Defence Mechanisms of Olive Tree (Olea europaea) under Heavy Metals Stress

The rapid urbanization in China may lead to heavy metal pollution in urban soil, threatening the health of residents. By collecting literature data published in the last 15 years, the characteristics and risks of heavy metals in the urban soils of 52 cities in China were analyzed. The results showed that the average ω(Pb), ω(Cd), ω(Cu) and ω(Zn) in the urban soils of China were 58.5, 0.49, 42.1, and 156.3 mg·kg-1, respectively, and the average Igeo values were ordered as follows Cd(1.10) > Zn(0.36) > Pb(0.28) > Cu(0.13). The high concentrations of heavy metals in the urban soils were mainly found in cities located in coastal economically developed provinces (such as Jiangsu, Zhejiang, etc.) and resource-based provinces (such as Hunan, Henan, Inner Mongolia, etc.). The cities of Kaifeng, Yangzhou, Hohhot, Taiyuan, and Xiangtan had relatively high Igeo values for heavy metals in the soils. The concentrations of heavy metals in soils from industrial areas and roadsides were significantly higher than those from residential areas and parks, suggesting that heavy traffic and developed heavy industry were the main causes of heavy metal accumulation in the urban soils. No significant correlations between the average concentrations of heavy metals in urban soil and urban economic and environmental indicators[such as permanent population, GDP, ρ (PM10), ρ(PM2.5), and SO2 emissions] were found. The concentrations of heavy metals in urban soils showed large spatial heterogeneity, and hence the average concentrations may not reflect the overall accumulation level in a city. The non-carcinogenic risks for children posed by heavy metals in urban soils were generally low, and the main risk contributor was Pb. However, the exposure to heavy metals in soils in cities with developed smelting industries is worthy of attention.

Taking Shouguang Facility agriculture in Weifang City as the research object, heavy metals and other pollutants in new and old facility agriculture soil were investigated and analyzed from 2017 to 2019. The content of heavy metals in soil was analyzed, and the environmental quality of heavy metals was evaluated by single-factor pollution index method and Nemerow index method. The correlation between heavy metal content in surface soil and cultivation years, vertical distribution of heavy metal content in soil, frequency distribution of heavy metal in surface soil, and correlation between heavy metals in surface soil and soil nutrients were analyzed. The results showed that the average contents of the eight heavy metals were Cd 0.23 mg•kg−1, Hg 0.05 mg•kg−1, As 8.09 mg•kg−1, Pb 23.31 mg•kg−1, Cr 70.81 mg•kg−1, Cu 38.54 mg•kg−1, Ni 25.87 mg•kg−1 and Zn 147.52 mg•kg−1. Aside from Pb and Ni, the average content of all other heavy metals in the surface soil of facility agriculture was higher than the average of the control and the geochemical background level of soil in Weifang. Compared with the Environmental Quality Evaluation Standard for Farmland of Greenhouse Vegetables Production (HJ333-2006) and the Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (trial) (GB15618-2018), the average content of heavy metals met the standards, with Cd, Hg and Zn content in some samples exceeding the standards. Most surface soil environmental quality is clean or relatively clean, but there is also part of the soil has reached the level of mild or moderate pollution. The content of heavy metals in the soil of the old facility agriculture (cultivation years > 10) was higher than that of the new facility agriculture (cultivation years ≤ 10), and the content of heavy metals in the surface soil (0∼20cm) was higher than that in the deep soil. The quality distribution of heavy metals in the surface soil is affected by exogenous heavy metals, among which Hg and Cd have the largest skewness coefficient and are most affected by exogenous. There was significant positive correlation between heavy metals in surface soil and available phosphorus, hydrolytic nitrogen, available potassium and organic matter. The results indicated that the accumulation of heavy metals in soil was related to the application of organic fertilizer, phosphate fertilizer and compound fertilizer.

Chemical fertilizers contain traces of heavy metals and long-term use of fertilizers in agriculture could lead to the accumulation of heavy metals in the soil. Specific amounts of fertilizers and manure have been consistently applied for the past 43 years. Soil and plant samples were collected and quantified for heavy metals. The results revealed that the application of FYM and inorganic fertilizers led to a higher concentration of heavy metals in surface soil and decreased with soil depth. The application of 100% RDF resulted in higher concentrations of metals in samples of finger millet and all the heavy metals were below toxic limits. The PLI of heavy metals was found to have a value <10, indicating that soils are less polluted. Cd and Pb had BCF values of <1 for grain and straw, which indicates a lower concentration of metals in soil than those taken up by plants, while >1 for As and Cr indicates a higher uptake in grain and straw than in soil.

