Soil Zn Concentrations Research Articles

Change of microbial communities in heavy metals-contaminated rhizosphere soil with ectomycorrhizal fungi Suillus luteus inoculation

Ectomycorrhizal fungus Suillus luteus has been recognized to harbor the ability of improving rhizosphere soil nutrients and absorbing heavy metals (HMs), but effects of S. luteus inoculation on microbial communities in HM-contaminated rhizosphere soil remain unclear. A comprehensive study involving physicochemical analysis and comparative metagenomics was employed to determine the differences in soil properties, structure and function of microbial communities between inoculation and non-inoculation groups. Results showed that the concentrations of soil organic carbon, total carbon, and total nitrogen of rhizosphere soil in inoculation group were 2.1, 1.7, and 1.3 times as high as that in uninoculated group. Besides, concentrations of Cd, Pb, As, Cu, and Zn in inoculation soil were 79 %, 33 %, 65 %, 14 %, and 51 % lower than that in uninoculated soil. Metagenomic study indicated that S. luteus inoculation had no strong effect on diversity and richness of microbial communities in rhizosphere soil, but increased the relative abundance of certain HM-resistant microorganisms such as phylum Actinobacteria and genus Streptomyces. Metabolism-oriented functional annotation further revealed that in inoculation group the abundance of coding sequences related to nutrients metabolism (e.g., carbon, nitrogen, and sulfur metabolism) and HMs resistance (e.g., HMs transformation and efflux) distinctly differed from that in uninoculated group. In short, our findings may elucidate the potential contribution of S. luteus inoculation that affects the structure composition and metabolic functions of microbial communities to mediate the concentration variation of nutrients and HMs in rhizosphere ecosystem.

Comparison of urban and rural soils based on speciation of heavy metals by BCR sequential extraction procedure: A case study in the historical and industrial city of Sisak, Croatia

Within the framework of the pan-European project “URban GEochemistry (URGE) in Europe – Soil, children, health”, pedological and geochemical investigations of the soils of the city of Sisak and its adjacent surroundings were carried out, and three urban and two rural soil profiles were examined. The mineralogical composition and concentration of selected potentially toxic elements (PTEs) Cr, Cu, Ni, Pb and Zn in the soil were determined. The Community Reference Bureau of Reference (BCR) sequential extraction procedure (SEP) of these PTEs was undertaken and the potential risk to human health and the environment was assessed. The concentrations of Cr and Ni are generally similar in urban and rural soil profiles, while the concentrations of Cu, Pb and Zn in soil horizons/layers are higher in urban profiles. The extracted fractions of PTEs gave the following general distribution: in urban soil profiles residual (RES) > reducible (ORG) or oxidisable (FEMN) > exchangeable (CARB), except for Cu where ORG > RES > FEMN > CARB, while in rural soil profiles RES > FEMN or ORG > CARB, except for Pb where FEMN > RES or ORG > CARB. The differences between soils in urban and rural profiles depend mainly on the historical land use, i.e. on the duration and intensity of anthropogenic influences on the soil and, to a lesser extent, on the geogenic origin of the parent material and the pedogenic processes. The studied elements in the urban soil profiles are predominantly of anthropogenic origin, indicating a possible influence of the ancient settlements of Segestica and Siscia and of heavy industry in the 20th century. The anthropogenic influences on the rural profiles are low and geogenic influences dominate. Risks to the environment were assessed in the soil profiles based on PTE concentrations in the CARB fraction and the sum of the CARB, ORG and FEMN fractions from BCR SEP. All calculated risks to human health and the environment were rated as no-risk, very low risk and low risk.

