[Quantifying the Contribution of Soil Heavy Metals to Ecological and Health Risk Sources].

Quantifying the risk of soil heavy metal sources can identify the main pollution sources. It can provide a scientific basis for reducing the ecological and human health risks of soil heavy metals. Taking the shallow soil in a Pb-Zn mine watershed in northern Guangxi as a research object， ecological and human health risk assessments were conducted using potential ecological risk assessment （RI） and human health risk assessment （HRA）， and the source apportionment of soil heavy metals was completed using the absolute principal component-multiple linear regression receptor （APCS-MLR） model and random forest （RF） model. Then， a combined risk assessment model， consisting of RI， HRA， and APCS-MLR， was used to quantify the risk of soil heavy metal sources. The results showed that the contents of Pb， Zn， Cu， and Cd exceeded the environmental screening values for agricultural land with mean values of 342.77， 693.34， 61.27， and 3.08 mg·kg-1， respectively， and there was a certain degree of contamination. Pb， Cr， and As were the main health risk impact factors， with higher health risks for children than for adults. Three sources were identified： mining activities （Source Ⅰ）， soil parent material sources and original formation （Source Ⅱ）， and unknown sources. Pb， Zn， Cu， and Cd were mainly derived from Source Ⅰ， and Cr and As were controlled by unknown sources and Source Ⅱ. The source risk assessment results of soil heavy metals indicated that the potential ecological risk and non-carcinogenic risk were mainly from Source Ⅰ and Source Ⅱ， and carcinogenic risk was mainly from unknown sources. The unknown sources had a high proportion in source apportionment and risk assessment， and should be further researched to provide scientific basis for soil heavy metal control. The combined risk assessment model based on source analysis， focusing on the risk characteristics of different sources， can accurately identify high-risk pollution sources. It is a more reasonable and reliable risk assessment method.

[Analysis of Influencing Factors on the Accumulation and Distribution of Heavy Metals in Soil of a Typical Lead-zinc Mine Watershed].

Taking a typical lead-zinc mining area watershed in northern Guangxi as the research object, the total amount and morphology of nine heavy metals(Zn, Pb, Cd, Fe, Mn, Cu, Cr, Sb, and As) and fine soil property indicators(pH, conductivity, cation exchange, organic matter, and particle size) in the surface soils of the Yangshuo lead-zinc mine were analyzed and determined. The accumulation and distribution of soil heavy metals and their main controlling factors were revealed using correlation, redundancy(RDA), and GeoDetector analyses. In the analytical data of soil samples, the mean values of As, Cd, Fe, Cu, Mn, Pb, and Zn exceeded the background values, in which Cd, Mn, Pb, and Zn were 4.01, 3.15, 5.53, and 9.72 times higher than the background values, respectively, indicating that they were significantly enriched in the surface soil. There were more noticeable spatial differences in distribution, which were higher in the alluvial floodplain accumulation area(1-6) than those in the other areas(7-9). The available states(K) of Pb and Mn were 48.8% and 57.2%, respectively, with high bioavailability and average potential migration capacity(PMI 0.015-0.068 and 0.036-0.082, respectively). The Zn and Cu had some bioavailability degree, with available states(K) of 30.9% and 16.8% and moderately available states of 10.9% and 13.6%, respectively. The difference was that Zn had a strong migration capacity(PMI 0.160-0.203), and Cu had an average potential migration capacity(PMI 0.017-0.084). Fe and Cr had a difficult-to-use state(N)>95%, low bioavailability, and weak migration capacity(PMI<0.005). The results of the analysis of the main controlling factors affecting accumulation and distribution showed that Cr was controlled by cation exchange capacity(CEC) and clay; Fe was controlled by sand; As was controlled by electrical conductivity(EC) and pH; Cu, Zn, Cd, and Sb were controlled by pH and clay; Pb accumulation was controlled by pH and soil organic matter(SOM); Mn was controlled by pH. This study quantified the main controlling factors affecting the accumulation and distribution of soil heavy metals, which can provide a scientific basis for decision making in the prevention and control of soil heavy metal pollution.

[Spatial Distribution and Sources of Heavy Metals in Soil of a Typical Lead-Zinc Mining Area, Yangshuo].

Taking a typical lead-zinc mining area in Yangshuo county, Guangxi as the research object, the contents of 10 metal elements (Cr, Mn, Ni, Cu, Zn, As, Cd, Sb, Hg, and Pb) in the surface soil of Sidihe River basin in Yangshuo were analyzed and determined. Pearson correlation analysis, principal component analysis (PCA), positive definite matrix factorization (PMF), and other methods were comprehensively used to quantitatively analyze their contributions and identify pollution sources. In total, 168 surface soil samples were collected across the study area. The mean concentrations of Zn, Cd, Hg, and Pb in the soils were higher than the National Environmental Quality Standards for Soils in China. The mean contents of Sb, Cd, Cu, Pb, and Zn were higher than their corresponding local background values by approximately 1.01, 5.50, 3.29, 9.11, and 10.67 times, respectively, indicating that heavy metals have been enriched in topsoil. The Igeo showed that the major pollutant element in the soils was Hg, followed by Pb, Zn, and Mn. Correlation analysis and principal component analysis showed that the sources of metal pollution in surface soil in the study area were complex and mainly from human activities. Cu, Zn, Cd, Sb, As, and Pb were mainly derived from mining activities; Hg, Cr, and Ni were controlled by soil parent material sources; and Mn and Cd were mainly derived from mining activities and agricultural activities. PMF model analysis results showed that the metal pollution sources in the surface soil were jointly affected by these three sources. Mining activities, natural sources, and a mixed source of mining activities and agricultural activities were the main sources of heavy metal pollution in the soils, accounting for 58.0%, 13.5%, and 28.6% of the total heavy metal accumulation, respectively. Ni, Cu, Zn, As, Sb, Hg, and Pb were derived mainly from mining activities. Cr, Ni, and Hg were mainly attributed to natural sources, such as soil parent materials and rainfall erosion (44.6%, 23.2%, and 21.0%, respectively), and Mn and Cd were associated with a mixed source of mining activities and agricultural activities (75.4% and 70.4%).