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In this study, the seasonal variations in concentrations of Cd, Cr, Cu, Ni and Pb in soil and Abelmochus esculentus fruit grown near five (5) dumpsites in Kafanchan metropolis, Nigeria were investigated during the rainy and dry seasons of 2015 using Atomic Absorption Spectrophotometry. The dumpsite soils and control sites were sandy loam in nature and alkaline in the wet season. The cation exchange capacity, soil particle size distribution, pH, nitrogen, phosphorus and organic matter had higher values in the dry season compared to the wet. The mean levels of Cd in the dumpsite soils in the wet season was 21.86 – 58.27 mg/kg, Cu 41.33 – 81.21 mg/kg, Cr 25.86 – 44.69 mg/kg, Ni 31.44 – 77.44 mg/kg, Pb 23.62 – 56.63 mg/kg, while in the dry season, the ranges were Cd 11.38 – 30.67 mg/kg, Cu 106.52 – 158.42 mg/kg, Ni 52.09 – 119.69 mg/kg, Pb 94.19 – 308.35 mg/kg and Zn 98.43 – 332.83 mg/kg. The concentrations of the studied metals increased from wet to dry season at most dumpsites. The speciation of the soil indicated higher concentrations of heavy metals in the residual fractions (wet season 3.18 – 24.03 mg/kg; dry season 4.08 – 132.37 mg/kg); while the water soluble fractions had the least concentration (wet season 0.55 – 17.35 mg/kg; dry season 0.00 – 25.50 mg/kg). The non-residual fractions (wet season 37 – 95%; dry season, 26 – 82%) had higher percentage than the residual (wet season 5 – 63%; dry season, 18 – 74%). The concentrations of the heavy metals in the dumpsite soils were at levels above the Federal Environmental Protection Agency FEPA (1991) and European Commission (1986) maximum tolerable limits for these heavy metals in soils with few exceptions. The soil pollution load index in the wet season was 1.95 and 1.73 in the dry; contamination factor was 0.90 – 4.55 in the wet season and 0.59 – 5.78 in the dry season, while the geo accumulation index (wet season -0.51 – 1.11; dry season -0.92 – 1.35) showed that the soils of the dumpsites were polluted with the heavy metals studied. The mean cadmium, chromium, copper, nickel and lead contents in Abelmoschus esculentus fruits ranged from 8.51 to 14.36; 7.98 to 14.29; 7.35 to 18.80; 1.33 to 16.75; and 4.08 to 12.63 respectively. A. esculentus fruits had relatively low transfer factor for the metals. This study showed that the soils within the vicinity of the dumpsites were polluted by heavy metals. This calls for proper waste management practices and policy implementation.
1.1 Heavy Metal Pollution Pollution is the cause of many diseases, which affect not only the old but also the young, the energetic likewise animals and plants (Kanmony, 2009). Pollution is a worldwide problem and its potential in influencing the health of human population is great (Khan and Ghouri, 2011). The impact of pollution on overcrowded cities as a result of industrial effluents and automobile discharge has reached a disturbing magnitude and is arousing public awareness (Begum et al., 2009). Excessive levels of pollution has caused a lot of damage to human and animal health, also to plants including the tropical rain forests as well as the wider environment (Khan and Ghouri, 2011). Pollution and subsequent contamination of the environment by toxic heavy metals are of great concern due to their sources, widespread distribution and multiple effect in the ecosystem. Heavy metals are elements of high molecular masses, most of which belong to the transition elements (Silberberg, 2000). Studies have shown that soils of refuse dumpsite contain different kinds and concentrations of heavy metals (Odukoya etal., 2000). In recent times, it has been reported that these elements accumulate and persist in soils at an environmentally hazardous levels (Alloway, 1996) Heavy metal concentration in soil is associated with biological and geochemical cycles and are related to actions such as agricultural practices, industrial activities and waste disposal methods (Eja etal., 2003). The knowledge of heavy metal accumulation in soils, the origin of these metals and their possible interactions with soil properties are a priority in many environmental monitoring (Qishlaqi and Moore, 2007).The most common environmental pollutants in the world are heavy metals (Papatilippaki etal., 2008). The accumulation of heavy metals in agricultural soils is of increasing concern due to food safety issues and potential health risks, as well as its detrimental effects on soil ecosystems (Qishlaqi and Moore, 2007). The presence of heavy metals at trace level and essential elements at elevated concentration do cause toxic effects if exposed to human population (Fong et al., 2008). Food chain contamination by heavy metals has become a burning issue in recent years because of