Phenanthrene release-migration characteristics and potential influencing mechanisms from paddy soil to overlying water under bioturbation in a rice-fish coculture agroecosystem

Currently, polycyclic aromatic hydrocarbons (PAHs) such as phenanthrene (Phe) in rice-fish (RF) coculture paddy fields in Northeast China pose widespread environmental pollution risks. This study constructed experimental microcosm systems to explore the release-migration rules and reveal the potential influencing mechanisms of Phe from paddy soil to overlying water under bioturbation in an RF coculture agroecosystem in this area. (1). The release of particulate Phe (P-Phe) and dissolved Phe (D-Phe) was significantly promoted by bioturbation (p<0.05). The results of Pearson correlation analysis revealed strong correlations between P-Phe and total suspended solids (TSS), D-Phe and dissolved organic carbon (DOC) (p<0.05). (2). The adsorption process of Phe at the paddy soil-overlying water interface conformed to the competitive adsorption-solubilization (CAS) model of large-molecule biological dissolved organic matter (Bio-DOM) at low concentrations (7 mg/L) (L-CBio-DOM-LM-CAS) and the coadsorption and accumulation model of small-molecule Bio-DOM at high concentrations (45 mg/L) (H-CBio-DOM-SM-CAA). (3). Ultraviolet fluorescence (UV-FS) tracing technology and reaction diffusion modeling were used to qualitatively and quantitatively simulate the migration pathway of Phe-containing paddy soil particles. The maximum fluorescent particle (f-ps) concentration of Phe migration in paddy soil was 8.23%, and the maximum bioturbation diffusion coefficient (D-b) was 23.6 x 10(-3) cm(2)/d. Bioturbation significantly altered the physicochemical properties of paddy soil (p<0.05). The results of principal component analysis (PCA) showed that particle size (<0.05 mm) is the key factor causing the Phe maximum migration concentration to be 68.39 ng/g in paddy soil. This study will provide an important research basis for the prevention and control of secondary release and migration of pollutants under bioturbation in RF coculture agroecosystems.