Spatiotemporal differentiation mechanisms of groundwater PAH-PAE co-contamination: Environmental drivers and seasonal...

Environmental contamination with combined conventional and emerging organic contaminants presents a critical global challenge. However, their composite contamination in groundwater remains poorly understood. This study examined the co-contamination mechanism of polycyclic aromatic hydrocarbons (PAHs) and phthalate acid esters (PAEs) in groundwater. It revealed the seasonal variations in PAH and PAE concentrations and the microbial community characteristics across different contamination gradients, and evaluated the key environmental drivers using correlation analysis and machine learning methods. The results showed that PAH contamination was dominated by 2-4 ring congeners (>95 %) during the wet season (WS) and dry season (DS). PAE contamination was mainly due to di-n-butyl phthalate (DnBP) and di (2-ethyl) hexyl phthalate (DEHP). The concentrations of contaminants in groundwater tended to be lower during DS compared to WS. Environmental factor significance screening identified oxidation-reduction potential (ORP) and pH as critical abiotic indicators for assessing and quantifying groundwater contamination with PAHs and PAEs, respectively. Additionally, seasonal differences were observed in diversity, indicator species and metabolism-related functional genes for microbial community response to PAH and PAE contamination. Groundwater table fluctuations were recognized as a potential regulating mechanism dominating seasonal changes in organic contamination and microbial community characteristics. These findings offer valuable insights for managing complex organic-contaminated groundwater.