Heavy Metals In Vegetables Sampled From Farm And Market Sites In Accra Metropolis, Ghana

ABSTRACT This study reports for the first time in Ghana long-term monitoring of heavy metal contamination of vegetables. As reliable residue data analysis resulting from monitoring programs in foods is of great value to the general populace; this could address the possible risk of heavy metal exposure to human health. In this study, monitoring of heavy metals (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in consumable vegetables was assessed for a period of 2 years, 2013-2014. In all, a total of 479 vegetables (cabbage (Brassica oleracea), carrot (Daucus carota), cucumber (Cucumis sativus), green pepper (Capsicum annuum) and lettuce (Lactuca sativa)) were purchased from farm (production) and market sites within Accra Metropolis, Ghana. Samples were subjected to acid digestion and analyzed with atomic absorption spectrometer (AAS). All the vegetables studied contained at least two (2) or more metals; 18.99% of the samples had metal detections below the European Union (EU) guideline values, whereas 81% were above limits. Vegetables from Mallam Attah market and the Ghana Broadcasting Corporation (GBC) sites registered the highest percentage exceedances (100%) with the largest violation occurring in lettuce (97.41%). Elevated concentrations of these metals were also observed in vegetables from markets compared to the farms except As, Cd, Co and Fe. Ni and Cr were undetected in vegetables from farms, however their maximum concentrations (1.236 and 2.459 mg/kg) were recorded in lettuce at market sites. Additionally, the significant metal increases in vegetables from the markets could be due to atmospheric depositions and mode of handling by both farmers and buyers. On the other hand, studies of the soils from the various farm sites had varying mean concentrations of heavy metals, Fe (189.703), Mn (142.246) and As (9.145 mg/kg). However, all the metal levels in the soil were below EU limits, except As (24.2 mg/kg) found at Dzorwulu site, which exceeded the 20.0 mg/kg limit for As in agricultural soil. The bio-accumulation or transfer  factors for the metals in vegetables were highest in leafy and fleshy vegetables than root vegetables. The estimated health risks, average daily intake (ADI) and hazard quotient (HQ) of these metals in the vegetables were far below the FAO/WHO tolerable limits and did not pose any imminent risk to consumers (except As in vegetables from farms). Even so, the calculated risk for children (15 kg) was about 3 times higher than that of adults, indicating that children were prone to metal toxicities.