Characteristics of Cadmium Enrichment and Pollution Evaluation of a Soil-Crop System in a Typical Karst Area

Topography can significantly influence the atmospheric deposition of heavy metals on the surface soil and further shape their spatial distribution. This study was carried out in Northwestern Guizhou Province, a key agricultural region contaminated with cadmium (Cd), lead (Pb), and zinc (Zn) in agricultural soil. In this study, geographical detectors were employed to quantitatively assess the impact of topography on the spatial distribution of Cd, Pb, and Zn in surface soils. Moreover, the influence of topography on the spatial distribution of Cd, Pb, and Zn in the surface soil was further ascertained using geographical detectors. The results demonstrated that the bulk atmospheric deposition fluxes of Cd in Dawan (DW), Dongfeng (DF), Jinzhong (JZ), Shuanglong (SL), and Heishitou (HST) were 1.538, 0.766, 0.802, 0.365, and 0.186 mg m− 2 a− 1, respectively; For Pb, the corresponding values were 47.13, 34.88, 38.25, 16.95 and 35.76 mg m− 2 a− 1, respectively; in the case of Zn, the fluxes were 579.26, 82.38, 83.20, 45.98, and 29.13 mg m− 2 a− 1, respectively. The atmospheric deposition fluxes of Cd, Pb, and Zn demonstrated a general downward trend from DW to SL because of rainfall reduction with increasing elevation. Industrial activities can significantly increase atmospheric deposition fluxes of Cd, Pb, and Zn. However, the atmospheric deposition fluxes of Cd, Pb, and Zn in the control area HST were significantly lower due to the interception effect of mountain. The results of the Pb isotopic analysis further supported the above conclusions. It also indicated that the atmospheric Pb in DW, DF, JZ, and SL were contaminated by multiple anthropogenic sources, whereas the atmospheric Pb in HST was primarily polluted by burning coal from residents. The geographical detector analysis results demonstrated that the spatial distribution of Cd, Pb, and Zn in the surface soil at JZ was affected by the interaction of topography with organic matter and particle size. In SL, the influence of the interactions of all topographies with physical and chemical characters on the spatial distribution of soil Cd and Pb was significant. The aspect was the only topographical factor influencing Zn. Furthermore, topography and pH were the leading factors affecting the spatial distribution of soil Cd, Pb, and Zn in HST. Therefore, this research provides a scientific basis for the identification of pollution sources and the development of effective soil heavy metal control strategies.

Soil heavy metals in karst areas have obvious high background value characteristics. Conducting county-level soil heavy metal ecological risk assessment and identifying heavy metal sources in karst areas are of great significance for soil pollution control and land resource management. Taking Pingguo City, a typical karst county in Guangxi Province, as the study object, 3 151 surface and deep soil samples were collected using the grid method and combined to form 785 analytical samples. The contents of eight heavy metal elements, including As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, were determined. The content characteristics and sources of heavy metals were analyzed using statistical analysis, interpolation analysis, factor analysis, and the absolute principal component-multiple linear regression model （APCS-MLR）. Using the content of heavy metal elements in deep soil （150-200 cm） as background values, the ecological risk assessment of heavy metals in surface soil （0-20 cm） in the study area was conducted using the geo-accumulation index （Igeo） and potential ecological risk index （RI） methods. The results showed that the average content of heavy metal elements in the deep soil of the study area was significantly higher than the background value of the C layer soil in Guangxi Province, and the average content of heavy metal elements in the surface soil was significantly higher than the background value of the A layer soil in Guangxi Province. The spatial distribution of soil heavy metal element content generally showed the characteristics of high in karst areas and low in non-karst areas. The main sources of As, Cr, Ni, Pb, and Zn were soil parent materials, with contribution rates of 74.36%, 84.59%, 93.69%, 79.67%, and 78.17%, respectively. The main sources of Cd were soil parent material sources and unknown sources, with contribution rates of 37.33% and 31.05%, respectively. The main sources of Cu were soil parent materials and unknown sources, with contribution rates of 59.07% and 40.23%, respectively. The main sources of Hg were tectonic activity and mineralization, as well as unknown sources, with contribution rates of 52.49% and 30.65%, respectively. The geo-accumulation index （Igeo） showed that the surface soil was mainly polluted by Cd, with mild or above pollution accounting for 47.78%. The potential ecological risk index （RI） showed that the proportion of surface soil heavy metal comprehensive potential ecological hazards with mild, moderate, strong, and very strong levels was 80.78%, 14.97%, 2.51%, and 1.64%, respectively.

