EVALUATION OF THE IMPACT OF HEAVY METALS ON THE ENVIRONMENT AROUND OJI COAL ASH DUMP IN ENUGU STATE, NIGERIA

SOURCE:

Faculty: Physical Sciences
Department: Pure And Industrial Chemistry

CONTRIBUTORS:

Enenchi, M.I;
Okoye, P.A.C;
Ogbuagu ,J.O;

ABSTRACT:

The impact of heavy metals on the environment around the Oji coal ash dump has been evaluated in other to determine the concentration of heavy metals in the soil, water and sediment of Oji-River, drinking water sources and leaves of five common plant species in the area of study. The identity and quantity of different chemical forms (speciation) in which the metals exist in the soil and sediment of Oji-River, and human health risk that may be caused by heavy metals to the inhabitants of the study area were studied. The metals in the soil and sediment samples were extracted sequentially using the modified Tessier sequential extraction protocol (SEP). Five plant leaves common to the environment ( Abelmoschus esculenta, Aspilia africana, Manihot esculenta, Panicum maximum and Zea mays) were sampled and digested. Water samples were collected from four drinking water sources (boreholes) within 100 m and 500 m and from the Oji River. Concentration levels of thirteen metals Fe, Mn, Ni, Pb, Cd, Cu, Cr, Co, Zn, As, Mo, Se and Hg were evaluated from all the samples using Atomic Absorption Spectrometer (AAS) Varian 240 AA. The bio-available fractions of 161.75 mg/kg and 8.38 mg/kg for As and Cd respectively, were above the values recommended for agricultural lands by United State Environmental Protection Agency (USEPA), European Union (EU) and National Environmental Standard Regulatory Agency (NESRA). The trend of percentage for bio-available metals in the soil of the study area was As > Pb > Cd > Fe > Co > Cu > Mn > Mo > Ni > Zn > Cr > Se. The speciation results showed that most of the metals were distributed more in the residual fractions. Also, depth profile showed decrease in concentration from top soil into the ground. The bio-available Cd was above the USEPA bench mark for Cd in sediments. Meanwhile, the mean extractable Pb, Co, Mo, were above the threshold effect concentration (TEC) and their non-residual fractions were above 50% of the extractable fractions in the sediment of Oji River. In the drinking water sources Fe, Mn, Cd, As, Mo and Se exceeded the WHO set limit. In Oji River, Fe, Cd, Zn, As, Mo, Se and Hg were above WHO standard limit for surface water. The metals; Ni, Pb, Cd, Co, As, Mo and Se respectively, were above the USEPA set limits for the five selected plant leaves. Analysis of variance (ANOVA) was significant at p<0.05 or p<0.01for the metals in the soil samples of the four axes. The correlations of the bio-available metals in the soil samples with the water samples were significant for Co and Se. Also, correlation of bio-available metals in the soil with the five selected plant leaves were significant for Fe, Mn, Ni, Cd, Co, Zn and Cu (p <0.05 or P < 0.01). The correlation analysis showed that the concentration of some metals in the water, and plant leaves were affected by the bio-available metals in the soil. The Hazard Index value for all pathways was found to be 2.12, making non-carcinogenic effects significant to the adult population. For children, the Hazard Index value was 17.88, a value >>1, which poses serious non-carcinogenic effect to children living in the study area. The carcinogenic risk of 5.54E-04 and 6.22E-04 poses carcinogenic effect for both adult and children respectively. Consequently, Water sources from the study area should undergo proper treatment before use. Also, further studies which will involve analysis of human blood are recommended.