Nutritional Quality and Heavy Metal Accumulation in Four Leafy Vegetables Cultivated on Abandoned Dumpsite versus Conventional Farmland in Offa, Nigeria

Abstract

Background: Leafy vegetables constitute a vital dietary component across sub-Saharan Africa, yet their cultivation on contaminated soils raises serious food safety concerns, particularly regarding heavy metal accumulation and associated health risks. Aim: This study compared the proximate nutritional composition and heavy metal content of four commonly consumed leafy vegetables grown on an abandoned dumpsite and a conventional farmland in Offa, Kwara State, Nigeria. Methods: Freshly harvested samples of Corchorus olitorius L., Abelmoschus esculentus L., Amaranthus hybridus L., and Celosia argentea L. were collected from both sites. Proximate composition was determined using standard AOAC methods, and heavy metal concentrations—iron (Fe), copper (Cu), zinc (Zn), nickel (Ni), lead (Pb), and cadmium (Cd)—were quantified in both vegetable tissue and soil by atomic absorption spectrometry (AAS). Results: Vegetables from the dumpsite recorded higher moisture (up to 29.5%), ash (up to 30.0%), and protein (up to 24.72%) contents compared with conventional-site counterparts. Carbohydrate levels were significantly higher at the conventional site. Amaranthus hybridus L. exhibited the highest iron content at the dumpsite (8.25%) compared with the conventional site (6.12%; p = 0.008). Lead and cadmium were not detected in any vegetable sample, and nickel was detected only as a trace in Celosia argentea L. (0.07%). Soil at the dumpsite contained markedly elevated Fe (1140.22 mg/L), Zn (29.58 mg/L), and Pb (2.85 mg/L) relative to the conventional site. Conclusion: All vegetable species displayed heavy metal concentrations below WHO permissible thresholds, indicating they are safe for human consumption. Nevertheless, ongoing monitoring and regulatory oversight of dumpsite-cultivated vegetables are strongly recommended.