Diagnosis of selenium status in grazing dairy goats on the Mexican plateau

Determining and mapping the spatial mismatch between soil and rice cadmium (Cd) pollution based on a decision tree model

Influence of landform, soil properties, soil Cd pollution and rainfall on the spatial variation of Cd in rice: Contribution and pathway models based on big data

Soil microbial communities are affected by environmental factors. Contamination with heavy metals such as cadmium (Cd) can decrease soil microbial species richness and substantially alter soil microbial species composition. Investigations of the microbial communities in Cd-contaminated soils are necessary to obtain data for soil bioremediation efforts. However, depth-associated variations in microbial community composition and structure in Cd-contaminated paddy soils are not well understood. Here, the effects of various degrees of long-term Cd pollution on soil microorganisms were investigated at different soil depths within the plough layer using 16S rRNA gene amplicon sequencing. We found that, in Cd-polluted soils, microbial communities were more similar between the surface soil and the underlying soil. In addition, microbial community richness and/or diversity were significantly reduced in the Cd-polluted underlying soil as compared with the non-polluted underlying soil. However, species richness in the surface layer was significantly greater in the mildly and severely Cd-polluted soils. The soil microbial communities in the same soil layer differed significantly between the non-polluted and polluted soils. Furthermore, Cd contamination affected the microbial communities of different soil layers differently. Soil pH had a synergistic effect on microbial community abundance and composition. The potential functions of the soil microbiota were mainly related to environmental processing, genetic processing, and metabolic pathways. Notably, our identification of the phyla that were differently abundant among sites with different levels of Cd pollution will provide experimental guidance for further explorations of the effects of Cd on soil microbes in natural environments. Our results not only demonstrate that long-term Cd pollution leads to a marked reduction in microbial richness and diversity in the underlying soil layer, but they also help to clarify how long-term heavy metal contamination affects the soil bacterial community.

Increased environmental awareness has prompted the need for improved feedlot runoff control. Vegetative treatment systems (VTSs) provide a cost effective option that may enhance environmental security. Vegetative treatment systems are typically designed on the basis of hydraulic performance, which may result in over-application of nutrients, especially phosphorus. This study assessed the retention, accumulation, and movement of phosphorus in vegetative treatment areas used for runoff control on six Iowa feedlots over a four year period. Phosphorus loadings and retention were calculated based on measured settled feedlot effluent, or vegetative infiltration basin, and vegetative treatment area runoff volumes and phosphorus concentrations. Results indicated that between 61 and 89% of all applied phosphorus was retained within the treatment area, resulting in phosphorus loadings of 124 to 358 kg P/ha-yr. Measurements of harvested vegetation phosphorus concentration and yield indicated that between 13 and 61 kg P/ha-yr were removed with vegetation harvest. However, this only accounted for 6 to 13% of all applied phosphorus, which suggests that these systems have potential for rapid phosphorus accumulation in surface soil, which could potentially lead to reduced treatment and loss of soluble phosphorus. Projected soil phosphorus accumulation was compared to annual measurements of soil Melich-3 phosphorus concentrations increases. Both approaches found similar increases in soil phosphorus levels, indicating that the majority of the phosphorus retained in vegetative treatment areas was due to interaction and retention in the surface soil. Deep soil sampling (0 to 122 cm) was utilized to evaluate vertical phosphorus movement of phosphorus through the soil profile. Sampling indicated that most accumulation was in the surface soil, but that signs of vertical transport and leaching were occurring after four years of operation especially near the VTA inlet.

Previous studies have reported that co-contamination can result in more complex effects on the phytoremediation efficiency of plants relative to those of a single pollutant. However, the effect of co-contamination on plant rhizosphere characteristics has rarely been revealed. This study was carried out to assess the changes in soil pH, the content and fractionation of dissolved organic matter (DOM), and the metal solubility in the rhizosphere of Arabidopsis thaliana when treated with Cd and Pb simultaneously. The results showed that co-contamination increased the concentrations of DOM by 24.8% and 30.9% in the rhizosphere soil of A. thaliana relative to individual Cd or Pb pollution, respectively. At the end of the experiment, co-contamination significantly decreased the initial soil pH from 6.6 ± 0.3 to 5.5 ± 0.4, whereas a decrease was not observed under Pb pollution alone. Variations in soil pH and DOM can change the fractions of the two metals in the rhizosphere soil of A. thaliana. DOM in co-contaminated soil showed a higher Cd (1.05mg L-1) and Pb (0.75mg L-1) extraction ability relative to that in the Cd-polluted (0.89mg Cd L-1 and 0.59mg Pb L-1) or Pb-polluted (0.68mg Cd L-1 and 0.63mg Pb L-1) soils. The soluble Cd content in the co-contaminated (0.44mg L-1) soil was significantly lower than that in the Cd-polluted (0.71mg L-1) soil because A. thaliana is a Cd accumulator, whereas the soluble Pb content showed the opposite trend (47.0mg L-1 vs. 37.4mg L-1) because the species is a Pb excluder. Therefore, A. thaliana in co-contaminated soil would pose a leaching risk for the non-hyperaccumulated metals, thereby increasing the potential ecological risk during the phytoremediation process.

