By Udo Godwin James
Heavy metal concentrations and degradation efficiency of total petroleum hydrocarbons (TPHs) on environment in Ibeno Local Government Area, Akwa Ibom State, Nigeria was investigated. Experimental design method was adopted for this study. Fifteen composite samples each of soil, leaves of Telfairia occidentalis, sediment and water were collected in December 2012 and June 2013. The sediment and water samples were collected using corer and clean plastic bottles respectively. Soil and sediment samples were air dried, mechanically ground using mortar and pestle, and 2 mm mesh size obtained for further analysis. The soil and sediment samples (1.0 g) each were weighed into Kjeldahl flasks. Aqua regia (15 cm3) was added, swirled to mix and kept overnight. The flasks were heated on a hot plate to 50 oC for 30 min; temperature was later adjusted to 120 oC and heated continuously for 2 h. The mixture was cooled, and 0.2 M HNO3 (10 cm3) added. The resulting mixture was filtered with a Whatman no. 541 filter paper. The filtrate was transferred into a 50 cm3 standard flask and made up to the mark with 0.2 M HNO3. The leaves samples were washed with de-ionized water, dried to constant weight in an oven at 105 oC, pulverized and 2 mm mesh size obtained for further analysis. The ground leaves were digested with 1.0 cm3 concentrated HClO4, 5 cm3 concentrated HNO3 and 0.5 cm3 concentrated H2SO4 in 50 cm3 Kjeldahl flask. Each water sample (10 cm3) was digested with 2 cm3 concentrated HNO3. Concentrations of the heavy metals were determined using AAS Unicam 939 model. The soil samples (150 g) each were transferred into four (4) plastic buckets labeled A, B, C and D. Varying concentrations palm bunch ash (PBA) (0.0 g, 50.0 g), Tween 80 (50.0 g) and PBA + Tween 80 (25.0 g) each were added to A, B, C, and D, where A served as control. Portions (5 g each) of A, B, C and D were weighed into standard flasks, 25 cm3 of xylene added and shaken, NaCl (5 g) was added and left for 72 h. The liquid portion was decanted into a separatory funnel, corked and shaken. The xylene layer was transferred into 100 cm3 centrifuge tube containing 5 g of Na2SO4 and agitated for 15 min, the absorbance of the solution was measured at 425 nm and used for calculating concentrations of TPHs. Concentrations of TPHs were determined at 20 days intervals for 60 days. The data were analyzed on the basis of first order kinetic model InC = InCo- kt. Heavy metal concentrations (mg kg-1) during dry season were, soil: Fe (15.15 ± 5.91), Mn (10.36 ±3.18), Cd (0.23±0.31 ), V (0.17 ± 0.29), Ni (0.19 ± 0.05), leaves of Telfairia occidentalis: Mn (7.73 ± 3.06), Fe (5.93±1.28), V (0.16±0.26), Cd (0.21 ± 0.16), Ni (0.02 ± 0.01), sediment: Fe (22.18 ± 14.82), Mn (9.67±2.75), V (3.39±3.30), Ni (2.18±0.78), Cd (0.48 ± 0.75), and water: Mn (2.80±0.93), V (1.53±1.42), Ni (1.50 ± 1.53), Fe (0.86 ± 0.25), Cd (0.27±0.21), During wet season, soil: Fe (12.09±4.98), Mn (9.66 ± 2.18), Ni (0.05±0.03), V (0.04±0.01), Cd (0.04±0.02); leaves of Telfairia occidentalis: Mn (7.75±3.76), Fe (5.96±4.07), V (0.21±0.09), Cd (0.19±0.06), Ni (0.03±0.06), sediment: Fe (23.28±0.24), Mn (9.45±2.63), V (3.31±3.34), Ni (1.94±1.48), Cd (0.48±0.74), and water: Mn (3.13 ± 0.79),V (1.88 ±1.45), Ni (1.45 ±1.04), Fe(1.05 ± 0.25), Cd (0.10 ± 0.13), were obtained. The correlation coefficients were: V (0.556), Ni (0.376), Cd (-0.043), Pb (0.856), Mn (0.813), Co