Assessment of Concentration levels of contaminants in groundwater of Soutpansberg Region, Limpopo Province, South Africa

Groundwater contribution towards improved food security and human health depend on the level of contaminants in groundwater. In rural areas, many people use groundwater for drinking and irrigation purposes without treatment and have no knowledge of contaminants levels in such waters. The reason for such lack of treatment and knowledge is due to the parachute type of research which emphasizes on scientic knowledge and records only and not sharing research outputs with communities for improved human health and food security. This study argued that parachute research type exposes groundwater users to health hazards and threaten food security. Concentration levels of contaminants were measured to ascertain suitability of groundwater for drinking and irrigation use. 124 groundwater quality samples from 12 boreholes and 2 springs with physiochemical data from 1995 to 2017 were assessed. This study found high concentration levels of contaminants such F − , NO 3− , Cl − and TDS in certain parts of the studied area when compared to water quality standards. In general, groundwater was deemed suitable for drinking purposes in most part of the studied area. Combined calculated values of SAR, Na%, MH, PI, RSC and TDS determined that groundwater is suitable for irrigation purposes. The discussion in this paper showed that scientic knowledge generated on groundwater quality should be shared with water users as it will improved human health and food security and also enhance the achievement of Sustainable Development Goals. This study recommended that skills and research outputs should be shared with groundwater users through various initiatives.


Introduction
Availability of water in general is declining owing to climatic variation such as drought in arid and semiarid regions and increasing demand owing to socio-economic activities. Groundwater has become the main or only source of freshwater for various activities such as irrigation and domestic uses across the world (38, 27,53,20), and this is especially common in rural areas where there is lack or no alternative water supply. Increasing reliance on groundwater can lead to other ecological factors such as decreasing groundwater level, pollution and deterioration of water quality (24). Globally it is being reported that groundwater that was considered fresh is increasingly being contaminated or polluted and this can have a negative impact on the livelihood of vulnerable people relying on groundwater for various uses (43,2).
There are various components that in uence groundwater quality and determine the concentration levels of contaminants in rural areas. These components include anthropogenic activities (irrigation and pitlatrines), leaching, regional geology as well as climatic conditions (32,26,22,52). For groundwater to contribute towards food security and improved rural livelihood through irrigation and domestic use, concentration levels of contaminants should be determine to ensure groundwater is suitable for various uses. The challenge is that majority of groundwater users in many rural areas uses groundwater without treatment or knowledge of the concentration level of contaminants; a situation which poses a huge threat to food security, human health and their livelihoods. Understanding and communicating the concentration levels of contaminants and groundwater quality in general is important as it ensure that people use groundwater that is safe for consumption (36). Various researchers (29,46,28,9,31) assessed groundwater quality data across the world to determine the suitability of groundwater for human consumption. They evaluated major cations (Ca 2+ , Mg 2+ , Na + , K + ) and anions (Cl − , HCO 3 − , F − ).
These studies compared groundwater quality data with drinking water standards such as (51) and various local standards such as (40) in South Africa. Suitability of groundwater for irrigation contributes towards food security (17). Groundwater that is not suitable for irrigation may reduce crop yield and damage soil structure (3). Studies conducted by (40,28,10,35,1,16) assessed the suitability of groundwater for irrigation purposes using methods such as SAR, PI, RSC, Na% and MH and found contrasting results from methods applied. Contaminants are input of foreign and possibly toxic materials into the environment and pollutants are described as substances that are anthropogenically introduced that may be harmful to the environment (44). It is not simple to distinguish between contaminants and pollutants as it is not always possible to de ne the concentration level where contaminants become pollutants (44). However, it has become a norm with various authors to compare concentration levels of contaminants in groundwater to various standards that are largely for surface water or drinking water in order to determine if contaminants in groundwater are pollutants. This practice may be misleading as some aquifers are highly concentrated in some contaminants in nature and not polluted; this study tapped in the subject of comparing contaminants in groundwater to various international and local standards. The purpose of this study was to determine the concentration levels of contaminants, spatial distribution of contaminants and evaluate suitability of groundwater for domestic and irrigation purposes using long-term data. This study also discussed the parachute type of research that does not share the outputs and skills on groundwater quality with affected communities.

