Pollution transfer and environmental health implications: network evolution and proximity mechanisms in the Yangtze River Delta, China.

Pollution transfer across regions has become an important source of environmental health risks and spatial health inequalities, yet its underlying transfer mechanisms and structural pathways remain insufficiently understood. This study investigates the spatiotemporal evolution of pollution transfer in China's Yangtze River Delta (YRD) from both national and local perspectives. Using off-site environmental penalty data from large-scale enterprises between 2012 and 2023, we construct pollution transfer networks and apply social network analysis and the geographical detector method to identify structural characteristics and multidimensional driving mechanisms. This study addresses three interrelated challenges: identifying pollution transfer relationships from regulatory records, disentangling multidimensional proximity mechanisms and their interaction effects, and assessing whether pollution transfer structurally reinforces environmental health inequality across cities, which are tasks that are methodologically demanding due to the hidden nature of transfer processes and the nonlinearity of proximity effects. The results reveal that the pollution transfer network in the YRD has continuously expanded, exhibiting a pronounced core-periphery structure centered on Shanghai, Hangzhou, Nanjing, and other core cities, with strong internal linkages and outward diffusion at the national scale. Pollution transfer intensity has increased over time and displays significant proximity effects. Multidimensional proximity factors jointly shape pollution transfer, with economic proximity dominating intra-regional transfers, while institutional and technological proximity play a more critical role in extra-regional transfers. Notably, public health proximity exhibits limited independent explanatory power but significantly enhances pollution transfer when interacting with economic and institutional factors, suggesting a structural linkage between pollution redistribution and environmental health inequality. Scientifically, this study advances the understanding of pollution transfer as a networked and interaction-driven process. Practically, the findings provide quantitative support for regional collaborative governance and integrated environmental and health management in the YRD.