Physico-Chemical Analysis in Surface Waters around the Closed Gaborone Sanitary Landfill in Botswana

The aim of the study was to ascertain the pollution levels in water sources in the areas surrounding the closed Gaborone landfill site. The study focused on the physico – chemical analysis of surface water resources around the closed Gaborone landfill site. The specific objectives were to determine the properties of surface water around the landfill and compare them along a transect with the water sources upslope and downslope of the landfill. Furthermore, the probable impacts of the wastes on water resources are highlighted and the levels of heavy metal contamination in surface waters around the closed Gaborone landfill are shown, in addition to compare the findings in this study with set standards (WHO, USEPA, FAO, EU, USSR and BOBS) and other yardsticks from previous studies. Due to scarcity of water resources and poor drainage water levels, five (5) existing surface water samples were collected offsite along a spatial gradient transect while the sampling interval was based on the length of the slope below the landfill. Field sampling and laboratory analysis of surface water resources was done so as to ascertain physico – chemical and heavy metal pollution levels. The findings of the investigations show that physical parameters such as pH, Electrical Conductivity, turbidity, TDS and TCU levels at the closed Gaborone landfill are above the drinking water standards BOS 32: 2000, WHO (2004) and USEPA (1991) limits and there is a general decline in pH, EC, TSS, TVS, TSD and TCU with increasing distance from the landfill site. While the chemical properties show that alkalinity, nitrates, phosphates, sulphates, chlorides, calcium, magnesium, chromium, and ammonia levels for the closed Gaborone landfill are higher than BOS 32: 2000, WHO (2004) and USEPA (1991) limits indicating toxicity. The general trend patterns show that there is a general decline in alkalinity, BOD5, sulphates, phosphates, nitrates, magnesium, calcium and chromium levels with increasing distance from the closed Gaborone landfill while chlorides levels are increasing. There was a significant decline in alkalinity, EC, sulphates, and calcium with increasing distance at P = 0.05. On the other hand, BOD5 levels can be classified as clean to moderately polluted. Overall, sanitary landfills have a far-reaching impact on the surrounding water resources and if left unmonitored increased pollution levels could lead to compromised drinking water quality, public health deterioration and descending environmental eminence.


