Municipal solid waste disposal is a global concern especially in developing countries, and as urbanisation continues to advance, the management of solid waste becomes a public health and environmental concern in urban areas [1
]. A variety of waste management strategies exist, with management practices ranging from the avoidance and reduction of waste, re-use, recycling, recovery, and ultimately treatment and disposal [2
]. For a developing country like South Africa, landfilling is the most common method of waste disposal, with almost 90% of waste disposed at landfills [3
]. “Landfill is an engineered waste disposal site facility with specific pollution control technologies in order to minimise potential impacts. Landfills are usually located above ground or contained within quarries or pits” [4
]. It is the “simplest, cheapest and most cost effective method of disposing waste” in several parts of the world [5
]. Despite these benefits, it still poses a significant threat to various spheres of the environment due to the presence of toxic inorganic and organic constituents in the leachate [6
] and “poorly developed solid waste management systems” [7
]. According to Aljaradin and Persson [8
], a variety of environmental, health, and social impacts associated with the disposal of waste by landfilling exists and these include amongst others explosion hazards from methane build up, air pollution from odour produced as a fraction of the degradable waste decays and the overall dilapidation of the immediate environment where the landfill is situated.
Many developing countries operate landfills without proper leachate collection and treatment facilities with adverse impacts on the environment. The extent of the impact depends on the nature of the leachate [5
]. Leachate composition varies widely and depends on factors such as the composition and depth of waste, availability of moisture and oxygen, landfill design, operation, and age [9
]. The leachate contamination of soils has a significant impact on the quality of the soil. According to Magaji [10
], soil is in most cases the most polluted part of the ecosystem around landfills, because chemical elements are transported and distributed when water seeps through it. Several pollutants, including heavy metals, polyaromatic hydrocarbons, and pharmaceutical compounds accumulate in the soil [11
]. According to Shaikh et al. [12
], some of these pollutants may be adsorbed on to the soil during their diffusion in the soil. The implication associated with these pollutants, especially heavy metal contamination, is of concern in agricultural production systems [10
Leachate emanating from landfills built without engineered liners and leachate collection systems could impact negatively on surface water and groundwater quality with severe consequences for human and ecosystem health [13
]. Wastes placed in landfills are subject to either groundwater underflow or infiltration from precipitation. As water percolates through the waste, it picks up a variety of organic and inorganic compounds, which flow out of the waste and accumulates at the bottom of the landfill resulting in contaminated water, termed leachate [9
]. Leachate that accumulates at the bottom of a landfill, seeps through the soil, and sometimes reaches the groundwater [5
]. The contamination of groundwater by landfills, affects the overall quality of water and results in the water becoming unfit for use.
According to Vaverková and Adamcová [14
] “the environmental impacts of landfill leachate, particularly on groundwater quality, has been noticed in several studies regardless of an ideal site selection and a monitoring network”. Adamcová et al. [15
] further indicate that landfills containing hazardous materials are monitored by analysing the soil and groundwater, which has been contaminated with leachate. Several studies have determined soil, surface water, and groundwater pollution from landfill leachate with diverse findings. Aderemi et al. [5
] found in their research that the absence of a leachate collector in their study area could lead to uncontrolled accumulation of leachates over time, posing significant threat to groundwater quality. Findings from Vaverková and Adamcová [14
] indicate that the landfill was not a major contributor to pollution in the water samples analysed in their study despite the high concentrations of some parameters in the leachate but concluded that other land use activities such as agriculture could be the possible source of pollution. Kanmani and Gandhimathi [16
] also conducted research on the impact of leachate from a landfill site on nearby soil quality and concluded that there is ”appreciable contamination of the soil by leachate migration” with possible contamination of the groundwater system over a period of time if there is no mitigation procedure in place. Findings from Lin et al. [17
] indicate that leachate from landfills degrade the quality and safety of soil and water, contaminating the food system, which poses long-term health risks. This scenario compromises water security, which according to Frone and Frone [18
], “underlines all dimensions of human health and wellbeing and is fundamental to food production”.
