Impact of Dumpsites on the Quality of Soil and Groundwater in Satellite Towns of the Federal Capital Territory, Abuja, Nigeria

Background. Urbanization, industrialization and changes in consumption patterns have compounded the problem of solid waste management in Nigeria. Poor waste management threatens the well-being and health of the local population, particularly those living adjacent to dumpsites. Objectives. An assessment of the impact of dumpsites in a satellite town of the Federal Capital Territory, Abuja, Nigeria was carried out to determine the level of biophysical/chemical parameters (pH, temperature, conductivity, nutrients (calcium and magnesium), heavy metals (lead, chromium, zinc), and microbial burden) on the quality of soil and groundwater and their impact on health and the environment. Methods. Soil and ground water samples were collected in four different dumpsites (Bwari, Gwagwalada, Kuje and Azhatta) with reference samples taken from the Federal Capital Territory, Abuja, and taken to the laboratory for biophysical/chemical analysis using standard methods. Results. The results were compared with the national and World Health Organization (WHO) standard limits for soil and water respectively. Except for zinc, the average concentrations for heavy metals in the soil samples were higher in all four dumpsites than the permissible levels. Soil and water parameters that exceed the standard limits pose significant health and environment risks to nearby residents. Conclusions. There is a need for raising the awareness of residents living close to dumpsites and those who use the well or nearby streams for domestic activities on the need to carry out adequate water treatment prior to its use.


Introduction
Waste generation has been an issue for communities since the beginning of civilization. Waste is generated due to goods and service production and the utilization of natural resources. 1 There are many barriers to the proper management of waste. In Nigeria, regular increases in population, industrialization and changes in consumption patterns have complicated solid waste management. 2 The impact of poor waste management on human health and well-being cannot be overemphasized. Individuals living adjacent to dumpsites are at high risk due to the potential of waste to pollute water, food, land, vegetation and air. 3 Waste comes from various sources: domestic residences, offices, institutions, commercial buildings, restaurants, agriculture, construction, and hospitals. The majority of the wastes generated from these sources ends up in dumpsites. Across many cities in Nigeria, collected wastes are usually burnt outdoors and ashes are poorly disposed of on-site. This act destroys the organic components and causes the oxidation of metals. The ashes left behind are enriched with metal, which results in pollution of the surrounding environment. 4 The movement of contaminants from sites where wastes are disposed of to adjoining ecosystems is complex and involves biological and physicochemical processes. 5 Open dumpsites could be a source of microbial and toxic chemical pollution of the soils of the dumpsites. This can also pollute hand dug wells, posing serious health risks and leading to the destruction of biodiversity in the environment. 6 Water can percolate through the refuse pile in the dumpsites. This leads to the formation of leachates that are enriched in nutrients (nitrogen, potassium and phosphorous), heavy metals, and other toxic substances, including cyanide and dissolved  Figure 1. The reference site (8.52 N, 7.45 E) was selected outside the study area.

Sample Collection and Analysis
The analytical phase involved the analysis of physicochemical, heavy metal concentrations and microbial parameters in soil and water samples collected from the dumpsites and the reference site to measure the impact of the dumpsite on the quality of the soil and water.

Impact of Dumpsites on the Quality of Soil and Groundwater in Abuja, Nigeria
Abbreviations

Soil
The pH values of the soil samples from the selected dumpsites were similar, ranging from 7.1 to 7.8 ( The mean concentration of nitrates

Table 4 -Physico-chemical Parameters of Water Samples Collected from the Groundwater near the Dumpsites
Research from the sample sites was higher than the reference site and WHO standards, as shown in Table 1. Due to the high solubility of nitrate in soil and its inability to retain anions, nitrates leach during rains and contaminate surface and ground waters. 20 Except for zinc, the average concentrations for the other studied heavy metals were higher at all the dumpsites than the permissible levels stipulated by the reference 18,19 ( Table 2), even at the reference site.
Four genera of bacteria were identified: total heterotrophic bacteria, total coliform, Escherichia coli and Shigella/Salmonella. The results in Table 3 illustrate the high levels of total heterotrophic bacteria of the soil samples with regard to total coliform count, Escherichia coli, and Shigella/ Salmonella, which were higher than the reference limits. 18,19

