ABSTRACT

The study was carried out to assess heavy metal concentrations in soil and their accumulation in cassava plant parts at the metal waste dumpsite in Umuahia South Local Government Area, Abia State, Nigeria. Soil samples were collected randomly at depths of 0 – 10 cm, 11 – 20 cm, 21 – 30 cm, 31 – 40 cm and 41 – 50 cm from nine (9) sampling points, three (3) each at entry, middle and exit positions within the site. Cassava plant samples were collected randomly at nine points from the nearby farmland, about 1m away from the dumpsite. The chemical properties of soil and macro elements assessments were carried out to examine heavy metals and polycyclic aromatic hydrocarbons (PAHs). Soil chemical properties analysed were pH, organic matter and electrical conductivity. Macro elements studied were zinc (Zn), calcium (Ca), sodium (Na) and potassium (k). Heavy metals were assessed using Agilent FS240AA Atomic Absorption Spectrophotometer (AAS). PAHs were assessed using Gas chromatography (GC-MS). In soil, total heavy metal levels ranged from (mg/kg), 0.01 to 0.13 for Cr, 0.27 to 1.28 for Cu, 0.93 to 2.57 for Pb, and 0.11 to 0.26 for Cd. Their mean values were (mg/kg), 0.062 for Cr, 0.606 for Cu, 1.544 for Pb, 0.212 for Cd. The rank profile of the metals were Pb > Cu > Cd > Cr. In the cassava plant, total heavy metal levels ranged from (mg/kg), 0.018 to 0.051 for Cr, 0.10 to 4.01 for Cu, 0.82 to 2.08 for Pb, 0.20 to 3.24 for Cd. The result shows that high Pb content was obtained for the different cassava plant parts when compared with the FAO/WHO permissible limit, whereas other metals were well below their permissible limits, except Cd which exceeded its permissible limit of 0.7 – 1.1mg/kg in the root only. Eleven PAHs were detected across the different soil depths, they include, fluorine, flouranthene, benzo(a)flouranthene, benzo(b)flouranthene, benzo(ghi)perylene, 1– 2benzanthrene, xylene, phenanthrene, naphthalene, anthtacene and dibenzyl(ah)anthracene. The root accumulated the most mean concentration for PAHs (0.003μg/g), followed by the leaf (0.00224μg/g), then the stem (0.0016μg/g). The results show that the levels of heavy metals and polycyclic aromatic hydrocarbons in the soil and cassava plant were small and were way below their permissible limits, only Pb exceeded its permissible limit at all parts of the cassava plant. The result also shows that at 41 – 50cm, there were concentrations of the studied contaminants. This could be call for concern as further contamination deeper into the soil horizon could pose threat on underground water quality. Therefore, proactive measures should be adopted to remediate contamination.