Effect of Urban Flood Waters and Sediments on the Presence and Levels of Heavy Metals in Valley Bottom Soils of Ekpoma Metropolitan, Southern Nigeria

Abstract

An experiment was conducted on some selected valley bottom soils in Ekpoma metropolitan, to investigate the presence and levels of heavy metals as affected by urban flood waters and sediments. Three sites were chosen for the investigation: Ambrose Alli University Teaching and research farm, Ekpoma (AAU), Emaudo (EM) and Uhiele (UH) quarters. AAU was used as control since it received no flood waters and sediments. At each site, a plot (25m x 25m) was demarcated for soil sample collection. Within each plot five spots were randomly chosen and soil samples were augered at two depths (0-15 cm and 15-30 cm), making ten samples per site. Samples were bagged, labelled and taken to the laboratory for analysis. The following metals were investigated – Mn, Pb, Co, Ni, Fe, Cd, Cu, Zn. Some chemical and physical properties were also investigated. Results were analysed statistically using (ANOVA) to determine significant differences between treatment means (p=0.05) and LSD was used to separate the means. Results revealed soils of Uhiele to be sandy clay loam, while Emuado and A.A.U were sandy loamy. pH values for all the sites and depths showed that the soils were acidic. Values for organic matter for the two sites were significantly higher (p=0.05) when compared to the control AAU. For heavy metals, the levels were below risk level for all the sites. All the metals showed increased values except Cobalt and Nickel, compared to the control (A.A.U). This experiment confirmed increase levels of heavy metals in valley bottom soils of Ekpoma metropolitan that regularly receive flood waters and sediments. Since anthropogenic activities will always be there, and with uncontrolled waste disposal systems, it is recommended that levels of heavy metals in these cultivated valley bottom soils be periodically monitored, so as to detect when the levels will pose health risk for those who may consume harvested products from these soils.