Analysis of soil pollution characteristics and spatiotemporal changes of construction land in Chongqing City

As one of the core cities of the Yangtze River Economic Belt, Chongqing plays an important role in promoting the construction of ecological protection civilization in the Yangtze River Basin. To understand the characteristics and changes in soil pollution in Chongqing after optimizing industrial layout and implementing policies such as the Soil Pollution Prevention and Control Law of China, this study focused on the construction land in Chongqing and analyzed industry category, soil pollution type, pollution degree, and risk level of 138 polluted plots surveyed from 2019 to 2022. The results showed that: (1) Compared to before 2019, the proportion of polluted plots from the top three industries in Chongqing has changed. After 2019, the top three industries were the metal surface treatment and heat treatment processing industry (18.12%), the basic chemical raw material manufacturing industry (15.22%), and the common non-ferrous metal smelting industry (13.04%) in succession. Polluted plots were mainly distributed in the central urban area, which was consistent with the industrial types of main polluted plots in Pearl River Delta, Guangdong-Hong Kong–Macao Greater Bay Area, Yangtze River Delta, and other regions of China. (2) Compared to before 2019, the soil pollution type remained unchanged, but the key pollutants of concern changed. After 2019, heavy metal-organic complex pollution accounted for 67.39% of polluted plots, and polycyclic aromatic hydrocarbons (62.32%), As (52.9%), total petroleum hydrocarbons (51.45%), Cr(35.51%), Pb (32.61%), and Ni (31.16%) were the main pollutants. (3) The Technical Guidelines for the Grading and Evaluation of Soil Pollution Degree of Chongqing Construction Land (Trial) was used to evaluate the pollution degree of the plots. Most plots were moderately and lightly polluted, accounting for about 81%. Among them, the coking, basic chemical raw material manufacturing, pesticide manufacturing, and common non-ferrous metal smelting industries had higher pollution degrees, large pollution ranges and higher soil pollution risk levels.