Abstract
Background:
Polycyclic aromatic hydrocarbons (PAHs) are among the environmental pollutants that are classified according to the United States Environmental Protection Agency (USEPA) as a priority concern. Generally, the primary source of PAHs is the incomplete combustion of organic matter from sources like coal, oil, gas, wood, tobacco, and garbage. In addition, the natural sources that may cause PAH-environmental pollution are volcanic eruptions and natural oil seepage. Thus, a PAH-polluted environment poses risks to human and animal health. Among the compounds that were monitored in great concentrations in water and soil environments are naphthalene (Nap) and phenanthrene (Phe).

Aim:
This study aimed to remediate the environmental contamination of a PAH mixture using a minimal and effective dosage of titanium dioxide nanoparticles (TiO₂ NPs).

Methods:
A commercially available TiO₂ NPs were characterized using transmission electron microscopy and particle size distribution, while X-ray diffraction was used to characterize both the tested soil mineralogically and the TiO₂ NPs. In addition, the remediation efficacy of different TiO₂ NPs concentrations (125, 250, and 500 mg l−1) with and without sunlight exposure was investigated and evaluated by Gas Chromatography-Mass Mass Spectrometry.

Results:
The results revealed that by increasing the TiO₂ NPs concentration, the remediation efficacy was increased. When the TiO₂ NPs concentration was increased from 125 to 500 mg l−1, Nap removal efficacy was increased from 21% to 92% under dark conditions from water. In addition, the removal efficacy of Phe without sunlight exposure was elevated from 44.63% to 73.53% from soil when TiO₂ NPs dosages were increased from 125 to 500 mg l−1, respectively.

Conclusion:
TiO₂ NPs have potent soil remediation efficacy, especially under dark conditions. The following factors should be considered for the best remediation efficacy: the source of light, catalyst concentration, and the pollutant itself. To the best of our knowledge, this is the first study to offer an environmentally sustainable, practical, and economically feasible solution for remediating polluted environments, especially subsurface soil, using low, safe TiO₂ NP doses.

Key words: Drainage water remediation; Naphthalene; Phenanthrene; Photocatalysis; Soil remediation; TiO₂-NPs.