their potential accumulation in biosystems through contaminated water, soil and air (Begum et al., 2009). Heavy metals can accumulate in soils to toxic levels as a result of long term application of untreated wastewater and fertilizers. Soil being irrigated by wastewater do accumulate heavy metals in the surface, and when the capacity to retain heavy metals is reduced due to repeated application of wastewater, heavy metals will leach into ground water or soil solution will be available for plant uptake (Papafilippaki et al., 2008). Research findings indicate that application of heavy doses of fertilizer, pollute ground water by nitrates and heavy metals through leaching (Mico et al., 2006). Metal poisoning arises from heavy metals that have toxic properties being released, leading to adverse effects on human and the ecosystem (Voet et al., 2008). Although acute poisoning from heavy metal poisoning is rare through ingestion or dermal contact, chronic exposure to even small doses can be disastrous (Sherameti and Varma, 2010). Chronic exposure to heavy metals leads to accumulation in the food chain which leads to an increased stock in the biota, therefore magnifying human dose accumulated (Voet et al., 2008). The chronic problems associated with long term heavy metal exposure include: serious haematological and brain damage, anaemia and kidney malfunctioning (Sonayei et al., 2009). Heavy metals such as Pb and Cd are lethal even in very small doses. Lead has a negative influence on the somatic development, decreases the visual acuity and auditive thresholds (Simeonov et al., 2010). Acute exposure to lead causes brain damage, neurogical symptoms, brain damage and could lead to death (Simeonov et al., 2010). Cd exposure on the other hand, causes renal dysfunction, calcium metabolism disorders and also increase incidence of some forms of cancer (Kumar, 2009). Manganese toxicity affects the central nervous system, visual reaction time, hand steadiness and eye-hand coordination (Calkins, 2009). A syndrome named manganism is characterised by feelings of weakness and lethargy, tremors, a masklike face and psychological disturbance. Respiratory effects have also been noted in workers who were chronically exposed to inhaled Mn dust. Impotence and loss of libido have also been noted in male workers afflicted with manganism (Calkins, 2009). Zinc toxicity is rare, but at concentrations in water up to 40 mg/L, it may induce toxicity characterised by symptoms of irritability, muscular stiffness and pain (Al-Weher, 2008). 1.2 Heavy Metals in Dumpsites Modern civilization is completely dependent on a large range of metals for all aspects of daily life. There is a long historic association between metals and human development. Heavy metal pollution not only affects the production and quality of crops, but are environmentally problematic due to their high persistence and toxic effects (Esakku et al., 2003). Nigeria is becoming a dumping ground for technological waste, especially used electronics and automobiles from the developed countries. It is a known fact that some of these products contain hazardous metals such as lead, mercury, nickel, cadmium, copper, zinc, arsenic etc. The indiscriminate dumping of damaged parts of these imported and other similar locally produced materials in different forms can perturb the distribution and concentration of these metals in the environment. The Nigerian government at all levels through their agencies have invested much in waste management and enforcement of sanitation laws but little has been achieved so far (Ojeshiria, 1999). 1.3 Solid Waste According to Oxford Advanced Learners Dictionary of current English (2000), waste are ‗‗materials that are no longer needed and are thrown away‘‘. Waste is any substance that could be solid, liquid or gas or mixture for which no direct use is envisaged but which is transported for processing, dumping, elimination or other methods of disposal (Yakowitz, 1988). Waste is directly linked to human development, both technologically and socially (Adriano, 2005). Solid waste could be any non-liquid and non-gaseous product of human activities, regarded as being useless, it could take the forms of refuse, garbage and sludge (Leton and Omotosho, 2004). Sources of solid waste in Nigeria among others are commercial, industrial, household, agricultural and educational establishments. The solid waste types include pesticide containers, paint cans, batteries, nylon, various cleaning agents, dead animals, disposable diapers, grease and oils, bottles, woods, bones, electronic gadgets wastes and rubber among others. Out of the total solid waste generated in Ibadan, 66.1 % are domestic, 20.3 % commercial and 11.4 % industrial (Adewumi et al., 2005). Solid waste management has