IMPACT OF VEHICULAR TRAFFIC ON CONCENTRATIONS OF SELECTED HEAVY METALS IN CASSAVA TUBERS HARVESTED FROM ROADSIDE IN OWERRI, NIGERIA

Abstract

Cassava tubers and soil samples on which they were cultivated were collected at 10m, 15m and 20m from two sections of roadsides of Owerri-Aba expressway. Samples from section 1 were analyzed for the presence of lead (Pb), cadmium (Cd), copper (Cu) and manganese (Mn) while those from section 2 were analyzed for lead, zinc (Zn), chromium (Cr), cadmium and nickel (Ni) using atomic absorption spectrophotometer (AAS). Results obtained showed that at section 1, the concentrations of heavy metals in cassava samples were in the range (0.0-13.5mg/kg) Pb, (0.0-0.5mg/kg) Mn, (1.5-16mg/kg) Cu and (0.05-0.4mg/kg) Cd. At section 2, they ranged from 3.22-5.48mg/kg (Pb), 8.70-14.18mg/kg (Zn), 0.0-0.16mg/kg (Cr), 1.70-2.12mg/kg (Ni) and 0.03-0.22mg/kg (Cd). Similarly, in soil samples from section 1, the concentrations were (0.0-25mg/kg) Pb, (0.5-4.5mg/kg) Mn, (0.0-10mg/kg) Cu and (0.1-0.55mg/kg) Cd, while those from section 2 were (7.4-9.6mg/kg) Pb, (9.5-15.5mg/kg) Zn, (0.2-0.7mg/kg) Cr, (3.1-4.8mg/kg) Ni and (0.3-0.5mg/kg) Cd. In both samples from section 1, as well as only soil samples from section 2, the average concentrations of heavy metals studied decreased from 10 to 20m from the roadsides, except for Pb. Moreover, at section 1, the order of concentration of heavy metals is Pd>Cu>Mn>Cd for both soil and cassava tuber samples but Zn>Pb>Ni>Cr>Cd in samples from section 2. Only Pb in cassava tubers harvested at most of the locations in the two sections far exceeded the 2.0 mg/kg maximum permissible limit (MPL) set by WHO/FAO. Furthermore, result of bioaccumulation factor showed that the cassava samples moderately bioaccumulated the heavy metals.