South Africa is a water scarce country [19
] with limited arable land suitable for agriculture, a large portion of which is already degraded [20
]. Bloemfontein, a metropolitan city within the Free State Province of South Africa has an increasing population with people migrating from rural areas, resulting in an increase in waste generation. Agriculture is the main economic sector of the city, but due to the variable and average rainfall in the area, groundwater has become the main source of water for irrigation of crops and often used as a source of drinking water in some households [21
]. Presently, there are two landfills in the city, one situated south and the other north of the city. The northern landfill site is situated close to residential areas. In 2018, residents complained to the local municipality about odour emanating from the decomposing waste and constant fire outbreaks on the landfill [22
]. This prompted a concern about the hazard this landfill might pose to the environment and nearby residents. Hence, the characterisation of leachate generated from the landfill and its influence on the surrounding soil and water quality, bearing in mind the arid nature of the area, was worth investigating. A previous study on groundwater contamination of the landfill, more than two decades ago, indicated contamination of the monitoring boreholes [23
There are several ways of investigating soil and water contamination due to leachate, of which the two most common approaches are the experimental determination of contaminants and the estimation of contaminants via mathematical modelling [24
]. Very few studies have been conducted in South Africa to assess the impacts of landfills on the environment, despite landfills being the preferred choice of waste disposal. In this study, we estimated the impact of leachate contamination from an unlined landfill site on the soil and water quality within the vicinity of the landfill. Diverse physiochemical and biological parameters were analysed in leachate, soil, surface water, and groundwater samples to determine the possible implications for water and food security in the study area.
All the soil samples had a high pH with a common origin based on the similarities of their chemical enrichment. Lower pH (6.3 to 7.1) was observed from soil profiles along the drainage C slope, especially from the shallow rocky soil profile (SP3) with clay content less than 20%, which meant a low buffering and adsorption potential for exchangeable cations and other dissolved leachate compounds (Table 2
). Clay minerals tend to stick together, reducing the downward movement, and their electrically charged complex sites give clay soils a high cation exchange capacity. In this regard, SP1 demonstrated decreased concentrations with depth of exchangeable cations and metals compared to SP2 and SP3, which had variable vertical concentrations. The C drainage also had the highest mean total % C (1.9%), Na (195 mg/kg) and mean metal concentration. High Na levels are associated with soil structural instability due to clay dispersion and swelling properties that exacerbate poor internal drainage and high surface runoff generation [5
]. The higher clay content of up to 44% from SP1 and SP2 (C drainage slope) could have been the reason for the higher Cu concentrations for all three downslope positions falling above the norm value of 6.5 mg/kg (Table 2
). The high levels of Cu along the drainage slope posed the risk of contaminating downslope vegetation and surface water bodies used by livestock and humans. If ingested in large doses, Cu could cause anaemia, liver and kidney damage, as well as stomach and intestinal irritation [48
All the water samples had pH within the recommended drinking water and irrigation standards. The WHO [44
] and SANS241 [43
] recommends that a TDS concentration below 500 mg/L and 1200 mg/L respectively is suitable for drinking water. All the borehole samples had TDS concentrations above these permissible limits. According to Ngabirano et al. [49
], high temperatures during dry seasons facilitate dissolution, ion-exchange capacity, desorption, and weathering processes. Considerable rainfall had been received prior to sampling in March 2018 after a long summer period where the study area had been relatively dry. This would have facilitated long-term dissolution, since the change in groundwater composition is not an instantaneous process, but occurs over time, thereby contributing to an increase in TDS.
Groundwater recharge through the dolerite dykes and fractures from rainfall that already contained elements in solution from the landfill could have facilitated more dissolution and caused considerable increases in TDS during autumn. The winter months were dry with much lower temperatures up to −0.75°C according to the Bloemfontein weather office monitoring stations. This explained why the TDS concentrations were much lower in winter than autumn. This supported the idea that seasonal variation had an influence on the composition of the water samples. The surface water body had TDS concentrations that were within the permissible limits for drinking water over both seasons.