Introduction
Initiatives in solid waste management are growing phenomenon in developing nations that have created employment (Areola, Segosebe and Gwisai, 2015;Strange, 2002;Abdelatif, 2001; Abd Malek et al., 1996). On the other hand, the under -privileged have found opportunities to earn a living from landfill sites (Areola, Segosebe and Gwisai, 2015; Manyanhaire et al., 2009;Masocha and Tevera, 2003). However, it has been observed that most employees in the sector have limited to no personal protective equipment. This poses serious risks on health hazards (Areola, Segosebe and Gwisai, 2015;Noel, 2010). Several studies note that limited attention has been granted towards investigations involving human health risks to which scavengers are exposed to (Areola, Segosebe and Gwisai, 2015; Noel, 2010; Chattopadhyay, Dutta and Ray, 2008; Mwiganga and Kansiime, 2005;Chofqi, et al., 2004) and to the human health concerns of the communities residing in the neighbourhoods of landfills (Gwebu, 2003). According to Elliot (2006), 80% of the population in developed nations live within a 2 -kilometre radius of a current or closed landfill site and have experienced serious health effects. In this regard, the closed Gaborone landfill site in Botswana, has been criticized poor waste operations and management (The Botswana Gazette, 2010; Ngole, 2000). In Botswana, generally there are fewer engineered landfill sites than dump sites (Gwebu, 2003); a situation Environment and Ecology Research 7(4): 220-238, 2019 221 which makes the environmental health risks associated with waste disposal a major public concern.
Although sanitary landfill sites have been observed to constitute a potential hazard to the environment (Khan and Agarwal, 2006;Misra and Pandey, 2004;Christensen and Christensen, 1999;Moyo et al., 1993), in many cases, the effects of the landfills are not easily discernible. The pertinent effects include ground and surface water pollution (Areola, Segosebe and Gwisai, 2015;Odukoya and Abimbola, 2010;Miller, 1996). Health risk related studies on employees in the handling, transporting, clean-up or maintenance of substances at landfill sites have been found to be very scarce. Yet, many chemicals present in landfill sites have been shown to have adverse effects on human health (Vrijheid, 2000). Hence, the focus of this study was to examine the environmental pollution challenges in surface water resources in and around municipal landfill sites as revealed in some studies (Areola, Segosebe and Gwisai, 2015). The concern for the plight of surface water resources near landfills is partly due to the lower levels of public awareness and respect for public opinion in decision making in developing countries as compared to what obtains in the developed world. Indeed, there are instances in some countries where governments and government officials have deliberately accepted the dumping of hazardous wastes at some locations in the developing world (Areola, Segosebe and Gwisai, 2015).
The aim of the study was to investigate and evaluate the surface water pollution levels of surface water resources nearby the closed Gaborone Municipal landfill. These investigations were based on the Gaborone landfill in Botswana in the southern African region of the continent. The specific objectives of the study were to determine the level of contamination, around the landfill sites by analyzing specifically the types and levels of physicochemical elements pollution and heavy metal contaminants in surface water sources around the Gaborone landfill site. Furthermore to establish how physico -chemical properties and heavy metal concentrations in the closed Gaborone surface water sources compare with other yardsticks from previous studies and set standards (e.g. Areola, Segosebe and Gwisai, 2015; Matsa and Mutekwa, 2009; Odukoya and Abimbola, 2010).
Waste management has been one of the core values of the National Development Plan, NDP 10, in Botswana, which aimed at achieving the sustainable development goal. Thus, this study would contribute to knowledge specifically by helping to identify the primary chemical and heavy metals that constitute the major hazards. Such knowledge would help governments and international organizations to develop appropriate mitigation or otherwise intervention measures as an aftermath of the decommissioning of landfills and dumpsites. Urbanization levels in Gaborone could have a significant influence on waste types and quantities and therefore pollution levels of water resources in the surrounding environment as shown in other studies (Areola, Segosebe and Gwisai, 2015). With the notion of almost two decades after the development of the landfill disposal ideology, legislation and implementation in 1998, it is necessary to carry out an audit on water contaminations related issues that will contribute to new knowledge on the impacts of landfills specifically on the surface water resources as recommended by other studies (Areola, Segosebe and Gwisai, 2015; Ngole, 2000).

Study Area
Botswana is located in the southern part of the African continent. It is bounded to the south and southeast by South Africa, to the west by Namibia, to the north by Zambia and to the northeast by Zimbabwe. The closed Gaborone landfill site was commissioned in 1993 close to the Gaborone dam and the Notwane river catchment area is one of the landfill sites that was commissioned before landfill legislature in 1998 (Government of Botswana, 1998). The landfill which served the capital city of the country was commissioned without a landfill leachate liner while management operations were poor and done haphazardly (Gwebu, 2003). Therefore the main focus of the study was to assess landfill site impacts, and the extent to which these pollutants have contaminated the environment and human health (Ngole, 2000). Gaborone landfill appeared to lack a lot of equipment that could have ensured a smooth running of operations, and this led to shortage of space in waste cells, possibilities of finding an admixture of items in the same zone of the landfill, and rare waste compaction (Ngole, 2000;Gwebu, 2003). The closed Gaborone landfill site is undergoing rehabilitation. Assessing the effects of landfill pollutants at this stage of the landfill site may act as a guide to future landfill rehabilitation programmes, which Local Authorities (LAs) and the central government may wish to take note of as this may reduce operational costs of landfill sites and help to develop sustainable economic budgets. The temperatures and rainfall have an influence on the biochemical reactions taking place in the landfill sites. This results in varying pollutant production rates affecting the environment and human health (Areola, Segosebe and Gwisai, 2015; Lobatse Town Council, 2002).