Rapid and Convenient Assessment of Trace Element Contamination in Agricultural Soils through Slurry-TXRF and Ecological Indices: The Ñuble Region, Chile as a Case Study

The study aims to evaluate the applicability of the slurry-TXRF method for estimating background contents and ecological indices in a rapid and convenient way. For this reason, the agricultural soils of the Itata Valley were used as a case study, where 48 soil samples were collected and analyzed. This rapid, minimally sample-intensive, and simultaneous multi-element quantification technique presented high accuracy but lower precision (approx. 20% RSD) compared to the classic total reflection X-ray fluorescence and flame/graphite furnace atomic absorption spectrometry methods, which require sample digestion. Due to the analytical characteristics of Slurry-TXRF, it can be concluded that the lower precision is likely compensated for, and this method represents a valuable alternative for the rapid and efficient assessment of trace element contamination in agricultural soils. The regional median concentrations of Cr, Ni, Cu, Zn, and Cd in the Itata Valley surface soils were found to be 63.7, 9.57, 31.0, 41.1, and 0.56 mg kg−1, respectively, with corresponding upper limits of 47.6, 6.82, 17.0, 30.7, and 0.284 mg kg−1. The ecological indices, including the geoaccumulation index, contamination factor, enrichment factor, and degree of contamination, suggest moderate levels of contamination in the region.

Spatial assessment of topsoil zinc concentrations in Europe

Zinc (Zn) is essential to sustain crop production and human health, while it can be toxic when present in excess. In this manuscript, we applied a machine learning model on 21,682 soil samples from the Land Use and Coverage Area frame Survey (LUCAS) topsoil database of 2009/2012 to assess the spatial distribution in Europe of topsoil Zn concentrations measured by aqua regia extraction, and to identify the influence of natural drivers and anthropogenic sources on topsoil Zn concentrations. As a result, a map was produced showing topsoil Zn concentrations in Europe at a resolution of 250 m. The mean predicted Zn concentration in Europe was 41 mg kg−1, with a root mean squared error of around 40 mg kg−1 calculated for independent soil samples. We identified clay content as the most important factor explaining the overall distribution of soil Zn in Europe, with lower Zn concentrations in coarser soils. Next to texture, low Zn concentrations were found in soils with low pH (e.g. Podzols), as well as in soils with pH above 8 (i.e., Calcisols). The presence of deposits and mining activities mainly explained the occurrence of relatively high Zn concentrations above 167 mg kg−1 (the one percentile highest concentrations) within 10 km from these sites. In addition, the relatively higher Zn levels found in grasslands in regions with high livestock density may point to manure as a significant source of Zn in these soils.The map developed in this study can be used as a reference to assess the eco-toxicological risks associated with soil Zn concentrations in Europe and areas with Zn deficiency. In addition, it can provide a baseline for future policies in the context of pollution, soil health, human health, and crop nutrition.

Levels of heavy metal in soil and vegetable and associated health risk in peri-urban areas across China

Peri-urban vegetable field plays an essential role in providing vegetables for local residents. Because of its particularity, it is affected by both industrial and agricultural activities which have led to the accumulations of heavy metal in soil. So far, information on heavy metal pollution status, spatial features, and human health risks in peri-urban vegetable areas across China is still scarce. To fill this gap, we systematically compiled soil and vegetable data collected from 123 articles published between 2010 and 2022 at a national level. The pollution status of heavy metals (i.e., cadmium (Cd), mercury (Hg), arsenic (As), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn)) in peri-urban vegetable soils and vegetables were investigated. To evaluate the levels of heavy metal pollution in soil and human health risks, the geoaccumulation index (Igeo) and target hazard quotient (HQ) were calculated. The results showed that mean concentrations of Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn in peri-urban vegetable soils were 0.50, 0.53, 12.03, 41.97, 55.56, 37.69, 28.55, and 75.38 mg kg−1, respectively. The main pollutants in peri-urban vegetable soil were Cd and Hg, and 85.25% and 92.86% of the soil samples had Igeo > 1, respectively. The mean Igeo values of this regions followed the order of northwest > central > south > north > east > southwest > northeast for Cd and northeast > northwest > north > southwest > east > central > south for Hg. The mean Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn concentrations in vegetables were 0.30, 0.26, 0.37, 0.54, 1.17, 6.17, 1.96, and 18.56 mg kg−1, respectively. Approximately 87.01% (Cd), 71.43% (Hg), 20% (As), 65.15% (Pb), 27.08% (Cr) of the vegetable samples exceeded the safety requirement values. The vegetables grown in central, northwest, and northern China accumulated much more heavy metals than those grown in other regions. As the HQ values for adults, 53.25% (Cd), 71.43% (Hg), 84.00% (As), and 58.33% (Cr) of the sampled vegetables were higher than 1. For children, the HQ values were higher than 1 for 66.23% (Cd), 73.81% (Hg), 86.00% (As), and 87.50% (Cr) of the sampled vegetables. The findings of this study demonstrate that the situation of heavy metal pollution in peri-urban vegetable areas across China are not optimistic and residents who consume the vegetables are at high risk of health issues. To ensure soil quality and human health, strategies should be taken to guide vegetable production and remedy soil pollution in peri-urban areas with the rapidly urbanizing China.