Description Of Study Location
The Soutpansberg region is located in the far Northern part of the Limpopo Province in South Africa In terms of climatic condition, the area is located in an arid region with average minimum temperature of 11•C and average maximum temperature of 32•C based of the 7 South African Weather Services (SAWS) station with data from 1980 to 2020. Soutpansberg region experience dry winter season (May-August) and wet summer season (December-February) with the average precipitation of 497.7 mm/a. The dominant geology that support groundwater is the volcanic-sedimentary unit of Soutpansberg Group deposited as an east-west gravitating asymmetrical rift beside the palala shear belt about 1800 million years ago (7,8). The Soutpansberg basin was formed between the Limpopo belt in the north and the Kaapvaal craton in the south. This volcanic-sedimentary Soutpansberg Group mainly outcrops in the Soutpansberg Mountains stretching from Punda Maria at the eastern side to Vivo at the western side (11,5). The Soutpansberg Group is subdivided into ve Formations (

Sampling
There is an active groundwater quality monitoring network in the study area. The network is comprised of 12 boreholes and 2 geothermal springs where sampling has been taking place since 1995 twice a year

Determination of concentration levels of contaminants
The analysed 124 samples of major ions and physical parameters were statistically assessed using Microsoft Excel in order to determine the concentration levels of contaminants in the Soutpansberg region. The statistical analyses tool was used to determine the mean, minimum, maximum and standard deviation of various contaminants. ArcGis tool was used to map the spatial distribution of the concentration levels of contaminants. The determined concentration levels of contaminants in groundwater were used to discuss the subject of comparing ambient groundwater quality to various standards and sharing of outputs with concerned communities.

Evaluation of groundwater quality for domestic and irrigation purposes
To evaluate suitability of groundwater for domestic use in the Soutpansberg region, 124 samples of major ions and physical parameters were compared to (51,40) drinking water standards. Suitability of groundwater for irrigation purpose was evaluated by using equations 2-6 below. Sodium adsorption ratio (SAR), sodium percentage (Na%), permeability index (PI), residual sodium carbonate (RSC) and magnesium hazard (MH) were calculated in meq/l from the 124 samples. The subject of parachute research and sharing of knowledge with groundwater users was discussed based on the outcome of these methods.