Water
The mean temperature values of the water samples were within the range of the NESREA limit of 30 o C. The mean concentrations for total suspended solids were higher in the Bwari and Kuje dumpsites, but not at the Gwagwalada and Azhatta dumpsites or the reference sample, which were within the standard limit as shown in Table 4. The mean concentration of total dissolved solids was lower than the WHO standard of 500 mg/l for the discharge of wastewater into surface water ( Table 4).
The mean conductivity values of the effluent from the dumpsites were very low compared to the NESREA and WHO guideline limits of 1000 µScm-3 for the effluent.
The mean biochemical oxygen demand values of the water samples were significantly higher than the WHO limits, but within the NESREA limits for effluent ( Table 4). The mean concentrations of nitrate in the water samples were lower than the WHO limit of 45 mg/l. 21 Iron concentrations in the Bwari dumpsite (1.7 mg/L) and Kuje dumpsite (2.1 mg/L) were above the standard limits, as shown in Table 5. The findings were similar to the values reported by Adeolu in the analysis of heavy metals in the effluent from an acid battery recycling plant. 22 Mean concentrations of lead were higher in the Bwari, Kuje and Gwagwalada dumpsites, but not at the Azhatta dumpsite, which had a low appreciable concentration (0.002 mg/l) below the NESREA and WHO guideline limits. In addition, the concentration of cadmium in the Bwari dumpsite was higher than the WHO limits. Cadmium is carcinogenic, and long term exposure contributes to kidney disease, lung damage and fragile bones. 23 As shown in Table 6, the values of total heterotrophic bacteria, total coliform count, Escherichia coli and Shigella/ Salmonella in the water samples collected from the wells near the selected dumpsites were higher than at the reference samples from the control site and WHO limits.

Soil
Soil conductivity is primarily due to an increase in the concentration of soluble salts in the soil. Some metals like zinc and copper are needed for metabolism  Research in organisms and concern over these metals lies in the thin line between their toxicity and essentiality. 22 Under prolonged waterlogged conditions, soluble manganese leaches out of soil. 20 Exposure to chromium can be carcinogenic, and chromium therefore poses a threat to public health. 24 It is worth mentioning that metal ion concentrations in the selected dumpsites were higher than the thresholds set by the WHO even at the control site. Excess of some heavy metals in the environment can cause serious environmental health consequences because of their biomagnification and bioaccumulation. 6 It should be noted that bacterial isolates with high frequency of occurrence are important human pathogens associated with a variety of infectious diseases such as gastroenteritis, typhoid fever, dysentery, cholera, and urinary tract infection. 25 The source of these pathogens is attributed to the biological degradation of waste materials in the dumpsites over time.

Water
Temperature has an important effect on other properties of wastewater.
High conductivity values (high salt concentrations) increase the salinity of the receiving river, which may result in adverse ecological effects on the aquatic biota and therefore high salt concentrations are a potential health hazard. 26,27 Biochemical oxygen demand reflects the presence of organic matter which will be oxidized biologically in the receiving water. 28 The greater the decomposable matter present, the greater the oxygen demand and the greater the biochemical oxygen demand value. Continuous discharge of effluent with a high biochemical oxygen demand into a river has negative effects on the quality of fresh water and can cause harm to aquatic life, especially fish downstream, and is hazardous to the survival of the aquatic biota in the receiving stream. 22 The concentrations of magnesium were very high, which could result in water hardness and pose a threat to public health. 5 The high levels of nitrate can give rise to blue-eye syndrome in infants and pregnant women and when combined with phosphate causes eutrophication. 29,30 Excess iron concentration in water impacts taste, imparts a reddish color, and increases the turbidity of water which promotes the growth of ferrous bacteria that accelerate the rusting process of metals that come in contact with water. The accumulation of metals in an aquatic environment has direct consequences to humans and the ecosystem. It should be noted that the ingestion of chromium in low concentrations is carcinogenic. When inhaled, chromium (hexavalent) damages the lining of the nose and throat, and irritates the lungs as well as the gastrointestinal tract. 22 When swallowed, it upsets the stomach and damages the liver and kidneys. Some individuals have an allergic skin reaction after touching materials containing chromium.
Exposure to high concentrations of lead through drinking water or residing near a lead-contaminated toxic dump can cause brain dysfunction in children, neurobehavioral changes in adults, hypertension and chronic kidney diseases. 22, 31 The mean levels of copper from the water samples were higher than the standard permissible limits, which can result in an astringent taste, discoloration, corrosion of pipes, fittings and utensils, and induce brain damage in mammals. 17 In addition, the concentration of cadmium in the Bwari dumpsite was higher than the WHO limit. Cadmium is carcinogenic, and long term exposure can contribute to kidney disease, lung damage and fragile bones. 22 The high incidence of fecal coliforms in these selected dumpsites was indicative of increasing pollution of groundwater by organic contaminants. Fecal coliforms have serious health implications and can cause urinary tract infections, bacteremia, meningitis, diarrhea and acute renal failure. 32,33

Conclusions
The findings on the impact of dumpsites on soil and ground water quality in satellite towns of the Federal Capital Territory revealed that the measured soil and water parameters exceeded the standard limits and pose significant health and environmental risks to nearby residents or users if care is not taken. There is a need for a standard policy framework that will guide the management and maintenance of dumpsites in these satellite towns either by the government or through a publicprivate partnership. There is also a need for greater public awareness by residents living near these dumpsites or those who use the wells or nearby stream water for domestic activities on the need to carry out adequate water treatment prior to use to prevent health problems. Proper methods of waste disposal need to be undertaken to ensure that the surrounding environment is not affected and to mitigate health hazards to the local population. At the household level, education on proper segregation of waste is needed and it should be ensured that all organic matter is sorted for biogas and compost, which is the preferred method for the sanitary disposal of waste.