Composition of some trace elements in wheat plant and soil

Zinc, copper, nickel, and manganese are essential nutrients for plants. However, excessive accumulation in the plant can lead to significant risks and problems in terms of human health after consumption. Also, the accumulation of chromium, cadmium and lead elements in plants can have a toxic effect on human health. This study aimed to determine the concentrations of copper (Cu), chromium (Cr), cadmium (Cd), nickel (Ni), manganese (Mn), zinc (Zn), and lead (Pb) trace elements in wheat plants and soil. Mean trace element levels in soil samples taken from the city center Mn 556.9 mg kg-1, Ni 62.45 mg kg-1, Cr 24.98 mg kg-1, Zn 40.75 mg kg-1, Cu 17.25 mg kg-1, Pb 7.65 mg kg-1, Cd as 1.63 mg kg-1 and the average trace element levels in soil samples taken from villages Mn 418.7 mg kg-1, Zn 48.53 mg kg-1, Ni 32.34 mg kg-1, Cu 15.93 mg kg-1, Cr 13.7 mg kg-1, Cd 1.033 mg kg-1 was determined. Cd, Cr, and Pb concentrations were not detected in wheat samples. Average Cu (4.462 mg kg-1), Mn (30.03 mg kg-1), and Zn (20.39 mg kg-1) concentrations in wheat samples were determined at lower levels compared to soil samples. In the process of transporting trace elements from the soil to the plant, even if the plants are grown under the same conditions, the trace element levels accumulated in the plant may differ.

Effects of Nitrogen and Zinc Fertilization on Alleviating Cadmium Accumulation in Durum Wheat Grains

ABSTRACT Cadmium (Cd) accumulation in durum wheat (Triticum durum L.) is of particular concern compared to the other commonly cultivated cereals. This study was conducted to determine the effects of zinc (Zn) and nitrogen (N) applications on grain Cd concentration of durum wheat grown in a Cd contaminated soil. The experimental design consisted of randomized plots with four replications. The treatments included low and adequate (0.05 and 5 mg kg−1) Zn doses, and inadequate, optimal and high (200, 400 and 600 mg kg−1) N doses. Cadmium application rates were 0 and 5 mg kg−1. The findings demonstrated that Cd application caused a significant increase in grain Cd concentrations, and a decrease in straw and grain yields under low and adequate doses of Zn and all N doses. However, increasing N applications with adequate soil Zn caused an increase in the straw and grain yields and a significant decrease in grain Cd concentration. The grain Cd concentration in low Zn and optimum N treatment under Cd application was 6206 µg kg−1, while the grain Cd concentration decreased by 26.3% (4574 µg kg−1) in the Zn and optimum N treatment. In addition, the grain Zn concentration of durum wheat under low soil Zn conditions was decreased in Cd application, whereas the grain Zn concentration increased in Cd application under adequate soil Zn concentration. The results revealed that combined application of N and Zn in Zn deficient soils is highly effective at decreasing Cd accumulation in wheat grains compared to individual applications.