Soils from three agricultural fields in the western San Joaquin Valley were analyzed for soluble, adsorbed, and total concentrations of selenium (Se) to assess the distribution and forms of Se, and the relation of the distribution and forms of Se to the leaching of Se from soils. Of three fields, concentrations of soluble Se and salinity were highest in soils from the field drained for 1.5 yr and lowest in the field drained for 6 yr. The field drained for 1.5 yr also had the highest concentration of total Se in soil; a median of 1.2 microgram/gm. Of the total concentration of Se in soil from all three fields, the proportion of adsorbed Se and soluble Se ranged from 1 to 11% and 0.68) in saturation extracts of soils sampled from below the water table, reflecting evaporative concentration of Se and salinity. In contrast, most soluble salts and Se apparently have been leached from the unsaturated soils in the fields drained for 6 and 15 yr; therefore, the correlation was lower between Se and salinity in saturation extracts of those soilsmore » (r sq < 0.33). Among soils from all three fields, the ratio of Se to salinity in saturation extracts increased with increasing salinity. 26 refs., 6 figs., 6 tabs.« less

Although Selenium (Se) plays a role as a micronutrient for humans through vegetable consumption, it is also recognized as toxic when present in excessive quantities. Therefore, quantifying Se contents in soils can prevent diseases influenced by crop Se deficiency or excess. We aimed to measure background contents, establish quality reference values (QRV) for Se in soils from two Brazilian biomes (Cerrado and Caatinga), and assess how geopedological factors affect Se content and spatial variability. Two hundred and eight composite topsoil samples were analyzed for Se content, covering an area of about 251,578 km². Sampling sites were under the minimal anthropogenic influence to represent Se background contents. Selenium contents were determined by hydride generation atomic absorption spectroscopy (HGAAS), ranging from 0.002 to 4.78 mg kg -1 . Most soils had contents below the world average of 0.44 mg kg -1 but still above the soil content that causes human Se deficiency (0.125 mg kg -1 ). Soils from Cerrado and Caatinga biomes showed similar average contents of Se, 0.41 and 0.47 mg kg -1 , respectively. Organic carbon content and soil particle size (clay fraction) were the main factors governing Se content in the soils. Our results contribute to understanding the Se content and spatial distribution in tropical soils and the factors governing them. They also provide a tool for agriculture and environmental decision-makers to plan public policies regarding the management of Se levels in these and similar tropical soils in the world.

The origin of soil selenium in a typical agricultural area in Hamatong River Basin, Sanjiang Plain, China

The spatial distribution and source of heavy metals in soil-plant-atmosphere system in a large coal mining area

Selenium bioaccessibility in native seleniferous soil and associated plants: Comparison between in vitro assays and chemical extraction methods

Agricultural soil Cd (Cd) pollution threatens global food safety. Based on a meta-analysis of 55 global studies involving 464 maize cultivars, this research systematically elucidates the potential of maize for safe production and remediation in cadmium (Cd)-contaminated farmland. For low to moderately polluted fields, multiple cultivars with low grain Cd accumulation were identified, including 15 cultivars such as TieYan 919 and DanYu 508, which achieved over 90% lower grain Cd content than the legislative limits. DongDan 118 demonstrated simultaneous grain Cd reduction and yield increase, while XianYu 335 and ZhengDan 958 showed comprehensive performance in Cd reduction and yield stability. Maize genotype was identified as the decisive factor for grain Cd accumulation, soil pH was the key environmental factor regulating Cd translocation to grains, and field cultivation was conducive to the expression of low-accumulation traits. Accordingly, a “production coupled with remediation” technical pathway is proposed, centered on “low-accumulation cultivars as the core, soil pH regulation as the key, and field validation as the safeguard.” For heavily polluted fields, high-Cd-accumulating cultivars such as GuangTian-2 and JinZhuMi (pot cultivation) and HuaCaiNuo3 and QiuQing88 (field cultivation) were identified. Their remediation efficiency was driven by soil available Cd content, with significant local environmental influences, necessitating a remediation strategy guided by “cultivar selection as the core, soil management as the supplement, and local validation as the prerequisite.” This study provides a cultivar selection basis and agronomic regulation framework for the tiered management of Cd-contaminated farmland.

Rice has a strong ability to accumulate Cd in soil, and it is of great significance to study Cd pollution and safe planting zoning in paddy soils. In this work, 300 sets of paddy soil-rice samples were simultaneously collected in 22 towns in a District of Chongqing, and soil pH, soil total and available Cd contents, and brown rice Cd contents were determined. Soil Cd pollution was assessed using the geoaccumulation index, bioconcentration factor, and the single-factor pollution index. Based on the Cd pollution indices of soil and brown rice, safe planting zoning for rice was determined. The results showed that the paddy soils were generally acidic, and total Cd contents ranged from 0.09 mg·kg-1 to 1.60 mg·kg-1, with 35.0% of sites exceeding the risk screening value. The Cd contents of the brown rice ranged from 0.002 mg·kg-1 to 0.808 mg·kg-1 and exceeded the food safety limit in 13.7% of cases. Pearson correlation analysis showed that the Cd content of brown rice was significantly positively correlated with soil total and available Cd (P<0.01). The pollution evaluation indicated that significant Cd accumulation occurred in the paddy soils, with some areas showing light-to-moderate pollution levels. The enrichment coefficients of rice to soil Cd ranged from 0.004 to 1.72. Overall, the paddy soils in the studied area were considered generally safe with respect to Cd pollution, with low-risk areas distributed in the south, west, and east, whereas some medium-high risk areas were detected in eight towns.