl et al., 2019; van Rensburg et al., 2016.

Numerous studies have been conducted on the Vaal River water system and its pressing problems (Ajibade et al., 2021; Chokwe and Okonkwo, 2019; Claassens et al., 2016; Davies and Mundalamo, 2010). There are reports and guidelines regarding pollution of the Vaal River; however, progress has not been made in addressing issues related to river pollution of the river (du Plessis, 2021 and van Rensburg et al., 2016). Furthermore, few studies on radionuclides and heavy metals in the Vaal River have been conducted. Recent studies conducted around the Vaal River have focused on the radioactivity levels and dosages of mine dam tailings and the exposure of people to (Moshupya et al., 2022; Zupunski et al., 2023). The Vaal River challenges were not addressed in terms of satisfaction. The state of the river showed no signs of improvement (Chokwe and Okonkwo, 2019; Wepener et al., 2011). At this rate, the continued pollution of the river will potentially have serious impacts on human health, food production, and the environment (Chokwe and Okonkwo, 2019; Plessl et al., 2019; van Rensburg et al., 2016.

The study area was selected based on several pollution concerns from various studies on the Vaal River (Chokwe et al., 2017; Moloi et al., 2020). This study is based on rivers as a possible pathway for heavy metals and radionuclides. The intention of this study is to assess the water quality of rivers for future reference. This study considers possible angles that may contribute to river water pollution, which affects the water quality of the river, and proposes a conceptual management model for the Vaal River.

Furthermore, it is important to note that many South African gold mines extracting ore contain not only gold but also a substantial amount of uranium (U), which is inadvertently transported to the surface inadvertently (Winde and de Villiers, 2002). The main problem with uranium mining is its widespread effects on the environment, such as increased levels of radiation, radioactive dust, and water-borne toxins (Madzunya et al., 2020).

Aim of the study

The intention of this assessment was to investigate the concentration levels of radionuclides and heavy metals in the water quality of the Vaal River.

Objectives

The objectives of this study were to:

Methods

This study was carried out within the Vaal River borders of the North - West, Gauteng, Free State, and Mpumalanga provinces of South Africa. The Vaal River is the longest river within South Africa borders (Wepener et al., 2011). The river provides potable water to Gauteng and its neighboring provinces for various consumers and industries (Manyatshe et al., 2017). Apart from Gauteng, the river provides water to North - West, Northern Cape, Free State, and Mpumalanga provinces. The focus of this study was primarily on accessible parts of the river, located in Gauteng, North - West, and some parts of the Free State. It is worth noting that the Vaal River is the primary water source for various anthropogenic activities such as mining, agriculture, and recreation in Gauteng and the North - West Province (Manyatshe et al., 2017). The river flows through Gauteng and North - West provinces, including but not limited to Vanderbijlpark, Orkney, Potchefstroom, and Klerksdorp (van Rensburg et al., 2016).

The Vaal River flows through the Northern Cape, Mpumalanga, Free State, Gauteng, and the North - West province, as shown in Figure 1 (Weideman et al., 2020; Wepener et al., 2011). Water drawn from the upstream of the Vaal River was used to meet the industrial needs of Gauteng and the surrounding provinces (Wepener et al., 2011). Other uses of the river for consumers and industries include coal mining, electricity generation, and urban use (Davies and Mundalamo, 2010; du Plessis, 2021; Durand, 2012). Figure 1 shows the study area and its boundaries.

Figure 1. Study area.

Results and discussions

This study analyzed water samples from the Vaal River for radionuclides and heavy metals. The aim was to assess potential health risks to people. The risks were measured using the (Raeq), absorbed dose (D), annual effective dose equivalent (AEDE), external hazard (Hex) and internal hazard (Hin) indexes (UNSCEAR, 2000). The heavy metal concentrations of Li, B, P, Ni, Se, Fe, Mn, Pb, Zn, and Co were also examined. Following the 2011 USEPA guidelines, the CDI, HQ, and HI of the Vaal River were measured using calculations adopted from US EPA guidelines. The risk values were estimated using an adult of 70 years at 70 kg body weight and a child of 15 years at 15 kg body weight. The results were compared with the world average permitted values. This was done to confirm that the concentrations adhered to global guidelines. Studies conducted in the Vaal area have also been used to investigate the evolution of pollution problems in the Vaal River.

