Assessment of selected metal levels in Ishiagu Pb-Zn mine district soils and Oryza sativa, southeast, Nigeria

Abstract

Pollutants have a tendency to sequestrate into remote sites in different environmental matrices thereby reducing the level of available fraction for uptake in living organisms. We examined availability of metals by subjecting soil and rice plant samples from Ishiagu mining district to a sequential extraction procedure and subsequently analyzed the extracts using Atomic Absorption Spectrophotometer (AAS). Our results revealed that metals were moderately available in samples in the following decreasing order: Zn>Pb>As>Cd>Se>Cu. Though metal levels differed in rice plant samples compared to soil, we noted also that availability of these pollutants varied spatially among various study locations. Based on available acceptable range, copper and zinc were within tolerable limits while cadmium was in excess in some study locations. On the other hand, levels of lead in rice plant samples exceeded acceptable limits. Considering the levels reported from different locations, it is possible that metals were immobilized in soil organic matter or trapped in other forms. Though in general metal levels were within acceptable limits in our study locations, we recommend that deliberate steps be taken by authorities to curtail indiscriminate mining activities capable of polluting soils and farm lands. For this reason, farmers should be encouraged to plant safe cultivars since this rice variety is a known poor metal accumulator.

Keywords: Heavy Metals, Soil, Rice Plants, Ishiagu, Mining District