Phosphate, Lime and Bentonite Affect Heavy Metals and Phosphorus Availability in Acidic and Calcareous Soils

ABSTRACT This work investigated the effect of soil amendments on the mobility of heavy metals and P in acidic and calcareous heavy metal polluted soils after incubated for one year. Compared to phosphate alone, the phosphate+bentonite amendment had lower available P concentrations (13.1 and 16.3% in the acidic and calcareous soils, respectively) and similar heavy metal immobilization capacity. The lime amendment increased soil P availability possibly by increasing the negative charges of soil particles in both soils. Lime amendment greatly reduced the DTPA-extractable concentrations of Cd, Cu, Mn, Ni, Pb and Zn in both soils; greater reductions were observed with higher rate compared to the lower rate and in the acidic soil compared to the calcareous soil, especially for Cd, Mn, Ni and Zn (23.9–95.3% lower than the control). The bentonite in the phosphate+bentonite treatment may have reduced soil P availability by adsorption of soluble P. Based on the results, phosphate+bentonite instead of phosphate alone may be used to reduce heavy metal and P availability in heavy metal contaminated soil. When only lime is used, caution should be taken with respect to potential soil P losses and subsequent off-site degradation in water and environmental quality.

Transfer and transformation characteristics of Zn and Cd in soil-rotation plant (Brassica napus L and Oryza sativa L) system and its influencing factors

Rice–rape rotation is a widely practiced cropping system in China. However, changes in soil properties and management could change the bioavailability of Cd, In order to explore the occurrence state, transportation and transformation characteristics of heavy metals Cd and Zn in rice-rape rotation system in Guizhou karst area with high background value of Cd. In the karst rice–rape rotation area, the physical and chemical properties of soil, chemical specifications and activities of Cd and Zn at different soil depths and during various crop growth stages, and the bioaccumulation of Cd and Zn in different tissues of rice and rape were studied by field experiment and laboratory analysis. The bioaccumulation of Cd and Zn and the effects of physical and chemical soil properties on the activities and bioavailabilities of Cd and Zn during rice–rape rotation were explored. The findings revealed that soil particle size, composition, pH, redox potential, soil organic matter, and Cd and Zn contents varied dramatically, especially in deep soils. The physical and chemical properties of the deep and surface soils were significantly related to the bioaccumulation of Cd and Zn. Cd and Zn are activated during crop rotation. Cd was easier to be enriched in rice, while Zn was easier to be enriched in rape. The correlation between Cd and Zn contents in Brassica campestris L and their enrichment abilities were not significant, but that in Oryza sativa L were significant. During rice-rape rotation, the chemical speciations and activities of Cd and Zn changed with the changes of soil properties and waterlogging environment. This study had important basic guiding significance for the evaluation, prevention and control of heavy metal pollution, and improving soil quality in different rotation systems in karst areas, and was conducive to promoting the safe production of rape and rice.

Characteristics, Chemical Speciation and Health Risk Assessment of Heavy Metals in Paddy Soil and Rice around an Abandoned High-Arsenic Coal Mine Area, Southwest China

The concentrations of the heavy metals Pb, Cd, Cr, Hg, As, Cu and Zn in soil and locally produced grain (rice) were determined in paddy soil and rice around an abandoned high-arsenic coal mine area of Xingren county, southwest China. The health risk assessment was used to assess the multimedia and multipathway health risks of HM exposure in the study area. The results showed that the concentrations of As, Pb and Cd in soil were all higher than the corresponding limits for HMs in China. In terms of the accumulation and transfer capacity, Cd was more likely to transfer from the roots to rice, and its strong mobility may pose potential risks to local residents. The non-carcinogenic risks and carcinogenic risks of HM exposure in different media and exposure pathways were higher in children than adults. The total non-carcinogenic risks and carcinogenic risks in adults and children were higher than the standard limit values because of the HM exposure through ingesting rice husk. Among the exposure pathways evaluated, the contribution of diet was the largest, and As was the most important heavy metal in terms of the non-carcinogenic risk and carcinogenic risk factors. The total non-carcinogenic risks and carcinogenic risks caused by As in dietary crop (rice) accounted for 52% of the total in both adults and children. In order to maintain the health of residents in the study area, it is necessary to strictly strengthen the monitoring of heavy metal pollution in the study area and find effective soil improvement methods to reduce the health risks caused by heavy metal exposure.