The K, Th, and U in Bq/l from the ICP-MS technique were converted into activity concentrations, and the Raeq, D, AEDE, Hex, and Hin hazard parameters were used to determine human health risks. Correlation factors for ICP-MS were used to measure the radionuclides.

Activity concentrations of radionuclides in water

Water samples collected along the Vaal River were analyzed for K, Th, and U using ICP-MS. The average, maximum, minimum, and standard deviations of the samples were calculated, as shown in Table 1. From the calculated concentrations of each sample, hazard parameters such as Raeg, D, AEDE, Hex, and Hin were calculated, as indicated in Table 1. The average radiation hazards of Raeg, D, AEDE, Hex, and Hin were 33,803 Bq/l, 18,158 nGy/h, 0, 0222 nGy/hr, 0,091 and 0,096 respectively. These hazard parameters pose no radiological risks to people owing to the ingestion of water. This is because of the lower concentrations when compared to the UNSCEAR limit of 370 Bg/l for Raeq, 55 nGy/h for D. 1 mSv/yr, and 1 ratio for Hex and Hin.

Table 1. K, Th and U activities and the hazard indices.

	K (Bq/l)	Th (Bq/l)	U (bq/l)	Raeq (Bq/l	D (nGy/hr)	AEDE (nGy/hr)	Hex	Hin
EM1	467.3	0.021	2.46	38.5	20.634	0.025	0.104	0.111
PB1	359.4	0.002	0.643	28.3	15.285	0.019	0.076	0.078
PB2	428.9	0.005	0.547	33.6	18.142	0.022	0.091	0.092
PB3	429.2	0.003	0.642	33.7	18.198	0.022	0.091	0.093
PB4	392.1	0.004	0.511	30.7	16.59	0.02	0.083	0.084
PB5	412.5	0.003	0.539	32.3	17.452	0.021	0.087	0.089
PB6	432.3	0.002	0.52	33.8	18.269	0.022	0.091	0.093
PB7	423.9	0.004	0.486	33.1	17.904	0.022	0.089	0.091
PB8	432.4	0.002	0.455	33.8	18.243	0.022	0.091	0.092
PB9	402.7	0.039	0.632	31.7	17.108	0.021	0.086	0.087
PB10	412.4	0.004	0.449	32.2	17.406	0.021	0.087	0.088
PB11	401.9	0.002	0.412	31.4	16.95	0.021	0.085	0.086
PB12	427.6	0.002	0.486	33.4	18.054	0.022	0.09	0.092
PB13	439.1	0.002	0.485	34.3	18.563	0.023	0.093	0.094
PB14	446.8	0.006	0.598	35.1	18.913	0.023	0.095	0.096
PB15	362.7	0.003	0.543	28.5	15.376	0.019	0.077	0.078
PB16	392.9	0.003	0.513	30.8	16.622	0.02	0.083	0.084
PV1	441.5	0.006	0.774	34.8	18.772	0.023	0.094	0.096
PV2	454.7	0.006	0.612	35.6	19.247	0.024	0.096	0.098
PV3	444.3	0.005	0.691	34.9	18.85	0.023	0.094	0.096
SD2	386.9	0.013	0.639	30.4	16.437	0.02	0.082	0.084
SD3	430.1	0.013	7.751	40.9	21.525	0.026	0.11	0.131
ST2	444.1	0.09	0.65	34.9	18.82	0.23	0.094	0.096
VW2	243.8	0.006	22.796	42.6	21.155	0.026	0.115	0.177
VW3	463.9	0.737	0.209	36.1	19.449	0.024	0.097	0.098
Av	414.928 ± 42.000	0.036 ± 0.005	1.802 ± 0.900	33.803 ± 2.500	18.158 ± 1.800	0.022 ± 0.002	0.091 ± 0.001	0.096 ± 0.010
Max	467.3	0.737	22.796	42.62	21.525	0.026	0.115	0.177
Min	243.774	0.002	0.209	28.319	15.285	0.019	0.076	0.078
Std	45.391	0.146	4.617	3.336	1.565	0.002	0.009	0.02

