Rainfall-driven dynamics of the composition and toxicity impact of organic compounds in soil interflow in mountainous...

Soil interflow, a critical pathway for pollutant transport in mountainous regions, remains poorly characterized in terms of its organic contaminant composition and associated ecological risks. This study employed non-targeted screening (NTS) coupled with zebrafish embryo toxicity testing (ZET) to investigate the dynamics of the composition and toxicity impact of organic pollutants across four hydrological interflow stages (initial, early, mid, and late) following rainfall events in China's southwestern hilly region. We identified 173 organic compounds, predominantly aliphatic and aromatic species, with their distribution and toxicity significantly influenced by rainfall-driven transport mechanisms. Notably, compounds with aromatic rings or acidic functional groups (e.g., 2,4-xylidine) exhibited strong correlations with embryotoxicity, highlighting their role as key risk drivers. Temporal analysis revealed three distinct pollutant transport patterns: inverse parabola (e.g., aliphatic amines), parabola (e.g., aromatic amides), and monotonic trends (e.g., steroids) in the peak area profiles, reflecting solubility- and structure-dependent fate processes. The integration of NTS and ZET uncovered previously overlooked risks, emphasizing the need for targeted monitoring of persistent aromatic and heterocyclic contaminants in interflow-dominated ecosystems. These findings underscore the urgency of implementing soil conservation and pollution mitigation strategies to safeguard mountainous water resources.