Geoassessment of heavy metals in rural and urban floodplain soils: health implications for consumers of Celosia argentea and Corchorus olitorius vegetables in Sagamu, Nigeria

Abstract

Vegetable gardening in floodplains in western Nigeria has assumed economic significance but with attendant pressure on urban field in the dry season. This study assessed soil properties and bioconcentration of cadmium (Cd), iron (Fe) and lead (Pb), in edible parts of Celosia argentea and Corchorus olitorius grown in floodplains. Soil and vegetable samples were collected at 20 m intervals from rural (Atoyo and Ewuga) and urban (GRA Rd. and Lafarge) floodplain gardens in Sagamu. Six samples were collected per location making a total of 24 samples each of soil and vegetable. Samples were analyzed for soil properties and heavy metal concentration in the vegetables. Transfer factor (TF), contamination factor (CF), daily intake of metals (DIM), health risk index (HRI) and geoaccumulation index (I_geo) were also determined. Soil properties varied significantly, with the highest soil concentration of Cd (0.91 mg kg^-1) and Fe (208.20 mg kg^-1) recorded at Lafarge. The highest soil Pb (223.77 mg kg^-1) was at Atoyo. Bioaccumulation of Fe was significantly (p ≤ 0.05) higher in C. argentea than C. olitorius. Heavy metal bioaccumulation beyond allowable limits was recorded for Cd (0.46 mg kg^-1) and Pb (49.30 mg kg^-1) by C. argentea and C. olitorius, respectively. Soil contamination was dominated by Cd at Lafarge and by Pb at Atoyo. The DIM and HRI indices indicated no risk of Cd, Fe and Pb consumption in the vegetables. Geoaccumulation index revealed that Lafarge and Atoyo soils were extremely contaminated with Cd and Pb, respectively. Leafy vegetables grown in urban and rural floodplain soils adjacent to waste dumpsite are accumulators of Cd and Pb with food poisoning as the consequence.

Keywords: Bioconcentration; Celosia argentea; Corchorus olitorius; Floodplain; Health risk; Sagamu.