Decoding China's urban topsoil contamination patterns through magnetic parameters and socio-economic drivers from monocentric to polycentric urban systems.

This study focuses on Hangzhou, China, where 494 topsoil samples were analyzed using environmental magnetism to assess their magnetic parameters and identify pollution influencing factors. An innovative framework integrating environmental magnetism with socio-economic analysis is developed to investigate the magnetic response characteristics of urban topsoil pollution and their socio-economic drivers. Results indicate that magnetic minerals in Hangzhou's topsoil are predominantly ferromagnetic, with an average χ value of 103.80 × 10mkg. Significant increases in regional magnetic susceptibility are attributed to industrial activities and traffic-related emissions. Nationwide analysis reveals a distinct non-linear relationship between topsoil magnetic susceptibility and socio-economic development, enabling the classification of cities into three types based on their characteristic patterns: (1) Regional growth pole cities (e.g., Beijing, Shanghai, Hangzhou, Fuzhou, Ningbo, Xi'an). These cities achieve decoupling of magnetic susceptibility from economic growth through industrial upgrading. (2) Mineral resource-dependent cities (e.g., Wuhai, Karamay, Jiayuguan, Baotou) display polarization between "high output value-low magnetic response" and "high magnetic response-low development"; (3) Developing cities. The strengthened interconnection between magnetic susceptibility and economic factors in developing cities reflects a concurrent rise in urbanization levels and ecological pressures. The significant spatial heterogeneity observed in the relationship between urban topsoil magnetic susceptibility and socio-economic factors highlights the distinct potential of environmental magnetism to clarify the mechanisms driving anthropogenic pollution impacts in urban surface environments. Consequently, environmental magnetism serves as an efficient tool not only for mapping pollution distribution but also for establishing a framework connecting environmental magnetism with socio-economic factors, offering a methodological foundation for optimizing urban development and balancing ecological protection with economic growth.