The average radiation hazards of Raeq, D, AEDE, Hex, and Hin were 33,803 ± 2,500 Bq/l, 18,158 ± 1.800 nGy/hr, 0,222 ± 0.002 nGy/hr, 0,091 ± 0.001 and 0,096 ± 0.010, respectively. These hazard parameters pose no radiological risks to people due to the ingestion of water. This is because of the lower concentrations when compared to the UNSCEAR limit of 370 Bg/l, 55 nGy/h, 1 mSv/yr, and ratio of 1 for Raeq, D, AEDE, Hex, and Hin, respectively, as shown in Table 2.

Table 2. K, Th, U activities and UNSCEAR recommended limits.

River Water
	K (Bq/l)	Th (Bq/l)	U (Bq/l)	Raeq (Bq/l)	D (nGy/yr)	AEDE (mSv/yr)	Hex	Hin
Average	414.928	0.036	1.802	33.803	18.158	0.222	0.091	0.096
Max	467.259	0.737	22.796	42.62	21.525	0.026	0.0115	0.177
Min	243.774	0.002	0.209	28.319	15.285	0.019	0.076	0.078
Std	45.391	0.146	4.617	3.336	1.565	0.002	0.009	0.02
Recommended limits ( UNSCEAR, 2000)				370	55	1	1	1

Table 2 presents the average, maximum, minimum, and standard deviation of each K, Th, and U in Bq/l for the selected radionuclide analyzed using ICP-MS. According to the tabulated concentrations, all hazard parameters were below the limits recommended by the UNSCEAR 2000 guidelines. This proves that the sites where samples were collected pose no radiological risk to people as of 2023.

Correlation factors were used for the dose rate (D) against the annual effective dose (AEDE) and the radium equivalent (Raeq), as shown in Figure 2 and Figure 3, shows the correlation between D and AEDE. The results showed that the annual absorbed dose (D) was strongly correlated with both Raeq and AEDE.

Figure 2. Correlation Factor D and Raeq.

Figure 3. Correlation Factor D and AEDE.

Heavy metal concentrations in water

The sample sites in which the Vaal River upstream and downstream waters were collected and analyzed increased the concentrations of the elements in the river course. The concentration of the elements increased as the river flowed downstream, as shown in Figure 4.

Figure 4. Heavy metals in water.

Conclusions

The study intended to investigate the concentration levels of the radioactive and heavy metals of the Vaal River, to evaluate the human health risks due to ingestion of water. The ICP-MS technique was used due to its lower interference, and quick multi-element analysis benefits for environmental samples.

The average radiation hazard of Raeq, D, AEDE, Hex and Hin comply with the safety limit of UNSCEAR. As a result, pose no radiological risks to humans. This is justified by using an adult of 70 years and a child of 15 years for a period of a year. This also implies that the sites where samples were collected have lower concentrations of radioactive materials.

In relation to the heavy metal concentration levels of the study, Mn and Fe presented higher concentration. These elements are known to be common and highly dissolved in water; however, higher concentrations could be due to the human activities of industrial and agricultural effluent. The HI of the study presented a ratio greater than 1, which implies a carcinogenic risk toward humans. The elevated concentrations are possibly due to the nearby mine effluent, especially taking into consideration that the river is situated near the mine. There is also the possibility of discharges from the local municipalities and agricultural run-off since the space is extensively used for various uses such as industrial and municipal activities.

Based on the findings of prior studies and this study, the site is not safe for public use until more investigation is carried out. As a result, additional monitoring and regulatory control measures are required to safeguard the safety of all residents in these areas.

Ethics

Ethical approval was not required.