Phytoextraction Potentials and Early Growth Performance of Groundnut (Arachis Hypogaea L) Seedlings on Spent Engine Oil Contaminated Soil Around Nigeria Police Academy Kano

Soil contamination with spent engine oil (SEO) poses a major environmental problem due to elevated concentrations of petroleum hydrocarbons and heavy metals. This study evaluated the phytoextraction potential and early growth performance of groundnut (Arachis hypogaea L.) seedlings on SEO-contaminated soils collected around the Nigeria Police Academy, Kano. A completely randomized design with three SEO levels (4, 8 and 12% w/w) plus a non-contaminated control was used for six weeks. Pre-experiment soil analyses showed markedly increased total petroleum hydrocarbons (TPH) (4,250–12,900 mg kg⁻¹) and heavy metals (Pb 8.9–23.7 mg kg⁻¹; Cd 0.14–0.30 mg kg⁻¹; Zn 28.6–57.2 mg kg⁻¹) compared with the control. Groundnut emergence, height and biomass decreased significantly with increasing SEO, yet seedlings survived even at 6% contamination (emergence 53%; shoot dry weight 0.58 g plant⁻¹). Post-experiment analyses showed substantially greater TPH and metal reductions in planted soils than in unplanted controls (30% compared to ≤12% TPH removal; Pb, Cd and Zn removal 22 to 33% compared to ≤9%. Heavy metals accumulated predominantly in roots, with bioconcentration factors (BCF) >1 for Pb and Zn and translocation factors (TF) of 0.66–0.80, indicating moderate translocation to shoots. Derived uptake values increased with contamination level (Pb 27.9–47.4 µg plant⁻¹; Zn 92.6–152.1 µg plant⁻¹). Soil biological indicators (dehydrogenase and catalase activities) were significantly higher in planted soils, evidencing rhizosphere recovery during phytoremediation. These findings demonstrate that groundnut seedlings tolerate moderate SEO contamination, accumulate heavy metals in roots and shoots, and accelerate TPH and metal removal relative to natural attenuation. Groundnut therefore showed promise, as a cost-effective species for initial remediation or stabilization of SEO-polluted soils.