Search

The Wanshan mercury mine, which is an abandoned mine located in northeastern Guizhou Province in Southwest China, has introduced serious Hg pollution to the local ecosystem resulting from previous mining and smelting activities. However, it is not clear to date whether soil pollution has actually improved after treatment by related departments. Therefore, the present study investigates the vegetation community and heavy metal contents of the soil and plants in the Wanshan mercury mining area. The results showed that most of Hg, Cd, As, Cu, and Zn contents in soil samples were higher than those of Soil Environment Quality Risk Control Standard for Soil Contamination of Agricultural Land in China (GB15618-2018). The observed plant species mainly consisted of Compositae, followed by Leguminosae. Unfortunately, this investigation found that heavy metal concentrations in these plants were not extremely high and far below the standard of hyperaccumulator. Despite all this, the maximum values of bioaccumulation factor for Pb, Cd, Hg, As, Cu and Zn were Serissa japonica (Thunb.) Thunb., Rhus chinensis Mill., Potentilla sibbaldii Haller f., Erigeron canadensis L., Clerodendrum bungei var. bungei. and Rhus chinensis Mill., respectively. Regardless of the carcinogenic or noncarcinogenic risk index, the potential risk to urban children is higher. Our results suggest that heavy metal pollution was indeed relieved since their contents in soil significantly decreased in comparison with those reported in other previous studies. This finding provides a reference for the long-term treatment of heavy metal pollution in the local environment and other areas employing analogous environmental protection measures.

Soil is a fundamental component to an ecological system. This study is aimed to clarify the spatial heterogeneity of soils in the Houzhai River basin and the factors controlling it. Overall, 2755 sites designed using ArcGIS were studied; soil thickness, vegetation, land use (human disturbance), and topographic characteristics were analyzed. Soils in the basin are characterized by the high spatial heterogeneity. Soils on the elevated convex elements of topography are thinner than those in the depressions and on flat lands. Soils in the western part of the Houzhai River basin are generally thicker than soils in the eastern part of the basin. The mean soil thickness of forestland, paddy fields, arid land, and grassland is 37.40, 84.43, 69.08 and 56.03 cm, respectively. Based on the present study, soil thickness in the Houzhai River basin is closely associated with landscape, land use, and vegetation. It is interesting that soils of croplands, including paddy fields and arid lands, are generally thicker than soils of other land uses under similar environmental conditions. The major reason for this—either the choice of soils with initially greater thickness for cropland or the result of soil protection measures by land owners—remains open to arguments and needs to be clarified.

Heavy metals in soil are in a high background state in Karst areas, and agricultural activities will affect the bioactivity of heavy metals. The heavy metal (Cd and Cr) bioactivity and their activation effects in rice-rape rotation lands in Karst areas were studied based on field experiments and laboratory analysis, and the influencing factors of heavy metal activity were analyzed based on the physical and chemical properties of soil. The results suggest that the residual fraction was the largest and the exchangeable fraction was the smallest for both Cr and Cd in rice-rape rotation lands in Karst areas. During the rice-rape rotation process, Cd and Cr tended to be released from the residual fraction and transformed into the other four fractions. The fractions with high bioactivity, including the exchangeable fraction and carbonate fraction, increased to different degrees. Rice-rape rotation could activate the activity of soil Cd and Cr in Karst areas. It is also revealed that the activity of soil Cd and Cr in Karst areas was closely associated with soil pH and electric potential (Eh). In the 0–20 cm soil layer, Cr showed a significant negative correlation with pH (r = −0.69, p &lt, 0.05), while both Cr and Cd showed significant negative correlations with Eh, and the correlation coefficients were −0.85 (p &lt, 0.01) and −0.83 (p &lt, 0.01), respectively. In the 20–40 cm soil layer, Cr showed significant negative correlations with Eh, and the correlation coefficient was −0.95 (p &lt, 0.01). No significant correlation between the activity of soil Cd and Cr and soil mechanical composition was observed. This study revealed that special attention should be paid to changes in pH and Eh in consideration of heavy metal activity in the rice-rape rotation process.

The content of heavy metals in the soil in Guizhou Province, which is a high-risk area for heavy metal exposure, is significantly higher than that in other areas in China. Therefore, the objective of this study was to evaluate the ability of CaCO3 and clay to accumulate heavy metals in topsoil sample collected from Lixisol using the method of indoor simulation. The results showed that the contents of Cu, Zn, Cd, Cr, Pb, Hg and As in the soil sample were 10.8 mg/kg, 125 mg/kg, 0.489 mg/kg, 23.5 mg/kg, 22.7 mg/kg, 58.3 mg/kg and 45.4 mg/kg, respectively. The soil pH values increased with the CaCO3 concentration in the soil, and the fluctuation of the soil pH values was weak after the CaCO3 concentrations reached 100 g/kg. The adsorption capacity of lime soil increased by approximately 10 mg/kg on average, and the desorption capacity decreased by approximately 300 mg/kg on average. The desorption of all heavy metals in this study did not change with increasing clay content. Pseudo-second-order kinetics were more suitable for describing the adsorption kinetics of heavy metals on the soil material, as evidenced by the higher R2 value. The Freundlich model can better describe the adsorption process of As on lime soil. The process of As, Cr, Cd and Hg adsorption on the soil sample was spontaneous and entropy-driven. Additionally, the process of Cu and Pb adsorption on the soil materials was spontaneous and enthalpy-driven. Generally, the adsorption and desorption of heavy metals in polluted soil increased and decreased, respectively, with increasing CaCO3 content. The effect of calcium carbonate on the accumulation of heavy metals in soil was greater than that of clay. In summary, CaCO3 and pH values in soil can be appropriately added in several areas polluted by heavy metals to enhance the crop yield and reduce the adsorption of heavy metals in soils.