Materials and Methods
Due to scarcity of water resources and poor drainage water levels, five (5) existing surface water samples were collected offsite along a spatial gradient transect while the sampling interval was based on the length of the slope below the landfill. Field sampling and laboratory analysis of surface water resources was done so as to ascertain physico -chemical and heavy metal pollution levels. The basic principle followed was sampling from the landfill down to the foot of the slope below it. Surface water samples were collected (bulk sampling) from the existing water sources around the landfill sites A control sample from upslope was collected for comparative purposes. . The main analytical tool used was the Atomic Absorption Spectrophotometer (AAS). The Flame AAS was used to determine the concentration of the metals selected above. The AAS technique basically involves the principle of free atoms in elements that will absorb light at wavelength characteristics of that element which is determined by the outer electron structure (Areola, Segosebe and Gwisai, 2015; Ngole, 2000;Alloway, 1995). The amount of light is directly proportional to the concentration of the element in solution. The absorbance is normally measured and is used to determine the concentration of the specific element. Normally the solution is atomized in a flame in the Flame AAS.

Results and Discussions Surface Water Physico-Chemical Pollution
Five (5) surface water samples were measured for pH, which ranged from 7.88 -8.75 ( Figure 2). All the samples recorded higher pH values than the standard pH values of 6.5 patently rendering them unsuitable for drinking purposes (Table 2)

EC (µS cm‫)¹-‬ Levels
Electrical Conductivity (EC) was measured at 25°C and all the surface water samples were in the range of 189.2 -1577. 70 . All the samples were below the recommended drinking water standard BOS 32: 2000 value of 3100 ( Figure 3) as observed by Areola, Segosebe and Gwisai (2015). This could have been because the Lobatse landfill is in the same geographical area and have similar rainfall and temperature patterns. On the other hand, this is contrary to findings by previous studies which found EC levels to be above the set EU limits (Table 2)

Total Solids (TDS, TSS, TVS, TFS, TSD) Levels
The range of Total Dissolved Solids (TDS) is between 110 -1015 mg which appears similar to those of previous studies (Akinbile, 2012;Longe and Enekwechi, 2007). All samples from Gaborone landfill have total solids more than the set drinking water standards (450 -500 mg) (see Figure 5 and Table 5

Turbidity (NTU)
Turbidity was measured using Nephelometric Turbidity Units (NTU) and the samples from Gaborone have a turbidity range of 1.65 -11 NTU (Figure 7). Some studies show a higher turbidity than the present study signaling a lesser impact universally (Osei et al., 2011)

Chemical Pollution Levels of Surface Water Samples Alkalinity
Alkalinity of the Gaborone samples is in the range, 200 -1101 . The majority (90%) of the samples are above the set drinking water alkalinity limits for Botswana ( Figure 8 and Table 2

Biological Oxygen Demand
The Biological Oxygen Demand ( ) measured among the surface water samples is from 1. 4 -2.5 for all the samples at the landfill site ( Figure 9). The levels are below the set standard in Russia of 3.0 although they have a similar range to other studies elsewhere (Areola, Segosebe and Gwisai, 2015). On the other hand Gaborone levels are also below the levels in other surface waters studied by others (Osei et al., 2011;Sholichin, 2012;Alslaibi, Mogheir and Afifi, 2011;Radojevic and Bashkin, 1999). This shows that samples from the landfill are in the range of between clean and moderately polluted (Table 1). However, as to be expected the general trend for shows that there is a decline in downstream with increasing distance from the landfill sites. As observed by Husain, Hoda and Khan, (1989) there is an increase in the concentration of pollutants closer to the landfill downstream although the concentrations are higher as compared to the present study. On the other hand some studies concur with the findings of this study (Areola, Segosebe and Gwisai, 2015;Bhambulkar, 2011).

