Assessment of the Level of Heavy Metals in Irrigation Water, Farm Soil, and Vegetables Grown in Gobbiya Dam, Bogoro Local Government Area Bauchi State, Nigeria.

Abstract

This study assessed heavy metal concentrations (Pb, Cd, Cu, Cr, As, Fe, Ni) in irrigation water, farm soil, and four vegetable species (kenaf, chili pepper, tomato, and spinach) cultivated around Gobbiya Dam, Bogoro Local Government Area, Bauchi State, Nigeria. Samples were collected from irrigation water, agricultural soil, and different plant parts (roots, stems, leaves, and fruits) and analyzed using Atomic Absorption Spectrophotometry (AAS). Results revealed significant regulatory violations in both soil and water sources, with soil chromium (0.116 mg/kg) exceeding WHO limits (0.10 mg/kg), while irrigation water showed elevated arsenic (0.014 mg/L) and cadmium (0.024 mg/L) above WHO standards (0.01 mg/L and 0.01 mg/L respectively). Soil contamination factors indicated very high contamination for both iron (CF = 10.62) and cadmium (CF = 8.30), while moderate contamination was observed for nickel (CF = 1.66) and chromium (CF = 1.16). Arsenic and lead showed low contamination levels (CF = 1.00 and 0.74 respectively), while copper exhibited the lowest contamination factor (CF = 0.08). Chili pepper demonstrated the highest heavy metal accumulation, particularly cadmium in fruits (0.295 mg/kg), exceeding WHO vegetable safety limits (0.2 mg/kg). Tomato fruits contained arsenic levels (0.055 mg/kg) matching WHO limits, while spinach showed efficient translocation of most metals to leaves. Translocation factor analysis revealed nickel as the most mobile metal across all species (TF range: 1.454 – 4.639), while bioaccumulation factors indicated significant bioaccumulation for arsenic in tomato fruits (BAF = 5.586) and cadmium in chili pepper fruits (BAF = 3.565). Leaves emerged as the primary accumulation site for iron, nickel, and cadmium across all species, while copper showed preferential root sequestration in kenaf and chili pepper. The study concludes that current agricultural practices around Gobbiya Dam pose significant food safety risks due to heavy metal contamination, with chili pepper and tomato fruits presenting the greatest concern for human consumption. Regular monitoring of irrigation water, soil, and vegetable produce for heavy metal contamination should be institutionalized, particularly in dry-season farming areas relying on dam water. Additionally, phytoremediation strategies should be adopted using crops such as kenaf, which demonstrated root retention and lower metal translocation to aerial parts, thus acting as a potential sink for toxic elements