Phytoremediation potential depends on the degree of soil pollution: a case study in an urban brownfield

Phytoremediation is a cost-effective nature-based solution for brownfield reclamation. The choice of phytoextraction or phytostabilization strategies is highly relevant when planning full-scale treatments. A suitable approach to identify such species involves the evaluation of plants that grow spontaneously on the contaminated sites. Here, we sought to determine the phytoremediation potential of three spontaneous plant species, namely the trees Acer pseudoplatanus L (A. pseudoplatanus) and Betula celtiberica Rothm. & Vasc (B. celtiberica), and the shrub Buddleja davidii Franch (B. davidii), for the recovery of an urban brownfield. To determine the response of the species to the degree of contamination, we conducted soil and vegetation sampling inside and outside the site. The concentrations of As, Cu, and Zn in soil and plant samples were measured, and then various indexes related to phytoremediation were calculated. The translocation factor and transfer coefficient indicated that vegetation outside the brownfield had phytoextraction capacity while the same plants inside the brownfield revealed phytostabilization properties. Given our results, we propose that the selected species are suitable for phytostabilization strategies in areas with high concentrations of contaminants, whereas they could be used for phytoextraction only in soils with low or moderate levels of pollution.Graphical

Brassica juncea as a Feasible Hyperaccumulator of Chosen Potentially Toxic Metals Under Extreme Environmental Conditions

Nowadays, many sites are considered waste, due to high potentially toxic metal (PTM) concentration. Recycling of globally critical metals requires development of environmentally friendly processes for metal recovery. To study plants response to elevated Zn and Cu concentration in soil, a greenhouse experiment was designed using hyperaccumulator Brassica juncea. Plants were irrigated daily with PTM solutions, with final mass of both Zn and Cu added to the soil reaching 104.5, 209, 313.5, and 330 mg. After 8 weeks, samples were harvested, dried, weighed, and elemental analysis was conducted using atomic emission spectrometry (Agilent Technologies 4210 MP-AES). Phytotoxicity was determined based on visual observation, biomass, and chlorophyll measurements. The highest accumulation of Zn and Cu was found in the stem and leaf material, with observed concentrations of Zn in the leaf being 16.750 mg kg−1 and 7.170 mg kg−1 of Cu in the stem. The highest allocated in the biomass mass of Zn and Cu was in T4 treatment reaching 25.8 mg and 9.5 mg, respectively. Treatment with 330 mg Zn and Cu application displayed a 62.3% decrease in stem mass, a 25% decrease in average root mass (LD30 reached), and a 59% decrease in leaf mass when compared with the control. With increasing PTM concentration, root, biomass (from about 0.4 to 0.1 g; from about 3.8 to 2.0 g, respectively) and chlorophyll “a” (from about 24 to 19 μg/cm2) decline was observed, which correlates with observed chlorosis. This study reaffirmed the capabilities of B. juncea to bioaccumulate Zn and Cu from an enriched soil and provided further understanding as to how Zn and Cu translocate within plant tissues.

Effect of Bio and Organic Fertilizations and Per-sowing Seeds Magnetic field Combined with Mineral Nitrogen Fertilizer on Some Soil Properties and Faba Bean Productivity and Quality under Saline Soil Conditions