Alkalinity of Landfill Surface Water
There is a general decline in levels with increasing distance from the landfill.
Sulphate levels are higher than the set standards for all the samples ( Figure 10 and Table 2 Table 2), (Raman and Sathiya -Narayanan, 2008;WHO, 2004;BOS 32:2000;USEPA, 1991). There is a sharp increase in levels with increasing distance from the landfill. This could be due to livestock which utilize the surface water sources for drinking. However this is contrary to the findings of prior studies (Alslaibi, Mogheir and Afifi, 2011).

Concentration
All samples have concentration in the range 0.004 -0.02 which is below the set limits ( Figure 11). Though appreciable the concentrations in the waters are below the set drinking standards of 0.05 (Gvozdic et al., 2011;Osei et al., 2011;Raman and Sathiya -Narayanan, 2008). The results are similar to those of previous studies conducted in developing countries (Raman and Sathiya -Narayanan, 2008;Longe and Enekwechi, 2007). On the other hand some studies reveal that water samples have statistically significantly high levels as compared to the current study Balogun, 2010, Salminen, 2005).

Sodium and Potassium Concentration
The concentration range of in the surface water samples for Gaborone landfill is 42.18 -120.92 . All the samples are below the WHO (200 ) drinking standards, while the majority of the samples are below the Botswana (100 ) drinking water threshold; on the other hand all samples are above the USEPA (10 ) and EU limits (23.1 ) of drinking water respectively ( Figure 12 and Table 3). The levels of the current study are statistically significantly higher than levels observed in other studies (    The range for concentrations in Gaborone is (0.145 -0.8977 ), (Figure 12). However, all the samples are below the set drinking water limits in Botswana (25 ), EU countries (12 ) and Canada (10  ), (Salminen, 2005 (Haertling, 1989). There is a general decline in levels with increasing distance from the landfill as observed in other literature (Omoniyi and Ogunsanwo, 2009).

Concentration
The range for concentrations is 54.67 -167.1 for both Gaborone samples ( Figure 13). Most of the surface water samples are above the WHO and EU drinking water threshold as observed by prior studies (Longe and Enekwechi, 2007;Salminen, 2005;WHO, 2004; Le Seur Spencer and Drake, 1987). However, some studies have shown lower levels than the current study (Haertling, 1989). There is a general decline in levels with increasing distance from the landfill. The same spatial trend has been observed by studies in some developing nations ( The range for concentrations is (24.37 -59.48 ) for Gaborone surface water samples ( Figure 13). On the other hand some studies have recorded higher levels than for the current study (Le Seur Spencer and Drake, 1987). There is a significant general decline in levels with increasing distance from the landfill (r = -0.9439, p = ≤ 0.05 with a R 2 = 0.8909), and the trend appears to be similar to that of previous studies (Al -Sabahi et al., 2009). Most of the samples at the landfill are above the set WHO and EU limits, (Salminen, 2005;WHO, 2004). On the other hand most studies have shown that levels are higher downstream than upstream (Haertling, 1989; Le Seur Spencer and Drake, 1987; WHO, 1984).

Conclusions
All of the surface water samples were alkaline and there was a general decline in pH values with increasing distance from the landfill sites. On the other hand the pH was higher than the BOS 32: 2000, WHO and USEPA limits. Some water samples in Gaborone closer to the landfill surpassed the set colour limits.
Alkalinity levels were higher than BOS 32: 2000 limits. The BOD 5 test showed that the surface water samples were moderately polluted. All surface water samples had phosphate levels above the USEPA set limits, while some samples had surpassed the nitrates limits in Botswana. All samples from the landfill had sulphate, chloride and ammonia concentration levels which were above the set limits (USEPA, WHO and BOS 32:2000). The sodium concentrations were above the USEPA set limits. Calcium and Magnesium samples close to the landfill were above the WHO limits for Gaborone landfill.