4. Conclusion
Multivariate statistical analysis, multiple spatial distribution indicators,, correlation analysis, , and correlation analysis have been used for evaluating space-time patterns underlying heavy metal pollution in arable soils in typical rapidly urbanizing areas of China and to assess the relationships between pollution sources and environmental variables of soil heavy metals. Compared with 2008, the accumulation trend of Cd, As and Cr contents in arable soil was obvious in 2017, with the mean contents exceeding the soil background values by 1.69, 1.43, and 1.26 times, respectively, and the relative increases RI were all in areas exceeding 100%. While the levels of lead and mercury remain stable, heavy metals from arable land soils were strongly affected from human industry and agriculture activities. The block-base ratios [C0/(C0 +C )] ranged from 50% to 93.5% in both periods, and the block-base ratios of all five soil heavy metals increased to some extent, indicating that the spatial autocorrelation of these elements decreased in 2017, and the variation was enhanced by anthropogenic random disturbance, forming a structural spatial distribution for an example of heavy metal Cd. Correlation analysis and PMF analysis showed four potential sources. However, after 10 years of rapid urbanization, heavy metal sources in arable land have changed considerably due to human activities, among which: 92.1% of Hg elements came from agricultural sources, 65.8% of As concentrations came from industrial activities such as sewage pollution, 66.3% of Cr came from the soil parent material, and transportation activities represented major contributors to Cd and Pb, contributing 59% and 45%, correspondingly, in 2008. and 45%.The source of Hg changed in 2017, 98.1% came from medical equipment, the source of As was the same as in 2008, but the contribution rate increased by 17.7%, 50.1% of Pb and 46.1% of Cr came from human activities, including the source of 2008 while increasing the source and contribution rate of pollution, and Cd changed from the source of soil parent material to industrial sources such as gold refining accounting for 85.5%.