Two filed experiments were conducted at Sahl-El-Hussinia, agricultural research station, El-Sharkia Governorate, Egypt, 31o - 8' – 12.461" N and 31o - 52' – 15.469 E. during two successive winter seasons 2020/2021 and 2021/ 2022 , to study the evaluation of used bio-fertilizer (Rhizobium radiobacter sp strain (Salt Tolerant PGPR), humate potassium and pre-sowing seeds faba bean magnetic field different times (5, 10 and 15 min) combined with mineral N fertilizer at rates (15, 30 and 45 N kg/fed) on some soil properties and faba bean productivity and quality. The studied treatments were arranged within the experimental units in a split split plot design in three replicates. Results indicated that the all treatments had improved soil properties i.e. decreased soil salinity and soil pH and increase of available N, P, K, Fe, Mn and Zn contents in soil. The soil treated with humat potassium combined the highest N mineral fertilizers rate and magnetic field time than other treatments. On the other hand, the maximum values of weight of yield and other yield components as affected with humat potassium combined with 45 kg mineral N fertilizers under magnetic field at 15 min compared other treatments. The highest values of macro-micronutrients (N, P, K, Fe, Mn and Zn) concentrations in faba bean seeds as affected with bio-fertilizer and potassium humate combined with mineral N fertilizer different rates compared with control. The bio-fertilizer was beast on faba bean quality.

Mobility indexes of Cu, Pb, and Zn in soil ecosystems with various levels of metal contamination (in Poland)

The aim of the study was to investigate and compare the soils of three groups of grassland ecosystems with varying degrees of heavy metal (Cu, Pb, and Zn) pollution as well as estimating of mobility on the basis of calculated mobility indexes (MI) expressed as a percentage of the EDTA-extracted forms of metals in their total content. A total of 55 surface soil samples were collected from various areas of Poland: urban soils, rural soils, and soils along communication routes. Heavy metal concentrations were determined in solutions after wet mineralization (using a mixture of acids) by atomic absorption spectrometry (AAS) with flame atomization. To isolate the mobile forms of metals in soils, a one-step extraction method was used with 0.05-M EDTA solution. The ranges of Cu, Pb, and Zn concentrations in soils were varied, respectively: 6.7–47.6, 61.1–563.9, and 86.4–644.5 mg·kg−1 (A); 5.7–39.8, 13.56–45.71, and 16.3–119.6 mg·kg−1 (B); and 1.0–195.8, 19.2–310.2, and 27.4–894.1 mg·kg−1 (C). The average values of mobility indexes of Cu, Pb, and Zn were at the level of 40.9, 33.5, and 22.2% (A); 23.2, 27.1, and 25.9% (B); and 37.5, 34.3, and 30.7% (C). Studies have shown that metals derived from anthropogenic sources are characterized by greater mobility compared to metals of natural origin (lithological associated with the ground). The inclusion of metal mobility indices in the environmental monitoring strategy may minimize errors in assessing the actual risk associated with the potential uptake of these metals by plants and incorporation into circulation.

Antioxidant Activity and Photosynthesis Efficiency in Melissa officinalis Subjected to Heavy Metals Stress

The aim of this study was to assess influence of cadmium and zinc treatments on antioxidant activity combined with the photosynthesis efficiency in a popular herb lemon balm (Melissa officinalis L.). Plants were grown under greenhouse conditions by the pot method. The Mn, Cu, Cd, and Zn contents in soil and plants were measured by HR-CS FAAS. The activity of net photosynthesis, stomatal conductance, transpiration rate, intercellular CO2, and index of chlorophyll in leaves were determined for all investigated species. Reduction of the net photosynthesis was observed for cultivations subjected to either Zn or Cd treatments. Phenolic contents were determined by the chemical Folin-Ciocalteu method, while enhanced voltammetric analysis was applied to assess the antioxidant properties of plant extracts. Both of these approaches yielded similar results. Herbal extracts had exceptional antioxidant capacities and were good scavengers of free radicals and reactive oxygen species. Structural similarity of cadmium and zinc facilitated their mutual structural exchange and prompted substantial expansion of phenolics under the mixed Zn and Cd treatments.