Chemical composition of groundwater
The descriptive statistical analysis of chemical constituents of the 124 samples of the Soutpansberg region is presented in Table 1. It is commonly accepted that pH is the primary parameter that is used to measure water quality if it is acidic (pH < 7), Neutral (pH = 7) or alkaline (pH > 7) in nature (25).
Groundwater in the Soutpansberg region is slightly acidic to alkaline as pH ranges from 6.7 to 9.6. The mean pH in groundwater of the area is 8.4 which indicate that groundwater is more alkaline ( Table 1).
High alkalinity in the Soutpansberg area is linked with high concentrations of sodium, magnesium, calcium and bicarbonates ions owing to the ma c-ultrama c igneous rocks dominant in the area. These ions are commonly known to increase the value of pH (13). In terms of seasonal variation, there is no much difference in pH between dry and wet season in the Soutpansberg region. Salinity as TDS in the region ranged from 32 to 1808 mg/l with mean of 327 mg/l. Spatial distribution of TDS is presented in Fig. 3 where mean concentrations of 1418 and 1784 mg/l at Maebane and Punda Maria villages were recorded respectively. Groundwater in these areas is considered to be brackish according to TDS classi cation in Table 2 (18). There is a strong correlation between the spatial distributions of Cl − and TDS ( Fig. 3-4) in the Soutpansberg region and this suggest that salinity in groundwater is high in the Maebane and Punda Maria villages as groundwater is classi ed as brackish.
There is a correlation between salinity and human settlements (including irrigated area) in the Soutpansberg region and this observation is common as activities in such areas are associated various types of anthropogenic factors such as fertilizers and pit-latrines. (34) Found that spatial variation of groundwater quality correlate with agricultural activities. Seasonal variation does not affect salinity in the area as there is no difference between wet (378 mg/l) and dry (372 mg/l) season mean TDS. In general, 91.1% of groundwater is the Soutpansberg region is classi ed as fresh and 8.9% is classi ed as brackish (Table 2). Classi cation of groundwater for TDS in this study is similar to (28) who determined that groundwater in the Soutpansberg region is fresh to brackish.   (1) found that NO 3 − was 8.8 times than the recommended limit and stated NO 3 − occurrence and distribution in groundwater is mostly associated with application of fertilizers, leakage from septic tanks/ sewage and leachate from land ll sites. In the Soutpansberg area, high NO 3 − can be associated with leaching from pit-latrines and application of fertilizers in this fractured aquifer. There is no major difference in mean NO 3 − concentration in groundwater between wet (2.5 mg/l) and dry (4 mg/l) seasons. NO 3 − concentration is slightly higher in dry season as compared to wet season. Spatial distribution of F − is presented in Fig. 6 where it is highly concentrated around Nzhelele area with a mean of 2.5 mg/l. The mean concentration level of F − in Nzhelele area is over the prescribed limit of 1.5 mg/l (51,40).
Groundwater from the geothermal spring in Nzhelele is highly concentrated with F − . The range of F − concentration levels in groundwater of the Soutpansberg region was determined to be from 0.03 to 2.9 mg/l and overall mean of 0.7 mg/l. Seasonal variation doesn't have any impact on F − concentration of groundwater as geothermal springs are associated with deep ancient groundwater. The determined concentration of F − correlates with the ndings of (33) that F − in Nzhelele (Siloam) area ranges between 1.7 to 5.6 mg/l in dry and wet seasons. The source of F − in groundwater in this area result from uorite mineral associated with sedimentary and igneous rocks that are found in the Soutpansberg area (33).
In the absence of de ned groundwater quality guidelines, majority of samples contains cations concentration levels that are within the (51,40) prescribed limits for drinking water. High concentration levels of various parameters does not necessary mean the aquifer is polluted as it could be the natural ambient groundwater. Mean wet and dry season's concentration levels of cations are below the prescribed limit (Table 1) Concentration levels of K + as the least dominance cation ranged from 0.2 to 10 mg/l with mean of 2 mg/l, which is within the prescribed limit (51,40). Comparing ambient groundwater with standards designed largely for surface and treated water such as (40) can be misleading as it may be perceived as groundwater resource is polluted. For instance, TDS in Maebane area has been over 1500 mg/l since 1994 and steady at that concentration level for over 22 years. Some contaminants in groundwater are naturally high owing to the geochemistry and geological setting of the host aquifer so there is need to develop groundwater quality standards guided by historical data and geochemistry of aquifers. In cases where anthropogenic activities are determined to be contaminating groundwater resource, sharing of concentration levels of contaminants and research outcomes can assist the community to manage and protect the resource. Enhanced management and protection of groundwater resource between communities and custodian of the resource will help countries to achieve United Nation's Sustainable Development Goal (SDG) 6 and this will improve water quality and provide clean water and sanitation for all.

Suitability of groundwater for drinking purposes
Groundwater should be free from pathogens and toxic chemicals in order to be deemed suitable for domestic use such as cooking and drinking (28). Concentrations of various parameters from the 124 samples were compared with (51,40) in Table 1. These samples were also compared to TDS classi cations by (18) in Table 2 and (12) in Table 3. In terms of seasonal variations, 62.1% of wet season samples were suitable for drinking purposes. 74.7% of samples taken in dry season were suitable for drinking purposes in the Soutpansberg area. Even though there is no major difference in concentration levels, groundwater seems to be more suitable for drinking purposes in dry season. This could be associated with lack of mechanism to enhance leaching/ transport contaminants in dry season. Overall, groundwater in 73.4% of the samples was deemed suitable for drinking purposed as all parameters were within the prescribed limit (51,40). This outcome is in contrast with (28) study that determined that groundwater in the Soutpansberg is not suitable for drinking and domestic purposes. However, the contrast can be associated with the spatial distribution of monitored samples, number of samples and time frame as (28)  basis. It is basic human rights and need to drink safe water to ensure good health (23). (50) Estimated that almost 80% of diseases are resulting from polluted water and poor sanitation and this could be the case in the rural villages of the Soutpansberg region due to continuous consumption of polluted groundwater. For instance, concentration of TDS in Punda Maria (ZQMPMA1) and Maebane (ZQMMBI1) areas were recorded at 1784 mg/l and 1418 mg/l respectively and water with elevated dissolved solids may affect individual suffering from heart and kidney diseases as well as causing constipation and laxative effects (41). NO3-as one of the common disease causing contaminants can expose infants to baby blue syndrome (51,30). F − which is highly concentrated in Nzhelele area (Siloam) can cause dental uorosis according to (51). A study by (33) found that of the 87% households that use groundwater for drinking purposes, 85% of the members already have mottled teeth/ dental uorosis. Based on TDS classi cation by (18), 91.1% of the samples were classi ed as fresh water type and 8.9% of the samples were classi ed as brackish ( Table 2). Classi cation of TDS by (12) indicated that 72.6% of groundwater samples were desirable for drinking purpose. 18.5% of groundwater samples in the Soutpansberg region were permissible for drinking purposes. Only 8.9% of the samples were not suitable for drinking purposes ( Table 3). The main challenge is how the status of groundwater with respect to suitability for drinking purposes can be shared with groundwater users. Communicating with users that groundwater is not suitable for drinking purposes without treatment will protect them from possible water borne diseases, improving their health and livelihood. For instance, rainfall and temperature are forecasted by weather services globally as an early warning system and shared on various digital and print media. Perhaps groundwater custodians should start sharing groundwater quality status with groundwater users through various digital and print platforms and also with traditional authorities in rural areas. Sharing of groundwater quality status with communities relying on groundwater for drinking purposes will improve their health and livelihood as proper actions can be taken before consumption. Sharing the reasons why groundwater is not suitable for drinking purposes with water users will decrease water-borne diseases around the world as users will be aware. The situation discussed by (33) where 85% of groundwater users had dental uorosis in Siloam can be avoided by sharing research outcome with users while also accelerating the achievement of SDG 3 dealing with good health and well-being.

