Accumulation of Heavy Metals in Vegetables Grown on Wastewater Irrigation Farms in Bauchi L.G. A.

Abstract

Vegetables provide minerals and nutrients essential for both humans and animal well-being. The continuous application of waste water for irrigation of these vegetables may likely increase their heavy metal load and contamination. The aim of this study is to investigate the concentration of heavy metal (Pb, Ni, Cd, Fe, Cr, Cu and Zn) accumulated in three different kinds of vegetables (onion, tomatoes, spinach) grown in some commercial wastewater irrigated farms in Bauchi L.G.A., and their possible pollution index. All the collected samples were analyzed for Cd, Cu, Pb, Ni, Fe, and Zn using the Atomic Absorption Spectrophotometer; and the measured parameters were compared to the WHO/FAO permissible limits. Results of analysis indicated that the accumulation of the metals in the study vegetables varied considerably. The ranges of the concentration (mg/kg) of Ni, Fe, Pb, Cu, Zn and Cd in the onions in all the study sites are 0.27 – 1.44, 1.00 – 2.25, 0.61 – 1.96, 2.14 – 3.25, 1.65 – 3.96 and 1.99 – 6.51 respectively.  For tomatoes, the concentrations (mg/kg) are 1.22 – 2.29, 0.69 – 1.23, 0.44 – 1.38, 2.71 – 10.61, 1.65 – 6.32 and 2.32 – 11.67, while in spinach, the levels in mg/kg were 0.71 – 1.32, 1.07 – 2.01, 1.00 – 1.56, 1.34 – 7.22, 0.90 – 5.79, 2.84 – 4.60. In all the sites, the level of Cd and Pb exceeded the WHO/FAO permissible limits of 0.30mg/kg and 0.21mg/kg respectively. The level of Ni in tomatoes in Bayara (1.93±0.02 mg/kg) and Kofar Idi (2.29±0.01 mg/kg) also exceeded the WHO/FAO permissible limits of 1.50mg/kg. MPI values obtained were greater than 1. Onions and tomatoes grown in Kofar Idi had the highest MPI levels (2.228, 2.201) while Spinach in Bayara had the highest MPI (2.517). The observed levels of metal, above the safe limits, and the MPI of the sampled vegetables indicate that these vegetables may not be suitable for human consumption.