[Variations in Heavy Metal Accumulation Characteristics and Spatiotemporal Identification of Principal Components in the Soils of Tongzhou District from 2005 to 2023].

To enhance the technical support of soil environmental quality monitoring services for territorial spatial planning and the sustainable development of ecological civilization in the Beijing Municipal Administrative Center， this study systematically investigated the changes in heavy metal contamination status and sources in the soils of Tongzhou District over the past two decades. Using inverse distance weighted （IDW） spatial interpolation， the geo-accumulation index， the single-factor pollution index， and the Nemerow comprehensive pollution index， this study conducted a sectional evaluation of the spatial distribution and accumulation characteristics of eight heavy metal elements （As， Cd， Cr， Cu， Hg， Ni， Pb， and Zn） in the soils of Tongzhou District from 2005 to 2023. Correlation analysis， principal component analysis （PCA）， and the positive matrix factorization （PMF） model were employed to identify the principal components and source contributions of heavy metals. The results showed that the concentrations of Cr， Cu， Ni， Pb， and Zn exhibited minimal variation across the four selected years （2005， 2011， 2018， and 2023）， while the median values of Cd， Hg， and Zn exceeded the background values of Beijing. The concentrations of Cd and Hg in top soil were significantly higher than those in deeper layers， with the proportion of Cd enriched sites showing a decreasing trend over the years， whereas Hg exhibited strong spatial heterogeneity. From 2005 to 2011， Cd， Hg， Cu， and Pb were highly enriched in areas with intense industrial activities， incineration sources， and traffic emissions. In 2018， high concentrations of Cd， Zn， Cu， and Pb were primarily distributed in the central and eastern agricultural lands of the study area. Compared to that in 2005， the enrichment extent of Cd， Hg， Cu， Pb， and Zn in 2023 was significantly reduced. In 2005， As， Cr， Cu， Ni， Pb， and Zn mainly originated from natural/agricultural mixed sources， while in 2011， these elements were primarily derived from natural， traffic， and agricultural mixed sources. Cd was mainly associated with industrial sources in both 2005 and 2011. In 2018 and 2023， As， Cr， Cu， Ni， and Pb were predominantly attributed to natural， traffic， and agricultural mixed sources， whereas Cd and Zn were mainly from industrial sources. Hg in soil across all four years was primarily derived from atmospheric deposition. Key factors influencing variations in source contributions included land development intensity， agricultural fertilization rates， traffic emissions， the scale of industrial pollution enterprises， energy combustion emissions， and overall atmospheric pollution levels.