Human health risk assessment of potentially toxic elements in vegetables irrigated with wastewater from an urban market drain in Zaria, Nigeria

Abstract

Abstract The use of wastewater for the irrigation of vegetables is on the increase because of its richness in nutrients and it reduces the pressure on available freshwater resources. Untreated wastewater may, however, be a source of contamination of the vegetables by potentially toxic elements, which may, in turn, constitute a health risk to consumers. Samples of seven vegetables: cabbage, onion bulbs, bitter leaf, jute mallow, spinach, tomato, and lettuce irrigated with wastewater were collected and analysed for potentially toxic elements using Energy Dispersive X-ray Fluorescence. The Target Hazard Quotient (THQ) and Health Index (HI) were determined based on the estimated daily metal intake of Cd, Ni, Pb, Zn, Cu, Fe Mg, and Mn through the consumption of these vegetables. Cancer Risk was assessed for Cd, Ni, and Pb. Except for Mg, for which no guideline value was found for vegetables, the concentration of Cu in cabbage and Mn in tomato were found to be within the permissible limit, whereas Cd, Ni, Pb Zn, and Fe were found to be above the permissible limits of the FAO/WHO in all the vegetables. The Target Hazard Quotient (THQ) shows that adult consumers of all seven vegetables are at risk of non-carcinogenic toxicity of Cd, Ni, and Pb, while in children, the risk extends to Zn, Cu, Fe, and Mn (with tomato as the only exception for Mn). The Health Index being greater than 1in all vegetables means there is a non-carcinogenic risk health risk associated with the consumption of all vegetables by children and adults. The Target cancer Risk shows that adults are exposed to cancer risk from the consumption of all the vegetables due to Ni and Cd contamination (except onion for cadmium), while in children, the risk extends to Pb (except for onion). The consumption of vegetables irrigated with untreated wastewater from the Sabon Gari market drain is an exposure route to potentially toxic elements such as Cd, Ni, Pb, Zn, Cu, Fe, and Mn, with resultant non-carcinogenic and carcinogenic health risks. These health risks were found to be higher in children.