Chloride is a common toxin in water and adds a distinctive salty taste to water [50
]. Chloride is also an indication of the corrosiveness and salinity of the water with respect to household appliances and irrigation [26
]. All the boreholes samples exceed the SANS241 [43
] and WHO [44
] recommended limit of Cl for drinking water and irrigation purposes in both seasons. However, the surface water Cl concentrations were below the recommended limit of the standards used in this study. The high Br concentrations in NB07 above the requirements of SANS241 [43
] for drinking water in both seasons with autumn having the highest concentrations could be due to the proximity of the borehole to the landfill site. According to Sasakova et al. [51
], bromide is introduced in surface waters and aquifers because of agricultural, industrial and residential activities. The wastes coming from different human activities that are deposited in the landfill site may be the potential origin of these significant bromide concentrations. Boreholes NB03A and NB03B were the only boreholes that had sulphate concentrations exceeding the SANS 241 [43
] and WHO [44
] for drinking water. Sulphate originates from a variety of sources, including natural and industrial effluents, with mineral resources like barite and gypsum being the dominant natural mineral resources for sulphate in groundwater. Sulphate concentrations in unpolluted water are typically less than 10 mg/L and is considered a common pollutant in mining areas [26
]. There are no given specifications for sulphate concentrations for irrigation purposes in the DWAF specifications for irrigation [44
]. All the borehole samples met the requirements of the FAO guidelines for irrigation [52
] of 1000 mg/L although NBO3B had concentrations almost close to this limit in both season.
Manganese concentrations for some of the borehole samples exceeded the DWAF specifications for irrigation [46
]. Borehole NB07 had manganese concentrations that exceeded the DWAF specifications for irrigation of 0 mg/L, with 5.3 mg/L for the autumn sample and 2.7 mg/L for the winter sample. According to Ahmad [53
], manganese is a common metallic element that occurs naturally in deeper wells with little or no oxygen present and can occur from the weathering of amphiboles as well as anthropogenic sources such as industrial effluents, landfill leakages and acid mine drainage. Boreholes NB07, NB06A, and NB06B had the highest bicarbonate concentrations over both seasons. Calcium and magnesium mainly originate from carbonate minerals such as calcite and dolomite, with magnesium also originating from ferromagnesian minerals, such as olivine, garnet, and amphiboles [42
]. Sodium is considered an important ion on the Earth’s crust [42
]. With reference to major ion concentrations and irrigation purposes, all the boreholes had sodium concentrations that exceeded the recommended limit for irrigation, with no given specifications for irrigation for both calcium and magnesium. Although all the boreholes had sodium concentrations exceeding the recommended limit, none of the boreholes had a sodium hazard as indicated by the SAR diagram (Figure 3
). Boreholes NB06A and NB06B in both seasons and the winter water surface sample had similar water chemistry of Ca(Mg)HCO3. Calcium bicarbonate water is typical of shallow, fresh groundwater and evidence of rock dissolution. Boreholes NB03A, NB03B, leachate, and autumn surface water had a similar chemistry and plotted as Ca(Mg)SO4 water type. Calcium (magnesium) sulphate water type is typical of gypsum rich groundwater and mine drainage [54
]. However, further analysis from the geochemical modelling showed that there was an under saturation of gypsum in all the samples including leachate. Borehole NB07 plotted as Ca(Mg)Cl in both seasons, which is due to the significant high concentrations of Cl in the water samples compared to other boreholes. All the boreholes and the surface water body had nitrate and nitrite concentrations that were within the SANS241 [43
] permissible limit for drinking water.
The EC values were very high in groundwater samples exceeding the SANS 241 [43
] and WHO [44
] standards for drinking water of 170 mS/m and 150 mS/m respectively in both the autumn and winter season. Borehole NB07 had the highest EC values over both seasons. The surface water body had EC values that were within the permissible limit for drinking water over both seasons according to the standards. All the boreholes also had EC values that exceeded the DWAF specifications for irrigation [46
] as an EC of 43 mS/m is recommended for irrigation purposes.