Paddy rice, one of the most important food crops in Southeast Asia, is considered a main source of human exposure to heavy metal contamination because it efficiently accumulates heavy metals. In the present study, of Japonica rice grains, straw, roots, leaves, and husks and rhizosphere paddy soils (0–20 cm and 20–40 cm depth) were collected from Zunyi in northern Guizhou Province, China. The forms of heavy metals, including Cr, Cd, Pb, Cu, and Zn, in the two soil profiles were investigated using Tessier’s five-stage sequential extraction procedure. There was no heavy metal pollution in the study area based on the evaluation of the geo-accumulation index and the potential ecological risk index. Accumulation varied from one area to another, and the highest metal accumulation was found in the order of root > stems > leaves. The bioaccumulation factor (BCF) results revealed that during the grain-filling stage, the rice had high BCF values (> 1) for Cd and Zn. The target hazard quotient (THQ) of ingestion peaked for Cd and reached its minimum level for Zn in not only in adults but also in children. The THQ was ranked as Cd > Cu > Pb > Cr > Zn for both adults and children. The hazard index values for adults and children for the five heavy metals were 1.81 × 10−3 and 1.55 × 10−3, respectively, indicating that these metals have little effect on the human body. The lifetime carcinogenic risk values for local adults and children were 4.28 × 10−5 and 5.92 × 10−5, respectively, both of which were within the tolerable to acceptable risk range. In summary, obvious hazards for local adults and children were not observed in this study. Considering the total amount and chemical forms of Cd, it is necessary to notify the appropriate departments about the possible rice contamination caused by Cd in the soil.

The assessment of soil organic carbon (SOC) in mountainous karst areas is very challenging, due to the high spatial heterogeneity in SOC content and soil type. To study and assess the SOC storage in mountainous karst areas, a total of 22,786 soil samples were collected from 2,854 soil profiles in Guizhou Province in Southwest China. The SOC content in the soil samples was determined by the oxidation of potassium dichromate (K2Cr2O7), followed by titration with iron (II) sulfate (FeSO4). The SOC storage was assessed based on different land uses. The results suggested that the average SOC density in the top 1.00 m of soil associated with different land uses decreased in the following order: Croplands (9.58 kg m&minus, 2) &gt, garden lands (9.07 kg m&minus, grasslands (8.07 kg m&minus, forestlands (7.35 kg m&minus, uncultivated lands (6.94 kg m&minus, 2). The SOC storage values in the 0.00&ndash, 0.10 m, 0.00&ndash, 0.20 m, 0.00&ndash, 0.30 m and 0.00&ndash, 1.00 m soil layers of Guizhou Province were 0.50, 0.87, 1.11 and 1.58 Pg, respectively. The SOC in the top 0.30 m of soil accounted for 70.25% of the total within the 0.00&ndash, 1.00 m layer in Guizhou Province. It was concluded that assessing SOC storage in mountainous karst areas was more accurate when using land use rather than soil type. This result can supply a scientific reference for the accurate assessment of the SOC storage in the karst areas of southwestern China, the islands of Java, northern and central Vietnam, Indonesia, Kampot Province in Cambodia and in the general area of what used to be Yugoslavia, along with other karst areas with similar ecological backgrounds.

The speciation and activity of heavy metals in farmland were changed with the different soil properties and flooded environment, especially in the complex and rainy environment in soil of Guizhou Province. The objective of this study was to explore the concentrations of a variety of heavy metal activity and the speciation of those heavy metals in rhizosphere soil at different growth stages of Brassica campestris L. in a Karst mountainous area. Tessier's five-stage sequential extraction procedure, the potential ecological risk index, a Bayesian network, accumulation factors, translocation factors and a laboratory simulation experiment were applied in this study. The results showed that (1) no heavy metal concentrations (except the Cd concentration) exceeded the limits of the soil environmental quality risk control standards for soil contamination of agricultural land in China (GB15618-2018). (2) The orders of the accumulation factor and translocation factor values were Zn > Cd > Cu > Pb > Cr and Cd > Cu > Zn > Pb > Cr, respectively. The order of the heavy metal contents of different tissues during the whole growth period was roots > leaves > stems. (3) The indoor simulation test exhibited that the dry-wet alternation and flooding can reduce Cd activity in soil. (4) Redox potential (Eh), rather than pH or organic matter, was the main factor impacting the total content and chemical speciation of heavy metals in the soil, based on a dynamic Bayesian network. Based on the results, we suggest that the activity of heavy metals should be improved by using dry-wet alternation, whereas the proportions of ion-exchangeable forms of heavy metals are relatively low in the study area (except for Cd). Several measures may be taken to enhance soil acidity and reduce the Cd activity during Brassica campestris L. cultivation.