Suitability of groundwater for irrigation purposes
High concentration of salt in irrigation water can increase solution osmotic pressure and can also negatively affect the structure of soils, aeration and permeability rate (47,21). Suitability of groundwater of the Soutpansberg region for irrigation was assessed by estimating a number of parameters such as Na%, SAR, MH, PI, RSC (Table 4) and TDS ( Table 3). The major ions used were expressed in milliequivalents per litre (meq/l). Sodium adsorption ration (SAR) is useful in determining suitability of groundwater for irrigation purpose as it measures both sodium and alkali hazards for plants (3). High concentration of sodium in irrigation water may have harmful effects in most soils such as increased hardness and reduced permeability (6).
High concentration of bicarbonate and relatively low calcium is also hazardous for irrigation water (39). High content of sodium relative to calcium and magnesium may cause sodicity in irrigation water. SAR calculations (Eq. 2) in the Soutpansberg region indicated that 75% of the samples were classi ed as excellent -good for irrigation purposes (Table 4). 24.2% of the samples were doubtful and 0.8% of the samples were unsuitable for irrigation purposes. Groundwater from Tshipise (geothermal spring) and Punda Maria were doubtful for irrigation purposes as presented in Fig. 8. Samples that are unsuitable for irrigation purposes (0.8%) are from Tshipise geothermal spring (ZQMTPS2) where the low mean concentrations of Ca 2+ (2 mg/l) and Mg 2+ in relation to Na + (66 mg/l) are responsible for the unsuitability of groundwater for irrigation purpose as low calcium is hazardous for irrigation (39). Similar to suitability of drinking status, the communities and farmers that are using groundwater for irrigation purposes are deprived of this information as most researchers and custodians of water are publishing research outputs and not share with communities affected and this can have a negative impact of livelihood and food security in general.

Sodium percentage (Na%)
Concentration of sodium in groundwater is important in the classi cation of irrigation water. Na% was calculated using Eq. 3 and results are presented in Table 4. Majority of the groundwater samples in the study area were classi ed as excellent (3.2%), good (33.9%) and permissible (34.7%) for irrigation purposes. Na% over 60 can cause destruction of the structures of the soil and negatively affects the growth of plants (6). In the Soutpansberg region, 4.8% of the samples were doubtful (Na%= 60-80) and 23.4% (Na% >80) were unsuitable for irrigation purposes. Samples with Na% > 80 contains very low concentration of Ca 2+ (< 3 mg/l) and this is hazardous for irrigation water according to (39). Groundwater from the Tshipise geothermal spring is not suitable for irrigation purposes due to low Ca 2+ concentration.

