PROXIMATE ANALYSIS AND HEALTH RISK ASSESSMENT OF HEAVY METAL POLLUTANT OF WATER AND SEDIMENTS IN OSUN RIVER

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INTRODUCTION
Heavy metal contamination has been a major challenge in every continent of the world. In Nigeria, due to the increasing number of industries and oil pumps, there has been constant assessment of water bodies per time in order to avoid diseases and illnesses caused by contamination of water bodies. Heavy metals have negative impacts on ecological stability of water ecosystems due to chronic environmental stress and bioaccumulation. They cause fish growth disturbances, reproduction failure, immune-suppression (Stave and Roberson 1985), histopathological changes in fish skin, gills, liver and kidneys and skeleton deformations (Sloof 1982;Hinton and Laurén 1990). Exposure of fish to heavy metals can cause metallothionein synthesis in the liver, kidneys and gills, and these metals can thus infiltrate the fish body directly by these non-alimentary routes (Hamilton and Mehrle 1986). In addition, copper and mercury slow down fish metabolism resulting from gill damage and enormous mucus secretion (Rice 1990). Heavy metal harmfulness in humans can bring about reduced mental and central nervous function, lower vitality levels, harm to blood synthesis, lungs, kidney, liver, and other essential organs. Long term accumulation may bring about progressive muscular and neurological degenerative cycles that impersonate Alzheimer's sickness, Parkinson's disease, strong dystrophy, and numerous sclerosis.
These metals may accumulate to a very high toxic levels causing acute impact on aquatic organisms without any immediate observable signs (Giguère et al., 2004). Presence of heavy metals is an indication of pollution in any aquatic environment and the toxicity of these metals' stems are biologically non-degradable and have the tendency to percolate in water and bioaccumulate in fish bodies (Gale et al., 2004). Heavy metals are accumulated and biologically magnified in fish tissues (Ayas et al., 2007). The investigation of heavy metals in water and sediment might be used to assess the anthropogenic and industrial impacts and risks posed by waste discharges in riverine ecosystems. (Zheng et al., 2008).
The Oṣun River (sometimes, but rarely spelt Oshun) is a river that flows southwards through the central Yoruba land in southwestern Nigeria into the Lagos Lagoon and the Atlantic Gulf of Guinea. The number of fisheries, dockyards, shipyards and factories over the years have increased significantly across the country which possibly could contribute to contamination of aquatic life. The polluting industries such as chemical complexes, fish processing plants, steel and paper mills, rayon mill complexes, cement factories, paint and dye manufacturing plants, several soap and detergent factories and a number of light industrial units directly discharge untreated toxic effluent in to the water bodies. Besides, the release of untreated toxic effluents are the major sources of heavy metals in any aquatic ecosystem. Unfortunately, very little research has been conducted to assess the level of metal pollution of the Osun River mainly in Osogbo including its biotic resources, sediment and water quality. The site of study is at Osogbo where the mystic belief of Osun river goddess is proposed to have emerged and also celebrated yearly as the culture and heritage of indigenes till date. Therefore, the study was carried out with an objective to assess physico-chemical

SAMPLING AND SAMPLE PREPARATION
Water and sediment samples were obtained five (5) times (from July 2018 to April 2019) for every 2 months from five sites in the river. The sampling bottles were pre-conditioned with 5% nitric acid and later rinsed thoroughly with distilled de-ionized water. At each sampling site, the polyethylene sampling bottles were rinsed at least three times before sampling was done. Pre-cleaned polyethylene sampling bottles were immersed about 10 cm below the water surface. About 0.5 L of the water samples were taken at each sampling site. Sediment samples were collected using grab sampler from five sites. Samples were transported to the laboratory and air-dried in the laboratory at room temperature. Once air-dried, sediment samples were powdered and passed through 160 µm sieve. The sieved samples were packed in polyethylene bags and stored below −20°C prior to analysis. Sediments samples were weighed, placed into the digestion bombs with 10 mL of HNO3 /HCl (1:3 v/v) and digested in a microwave digestion system. Sediments analysis was carried out according to the procedure described earlier.
The samples gathered were preserved and the analysis of various physico-chemical parameters was performed in the laboratory. pH, total dissolved solid (TDS), conductivity, salinity, total hardness, Alkalinity sodium, potassium, phosphate, nitrate, and exchangeable acidity of surface water and sediments were determined using IITA analytical standard methods. Organic matter in sediment was determined by measuring weight loss after burning in a preheated muffle furnace at 450°C for 4hrs. Sediment pH was measured in a suspension of 10g of sediment in 25mL deionized water after shaking for 2hrs using a digital pH meter.
Instrumental calibration was carried out prior to metal determination by using standard solutions of metal ion prepared from salts. Commercial annular grade 1000ppm stock solutions of Zn, Cr, Pb Fe, Ni, Co, Cd were diluted in 25cm 3 standard flask and made up to the mark with deionized water to obtain working standard solutions of 2.0ppm, 3.0ppm and 4.0ppm of each metal ion using atomic absorption spectrophotometer. The essence of the digestion before analysis was to reduce organic matter interference and convert metal to a form that can be analyzed by AAS.

RESULTS AND DISCUSSION
The physico-chemical parameters of water and sediments such as pH, electric conductivity, alkalinity, dissolved oxygen, total dissolve solid, calcium, magnesium, chloride, nitrate and phosphate, sodium, potassium, and organic matter, were analyzed for the water and sediments samples collected from the Osun River. The samples were taken from five different sites during different months of the year. All parameters with the mean value of the data with standard error were calculated as shown in the Tables below. Correlation of matrix of physico-chemical characteristics of water and sediment samples shows positive variance.
As shown in figure 1, sediments with grain size dominates, sediment is said to be sandy with 84%, less silky and clayey with no organic carbon present. pH is one of the most important factors that serve as an index of pollution.
Sediment pH in sampling is in acidic condition which makes it good and based on texture and composition, could be used as a raw material for constructions. Figure 3 show 105.6+0.50 is of no exemption which contributes to why edible foods in water bodies are more nutritious in Osun River. Ammonia, nitrate was not detected and can be said to be absent in Osun River sediment composition.