Understanding urbanization development process and the associated PCBs concentration in urban soils - A genetic...

How to quantify urbanization process and the associated environmental consequence is still a hot issue worldwide. This study established an in situ-controlled experimental system to quantify polychlorinated biphenyls (PCBs) accumulation along an urban-rural gradient in Shanghai, a rapidly urbanizing region. By incorporating landscape-scale urbanized metrics, through correlation analysis and stepwise linear regression analysis a Genetic Algorithm-Based Urbanization Index (GA-based UI) was developed to systematically quantify the relationship between urbanization and PCB accumulation in soils. Key variables contributing to the GA-based UI included road density (0.675), population change index (0.287), industrial land use (0.126), and vegetation indices (0.296). Through random forest and piecewise regression analysis, the study identified critical urbanization thresholds. Piecewise regression revealed that PCB concentrations significantly increased within an optimal UI threshold range of 2.148-3.203, corresponding to a distance of 22.36-26.74 km from the urban center. This finding highlights a critical inflection point in urbanization where PCB accumulation intensifies. This research provides novel insights to understand urbanization development process and the associated spatial distribution of PCB contamination, offering a quantitative basis for urban planning and environmental management.