Abstract
Mining activities throughout the world enable economic developments such as urban sprawling, formation of mining towns, industrial developments, and creation of job opportunities. South Africa is amongst the countries of the world in which mining is an economic cornerstone, supplying the globe with minerals such as gold, coal, iron, diamonds and many more. The formation of numerous mining towns resulted, some of which became large cities, such as Johannesburg and drew thousands of labourers from within the country and neighbouring countries such as Mozambique, Lesotho, Zambia and Malawi. Unfortunately, these mining activities are accompanied by negative impacts on the environment which includes release of toxic wastes contaminating water resources and agricultural land, air pollution due to dust, and deforestation of vast areas of land impacting the wellbeing of humans, plants, and animals. These environmental impacts arise during active mining operations and worsen post closures, especially in prematurely closed mines without any proper rehabilitation. In South Africa, there are over 6000 mines which have been abandoned, and owners cannot be traced, and increased demands for land has seen many of these abandoned mining sites encroached by human settlements who lack information health concerns associated with exposure to potential toxic elements (PTEs) from mining wastes.
Existing reports identified arsenic (As), lead (Pb), cadmium (Cd), uranium (U), chromium (Cr), mercury (Hg) among others PTEs released from abandoned mines. These PTEs are deleterious in small quantities and ascends the food chain through consumption of contaminated food crops grown on contaminated land and consumption of fish and drinking contaminated water and inhalation of dust amongst others. Populations around these abandoned mining sites are often at health risk, which include skin cancer, mental and reproductive disorders, stomach problems, high blood pressure, cancer, kidney failures and loss of immunity among others due to exposure to these PTEs. To ensure their health wellbeing, there is a need to characterise the mine wastes especially tailing dumps to identify the PTEs likely to be released to the environment, understand their behaviour in the environment such as water, sediments, soil and air, and identify their pathways, in order to propose informed mitigating measures and educate population at risk.
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The Sheba Community in the Barberton Greenstone Belt of South Africa have encroached the abandoned Bonanza goldmine and potential faces health threats from PTEs. Few reports documented occurrence of PTEs in agricultural soils and water in Barberton Greenstone Belt area, however there are no existing research on knowledge of health implications associated with usage of contaminated stream water for domestic purposes and growing food crops on contaminated agricultural soils. Furthermore, the abandoned goldmine has been infested by illegal miners that construct sluice plants along the rivers beds and use Hg for amalgamation of the gold bearing material exacerbating the contamination of the water resources. In addition, the community draw material from the abandoned goldmine tailings facility for building and softening of soccer fields which further suggests low level knowledge of health risk associated with goldmine waste. The present study was based on a multidisciplinary approach linking geo-environmental issues and the possible health implications associated with the abandoned goldmine and identified the knowledge gaps among the community members to educate them on the risk associated with the abandoned mine.
This was achieved through field samplings of garden soils, stream sediments, drinking water and food crops in order to (1) determine the stream sediment and water quality along the Fig Tree Creek and the latter Crocodile River and in particular, PTEs (including rare earth elements-REEs) geochemistry; (2) examination of the water quality of all sources of potable water for available to the local community; (3) examination of the soil quality in households gardens within the study area; (4) ascertain the daily intake of the PTEs by local residents through food crops ingestion, direct soil ingestion (geophagy) and drinking water using health risk assessment criteria described by U.S. Environmental Protection Agency; and (5) ascertain the health risk associated with residing in the vicinity of the tailings facilities due to exposure to the PTEs through various pathways (including drinking and irrigation with polluted water, and food crops grown in contaminated soil). Health data on prevalence of diseases in the area, awareness and knowledge of community members of the health implications associated with PTEs from mine waste was collected through interview surveys.
The concentrations PTEs in stream water samples indicated that 90% exceeded 10 μg/l of arsenic (As), 70% exceeded 300 μg/l of iron (Fe), 50% exceeded 0.1 μg/l of mercury (Hg) and 20 μg/l of nickel (Ni), and 10% exceeded 40 μg/l of manganese (Mn), surpassing the guidelines set by the World Health Organization (WHO, 2011)A positive correlation at a significance level p < 0.05 was also observed
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between As/Co (r = 0.85), As/Ni (r = 0.84), As/Zn (r = 0.76), As/Cr (r = 0.73), V/Cu (r = 0.97), Co/Zn (r = 93), Co/V (r = 87), Zn/Ni (r = 0.85), Cr/Zn (r = 0.84) and Co/Ni (r = 0.80) in the stream water samples suggesting same anthropogenic source in the tailings facility. Notably, Hg showed a poor correlation with other PTEs indicative of an external source, other than the abandoned goldmine tailings dump which is of the illegal mining activities. These PTEs were also detected in stream sediments with mean concentrations of As (43.9±169.5 mg/kg), Fe (107±89.4 mg/kg), Ni (28.7±16.2 mg/kg), Hg (0.3±0.1 mg/kg), and Mn (29.1±12.9 mg/kg), higher than the background levels in the region earlier described by Venter et al., (2018). The pollution indices; the geo-accumulation and potential ecological risk assessment revealed that As, Pb and Hg were the main elements of concern in the stream sediments.