Magnesium hazard (MH)
Magnesium in groundwater in uence the quality of soil by converting it into alkaline and reduces crop yield (19). Magnesium hazard was calculated using Eq. 6 as proposed by (45). MH above 50 is deemed to be unsuitable for irrigation purposes. Groundwater in 75.8% of the samples was unsuitable for irrigation as MH was calculated to be over 50 ( Table 4). The unsuitability of groundwater based on MH is a concerning issues as 125.4 Mm3/a has been allocated for irrigation use in the Soutpansberg region.
MH in groundwater was below 50 in 24.2% the samples of which most of them are from Tshipise (geothermal spring: ZQMTPS2). Samples that are not suitable for irrigation purposes based on MH is resulting from Ca 2+ > Mg 2+ ratio. Therefore, groundwater in most part of the Soutpansberg region is not suitable for irrigation purpose based on magnesium hazard. To ensure food security, this information should be shared with the farming community and everyone using groundwater for irrigation purposes. Various digital and media platforms can be used to share the status of groundwater for irrigation uses so precautions can be taken before irrigating.

Permeability Index (PI)
Permeability index is based on Eq. 4 and is used to classify irrigation water as proposed by (14). Water from class I (PI > 75) and class II (PI 75 − 25) is considered to be suitable for irrigation while class III is considered to be unsuitable for irrigation. The PI results from the study area are tabulated in Table 4

Residual sodium carbonate (RSC)
High concentration of carbonate and bicarbonate ions relative to calcium and magnesium (alkaline earth) can result in the complete precipitation of calcium and magnesium (37). Residual sodium carbonate (RSC) calculated using Eq. 5 has been measured in the Soutpansberg region in order to understand the effect of bicarbonate and carbonate of groundwater. High RSC value in water results in an increase of adsorption of sodium in soil (15). Water with RSC less than 2.5 is considered as suitable for irrigation purposes. All 124 groundwater samples were suitable for irrigation purpose as RSC was less than 2.5 (Table 4).

Total dissolved solids (TDS)
Suitability of groundwater for irrigation can be determined by using (12) TDS classi cation (Table 3).
Irrigation water with TDS less than 3000 mg/l is considered suitable/useful for irrigation purposes. TDS concentration levels in groundwater ranged from 32 to 1808 mg/l which is within the useful for irrigation limit. Therefore, groundwater in the Soutpansberg region is suitable for irrigation based on TDS.

Conclusions
Groundwater in the Soutpansberg region is slightly acidic to alkaline and classi ed as fresh to brackish in nature. Presence of contaminants such as F − , NO 3 − and salinity in groundwater poses a health risk to the communities using groundwater for drinking purposes without any form of treatment. To ensure food security, improved health and livelihood, this study recommends that the status of groundwater quality in relation to suitability for drinking and irrigation purposes should be shared on digital, print media and if possible to community leaders by researchers and custodians of groundwater. Sharing of information with affected community is important as it will stop the parachute type of research where researchers collect data, analyse and publish without informing affected communities of the hazards associated with groundwater in speci c areas. Various Sustainable Development Goals can be accelerated and achieved by sharing research outcomes with water users. There is also a need to develop groundwater quality guidelines for various aquifers to avoid comparing groundwater quality with treated water standards when measuring concentration level between contaminants and pollutants. This study further recommends that there is a need to determine hydro-geochemical in uencing groundwater quality in the Soutpansberg region. There is also a need to monitor groundwater for biological parameters in the area due to excessive usage of pit-latrines and livestock farming. Consequently, proper management of groundwater and remediation should be considered before utilizing groundwater for drinking purposes.

Declarations
Acknowledgments: This paper is a part of the Ph.D project of the corresponding author. The authors gratefully acknowledge the Department of Water and Sanitation (DWS) and South Africa Weather Services (SAWS) for assistance with historical data.
Funding: N/A Con icts of Interest: The authors declare no con ict of interest.
Author Contributions: LL was responsible for data collection, data analysis and drafting the manuscript.
TK was responsible for conceptualisation of the research problem, interpretation of the results and reviewing of the manuscripts. TK is the academic supervisor of the corresponding author.
Availability of data and material (data transparency): The data used to support the outcomes of this study have been included within the supplementary material.  Spatial distribution of TDS in the Soutpansberg region Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.

Figure 4
Page 21/23 Spatial distribution of Chloride in the Soutpansberg region Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.

Figure 5
Spatial distribution of Nitrate in the Soutpansberg region Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors.

Figure 6
Spatial distribution of Fluoride in the Soutpansberg region Note: The designations employed and the presentation of the material on this map do not imply the expression of any opinion whatsoever on the part of Research Square concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. This map has been provided by the authors. Figure 7