Evaluation of water quality and human risk assessment due to heavy metals in groundwater around Muledane area of Vhembe District, Limpopo Province, South Africa
© The Author(s) 2018
Received: 8 November 2017
Accepted: 20 December 2017
Published: 12 January 2018
Sustainable access to potable water have been achieved in different developed countries of the world, but this is not true for many developing countries. In Africa, access to potable water has been achieved in a few cities but not in the entire region. This problem is more pronounced in rural areas, some of which does not have water supply infrastructure . Residents of such rural communities often resort to different sources of water. The most commonly used sources include: Rivers, streams, boreholes, lakes, etc. Most of these various alternative sources are susceptible to water pollution. Some of the major sources of pollution include the discharge of domestic, industrial and agricultural wastewater into freshwater bodies.
Groundwater is often considered as the best of these alternatives, owing to natural protection from pollution when compared to surface and perceived natural filtration as water flows down during rainy period. Groundwater as one of the natural resources is of fundamental importance to human life, because of its perceived good microbiological quality in the natural state and as a result, it is often the preferred source of drinking water supply as treatment is limited to disinfection. Aesthetically, it looks clean and acceptable to various people as it is often free from odour and sometimes do have a pleasant taste. Despite the perceived safety associated with groundwater consumption, several researches have shown that groundwater can also be susceptible to contamination [2–4]. Some factors that influence the quality of groundwater include the geology of the aquifer, climate and anthropogenic activities [5–8].
The use of groundwater sources has increased rapidly in many countries of the world due to population growth, increased industrialization and scarcity of water related to climate change. Although surface water has been extensively used in various water infrastructure, increased utilization coupled with other aforementioned factors has led to an increase in the use of groundwater sources. Groundwater are often used for drinking, irrigation and several industrial processes. The global use of groundwater is often underestimated and climatic factor has also been extensively debated to influence the available water volume in the aquifer . Several countries of the world are experiencing acute water scarcity, but this problem is exacerbated in arid and semi-arid countries of the world. The use of shallow, such as hand dug wells and deep groundwater sources (boreholes) are common in South Africa. Most of the communities that depends on groundwater sources do not know the quality of water they drink as they often presume that groundwater has a good water quality. Groundwater can be contaminated by the ingress of human and animal waste into the aquifer . This could be through the grazing of animals, discharge of domestic and industrial wastewater, use of pesticides and fertilizers in agriculture .
In some part of South Africa, groundwater is a key component of the water resources, and one of the sources of water supply. Report have shown that about two-thirds of South African population depend on groundwater for drinking [12, 13] with about 65% of the total supply in the rural areas . As such, it provides some basic water requirement, since the country’s surface water resources are unevenly distributed and cannot meet the growing demand for water . In rural areas, boreholes are located either close to a pit toilet or downstream of soak away pits or adjoining landfills or dumpsites . Some groundwater is poorly managed due to its invisible nature and it usually takes a long time to notice when it has become polluted and once it is contaminated, its quality cannot be restored by just stopping the pollutants from source, because contamination may continue after the source has been stopped or removed [17, 18]. In the rural and peri-urban areas, most of the groundwater supplies are usually untreated and it has been reported that it is difficult for groundwater to purify itself, often impossible and very expensive to treat, thereafter . The use of groundwater sources of unknown quality puts the consumers at risk to possible waterborne diseases. Bessong et al.  reported high levels of fecal contamination in groundwater sources around Tshikuwi Community in Vhembe District of South Africa. High fluoride levels have been reported by Odiyo and Makungo  in groundwater sources around Siloam village. Arsenic contamination of groundwater sources has been reported in the world [2, 21].
Thohoyandou, Vhembe District of Limpopo, South Africa is experiencing a rapid population growth and this has led to an increase in the generation of waste. Muledane village in Thohoyandou consist of households that rely on groundwater while, some areas are reserved for municipal landfill site, farming, wastewater treatment plant and cemeteries. Landfills have been identified as one of the major threats to groundwater resources in this area . There is currently no published data on the status of groundwater quality in Muledane village and possible health risks that these water sources may have on humans, unlike other reports of groundwater quality in South Africa that reported the impact of heavy metals, physical and chemical properties on human health [23, 24]. Hence, there is an urgent need to assess water quality of groundwater in Muledane village because contaminated water by faeces, leachate and other non-point sources could have economic and social development implications and human health risks due to activities around this area. It is assumed that water quality impairment might be severe in Muledane village of Thohoyandou. To this end, the aim of this study was to assess the status of water quality from boreholes situated at Muledane area near Thohoyandou by quantifying heavy metal concentration and determine possible health risk due to exposure of human to heavy metals.