All garden soils exceeded the 5.8 mg/kg guideline for As (151.3±237.7 mg/kg) set by the South African Department of Environmental Affairs (DEA), with 85% exceeding the 20 mg/kg guideline for Pb (108.5±126.9 mg/kg), 50% exceeding the 16 mg/kg guideline for Cu (17.9±29.4 mg/kg), and 80% exceeding the 80 mg/kg guideline for Cr (102.3±187.3 mg/kg). Analyses of food crops grown in these garden soils showed that all the exceeded the permissible maximum limits for of 0.2 for As, 0.3 mg/kg for Pb and Co of 0.1 mg/kg set by WHO. The concentration of As in particular decreased in the order: Fig tree fruits (102.1 mg/kg) > Sweet potato (15.1 mg/kg) > Cabbage (5.33 mg/kg) > African pumpkin (4.44 mg/kg) > Spinach (4.2 mg/kg) > Soya beans and lettuce (3.1 mg/kg) > mangoes (2.6 mg/kg) > pumpkin leaves (1.4 mg/kg) > maize (0.89 mg/kg). There was a significant correlation (p<0.01) observed for As (0.96), Cr (0.94), V (0.94), Ni (0.90), Co (0.78) and Se (0.63) in agricultural soils and concentrations of these PTEs in food crops suggesting a that PTEs ascends to food crops through root uptake and the dispersion of mine waste from the tailings dump in the area significantly contributed to the high concentration of PTEs in soils and further accumulation in food crops.
The average daily intake (ADI) non-carcinogenic values of PTEs through drinking water by both children and adults followed the order: Fe>As > Zn> Ni> Cu>>Mn>Co>Hg > Cr and carcinogenic values: As> Ni > Cr. The calculated hazard quotient (HQ) and hazard index (HI) were above the acceptable limit of 1, indicating a high non-carcinogenic risk. The calculated carcinogenic risk exceeded the 1.0E-6 acceptable limits and the total cancer risk exceeds the 1.0E-4 set by DEA and As and Ni were main contributors. The estimated daily intake (EDI) of PTEs through consumption of these food crops ranged from 0.0004 to 0.134 mg/kg/day for As, Pb (0.0001 to 0.0261 mg/kg/day) and was higher in leafy vegetables and roots compared to legumes and fruits. The calculated health risk assessment through food crop consumption showed that
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As was greater than 1 in all the food crops ranging from 2.93 and 336 followed by Pb (0.121 to 28.8). Children were the most vulnerable compared to adults through drinking water from the stream and consumption of food crops.
From the field interview survey, 80 % of the respondents rely on stream water as tap water often suffer water cuts for domestic use which includes cooking, drinking and bathing. A total of 85 % of the population were aware of the pollution threat posed by erosion of waste from the tailings dump but were only limited to identifying pollution through colour and suspended solids. Only 15 % of the respondents identified Hg (local name: sigidi) as a threat to stream waters. Most of the participants (50%) consumed more than 2 litres per day and there was no linkage between knowledge of contaminated water with daily drinking water intake. About 25 % were aware of potential ill-health that can be induced by drinking contaminated water but never associated drinking of water from Fig Tree Creek with any health complications. Due to the high As and Pb in the stream water, participants were asked of symptoms such as lesions and aggression, 50% indicated that they have seen skin lesions especially among children. More than half of the participants experienced chronic diseases such as (high blood pressure, headaches, fatigue, arthritis) and are on medical treatment, and more were elderly (70 %) than school going children (20%), others (15%) but did not disclose the underlying medical conditions. From the interviews and interaction, the community lacks knowledge of the health risk associated with exposure to PTEs from the mine waste. Despite the existing reports of high As in stream water, most respondents (80 %) still use the water for domestic purposes and did not know the health complications of such. Skin lesions and aggressiveness amongst children though identified by some respondents were never perceived as ill-health condition associated with exposure to As and Pb.
The outcomes of this study reveal that, Sheba inhabitants are most likely exposed to PTEs especially As and Pb through drinking water and consumption of food crops grown on contaminated garden soils. Dispersion of mine waste from the abandoned Bonanza goldmine tailings facility has attributed to high concentrations of PTEs in surrounding soils, stream sediments and waters, as a result, reliance on stream water for domestic use and consumption of locally grown food crops could be major pathways and hence increase the health risks associated with PTEs intake. Observably, the concentration of PTEs in the stream varied along the longitudinal profile of the Fig Tree Creek, as indicated by its increase in concentration downstream of the tailings facility compared to upstream and further downstream. In the interim, it is
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recommended that community members draw water from upstream end user point to reduce daily intake of PTEs. Notably, different food crops indicated different accumulation potentials for PTEs, leafy vegetables and roots crops indicated high accumulation potential for PTEs when compared to legumes and fruits. Growing of leafy vegetables and root crops in local gardens should be discouraged to reduce daily dietary intake of PTEs. There is an urgent need for community engagements which must involve intervention from the Department of Health in the region and other scholars to raise awareness amongst the community members especially due to the high concentration of As and Pb in both water and soils, and the existence of illegal mining which uses Hg. Programs to for treatment of degraded soil and water should also be implemented in the area to reduce the concentrations of PTEs. This should also include proper rehabilitation of the tailings facility, to reduce continuous dispersion of waste into the environment. More multidisciplinary research work is required to characterise the tailings facility and ensure that it is properly rehabilitated and that it will not impact food security and water quality in the region.
Keywords: potentially toxic elements, abandoned goldmine, health risk assessment, Bonanza Goldmine