The high salinity hazards (high electrical conductivities) of boreholes NBO7 and NBO3B rendered them unfit for irrigation. The surface water body had an EC value within the permissible limit for irrigation in the winter season, but exceeded the limit during the autumn season. pH is one of the factors that influences the fate and transport of contaminants in the environment and a low pH can cause the dissolution of metals and nutrients in the water thereby releasing toxic elements that may pollute water [55
]. The neutral to alkaline pH of both the surface and borehole water might have been one of the driving factors behind the absence of both heavy and trace metals. The absence of heavy metals may also have been an indication of the type of waste deposited in the landfill site, which was not of industrial or mining origin as the site received mostly domestic waste.
Coliforms and faecal coliforms are established indicator organisms that are reliable for the detection of faecal contamination in water due to sewage disposal or other sources [45
]. All the borehole samples and surface water samples had total coliform above the permissible level for drinking water in the two seasons. Only the surface water had E. coli
concentration in both seasons with the highest amount (613 cfu/100 ml) in autumn. The total coliform and E. coli
concentration in the leachate was above the detention limit. Hossain et al. [56
] indicate that the surface water that flows through wastes can dissolve and leach harmful chemicals that are carried away from the landfill into surface water. According to Sanders et al. [57
], total coliform and E. coli
concentrations in surface water generally correspond to high rainfall and are usually higher in summer months. The landfill was a potential source of bacterial contamination through direct runoff since it is located at a higher elevation relative to the surface water body and there are no erosion control barriers in place.
Implications of Water and Soil Quality on Food and Water Security
According to Nagarajan et al. [58
], the determination of physicochemical and bacteriological characteristics of water is essential to assess the suitability of water for drinking and irrigation purposes. Kumar and James [42
] further illustrate that the reliability of water for various purposes depends on the chemical and physical quality of the water. The borehole water near the landfill site is currently not in use for both domestic and irrigation purposes. Bloemfontein is a semi-arid area and the protection of groundwater resources is important, because groundwater is the next available alternative source of water when surface water bodies are unable to meet the demand. Apart from the boreholes sampled for this study not being considered as a potential source of water, there is a possibility that boreholes located at the south-eastern direction of the landfill can be contaminated based on the geohydrology of the study area, because the groundwater flows in a south eastern direction. Based on findings from this study, where most of the parameters were above the permissible limit of SANS241 [43
], WHO [44
] for drinking water, and DWAF specification for irrigation [46
], there was an indication that the groundwater was unfit for drinking, domestic, and irrigation purposes. Irrigation water of poor quality changes the physical and chemical properties of soil leading to reduced soil productivity, produces toxic crops with ultimate reduction in yield [59
]. This could impact water and food security, especially during times of drought similar to the one that occurred in 2015–2017 in South Africa [19
The surface water body could have been a potential alternative source of water for irrigation purposes in the surrounding smallholdings. However, because of the elevated coliform and E. coli
concentrations, the surface water was unfit for both irrigation and domestic use. There are no given specifications for irrigation and the permissible total coliform concentration in water depends on the type of crop being irrigated [46
]. The water resources in the study area did not align with the definition of water security proposed by Frone and Frone [18
], namely “the sustainable availability of water quantity and quality acceptable for production, livelihoods and health, coupled with acceptable level of risk to society related to unpredictable impacts“.
