Monitoring of heavy metals in vegetables and soils of Lokoja riverside, Kogi State, Nigeria

Abstract

The purpose of this study was to assess the accumulation of heavy metals in riverside soils of rivers Niger and Benue and beyond the confluence and their uptake by Amarantus hybridus and Corchorus olitorius L grown on these soils. Four agricultural areas around the confluence point were selected. A total of nine samples each of soils, were collected from the selected areas and were analyzed for pH, textural class, percentage organic carbon and matter, moisture content, manganese, nickel, copper, zinc, lead and cadmium. Soil pH ranged from 6.4 to 6.7. There was no significant difference in the mean values of the organic matter, organic carbon and moisture contents of the soils, while the total metal content ranges from 3.0 - 8.4mg/kg for cadmium; 10.2 - 20.2mg/kg for copper; 170.0 – 205.2mg/kg for manganese; 201.0 – 269.4mg/kg for nickel; 23.5 – 33.4mg/kg for lead and 48.7 - 77.8mg/kg for zinc. Nickel and chromium were at levels higher than the European Union Standards. The levels of nickel, zinc, lead and Cadmium in the vegetables were higher than the World Health Organisation permissible value in plants. The total metal contents in A. hybridus and C. olitorius L grown on the riverside soils follow the ranking: Ni > Mn > Zn > Pb > Cu > Cd. Pb had the highest bioaccumulation factor, 0.5691 and 0.6301 in the soil from CN site for A. hybridus and Corchorus olitorius L. respectively. This indicated that the highly toxic metal lead has been entering our food chain through vegetables.