Heavy metals accumulation by maize (Zea Mays L.) grown on soils amended with municipal solid waste composts

An experiment was conducted to investigate the accumulation of some heavy metals by maize (Zea mays L.) grown on soils amended with different levels of municipal solid waste compost (MSWC) in Dakadda experimental farm, Uyo. Eighteen plants samples were collected from three different plots and analyzed for heavy metals (Cd, Fe, Mn, Cu, and Pb) contents using atomic absorption spectrophotometry. Results obtained revealed the following ranges for the metals in grain: Cd:0.041-0.059mgkg-1 , Fe:42.62-62.23mgkg-1 , Mn:7.92-12.20mgkg-1 ; Cu:6.26-19.40mgkg-1 and Pb:0.25-0.36mgkg-1 , while the ranges in stover: Cd:0.029-0.120mgkg-1 , Fe:41.62-54.30mgkg-1 , Mn:14.21-20.43mgkg-1 ; Cu:10.46-24.30mgkg-1 and Pb:0.21-0.31mgkg-1. The results obtained from this study have shown considerable and unacceptable levels of heavy metals in maize grain and stover for the amended soils. It was observed that compost application increased the status or level of micro-nutrients when compared with the control plots (treatments), except for Mn and Cd in grain and Mn and Pb in the stover. On a general note, the concentrations of micronutrients were found to be higher in grain than in stover, except for Cu and Mn. The study also reveals that concentrations of most of the heavy metals analysed for in maize grains varied positively with their corresponding levels in stover. However, worthy of note is that although the levels of heavy metal contents obtained were within the permissible WHO and FAO standards, except for Lead, Pb, which was slightly higher than normal. It is believed that the results could be more favourable in this study than elsewhere because of the low content of industrial or hazardous wastes. Also, the waste could have been more degraded than might result from use of less than two years old dumpsite wastes elsewhere where there could be less highly degradable matter, less exposure to air before application to soil, drier waste, or where decomposition has been otherwise inhibited. Thus, on a general note, cultivating edible plants on dumpsite soils or soils reclaimed from a municipal solid waste disposal site, may not be safely used as a soil conditioner due to the fact that they have the potential of posing risk to crops or public health.