Biochemical analysis of the Caspian Sea sediments: Implications for environmental pollution and bioremediation

The Caspian Sea, Earth's largest enclosed inland water body, faces significant environmental challenges due to anthropogenic pollution. This study aimed to assess pollution levels in the Caspian Sea sediments and evaluate the potential for microbial bioremediation. Sediment samples were collected from 15 sites along the Caspian coastline. Polycyclic aromatic hydrocarbons (PAHs) and heavy metals (lead and cadmium) were quantified using GC-MS and AAS, respectively. Microbial community analysis was performed through 16S rRNA gene sequencing. Native bacterial strains were isolated, characterized for their pollutant degradation capabilities, and tested in laboratory-scale bioremediation experiments. Total PAH concentrations ranged from 119.5 to 2032.7 μg kg-1 dry weight, while mean concentrations of lead and cadmium were 67.9 and 2.15 mg kg-1, respectively. Microbial analysis revealed diverse communities dominated by Proteobacteria, with genera known for hydrocarbon degradation (e.g., Pseudomonas and Alcanivorax) showing strong positive correlations with contaminant levels. Isolated bacterial strains demonstrated remarkable PAH degradation (up to 87% for naphthalene) and heavy metal removal capabilities. In microcosm experiments, bacterial consortia achieved up to 89.7% PAH removal and 61.4% lead removal after 30 days. This study provides comprehensive insights into the Caspian Sea sediments' pollution status and microbial ecology, revealing significant contamination and remarkable potential for intrinsic bioremediation. The identified native bacterial strains and consortia offer promising avenues for developing tailored bioremediation strategies, although further field-scale trials are necessary to validate their effectiveness under real-world conditions.