Heavy metals in five leafy vegetables from urban and periurban sites in Ngaoundere, Cameroon

Heavy metal concentrations were estimated in five leafy vegetables (Solanum nigrum, Brassica oleraceae, Lactuca sativa, Amaranthus hybridus and Corchorus olitorius) from urban and periurban sites in Ngaoundere (Cameroon) using an Atomic Absorption Spectrophotometer (AAS). Vegetable samples were collected at the two stages of maturity: stage I (60 days) and stage II (90 days) for analysis. The results showed that the concentrations of heavy metals in all vegetables were greater in urban site than in periurban site. The highest concentrations of Fe (673.92 mg/kg DW), Cu (10.42 mg/kg), Cd (1.70 mg/kg DW), and Pb (31.75 mg/kg DW) were recorded in Lactuca sativa, Zn (94.60 mg/kg DW) in Solanum nigrum, and Ni (16.91 mg/kg DW) in Corchorus olitorius. The concentrations of Cu, and Pb were greater in roots than in aerial parts, while Fe, Cd, Ni and Zn concentrations were greater in aerial parts than in roots. Some of the concentrations of Ni, Zn and Pb in crops reached the critical level for plant growth. In general, the results indicated that the consumption of leafy vegetables harvested at the stage II potentially provides the greatest amount of heavy metals. The transportation index (Ti) decreased in vegetables harvested at the stage II for Fe, Cu, Cd and Zn but slightly increased for Ni and Pb, suggesting that heavy metal transportation from roots to aerial parts depends on the plant phenology and metal species. In all farms and at the two stages of maturity, the lead concentrations in all vegetables were more than the FAO/WHO maximum recommended level in leafy vegetable for human consumption. Moreover, all vegetables had some Cd concentrations that were higher than limits set by FAO/WHO. So, they are not suitable for human consumption.