HEALTH RISKS ASSESSMENT OF HEAVY METALS FROM THE CONTAMINATED SOILS OF OKENE METROPOLIS, NORTH-CENTRAL, NIGERIA.

This study revealed the health risk associated with selected heavy metals (Mn, Cu, Zn, Cr, Co, Pb, Ni and Cd) in Okene Metropolis. Soil samples from workshops and other anthropogenic activities were collected and their heavy metal contents analyzed. The two pathways of exposure to heavy metals in soils are: ingestion and by dermal contact pathways. Children are the most susceptible part of the population and highly venerable to health risk Health risk assessment showed that the order of exposure was children > adults. This research revealed the health risk assessment for children and adults are less than 1 and therefore, heavy metals were not accessible to any health risks. Despite the lack of health risk at present, continuous activities from these workshops and other anthropogenic activities may likely lead to soil pollution in future. Therefore, it is recommended that there should be continuous monitoring of heavy metals in Okene Metropolis to ascertain the health risk associated with heavy metals.


INTRODUCTION
Heavy metals are the risk pollutants in our natural environment because of their toxicity, persistence, bioaccumulation, and bio magnifications in food chain process in the environment [12].The frequent increase in the population of the world in the urbanization, rapids in cities, social life, gradual economic growth, income level in urban areas, low efficiency of the waste collection system and waste treatment have contributed immensely to the rapid increase in solid waste generation [9].
Human activities also posed a lot of geochemical changes in nature, and unregulated waste dumping is causing an acute pollution of the surrounding environment, causing a great contamination of soil, water and atmosphere [13].
Several studies have shown human health risk (HHR) of potentially toxic metals (PTMs) pollution in soils and road dust [7].The soil receives most of the solid waste stream generated from human activities and by their nature some are easily degradable wastes such as food remains through the activities or indigenous microbes, while others may be recalcitrant to degradation (such as pesticides) or non-biodegradable (such as glass).Environmental pollution harms earth's ecosystems due to harmful substances and energy release into air, land and water.Heavy metals such as (Fe), cadmium (Cd), lead (Pb), copper (Cu), chromium (Cr), nickel (Ni), zinc (Zn) and manganese (Mn) are released from several such as routes, alloy, tires and pipes of vehicles into roadside surroundings [2] & [10].The sources of heavy metals include leather tanning, lead-acid batteries, fluorescent fuel, battery industry and thermal power plants [8].

Description of Sampling Point
Okene LGA is composed of Okene and Okengwe

Sample Collection
Exactly 18 composite soil samples were collected from artisans (mechanic workshops, blacksmiths, hospitals, abattoirs, poultry farms, construction areas etc.) with the aids of stainless steel Auger.
The collected samples were grounded, sieved (2 mm) and stored in properly labeled polyethylene bags for digestion and metals analysis.

Samples Pre-Treatment
All the collected soil samples were air dried in the laboratory for a period of seven days to avoid microbial and fungal growth.

Soil Sample Digestion
Exactly 1.0 g of the soil sample, air-dried was weighed into a Telflon crucible followed by the addition of 1 cm 3 HClO4 and 20 cm 3 of HF3 acids respectively.The mixture was digested for 10 minutes at a temperature of 100-150 0 C on a thermostat heater in a fume cupboard to obtain a clear, colourless digest and cooled, and filtered through a Whatman filter paper (No.9) into a 50 cm 3 volumetric flask and made up to volume with deionized water.This was stored in a polythene bottle for heavy metals analysis (Li et al., 2020).

Health Risk Assessment
Three processes are used to assess human potentially toxic element (PTE) exposure in preurban, urban, and rural settings [5].The two

Average Daily Dosage (ADD) Ingestion for
Children.2. revealed the values range from Cd (0.00)-Co (0.000067).The maximum value of cobalt (0.0000067) was obtained from forest land followed by refuse dumping location with a value of (0.0000064) while the minimum of (0.00) from Cd was obtained throughout the sampling locations.

