Heavy metals concentration in soils and crop plants within the vicinity of abandoned mine sites in Nigeria: an integrated indexical and chemometric approach

Abstract

ABSTRACT In the Okurumutet-Iyamitet Mine area, mining is done by the open-cast method, without environmental impact assessment, thereby exposing the environment and its inhabitants to risks. This study aimed to assess the toxicological processes that control the plants’ heavy metal uptake into their tissues, the suitability for human consumption, and the possible sources of heavy metals using an integrated approach. The concentration of selected trace metals in plant samples was analysed by the microwave digestion method using 1 mL and 6 mL of concentrated perchloric acid and nitric acid respectively. The concentration of heavy metals in soil samples was analysed by extraction and centrifugation following standard procedures. The extracts collected were analysed by placing them into the flame of the PerkinElmer Analyst 200 atomic absorption spectrophotometer and graphite furnace atomic absorption spectrophotometer for soil and plants respectively. The concentration of heavy metals decreased in the order: Fe > Zn > Mn > Ba > Pb > Cd and Fe > Zn > Ba > Mn > Pb > Cd for the soil and cassava plants respectively. When compared with the Food and Agricultural Organisation/World health organisation and soil quality guideline, Cd recorded values in soils above the required standards. Numerical models revealed a moderate to high extent of heavy metal pollution in soil with Cd and Fe posing the highest contamination level across all the samples. The translocation factor revealed that heavy metals are more accumulated in the leaves than tubers. Similarly, the bioconcentration factor (BCF) showed that the inhabitants are exposed to heavy metal contamination from the consumption of cassava tubers, as the BCF values were >1.00. Chemometric analyses identified anthropogenic activities as the major influence on the accumulation and bioavailability of heavy metals. Hence, emphasis should be placed on Cd and Fe to mitigate further heavy metal pollution in the area.