Abstract:
To assess the potential impact of the stability of residual pollutants in the restored pesticide site on secondary utilization, this study systematically analyzes the spatial distribution characteristics and key controlling environmental factors of soil organic pollutants, based on the detection data of a typical restored pesticide production site in Jiangsu Province. A total of 90 soil samples from depths of 0-13 m were analyzed for 138 organic pollutants to reveal the horizontal and vertical distribution characteristics of organic pollutants in the soil. Principal component analysis (PCA) was further employed to explore the vertical migration law of pollutants and their coupling relationship with soil physicochemical parameters. The results showed that phenols (Phes) and amines (Ams) remained significantly in specific areas, while light non-aqueous phase liquids (LNAPLs) were enriched in the dominant area of 0-3 m shallow silt particles due to capillary action, and positively correlated with the proportion of silt particles. Heavy non-aqueous phase liquids (DNAPLs) migrated towards deeper layers driven by gravity, and their penetration was enhanced in 3-6 m alkaline (pH 7.0-10.5) and low clay (11%) soils, with a peak concentration of 243.9 mg/kg. The analysis of the main controlling factors showed that shallow LNAPLs were controlled by capillary entrapment of fine sand particles, while deep LNAPLs were related to the adsorption of clay particles. DNAPLs were regulated by pH in shallow layers and affected by moisture content in deep layers. Although remediation projects had effectively reduced pollution levels, there was still a risk of secondary release due to the continuous migration and local high concentration aggregation of deep DNAPLs. It was recommended to optimize monitoring and remediation strategies according to the depth-specific pollution characteristics, with a focus on the long-term dynamics of deep DNAPLs, to provide a theoretical basis for the safe reuse of the site after remediation.