CONCLUSION
The health risk assessment revealed in the study showed the order of exposure was children > adults.In all the two routes of exposure to heavy districts.There are 11 wards in the Local Government which are Bariki, Otutu, Orietesu, Lafia/Obessa, Okene-Eba, Idoji, Onyukolo, Obehira-Eba, Obehira-Uvete, Abuga/Ozuja and Upogoro/Odenku wards.Okene LGA is on latitude 07°33 ′N and longitude 06°14′E and has an area of 328 km sq. and a population of 320,260 according to the 2006 National Population Census.The people of Okene are well known for the famous Okene cloth weaving, farming, hunting and commerce.
−6 ................ Equation (2) where ADDIing, and ADDIderm are the average daily dose heavy metal exposure of ingestion and dermal contact, respectively; C = soil heavy metal concentration (mg/kg); lngR = ingestion Soil frequency (mg⋅dm 3 ); lnhR = respiration frequency (m 3 ⋅dm 3 ); EF = exposure frequency (day/year); ED = exposure duration (year); BW = average body weight (kg); AT = average exposure time of heavy metals (day); PEF = particulate emission factor (m 3 /kg); SA = skin surface area (cm 2 ); AF = skin adherence factor (kg/cm 2 ⋅d); BAS = dermal absorption factor.RESULTS AND DISCUSSIONHuman health risk assessment profile is estimated to health-related diseases from exposure to hazardous heavy metals in order to determine the contaminant level, assessment of exposure, and dose-response assessment.This result shows for assessment of human exposure to heavy metals through estimating the Average Daily Dosage Intake (ADD) of the heavy metals by ingestion, and dermal contact pathways are presented in Tables 1 -2.Generally, ingestion constitutes the highest pathway of average daily dosage intake of heavy metals in all the sampling areas followed by dermal contact pathways respectively.This signifies that human beings working in these workshops are highly exposed to the heavy metals through oral and contact pathways.The results presented in this study indicate that the order of average daily dosage (ADD) in the two exposure pathways of heavy metals in adults and children via the order of ingestion > dermal contact.As observed in the results, the children are expected to be more susceptible than adults as playing with sand is predominant among children in the sub-urban areas of the research sites and the ingestion route in children is attribuTable to the frequency of hand-to-mouth habit.
Cr > Ni > Pb > Zn > Mn > Cu > Co > Cd.Moreover, average daily dosage of all the heavy metals in all the two routes in the locations were lower than their one (1) which shows the heavy metals has no significant risk health effects on the humans in the sampling locations.The sampling areas had Cd as the least value.The maximum value was obtained by Cr Ni that dominated the sampling research sites.The heavy metals had values less than unit (1) and it has no negative infulence on humans.Geological factors and anthropogenic impacts may be responsible for the sources of Cr.Chromium is an important element which was very poisonous at high levels and also is one of the essential elements.It caused health risks to humans because chromium can be stored in the skin, lungs, muscles, and liver, which can be connected to many health conditions (Reyes-Guti´errez & Romero-Guzm´an, 2007).At concentrations higher than the permissible level, chromium posed dermatitis and ulceration of the skin (Lajçi et al. 2017) and also posed kidney, liver, circulatory and nerve tissue damages emanated from long term exposure (Strachan, 2010).Ni is an element needed for various animal species, microorganisms and plants; but, its deficiency may result from too little or too much of it respectively (Bytyçi et al. 2018).Therefore, sampling environments required constant monitoring to prevent health hazard in all the sampling areas.
metals, ingestion was the main route of exposure and finally by dermal contact respectively.All the heavy metals analyzed proceeded in the sequential order Cr > Ni > Pb > Cu > Mn > Zn > Co > Cd.Selected metals indicate no health risk posed to the sampling locations since all their values were less than 1.Therefore, it is necessary that government should implement strategies for the regular monitoring of heavy metals of the soils in order to prevent the health predicaments posed by the ingestion and dermal pathways in our environment.

Table 1 .
indicates the average daily dose.
(MK), poultry (PM), abattoirs (AB), residential (RS) and refuse dumping (RD) sites.The mean concentrations follow the sequential trend as indicated in Cr >Ni >Pb > Zn >Mn > Cu >Co >Cd for the children category.