Characteristics of Soil Heavy Metal Pollution and Health Risk Assessment in Urban Parks at a Megacity of Central China

In this study, we compared the concentrations of the heavy metals Cd, Cr, Cu, Zn, Ni, and Pb in the surface soils of urban parks in Wuhan, Hubei Province, with those in the surface soils of urban parks worldwide. The soil contamination data were assessed using enrichment factors and spatial analysis of heavy metals using inverse distance weighting and quantitative analysis of heavy metal sources with a positive definite matrix factor (PMF) receptor model. Further, a probabilistic health risk assessment of children and adults using Monte Carlo simulation was performed. The average Cd, Cr, Cu, Zn, Ni, and Pb concentrations in the surface soils of urban parks were 2.52, 58.74, 31.39, 186.28, 27.00, and 34.89 mg·kg-1, respectively, which exceeded the average soil background values in Hubei. From the inverse distance spatial interpolation map, heavy metal contamination was primarily observed to be present to the southwest of the main urban area. The PMF model resolved four sources: mixed traffic and industrial emission, natural, agricultural, and traffic sources, with relative contributions of 23.9%, 19.3%, 23.4%, and 33.4%, respectively. The Monte Carlo health risk evaluation model demonstrated negligible noncancer risks for both adult and child populations, whereas the health effects of Cd and Cr on children were a concern for cancer risks.

Concentrations and bioconcentration factors of leaf microelements in response to environmental gradients in drylands of China.

Determining response patterns of plant leaf elements to environmental variables would be beneficial in understanding plant adaptive strategies and in predicting ecosystem biogeochemistry processes. Despite the vital role of microelements in life chemistry and ecosystem functioning, little is known about how plant microelement concentrations, especially their bioconcentration factors (BCFs, the ratio of plant to soil concentration of elements), respond to large-scale environmental gradients, such as aridity, soil properties and anthropogenic activities, in drylands. The aim of the present study was to fill this important gap. We determined leaf microelement BCFs by measuring the concentrations of Mn, Fe, Ni, Cu and Zn in soils from 33 sites and leaves of 111 plants from 67 species across the drylands of China. Leaf microelement concentrations were maintained within normal ranges to satisfy the basic requirements of plants, even in nutrient-poor soil. Aridity, soil organic carbon (SOC) and electrical conductivity (EC) had positive effects, while soil pH had a negative effect on leaf microelement concentrations. Except for Fe, aridity affected leaf microelement BCFs negatively and indirectly by increasing soil pH and SOC. Anthropogenic activities and soil clay contents had relatively weak impacts on both leaf microelement concentrations and BCFs. Moreover, leaf microelement concentrations and BCFs shifted with thresholds at 0.89 for aridity and 7.9 and 8.9 for soil pH. Woody plants were positive indicator species and herbaceous plants were mainly negative indicator species of leaf microelement concentrations and BCFs for aridity and soil pH. Our results suggest that increased aridity limits the absorption of microelements by plant leaves and enhances leaf microelement concentrations. The identification of indicator species for the response of plant microelements to aridity and key soil characteristics revealed that woody species in drylands were more tolerant to environmental changes than herbaceous species.

Multi-parameter optimization for Vis–NIR spectroscopic analysis of multiple indicators of soil heavy metal in the tideland reclamation area of the Pearl River Delta

ABSTRACT Using visible and near-infrared (Vis–NIR) spectroscopy combined with novel chemometric methods, the rapid reagent-free simultaneous analysis model for Cu, Zn, Ni, and Cr contents in tideland reclamation soil in the Pearl River Delta was established. Based on Savitzky–Golay (SG) smoothing and partial least squares (PLS) regression, a multi-parameter optimization platform (SG-PLS) covering 264 modes was constructed to select appropriate spectral preprocessing mode for each indicator. The equidistant combination PLS (EC-PLS) method with three cycle parameters was adopted for the first large-scale screening of wavelength models. In addition, wavelength phase-out PLS (WSP-PLS) and repetition rate priority combination methods were used as the secondary optimization method. The well-executed competitive adaptive reweighted sampling PLS was also used for comparison. The validation samples that were not involved in modeling were used to validate the selected three group models. For the four indicators, the method of EC-PLS combined with WSP-PLS achieved the best validation effect. In validation, the root mean square error (SEPV), relative root mean square error (RSEPV), and correlation coefficients (RP,V) of prediction were 2.46 mg kg−1, 4.5%, and 0.959 for Cu; 51.37 mg kg−1, 24.6%, and 0.900 for Zn; 3.59 mg kg−1, 9.1%, and 0.739 for Ni; and 9.15 mg kg−1, 8.4%, and 0.843 for Cr, respectively. Results indicated that low relative error and high prediction correlation confirmed the feasibility of using Vis–NIR spectroscopy to analyze soil heavy metal contents. The proposed multi-parameter, multi-stage integrated optimization algorithm could be applied to a wider field of spectral analysis.