Materials and methods
Study area and land use
The study area is located at Thohoyandou block J in Thulamela Municipality Government area of Vhembe District, Limpopo province. Geological coordinates of Muledane area is located approximately on longitudes 30°1′0″E and latitudes 23°29′0″N, respectively at 734 m elevation above the sea level. The Thulamela municipality area is approximately 2966, 4 km in extent which covers 13, 86% of the total area of the Vhembe District with an estimated population of 537,454 . Activities around Muledane area consist of schools, churches, agricultural activities, residential and hotels. It also encompasses dense bushes and trees, sewage treatment plant and the municipal landfill site which make up a large portion of the study area. Thohoyandou falls under the summer climatic conditions of South Africa with very warm conditions and the annual rainfall ranging from 400 to 800 mm. Rainfall during summer is very high with little rainfall in winter. The temperatures may reach up to 37 and 23 °C on the average in summer and winter, respectively . The 1:1,000,000 scale geological map of South Africa from the council for Geoscience shows that Muledane is dominated by fractured aquifers . The depth of water table derived from National Groundwater Database (NGDB) range from 15 to 30 m. The recharge map compiled by DWAF as part of the Groundwater Resources Assessment study of 2004 indicate that Muledane range from 10 to 50 mm/annum .
Sample collection, preparation and storage
Groundwater samples were collected as outlined by Fitfield and Haines . Briefly, plastic bottles were washed and stored in 10% nitric acid for 2 days and rinsed with double distilled water before sampling. A total of 24 groundwater samples were collected from eight randomly selected boreholes at Muledane area of Thohoyandou. Borehole samples were label according to their sources using the code B1–B8. The bottles were rinsed three times and taps were allowed to run for at least 5 min before collection of samples and labelled accordingly. Samples for metals were preserved by adding 3 mL of concentrated HNO3. All the samples were placed on an ice chest and transported to the University of Venda then preserved at − 4 °C in the refrigerator for further analysis.
Onsite analysis of the physico-chemical parameters such as electrical conductivity (EC) and turbidity were measured on-site using Cyberscan 500 conductivity meter (AQ2010 LABOTEC) and turbidity meter, respectively. The pH and temperature were measured using pH meter (H1 8014 HANNA instrument). Appropriate portion of the collected groundwater samples were digested with concentrated HNO3 for heavy metals analysis according to the method of Sharma  and analysed using an inductively coupled plasma optical atomic spectrophotometer (ICP-OES) (ThermoScientific). The instrument was standardized with seven working standard solutions (multi-point linear fitting) for Copper (Cu), Manganese (Mn), Iron (Fe), Chromium (Cr), Cadmium (Cd), Zinc (Zn) and Lead (Pb) and analytical precession was checked by frequently analysing the standards as well as blanks. An Ion Chromatography (Methrohm 850 Professional IC) was used to analyze the anions concentration including nitrates, chlorine, fluorine, and sulphates in water samples collected from different boreholes so as to check the groundwater’s suitability for domestic use. The IC has 20 μL injection loop, Ionpac AG144× 50 mm guard and AS144× 250 mm analytical columns with conductivity detector. Multiple working solutions of 1, 5, 10 and 20 units/ppm were prepared and used in calibrating each anion Fluoride (F−), Chloride (Cl−), Nitrate (NO3−) and Sulphate (SO42−). An eluent 1.0 Mm NaHCO3/3.5 Mm Na2CO3 was prepared and pumped through the IC system. The standards were injected into the instrument sequentially, in order to perform calibration for each element. The samples were filtered through a 0.45 μm Millipore filter and then injected into IC machine for analysis.
Quantitative health risk assessment
To assess the overall potential non-carcinogenic effects posed by more than one metal and pathway, the sum of the computed HQs across metals was expressed as hazard index (HI) using Eq. 4 . HI > 1 showed that exposure to the groundwater could have a potential adverse effect on human health [32, 34].
