Human health risks of heavy metals contamination of a water-soil-vegetables farmland system in Toke Kutaye of West Shewa, Ethiopia

Contamination of foods with heavy metals poses significant threats to human health. In this study, human health risks of heavy metals contaminated vegetables (cabbage, onion and green pepper) from irrigation farmlands in Toke Kutaye, Ethiopia were evaluated. Wet acid digestion of vegetables, supporting soil and irrigation water samples were employed prior to FAAS determination of heavy metals (Fe, Zn, Cu, Mn, Co, Cr, Ni, Cd and Pb). The measured average values of the studied heavy metals ranged from < 0.01-2.52 ± 0.06 mg/L, 2.25 ± 0.19-131.31 ± 0.13 mg/kg, and < 0.01-18.21 ± 0.17 mg/kg for water, soil and vegetable samples, respectively. The average concentration of the studied heavy metals in the vegetable samples were arranged in the order of Zn>Cu>Fe>Mn>Co>Ni>Pb>Cr>Cd. The heavy metals accumulation in the vegetables followed the order of cabbage > onion > green pepper. The mean values of Pb in the vegetables exceeded the WHO/FAO guideline value. The possible sources of the heavy metals were agrochemicals, domestic sewage wastes, manures and geogenic processes. The hazard quotient (HQ) and hazard index (HI) based human health risk assessment results indicated that the individual metals and their mixture could pose insignificant non-carcinogenic risk (HQ and HI < 1) to consumers. However, cancer risk assessment values for the individual Ni metal, and the mixture of Ni, Cr and Pb exceeded the threshold limit for both children and adults. These results highlight possible chronic carcinogenic risks due to exposure to heavy metals via consumption of contaminated vegetables from the study area, which requires the concern of the consumers and regulatory bodies.