remained an intractable environmental sanitation problem in Nigeria. This problem has manifested in the form of piles of indiscriminately disposed heaps of uncovered waste and illegal dumpsites along major roads and at street corners in cities and urban areas, this problem is compounded by rapid urbanization and population growth which have led to generation of enormous quantities of solid waste which are often discarded by open dumping (Uwakwe, 2012). Nigeria‘s major urban centres are today striving to clear mounting heaps of solid waste from their environments. Many strategic centres of beauty, peace and security are being overtaken by the messy nature of heaps of unattended solid wastes emanating from household sources, markets and business centres (Oyedele et al., 2008). City officials appear unable to combat unlawful and haphazard dumping of hazardous commercial and industrial wastes, which are a clear violation of the Clean Air and Health Edicts in our environmental sanitation laws. Refuse generation and its likely effects on the health, quality of environment and the urban landscape have become a burning national issue in Nigeria today (Uzairu et al., 2013). A United Nations Report in August 2004 noted that while developing countries are improving access to clean drinking water, they are falling behind on sanitation goals. At a summit in 2004, a joint report made by World Health Organization (WHO) and United Nations Children‘s Fund (UNICEF) that ―about 2.4 billion people will likely face the risk of needless disease and death by the target of 2015 because of bad sanitation‖. The report also noted that bad sanitation, decaying sewage system and toilets fuel the spread of diseases like cholera and basic illness like diarrhoea, which kill a child every twenty one seconds (Uwaegbulam, 2004). 1.4 Health Implications of Dumpsites Poor waste management poses a great challenge to the well-being of city residents, particularly those living around the vicinity of the dumpsites due to the potential of the waste to pollute water, food sources, land, air and vegetation. The poor disposal and handling of waste thus leads to environmental degradation, destruction of the ecosystem and may cause great risks to public health. The resultant accumulation of waste poses a health hazard to urban inhabitants, and also threatens the surrounding environment (UNEP, 2005). According to Marshal (1995), open dumpsites are a major problem to the environment, especially on the air that the people inhale. Dumpsites emit obnoxious odours and smoke that cause illness to people living in, around or closer to them. In a number of community health surveys, a wide range of health problems, including respiratory symptoms, irritation of the skin, nose and eyes, gastrointestinal problems, psychological disorders and allergies, have been discovered. A number of researches have been carried out in response to concerns of the public, often triggered by nuisances caused by emissions of volatile organic compounds. According to Dolk (1997), dumpsites closer to residential areas are always feeding places for dogs and cats. These pets, together with rodents, carry diseases with them to nearby homesteads. UNEP (2005) states that wastes that are not properly managed, especially excreta and other liquid and solid wastes from households and the community, constitute a serious health hazard and could lead to the spreading of diseases. Normally, wet waste decomposes and releases bad odour. The bad odour affects the people that are settled next to the dumpsite, which clearly shows that the dumpsites have serious effects on people settled around them (Ekwumemgbo et al., 2013). Wastes from agriculture and industries can also cause serious health risks. Other than this, co-disposal of industrial hazardous wastes with municipal wastes can expose people to chemical and radioactive hazards. Uncollected solid waste can also obstruct stream water runoff, resulting in the formation of stagnant water bodies that become breeding grounds for disease causing organisms. Wastes dumped near a water source also cause contamination of the water body or the ground water source. The direct dumping of untreated wastes in rivers, seas and lakes result in the accumulation of toxic metals and organic pollutants in man through the food chain (Medina, 2002). This clearly shows how waste disposal seriously affects the health of residents located closer to dumpsites. The smelly and unsightly conditions of dumpsites are worse in summer, because of extreme temperatures, which speed up the rate of bacterial action on biodegradable organic material. Disposal of solid wastes on land without careful planning and management can present a danger to the environment and the human health (USEPA, 2006).