GraphPad Prism version 5.0 for Windows (GraphPad Software, San Diego California, USA) was used for both statistical analysis at 95% confidence limit and the graphs. Mean values of the parameters obtained for the various locations were compared to DWAF  and WHO  guidelines for domestic water use. Multivariate statistics in terms of principal component analysis (PCA)/factorial analysis (FA) and hierarchical agglomerative analysis (HAC) were performed using Xlstart statistical software . The PCA is used to established major variation and relationships among the different metals. Pearson correlation was calculated for different metals in groundwater samples and significant principal components (PC) was selected based on the varimax orthogonal rotation with Kaiser normalization at eigenvalues greater than one. The HCA was used to identify groups that shows similar characteristics or variables and dendrogram to provide a visual summary of the results based on dimensionality of the original data .
Results and discussion
Mean value of physico-chemical parameters in groundwater samples collected from eight boreholes in Muledane village
Range of sample stations
Month of sampling
Standard limit for WHO for drinking water quality
Standard limit for DWAF for drinking water quality
The EC average level for each sampling point during the monitoring period were 63.2, 42.5, 23.92, 17.56, 15.69, 10.52, 17.71 and 51.1 mS/cm for samples B1–B8, respectively. The mean values recorded for conductivity were within the recommended guideline of < 70 mS/cm for domestic water use . However, measured values for B1 throughout the investigation were very close to the recommended guideline value of DWAF (Table 1). Hence, frequent monitoring of hotels such as the investigated B1 borehole is required, because this parameter might accumulate overtime and exceeds the recommended level. EC plays an important role in water quality as it gives an indication of salinity and TDS present in water . The total dissolved solids (TDS) that measures the dissolution mechanism of organic and inorganic materials in groundwater were low and below the WHO value of 1000 mg/L. Turbidity recorded (0.33–14.9 NTU) were within the acceptable limit set by DWAF (< 1 NTU) and WHO (< 5 NTU) for domestic water except in April where B3, B4, B5, B6, and B7 exceeded the DWAF limit but fell within the guideline value of WHO for domestic water (Table 1), while B3 (14.9 NTU) and B5 (5.76 NTU) samples during April exceeded both standard limits. Turbidity is caused by colloidal or suspended particles that may originate from organic or inorganic matter or combination of both in water, thus prevents transmission of light through the water. Its affect the appearance and the aesthetic property of water which shows that there is a slight risk of potential secondary health effects turbidity between 1 and 20 NTU and minor risk if used for food preparation .
Guidelines for drinking water quality set by South Africa and World Health Organisation (WHO)
Heavy metal concentration in borehole water
The concentrations of Manganese varied from 0.01 to 1.22 mg/L for samples B1–B8 (Fig. 1a–c). All boreholes complied with the WHO  guideline concentration of < 0.4 mg/L for domestic water use except for borehole, B1 in January (Fig. 1a) and B4–B7 in April (Fig. 1b). However, all boreholes failed to comply with the standard limit of < 0.05 mg/L set by DWAF  for domestic water. This may be as a result of landfill leachates leaching to the boreholes, industrial effluent or indirect contact of water in the boreholes with the sewage. According to DWAF , no aesthetic effects associated with the use of water with less than 0.05 mg/L Mn concentration, but concentration between 0.10 and 0.15 mg/L could cause critical stain and taste problems [38, 39].
Average concentration of Cu in all the groundwater samples ranged between 0.01 and 0.41 mg/L (Fig. 1a–c). The concentration is below the standard limits of < 1.0 and < 2 mg/L set by DWAF  and WHO , respectively for domestic purpose (Table 2). No adverse health effect associated with consumption of water with less than 1.0 mg/L concentration of Cu . Higher concentration was measured at site B4 as compared to other groundwater samples in the month of April (Fig. 1b). The higher concentration could be as a result of Cu particles from the pipes into the borehole water.
The concentrations of Pb ranged between 0.002 and 0.026 mg/L and the mean concentrations in water samples throughout the study period for all the boreholes (B1–B8) are depicted in Fig. 1a–c. Although, the mean value obtained was below the standard guidelines of 0.01 mg/L set by both DWAF  and WHO  for domestic water use, except sample B6 that exceeded the limits. Specifically, the concentration of B2 (0.026 mg/L) and B3 (0.023 mg/L) in April during autumn and B6 (0.023 mg/L) in June during winter was high (Fig. 1c). Studies have shown that chronic Pb exposure can cause anaemia and high blood pressure especially in older and middle age groups. Exposure to high concentration could cause kidney and brain damage in male , while water with less than 0.05 mg/L concentration of Pb could have slight risk of behavioural changes and possibility of neurological impairment in foetuses and young children developing their brain tissues .