Ecological risks of heavy metals in soil under different cultivation systems in Northwest China

The increasing population worldwide and high demand for food have changed the conventional open-field cultivation system (OFS) to plastic shed cultivation system (PSS), resulting in serious concern about soil contamination by heavy metals due to the intensive planting in PSS. However, there is limited research on heavy metals ecological risk after converting the cultivation system from OFS to PSS in Northwest China. Therefore, a total number of 341 soil samples were collected in Shaanxi province to measure heavy metals contents (As, Cd, Cr, Cu, Hg, Pb, and Zn) and assess the ecological risk. In this study, the PSS cultivation system exhibited more severe contamination than the OFS; whereas the heavy metals pollution in different regions was in the following order: southern Shaanxi (SS) > central Shaanxi (CS) > northern Shaanxi (NS). Although the mean values of the selected heavy metals were below the national limited standard, Cd and Pb posed considerable accumulation in both cultivation systems and the growing cultivation years increased the Cd, Hg and Zn contents in soils of PSS. The results of correlation analysis revealed a significant correlation between total phosphorus (TP) and Cd in PSS cultivation systems. However, soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) had different interactions with other heavy metals in each region under both cultivation systems due to the variations in crop management techniques such as planting intensity and fertilizer input. Partial least square path model (PLS-PM) analysis showed that the different cultivation regions had a greater impact than the type of cultivation system, which should be carefully taken into account in mitigating pollution risk. Additionally, research on heavy metals species and fractions in connection to their bioavailability under various agricultural production systems is advised for improved food safety.

Effect of Zinc Fertilizer Application on Cadmium Accumulation in Wheat Grain and Its Application Risk

The interaction of zinc (Zn) and cadmium (Cd) is an important research direction in the prevention and control of Cd pollution of wheat in recent years. In this study, a typical wheat field in North China was selected as the object to explore the control effect and application risk of Zn fertilizer on Cd pollution in a soil-wheat system through field experiments. The results showed that under the treatment of a low dosage of Zn, the Cd concentrations in wheat grains in Jiyuan City and Kaifeng City decreased by 33.4% and 25.3% compared with those in the control, respectively. By contrast, Cd concentrations in wheat grains treated with a high dosage of Zn increased by 22.4% and 34.2% compared with that of the low-dosage Zn treatment. After the application of Zn, the total amount and available Zn concentrations increased significantly, and Cd was partially activated in these two locations. Canonical correlation analysis (CCA) showed that when the Zn concentrations in the soils were less than 200 mg·kg-1, soil Zn was the main factor affecting Cd accumulation in the soil-wheat system, whereas when Zn concentrations in soils were greater than 200 mg·kg-1, the activation of soil Cd was the main factor affecting Cd accumulation in wheat grains. Regression analysis showed that when the soil Cd/Zn ratio decreased to 0.0089 (low dosage of Zn), Zn and Cd showed an antagonistic effect, whereas when the soil Cd/Zn ratio decreased to 0.0078 (high dosage of Zn), Zn and Cd showed a synergistic effect. According to the characteristics of regional Cd pollution, adjusting the amount of Zn fertilizer can improve the efficiency of pollution control and avoid aggravating the harm of Cd pollution.