Phytotoxic Impacts of Illegal Artisanal Refining on Soils in Bayelsa State: Evidence from Two Bio Indicator Crops

Abstract

Illegal artisanal crude oil refining is a major source of soil contamination in the Niger Delta, particularly in Bayelsa State, where petroleum-derived pollutants severely threaten agricultural productivity and ecosystem integrity. In this study, the phytotoxicity of soils impacted by illegal artisanal refining using two bioindicator crops under controlled conditions was assessed. Composite topsoil samples (0–20 cm) were collected from refining-impacted sites and an uncontaminated control location. Soils were characterized for physicochemical properties and total petroleum hydrocarbons (TPH), followed by pot-based phytotoxicity assays conducted across graded contamination levels (0–100%). Plant growth responses were evaluated over defined growth periods using, plant height as an indicator of phytotoxic stress. Results revealed a clear concentration-dependent inhibition of plant growth, with uncontaminated soils supporting sustained growth, while contaminated soils exhibited early growth stagnation and progressive decline. Moderate to highly polluted soils caused significant reductions in plant height indicating severe impairment of soil functionality. The observed phytotoxic effects highlight the disruptive influence of petroleum hydrocarbons on plant development and confirm the unsuitability of artisanal refining–impacted soils for agricultural use without remediation. This study demonstrates the effectiveness of bioindicator-based phytotoxicity assessment as a practical tool for evaluating soil health in petroleum-contaminated environments and emphasis the urgent need for eco-sustainable soil remediation and restoration strategies in Bayelsa State and similar oilproducing regions.