Concentration of heavy metals in leachate, soil, and plants in Tehran’s landfill: Investigation of the effect of landfill age on the intensity of pollution

Human activities (land use) and environmental change (land cover change) affect the concentration of Se and heavy metals in soils. The implementation of the "Return Cropland to Forest (RCF)" ecological project has changed the land use and cover, which has provided an ideal experimental area for studying the effects of land use and cover change on selenium (Se) and heavy metals in the soil. In this study, 91 top soil samples from different land use and land cover types, including dry land, paddy land, natural forest land, and secondary forest land, were collected, and the contents of Se, heavy metals, and soil organic matter (SOM) and pH were analyzed. The results showed that:① the average values of ω(Se) (0.42×10-6), ω(As) (13.0×10-6), and ω(Sb) (1.03×10-6) were higher than the soil background values of western Chongqing. ② The concentrations of Se, Cd, Cr, Ni, Pb, and Zn in soils from secondary forest land were significantly higher than those from dry land soils, suggesting that the Se and heavy metals might have significantly increased in the surface soil after the implementation of the RCF ecological project. ③ The SOM was the key controlling factor for the enrichment and distribution of Se and heavy metals in the top soils. Our results indicated that the land use and land cover change would deeply impact the concentrations of Se and heavy metals in the top soils via influencing the soil properties, especially the SOM.

Taking a city in Guangdong Province as the research area, the concentration and spatial distribution characteristics of heavy metals in the surface soil were studied to clarify the situation of soil heavy metal pollution and priority control factors, providing basic data for the prevention and control of soil heavy metal pollution in the city. The content characteristics of heavy metals in 221 soil samples in the city were analyzed, and the potential health risk assessment and source analysis were carried out through the Monte Carlo model, the potential health risk assessment (HRA) model, and the PMF receptor model. It was found that heavy metals ω(As), ω(Hg), ω(Cd), ω(Pb), ω(Cr), ω(Cu), ω(Ni), and ω(Zn) in the soil of the city were 18.16, 0.43, 1.46, 68.57, 98.34, 64.19, 26.53, and 257.32 mg·kg-1, respectively, with a moderate to high degree of variation. Except for Ni concentration, the soil concentrations of other heavy metal elements exceeded the background values of soil in Guangdong Province to a certain extent, and the concentrations of Cd and Zn exceeded the national secondary standards, resulting in severe heavy metal pollution; the main sources of heavy metals were industrial sources, and natural parent materials, lead battery manufacturing, transportation, artificial cultivation, and pesticide and fertilizer inputs also had an undeniable impact on the accumulation of heavy metals in the soil. Heavy metals in the soil had a certain degree of tolerable carcinogenic health risk for both children and adults, whereas non-carcinogenic risks could be ignored. The potential health risk of children was greater than that of adults, and the main exposure route was through oral intake. The input sources of pesticides and fertilizers and As should be the main controlling factors for the health risks of heavy metals in the city's soil, followed by mixed sources and Cr. There were differences in the spatial distribution characteristics and relative pollution levels of heavy metals, and it is necessary to deepen zoning monitoring and control, strengthen soil pollution prevention and control, and reduce human input of heavy metals in soil.

The problem of heavy metal pollution in soil has become a global environmental problem, and it is very important to predict and manage the heavy metals in the environmental soil in a timely manner. The changes in heavy metal content in soil have characteristics such as nonlinearity and large delay, making it difficult to predict heavy metals in soil using traditional methods. Traditional prediction methods are complex and cumbersome, which can lead to longer treatment time and easy secondary pollution. This article analyzed the Back Propagation neural network (BPNN) in artificial neural networks (ANN) and applied it to the prediction of heavy metals in environmental soils. BPNN has good nonlinear function approximation ability, so it can be well applied to complex problems such as soil heavy metal prediction. The methods of treating soil heavy metals include physical repair method, chemical repair method, microbial repair method, plant repair method, plant microbial combined repair method and so on. The use of BPNN can predict heavy metals in environmental soils through adaptive dynamic learning. However, the training time of the BPNN is relatively long and the convergence speed is relatively slow. Therefore, additional momentum terms were added to adjust the weights and thresholds of the network to improve the BPNN. In the experiment, the prediction performance of the improved BPNN was compared before and after the improvement. This article took 50 monitoring data of heavy metals in the same soil in a certain region in 2021 as sample data and predicted the content of heavy metals in the soil using improved and improved BPNN. Due to time constraints, this article only conducted experimental analysis on heavy metals such as lead and cadmium. In the first experiment, when the soil sample data was 50, the prediction accuracy of the BPNN for cadmium before and after improvement was 75.95% and 89.56%, respectively. In the second experiment, when the soil sample data was 50, the prediction accuracy of the BPNN for cadmium before and after improvement was 77.99% and 89.85%, respectively. The improved BPNN has good prediction accuracy and can effectively predict the status of heavy metals in soil. The analysis in this article can provide scientific basis for the comprehensive prevention and control of heavy metals in regional soil, and also provide reference for the development of pollution-free agriculture and ensuring food safety.

