This study aims to understand the sources and pollution of soil heavy metals. Taking Taicang City, Jiangsu Province as an example, the soil surface samples were collected to conduct the heavy metal content analysis. A novel receptor (UNMIX) model was selected to analyze the source and contribution of soil heavy metals. Geoaccumulation index and multivariate geostatistical techniques were used to quantitatively evaluate for the spatial prediction of heavy metal pollution. The results showed that: (1) The contents of As, Cd, Cr, Cu, Hg, Ni, and Zn were relatively high, exceeding the background values of soil heavy metals in the study area. The enrichment degree of Cd, Cu, Hg, Pb, and Zn was relatively high, while there were the normal enrichment coefficients of As, Cr, and Ni similar to the natural basic level. Except for Cr, the average content of the rest heavy metal elements exceeded the background values of soil heavy metals. The coefficients of variation for Cu and Zn were 0.60 and 0.64, respectively, indicating a high level of variation and a high skewness state. (2) The distribution trend of As and Pb gradually increased from west to east, with the highest content in Chengxiang and Ludu towns. The soil was mainly developed from basalt and metamorphic rocks, containing a certain amount of Ni element. There was the similar pattern of Cd, Cr, Cu, and Zn spatial distribution, where the high value areas were located in Shuangfeng Town and Chengxiang Town in the southwest. Overall, the high and low value areas of the eight heavy metal elements were distributed alternately with the island-like spatial feature, indicating the negative effects of human activities on the soil environment. (3) Soli heavy metals were comprehensively affected by transportation-industrial, natural-agricultural, industrial-natural, and agricultural-industrial sources, with the contribution rates of 35.18%, 27.32%, 20.26%, and 17.24%, respectively. Among them, Hg, Pb, Ni, Cu, and Zn were mainly from transportation-industrial sources, Cr, Zn, and Cu were from natural-agricultural sources, As and Ni were from industrial-natural sources, and Cd was from agricultural-industrial sources. (4) The ground accumulation index of Hg was ranked first among all elements with a mean of 1.12. A high degree of artificial accumulation of Hg was greatly influenced by non-natural factors. The elements with a ground accumulation index greater than 0 were Ni and Cd, with values of 0.68 and 0.42, respectively. The pollution levels of As, Cu, and Zn were in the middle. The soil condition was less affected by Cr and Pb. (5) The pollution areas of Ni, Cu, and Hg were the largest, reaching 107.42, 75.56, and 55.02 km² respectively. The area of Cd pollution was 342 km² (accounting for 8.6% of the total area) that distributed in industrial, tailings surrounding, and urban suburbs. The potential pollution space was distributed in patches, which should be given more attention. At the same time, it was also necessary to strictly prevent the expansion of Cr and Pb pollution space. This soil investigation can provide the scientific basis for the soil environmental management and heavy metal pollution remediation.

This study aims to explore the spatial distribution of soil heavy metals in the Main Stream of the Yangtze River. The contents of As, Cd, Cr, Cu, Pb, Ni and Zn were collected from the 741 topsoil samples. The positive matrix factorization (PMF) model was used to analyze the sources of heavy metals. The geoaccumulation index and potential ecological risk index were selected to assess the pollution and ecological risks of soil heavy metals. The results showed that: 1) The average contents of soil heavy metals As, Cd, Cr, Cu, Ni, Pb, and Zn were 13.50, 0.49, 79.96, 40.85, 34.33, 32.65, and 103.72 mg/kg, respectively. Except for Ni, the maximum content of the rest elements already exceeded the screening value, according to the national standard of soil environmental quality. But the average content of each element was within the screening value. Meanwhile, the accumulation of As, Cd, and Cu was found in the highest exceeding rate and severe pollution. The coefficient of variation of each element ranged from 0.34 to 2.20, where Cd and Cu shared the coefficient of variation higher than 1.0, indicating the uneven distribution and significant influence from local pollution sources. 2) The content of various heavy metals presented a strip-shaped spatial pattern with multiple high-value areas. The soil environmental quality was negatively affected by human activities. There were similar distribution patterns of As and Pb, Cd and Cr, as well as Cu and Zn. The spatial distribution of Cd differed significantly from As element. Specifically, the areas of high-value Cd were in Wuhan and Ezhou, Hubei Province, while the rest were in Anqing and Chizhou, Anhui Province. The content of soil heavy metals ranged from the middle and lower to the higher level in the study area, such as chemical, smelting, printing, and dyeing industries. 3) The natural, industrial emission, transportation, and agricultural production sources contributed the rates of 36.65%, 28.48%, 20.07%, and 14.80%, respectively. Among them, Cd was related to industrial activities, Pb and Zn were from transportation emissions, Cr and Ni were closely related to natural sources, as well as As and Cu were from agricultural production. Overall, 63.35% of soil heavy metals were from human activities. The important sources were chemical, steel, transportation, and agricultural production. 4) The highest degree of Cd pollution was 81.88% of points, indicating a level of mild pollution or above. Furthermore, more than 40% of the sites were contaminated with As, Cu, Ni, and Pb with a moderate level of pollution. More than 75% of the sites were not contaminated with Cr and Zn, where the soil condition was less affected by these two heavy metals. The average of the single ecological risk index was ranked in descending order as follows: Cd>As>Ni>Cu>Pb>Zn>Cr. The average comprehensive ecological risk index was 63.17 at a mild risk level, indicating the spatial distribution pattern. The soil investigation can provide the scientific basis for soil environmental management and heavy metal pollution remediation.