Co-occurring PAHs and Heavy Metals Drive Bacterial Community Shifts in China’s Beiluo River Riparian Soils

To comprehend the response of bacterial communities to environmental variables, we examined the dispersion patterns and soil attributes associated with polycyclic aromatic hydrocarbons (PAHs) and heavy metals within the soils neighboring the Beiluo River. The structure of bacterial assemblages present along the riverbank was determined through environmental DNA metabarcoding analysis, subsequently conducting an analysis of the relationships between these microbial populations and various environmental factors. The total concentrations of 16 US EPA-listed PAHs in the Beiluo River riparian soils ranged from 3.00 to 131.76 ng/g. Heavy metal concentrations varied by element: chromium (Cr) and zinc (Zn) exhibited the highest levels (123.75–153.46 mg/kg), while cadmium (Cd) and mercury (Hg) were detected at significantly lower concentrations (0.03–0.15 mg/kg). Proteobacteria, Actinobacteriota, and Bacteroidota were found to be predominant, as these phyla are capable of degrading PAHs and exhibit high adaptability to the environment, resulting in their higher abundance compared to other phyla. Several phyla exhibited significant associations with PAHs and heavy metals, which might be explained by the increased toxicity of heavy metals in settings where both PAHs and heavy metals are present together. Moreover, Pielou’s evenness and Simpson’s diversity index exhibited notable variations at varying distances from the riparian zone, likely influenced by the fluctuations in soil moisture content as distance changes. Higher water content correlated with increased bacterial activity and diversity. This study elucidates the complex interplay between bacterial communities and environmental factors in the Beiluo River riparian zone, offering valuable perspectives for the assessment and remediation of contaminated river ecosystems.