Lime bordeaux mixture (LBM) and lime sulfur mixture (LSM) are representative environmental friendly organic materials for prevention of insect pests in South Korea. Recently, those have been widely used as an alternative for chemical pesticides in eco-friendly farms. However, South Korea has not established even recommendation of LBM and LSM considering the stability of heavy metals in soil. The aim of this study was to evaluate the accumulation of hazardous heavy metals in soil and plant with long-term application of LBM and LSM. Firstly, we investigated the amount of LBM and LSM used per year in several eco-friendly farms to determine a standard application rate of both materials. The pepper plant was grown on the pot in greenhouse for 14 weeks. Both materials were applied at 0, 1, 3, and 9 times of standard application rates (2.56 and 1.28 L ha-1 of LBM and LSM per year, respectively). Dry matter yield of pepper and heavy metals (As, Cd, Cu, Hg, Ni, Pb, and Zn) concentration in soil and pepper plant were measured after 14 weeks. Yield of pepper plant did not significantly chang with up to application rate of 1 times, thereafter it markedly decreased with more than 3 times. With increasing LBM and LSM application, the concentration of Cu and Zn in soil significantly increased. Especially, Zn concentration in pepper significantly increased with increasing application rates of both materials. This might resulted in significant decrease in dry matter yield of pepper. The concentrations of those heavy metals in soil did not exceed safety levels (150 mg kg-1 for Cu and 300 mg kg-1 for Zn) established by the Korean Soil Environmental Conservation Act as well as concentration of heavy metals in pepper plant by Korean Ministry of Food and Drug Safety. However, particular attention should be paid for heavy metal safety and crop productivity when using LBM and LSM in the organic farm. Concentration of heavy metals in soil amended with different rate of Bordeaux and Sulphur mixtures at harvest time. †Criteria value: Maximum permissible concentration of heavy metal in soil established by Korean Soil Conservation Act.‡Average value: Average concentration of heavy metals in Korean arable soils.§tr: trace.

Heavy metals biomonitoring was performed using the Conocarpus erectus tree in Ahvaz city. Composite leaf and soil samples were collected from 23 selected stations. The concentrations of heavy metals (Pb, Zn, Cd, Cu, Fe and Mn) in leaf and soil samples, and bioavailability of metals in soil samples were determined. Examination of soil physicochemical parameters proved neutral to slightly alkaline nature, and low organic matter content in the soil samples. The mean concentration of heavy metals in soil was: Fe > Mn > Zn > Pb > Cu. Ecological risk assessment of heavy metals was in the range of safe to low risk (RI < 150). Although the concentration of metals in the more polluted areas was higher in both leaf and soil samples, there was no significant relationship between the concentrations of metals in the leaf and soil samples. This relationship is even lower between the bioavailable component of metals in the soil and the concentration of metals in the leaves. Transfer factor values based on total contents of metals in soil samples indicated that Conocarpus erectus is mostly contaminated with Zn and Cu. The results of Accumulation factor of plant revealed that Pb, Zn, and Fe were mostly enriched in the plant by anthropogenic activities. MAI values in heavy and light traffic, and industrial areas were 11.88, 8.01 and 8.15, respectively. In general, it is evident that the Conocarpus erectus leaves accumulate heavy metals in polluted areas, so it can be used as a bioindicator of air pollution with heavy metals in regions with similar conditions.