Relationships between pH and mobility of chemical compounds had an influence on the landfill soil and water quality. The neutral to alkaline pH of the soil, leachate, and borehole water illustrated the significant concentrations of basic forming exchangeable cations (Ca2+
, K+, and Na+
). These cations could have been enriched through weathering of the local parent material [60
] or the landfill leachate [13
]. Almost all the metal concentrations were lower than the threshold values, indicating that the waste disposed at the landfill had low metal content. Copper was the only metal that had concentrations (21 to 29 mg/kg) higher than the threshold value (16 mg/kg). Nevertheless, the high levels of Cu posed minimal risk to water and food security, given the complex interaction Cu has with the environment, which makes its concentration become rapidly stable and non-accumulative [61
Geochemical modelling showed that toxic metals and minerals such as smithsonite, otavite, hausmannite, and pyrolusite were undersaturated in all the water samples. The few minerals that speciated out of the groundwater (geothite, hematite, gibbsite, Fe(OH), and alunite) as a result of the leachate influence could adversely affect water quality and negatively impact on food security. The oversaturation of carbonate dominant minerals speciation collaborated the suggestions that rainfall induced the leachate generation in the landfill, while undersaturation of sulphate minerals speciation such as jarosite, malanterite and CdSO4 indicated their low presence and inability to dominate and influence the geochemical process. This suggested that their impact on the groundwater quality, and water and food security was minimal. The elevated elements in the hydrated minerals could have been harmful for irrigation of crops.
Based on the results from this study, the low metal content in the soil and water samples did not pose a threat to food and water security. Although the findings from the study showed that most parameters in the soil except Cu were within the permissible limit, because of the pH and soil type of the study area, the lack of good quality water needed for crops irrigation and livestock watering may compromise food security. According to Brown [62
], water security will be closely linked with food security in the future, which could impact the sustainable development of Bloemfontein as basic human needs could be compromised. Of note, is that the metal concentrations in the soil increased downslope with distance from the landfill along drainage lines. This could be a risk to land use downslope of the landfill. Considering the three pillars of sustainability and sustainable development, which consists of the triple PPPs (people, planet, and profit), the potential future loss of water and food security could lead to adverse impacts on residents’ safety, health and livelihoods, severe degradation of the surrounding ecosystems and environment, and ultimate reduction in economic growth [63
]. Based on the concept of sustainable development, research has shown that environmental degradation correlates positively with poverty [64
] and water security provides the platform on which sustainable multi-sectors can be built [63
]. Two of the factors that will affect food security in the study area are increased urbanisation and pressure on water resources [18
This study explored the influence of landfill leachate on the surrounding soil and water quality of the Northern landfill in Bloemfontein and the implication on water and food security. Based on findings, most of the parameters analysed were above the permissible limit of SANS241, WHO for drinking water, and DWAF specification for irrigation, an indication that the groundwater was unfit for drinking, domestic, and irrigation purposes. The piper diagram employed in the study showed that the leachate and most of the groundwater samples plotted in the same vicinity in the autumn season, an indication that the leachate influenced the quality of the borehole samples. The oversaturation of manganese, iron, and aluminium metals precipitating out of the leachate and groundwater samples close to the landfill made the groundwater unsuitable and unsustainable for water and food security. Since manganese is readily absorbed by plants, excessive groundwater rich manganese water use for irrigation will lead to enrichment of manganese in food. Excess manganese and iron in drinking water will cause aesthetic problems. Iron and manganese are essential nutrients in food yet toxic at high levels. Their toxicity will complicate the health of consumers of food irrigated with the iron and manganese enriched water in the region.
Almost all the parameters analysed in the soil were within the normal threshold except for Cu. However, contamination of water resources could affect water and food security since the quality of the water was unfit for drinking and irrigation purposes. Of note, is the fact that samples from boreholes close to the landfill had higher concentrations of most parameters analysed in the water samples while the soil samples showed an increase in concentration of parameters with distance downslope along drainage lines; a possible risk to land use downslope of the landfill. In terms of the triple bottom line of sustainability, namely people, planet, and profit, the findings indicated that all the three pillars can be compromised, thereby hindering the sustainable development of the Bloemfontein area and surroundings. We therefore proposed that a leachate collector be installed and a barrier be erected at the south-eastern side of the landfill to contain the leachate, especially when rain falls. Implementation of a circular economy in Bloemfontein city will reduce waste generation and disposal in landfills, which would translate to less pollution of surrounding environmental resources.