Toxicological impact of silver nanoparticles on soil microbial indicators in contaminated soil (pot experiment)

Silver nanoparticles (AgNPs), recognized for their unique properties, are widely applied in fields such as agriculture, biotechnology, food security, and medicine. However, concerns persist regarding their interactions with living organisms and potential environmental impacts. This study investigates the effects of AgNPs on key soil microbial indicators that are essential for ecological functioning. A pot experiment was conducted with varying concentrations of AgNPs (0, 30, 60, 120, 240 mg kg^-1) and incubation periods (0, 15, 30, and 45 days). The results demonstrated a substantial reduction in microbial indicators, including bacterial and fungal colony-forming units (B.CFUs and F.CFUs), total microbial population (MPN), microbial basal respiration (BR), substrate-induced respiration (SIR), and microbial biomass carbon and nitrogen (MBC and MBN). These declines were more pronounced with increasing AgNP concentrations and prolonged incubation times, particularly within the first 15 days. Notably, even at lower concentrations, AgNPs exhibited significant toxicity to microbial indicators. The most severe impact was observed at 240 mg kg^-1 of AgNPs after 45 days, where B.CFUs, F.CFUs, MPN, MBC, and MBN showed substantial declines, with the greatest reduction at the highest concentration. Additionally, the microbial quotient (qmic) decreased by 66%, and variations in the respiratory quotient (qCO₂) were observed. Strong positive correlations were found among the microbial indicators, highlighting their interconnected responses to AgNP exposure. Overall, the study emphasizes the significant toxicity of AgNPs, raising concerns about their potential to disrupt soil ecosystems.