[Chemical Speciation, Influencing Factors, and Regression Model of Heavy Metals in Farmland of Typical Carbonate Area with High Geological Background, Southwest China].

The speciation of heavy metals in soil is an important factor determining their bioavailability and toxicity, and it is crucial for the scientific assessment of ecological risks posed by heavy metals in soils of typical carbonate areas with high geological background in southwest China. In order to investigate the distribution of speciation of heavy metals in soils of carbonate rock with high geological background, we selected a typical carbonate rock distribution area in Guizhou Province and used the second national soil survey plots as sampling units. A total of 309 topsoil samples were collected from farmland. The improved Tessier seven-step sequential extraction method was used to analyze the seven chemical forms of heavy metals:water-soluble (F1); exchangeable (F2); carbonate-bound (F3); weakly organic-bound (F4); iron-manganese oxide-bound (F5); strongly organic-bound (F6); and residual (F7) forms of arsenic (As), cadmium (Cd), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn). The study found that the residual forms of heavy metals As, Cu, Hg, Ni, Pb, and Zn in the soil accounted for more than 50%, the effective components (F1-F3) accounted for less than 5%, and the potential biological effective components (F4-F6) were less than 45%, indicating low reactivity and low ecological risk. The effective and potentially bioavailable components of Cd accounted for 55.49% and 29.37%, respectively, which were much higher than those of other heavy metals. The ecological risk based on the speciation of heavy metals in the soil was much lower than that based on the total content of heavy metals. The stepwise regression equations could effectively establish the relationship between the bioavailable and potentially bioavailable fractions of Cd, Cu, and Pb and their influencing factors. Total heavy metal contents and pH value were important factors influencing the speciation of heavy metals in soils of carbonate rock with high geological background areas. The enrichment of heavy metal elements in the residual fraction was influenced by long-term zinc smelting activities and the weathering of carbonate rocks into soil. Soil organic matter (OM) and oxide content had a relatively small influence on the speciation of heavy metals in the soil.

[Potential Source Identification and Ecological Risk Assessment of Heavy Metals in Surface Soil of Heze Oil Peony Planting Area Based on PMF-PCA/APCS and PERI].

To study the sources and potential risks of heavy metals in soils of characteristic agricultural product producing areas is of great significance for the scientific management and safe utilization of soil and crop resources. The contents of heavy metals As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the 254 surface soil samples collected from the Heze oil peony planting area were determined. The content characteristics and correlation of heavy metals were analyzed using multivariate statistical methods. The sources of heavy metals in topsoil were analyzed using Igeo, PMF, and PCA/APCS. The ecological risks of the eight heavy metals were assessed through the potential ecological risk index (PERI). The results showed that the average contents of seven heavy metals in the soil were basically consistent with the background values of soil elements in Heze City, except that the average value of Cd was 1.44 times higher than the background value in Heze City. Correlation analysis and cluster analysis revealed that Pb, Hg, and Cd elements in the soil were greatly affected by human activities in the later period. The sources of eight heavy metals in the study area were natural sources, agricultural fertilizer sources, industrial coal sources, and domestic transportation sources, with the contribution rates of 81.31%, 15.45%, 2.74%, and 0.50%, respectively; 84.25% of the sites in the study area were at slight ecological risk, whereas the moderate risk and strong risk sites accounted for 14.96% and 0.79%, respectively. Among them, Cd and Hg were the dominant elements of ecological risk in the study area.

[Accumulation Characteristics and Health Risk Assessment of Heavy Metals in Soil-Crop System Based on Soil Parent Material Zoning].

This study used both the element occurrence form analysis and the chronic health risk assessment method to investigate the accumulation characteristics of heavy metals in the soil-crop system and the health risk assessment of agricultural products in northeastern Yunnan, which is a typical area of Southwest China where heavy metals are enriched in soil. Based on the study of 1137 groups of agricultural products and corresponding root soils, the results showed that the soil cadmium (Cd) and lead (Pb) in the lead-zinc ore concentration area were higher than the risk-intervention values of the "Soil Environmental Quality Risk control standard for soil contamination of agricultural land" (GB 15618-2018), whereas the soil Cd in the other parent material areas was within the screening-intervention buffer zone, and Pb was below the minimum risk-screening value. According to the National Food Safety Standard of China (GB 2762-2017), the heavy metal Cd in potatoes and soybeans in the area seriously exceeded the standard, the heavy metal Pb in tartary buckwheat and walnut exceeded the limit value, and the exceeding rate of heavy metal Cd in crops from these parent material areas showed: clastic rock>basalt>lead-zinc ore>carbonate ≈ Quaternary sedimentary>sand (mud) rock. According to the U.S. Environmental Protection Agency's assessment method for the chronic health risk of heavy metal intake by humans, the grains and potatoes, staple foods, and fruits had low chronic health risks of heavy metal intake. Agricultural products from the parent material area of clastic rock, sand (mud) rock, Quaternary sedimentary, and lead-zinc ore concentration showed health risks; with the change in soil physical and chemical properties and the increase in the types of edible crops, the risk will gradually increase. Based on this research, it is urgent to carry out real-time monitoring of agricultural products in the area.

[Spatial Distribution, Source Apportionment, and Ecological Risk Assessment of Soil Heavy Metals in Jianghugongmi Producing Area, Shandong Province].

Taking the Jianghugongmi producing area as the research object, As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the soil of the study area were sampled and determined. The correlation of heavy metals was discussed using the multivariate statistical method, the spatial distribution interpolation analysis of heavy metals was carried out using ArcGIS 10.2, the quantitative source analysis of heavy metal pollution was carried out using the enrichment factor (EF) and PMF methods, and the potential ecological risk was evaluated. The results showed that the contents of the soil heavy metals As, Cd, Cu, Hg, Pb, and Zn were lower than the screening values specified in the standard for soil pollution risk control of agricultural land (GB 15618-2018), and the soil ecological environment risk was low; the maximum values of Cr and Ni exceeded the risk screening values, but the risk was low. The main distribution range of pH in the study area was 6.05-6.69, which was suitable for rice growth. The Mohe River indicated the spatial distribution of pH and heavy metals, which was closely related to the supergene geochemical characteristics of the elements. However, Hg and Cd showed different spatial distribution characteristics under human influence. Hg was distributed in the middle and high value distribution area along the west side of the river, and the spatial distribution of Cd was significantly different from north to south. The quantitative source analysis results based on the EF method and PMF showed that the main sources of heavy metals in the study area were agricultural sources, mixed sources, coal sources, and natural sources. The contribution rates of various sources accounted for 24.2%, 35.4%, 9.5%, and 30.9%, respectively. The medium strong ecological risk points of Hg in the study area were distributed along the west side of the Mohe River, whereas the moderate potential ecological risk points of Cd were concentrated in the cultivated land on both sides of the Mohe River, and the potential ecological risk index (Er) of the other elements was<40. Cd and Hg were the main potential ecological risk elements in the study area, whereas Cd was still the main potential pollution element in the cultivated land soil in the study area.