Effect of spent engine oil (SEO) contaminated soil on the phytobiomass and nutritional composition of groundnut (Arachis hypogaea)

Abstract

The improper disposal of spent engine oil (SEO) threatens agricultural productivity and food safety. This study examined the effects of SEO-contaminated soil on the growth, nutritional quality, and heavy metal content of groundnut (Arachis hypogaea). A pot experiment employed a completely randomized design with five SEO concentrations; 0 (control), 50, 150, 250, and 350 ml/kg soil. Results showed a significant (p < 0.05) dose-dependent reduction in all growth parameters. The highest concentration (350 mL/kg) reduced plant height, root length, and dry biomass by 72%, 66%, and 94%, respectively. Seed analysis revealed a significant decline in valuable crude protein (26.5% to 18.9%) and crude fat (48.2% to 37.6%), with a concurrent increase in carbohydrates. Critically, SEO led to heavy metal bioaccumulation in seeds. Concentrations of Lead (Pb) and Cadmium (Cd) surpassed WHO/FAO safety limits (0.3 and 0.1 mg/kg) at the 150 mL/kg level, reaching 2.10 and 0.87 mg/kg at the highest concentration. The study concludes that SEO contamination severely impaired groundnut growth, reduced its nutritional value, and rendered seeds unsafe for consumption due to toxic metal accumulation, highlighting an urgent need for improved waste oil management and soil remediation.