Eco-remediation of light petroleum-impacted soils: a case for sea buckthorn (Hippophae rhamnoides L.) application

Abstract

This study investigates the use of Hippophae rhamnoides L. (sea buckthorn) for phytoremediation of oil-contaminated soils in the Balakhani Oil Field, Azerbaijan. The region is affected by petroleum extraction, resulting in significant soil contamination. To assess the remediation potential, 40 soil samples were collected and analyzed for total petroleum hydrocarbons, heavy metals, and physicochemical properties. TPH concentrations ranged from 6% to 9%, indicating moderate contamination. Soil pH varied between 6.94 and 7.93, reflecting a neutral to slightly alkaline environment suitable for plant growth. Heavy metals including lead (Pb), cadmium (Cd), arsenic (As), and nickel (Ni) were detected within permissible limits, although Pb showed slightly elevated levels (20-31 mg/kg). The presence of polycyclic aromatic hydrocarbons pointed to soil toxicity concerns. Biochemical analyses of sea buckthorn’s roots, stems, leaves, and fruits revealed high levels of antioxidants such as carotenoids, phenolic compounds, and vitamins C and E, which are essential for combating oxidative stress caused by hydrocarbons. Amino acids like proline, glutamine, and asparagine were abundant, aiding the plant’s stress tolerance and detoxification mechanisms. Elemental analysis via Atomic Absorption Spectroscopy (AAS) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) demonstrated significant uptake of microelements vital for plant metabolism and remediation processes. Over a six-month period, sea buckthorn reduced soil TPH levels by up to 60%. This decline correlated with enhanced microbial biomass (7-15 mg/g) and improved soil properties including organic carbon (16-25%) and cation exchange capacity between 9 and 14 cmol/kg. The plant’s root system contributed to soil stabilization and nutrient cycling, promoting recovery of essential elements like nitrogen and phosphorus. Increased microbial activity, stimulated by root exudates, likely accelerated hydrocarbon degradation through symbiotic interactions. However, hydrocarbon reduction efficiency was influenced by initial pollutant concentrations, with higher contamination requiring longer remediation. Sea buckthorn’s resilience is supported by its antioxidant defense system and nutrient acquisition capabilities. The plant’s deep roots not only absorb contaminants but also prevent soil erosion and immobilize heavy metals, reducing their ecological risks. Economically, sea buckthorn phytoremediation proved cost-effective compared to conventional treatments, suggesting a sustainable option for environmental restoration. In conclusion, sea buckthorn offers a promising phytoremediation approach for oil-polluted soils, effectively lowering hydrocarbons while enhancing soil health and ecosystem stability. Further studies should optimize treatment conditions and explore genetic traits to improve remediation performance.