Geochemical Assessment of Trace Metals in Peri-Urban Drainage and Bioaccumulation in Selected Food Crops in the Kumasi Metropolis, Ghana

Abstract

This paper evaluates some geochemical properties of trace metals in peri-urban drainage and bioaccumulation in cassava, plantain, lettuce and sugarcane in the Kumasi metropolis in Ghana, West Africa. The aim is to establish water quality and food safety. Water, sediment and the food crops were sampled along the profiles of Wiwi and Subin rivers for analysis. T-test statistic shows that pH, HCO3, Cl, Cu, As, Pb and Ni are significant in water and sediment. Mean concentrations of Cu, As, Pb and Ni in water and sediment are (0.01mg/l; 3.2mg/kg), (3.08mg/l; 4.9mg/kg), (0.034mg/l; 8.7mg/kg) and (0.021mg/l; 6.1mg/kg), respectively. In water, As, Pb and Ni concentrations are above primary maximum contamination limits of 0.05 mg/l, 0.015 mg/l and 0.020mg/l with metal ratios of 61.54, 2.27 and 1.05, respectively. In sediment, As concentration is above the continental crustal background value of 1.8mg/kg with a metal ratio of 2.72. From geochemical process models: (1) As and Ni adsorbs into sediment and may lead to attenuation in water in closed systems; (2) Cu and Pd are in equilibrium and may affect water quality at higher concentrations. The food crops have trace metals concentrations below reference values and bioaccumulation factors<1. The food crops are therefore excluders, and safe for dietary intake. Members in cassava-plantain-lettuce and cassava-lettuce-sugarcane suites have translocation factors (TFs)>1 for Cu and As, respectively, while lettuce has TF>1 for Pd and Ni. Crops with TF>1 may bioaccumulate the respective trace metals in over a prolonged period.