Zinc and cadmium
During the study period, all boreholes complied with the recommended standard limits of < 5.0 and < 3.0 mg/L set for Zn by both WHO and DWAF, respectively for domestic purposes. The maximum and minimum detection values of 0.003 and 0.24 mg/L were recorded in April (B3 sample) and June (B5 sample) as shown in Fig. 1b and c, respectively. The concentration in the collected samples might be due to high water infiltration in April due to rain as compared to other months (Fig. 1). Hence, all boreholes water has little to no health effects because Zn is known to have antioxidant properties that protect humans against accelerated aging of muscles and skin. It’s also helps in healing process after an injury if moderate and recommended dosage is ingested . In addition, the concentration of Cd throughout the study period was below the standard limits set by DWAF  and WHO  which is 0.005 and 0.003 mg/L, respectively for domestic water use.
Factor loadings of selected heavy metals in the borehole water samples during the monitoring period
Pearson correlation matrix among metals in the groundwater samples
Evaluation of human health risk due to heavy metals in groundwater samples
Health risk assessment model by the US. EPA were used to evaluate the health risks that heavy metals could pose on human via direct ingestion and dermal absorption of groundwater in Muledane village. The level of exposure through EXing and EXderm were estimated for the months of January, April and June. The results suggested that contaminants from the boreholes around Muledane via ingestion and dermal pathways were the major exposure routes to humans in this village. Health related risk associated with the exposure through ingestion depends on the weight, age and volume of groundwater consumed by an individual this was determined using the measured minimum and maximum concentration of Cr, Cd, Zn, Pb, Mn, Fe and Cu.
Hazard quotient for potential non-carcinogenic risk (HQ) and cumulative hazard indices (HI) for each heavy metal present in the groundwater samples from the boreholes in Muledane village as consumed by adults and children via ingestion and dermal absorption pathways between January and June
The calculated cumulative hazard quotients (HI) across metal served as a conservative assessment tool to estimate high-end risk rather than low end-risk in order to protect the public (Table 5). This served as a screen value to determine whether there is major significant health risk that exposure of heavy metals in the groundwater may pose on the villagers and if there is any difference in total health risk during the study period. The estimated total HQ values were less than one (Table 5), therefore, exposure to these elements through mouth ingestion and dermal adsorption through the skin may likely not exert negative or cumulative adverse risk on the inhabitants of this village.
Chronic risk assessment (CDIing) of heavy metals in groundwater samples taken around Muledane village through daily ingestion pathway during January, April and June for adults and children
Carcinogenic risk assessment (CRing) of Cr, Pb and Cd at different times of groundwater samples collected around Muledane village through ingestion pathway for adults and children between January, April and June
Only 12.5% boreholes have ideal water quality in terms of NO3− and Mn concentration with 25% found to be in the marginal water quality class, while 75% percent fell in the unacceptable water quality class. In terms of chemical properties, it is unsafe for resident around Muledane within the investigated area to use the boreholes water for domestic purposes without treatment. This study reveals that 87.5% borehole water have high concentration of NO3; Fe and Mn among the selected anions and heavy metals. The measured concentration of Cr, Fe and Mn for some of the investigated boreholes were observed to be higher than the recommended standard limits by WHO and DWAF. The HQ and the overall non-carcinogenic health hazard indices (HI) through the ingestion and dermal adsorption of the groundwater were less than one. However, the results showed the potential risk of some of the selected metals on human, especially children. The main contributors to non-carcinogenic risk were Mn, Zn, Pb, Cr and Cd for both pathways. The results of this study further revealed that ingestion of the investigated boreholes poses carcinogenic risk (CRing) regarding the estimated Mn, Fe and Cu for adults and children. In addition to the aforementioned metals, estimated CRing for Zn among children were high throughout the study. It is therefore recommended that water quality studies should be given a priority by adding it into the integrated development plans (IDPs) and be conducted on a regular basis to assess risks of contamination. Health and hygiene education is highly needed for people in rural areas because of lack of proper sanitation and proper water handling practices. In addition, further studies are recommended to investigate the point sources of contamination and possible causes of high concentration of nitrate level in the boreholes around Muledane village.
JNE, NM and JOO designed, collect the data and laboratory experimentation, AME and JNE handled data analyses, Interpretation of results and preparation of the manuscript. All authors read and approved the final manuscript.
The authors are grateful to Directorate of Research and Innovation, University of Venda, South Africa for the financial assistance in covering the costs of publishing this article in an open access journal.
The authors declare that they have no competing interests.
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