Accumulation of heavy metal pollutants in soil and cassava leaf and their effects on soil microbial population on roadsides in Ogbomoso, Nigeria

Abstract

Acute toxicity of heavy metals is a rare phenomenon in nature but the intake of sub-­‐lethal doses over an extended period is of great concern. This research investigated the heavy metal concentrations in soil and cassava leaf and assessed the effects of the metals on microbial populations along Ogbomoso-­‐Oyo, high traffic density (HTD) (A) and Ogbomoso-­‐Ife Odan, low traffic density (LTD) (B) roads. The results show that the metals were statistically higher in concentration at A (Pb= 0.53, Cd= 0.57. Cr =0.19, and Zn= 4.67 mg/kg) than B (Pb= 0.36, Cd= 0.40, Cr= 0.12, and Zn= 2.70 mg/kg) road. The mean metal content of cassava leaf indicated that all the metals were higher in the leaf at high traffic density than at low traffic density road. Also, at A 20-­‐30 m recorded lowest heavy metal concentration in the leaf (except Zn = 3.87±0.35 mg/kg) than the distances closer to the road. The same trend was observed at B except that Zn was highest (2.90±0.20 mg/kg) at 10-­‐20 m than 0-­‐10 m and 20-­‐30 m from the road edge. The total microbial count was significantly higher at low traffic density (17.23 Cfug¹(x10⁵)) than high traffic density (11.58 Cfug¹(x10⁵)). Total microbial count and Total fungi count were found to be lowest at 20-­‐30 m away from the road compared with 0-­‐10 and 10-­‐20 m. The results of this research show that crop cultivation along the roads within 30 m from the roads constitutes a potential source of chronic heavy metal toxicity to the general populace who feed on the crops.