Multi-biomarker forensic assessment of petroleum pollution in a tropical riverine ecosystem using hopanes and polycyclic aromatic hydrocarbons with a wet-dry season comparison.

This study presents a wet-dry seasonal comparison of hopanes and polycyclic aromatic hydrocarbons (PAHs) as molecular markers for the forensic tracing of petroleum pollution in the sediments of the Selangor River, Malaysia. Sediment samples were collected from 13 stations during wet and dry seasons to determine concentrations, sources, and distribution patterns. Hopane concentrations exhibited variation between wet and dry seasons, ranging from 208 to 1492 ng g⁻¹ in the wet season and from 145 to 1737 ng g⁻¹ in the dry season. Complementarily, total PAHs (Ʃ25PAHs) ranged from 215 to 964 ng g⁻¹ (wet) and 203-665 ng g⁻¹ (dry), with notably higher loads observed during the wet season. Diagnostic ratio analysis for hopanes identified Middle East crude oil (MECO) and used crankcase oil as the predominant sources. In contrast, PAH isomeric ratios indicated a dominant contribution from pyrogenic sources (combustion of fossil fuels and biomass), alongside petrogenic inputs. This divergence reveals the river's mixed pollution from direct petroleum and combustion sources. Grain size analysis revealed sediments were predominantly sandy, and total organic carbon (TOC) showed no significant correlation with hopane or PAH concentrations, indicating distribution is governed by chronic anthropogenic input and hydrodynamic seasonal forcing rather than sedimentological processes. Ecological risk assessment using sediment quality guidelines (ERL, ERM, TEL, PEL), toxic equivalent concentrations (TEQ: 15.3-89.7 ng TEQ g⁻¹), and mean ERM quotients (M-ERM-Q: 0.016-0.045) indicated low probability of adverse biological effects. The results provide critical baseline data and demonstrate that single-timepoint assessments underestimate pollution dynamics. This study underscores the necessity of continuous monitoring and provides actionable insights for targeted mitigation strategies, establishing a combined hopane-PAH fingerprint as an essential tool for forensic tracking in tropical riverine environments.