This study uses 68 sets of paddy soil and rice grain samples collected from an area of carbonate rocks in Guangxi Province, China, to explore the ecological risks of heavy metals (As, Cd, Cr, Cu, Hg, Pb, Ni, and Zn) in soils from a high background area. We analyzed the concentrations of these heavy metals in soil and grain samples, and their chemical speciation in soil, and use these data to assess the associated ecological risks by means of statistics, a geo-accumulation index, bioconcentration factors (BCF), and correlation analysis. The arithmetic mean values of heavy metals concentrations in soil samples from the study area were (75.8±50.1), (1.91±1.02), (467.0±253.1), (48.5±9.8), (0.21±0.08), (76.2±28.1), (84.2±25.0), and (258.0±122.6) mg·kg-1 for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively, which were remarkably higher than of those from other regions within Guangxi Province and China. In comparison to China's soil environmental quality standard risk screening values (GB 15618-2018), the over-standard rates of Cd, As, and Cr were 95.6%, 86.8%, and 69.1%, respectively. In comparison to risk intervention values, the over-standard rates of Cd, As, and Cr were 27.9%, 17.6%, and 5.9%, respectively. Speciation analysis on heavy metals indicated that As, Cr, Cu, Ni, Pb, and Zn were mainly found in a residual form, and accounted for>80% of the total concentrations, and had a low bioavailability. The bioactive components (F1+F2+F3) of Cd accounted for 21%, and the bioactivity of Cd was higher than other elements. The potential bioavailable components (F4+F5+F6) of Hg accounted for 44%, with low total concentrations, which are understood to have little potential ecological harm for crops. However, the over-standard rates of Pb, Cd, and Cr in rice grains were only 23.5%, 8.8%, and 2.9%, respectively. Correlation analysis showed that there was no significant correlation between the concentrations of heavy metals in soils and the corresponding rice grains. The mean BCFs of each heavy metal were <0.1, and the BCFs of Hg, Pb, As, Cr, and Ni were <0.05. Overall, we found relatively high concentrations, low activity, and low ecological risks for heavy metals in the study area. For high geological background materials such as carbonate rocks, factors such as metal speciation, biological activity, and crop over-standard rates should be taken into account along with the traditional use of the total amount of heavy metals in a soil as the evaluation standard when formulating pollution control policies.

In this study, the contents of five representative heavy metals (Cr, Pb, Zn, Cd and Cu) were determined in soil and propolis samples from four locations in southwestern Macedonia using atomic absorption spectrometry. The aim was to pinpoint the key factors that influence the content of heavy metals in propolis and to establish whether there is a connection between the contents of heavy metals in soil and in propolis from the same location. Generally, at all of the locations, the relative concentrations of heavy metals in soil were found to decrease in the following order: Zn&gt;Cr&gt;Cu&gt;Pb&gt;Cd. The highest mean values for concentrations of heavy metals in these soils were found to be: 72.03, 38.28, 26.64, 17.15 and 0.60 mg kg–1 for Zn, Cr, Cu, Pb and Cd, respectively, and they are all below the target values from the new Dutch list. The general trend of the heavy metal contents in propolis from the same four locations, in decreasing order, is: Pb&gt;Cr&gt;Zn&gt;Cu≈Cd. Generally, the propolis samples from the highland locations (Orle and Rapeš) had lower overall contents of heavy metals than the lowland locations (Novaci and Makovo). All of the analyzed propolis samples meet the requirements of the Macedonian legislation and the international organizations for the maximum allowed levels for heavy metals. Attempts were made to find a correlation between the heavy metal contents in soil and propolis. According to our aim, the investigation presented herein offers one step towards a complete picture of ecological safety of the specific areas in the Republic of Macedonia. To do so, it is necessary to perform additional studies and to find appropriate biomonitoring methods. Further studies are needed to complete the picture and to determine the major pathways of incorporation of heavy metals in beehive products.

Heavy metal pollution in agricultural soils poses a direct threat to food safety and human health. It has been shown that the colloids is the carrier of heavy metal transport in the polluted soil by heavy metals, but the sources of heavy metals in the soil and colloids and their interrelations are not transparent at present. This study aims to investigate the distribution characteristics of heavy metals in agricultural soils near mining areas, and reveal the relevance of heavy metal content in colloids with total content in soils and their chemical species in soils. Results showed that the concentrations of Mn, Zn, and Pb in agricultural soils and colloids were higher than those of other heavy metals. The content of heavy metals in colloids was positively correlated with the total content of heavy metals in soil. Heavy metals in soil could be easily combined by humus-like substances and tryptophan-like protein in the colloids. The primary source of heavy metals in soil and colloids was mining activities. This study provides theoretical support for revealing the pollution characteristics and migration of heavy metals in agricultural soils and colloids around mining areas.

With the excavation of landfill sites, the disposal and reduction of organic-rich soils with high proportions of heavy metals have become urgent issues. This study focuses on the pollution characteristics and ecological risks associated with heavy metals in the humus soil of a municipal solid waste (MSW) landfill. The results indicate that the concentrations of heavy metals in the humus soil followed the sequence of Cu > Zn > Cr > Pb > Ni > As > Cd > Hg, and Cu and Cd exhibited the highest exceedance multiples. Except for Cr, the concentrations of the heavy metals in the humus soil were higher than those in combustible components, with a strong Hg correlation. Heavy metal forms indicate varying degrees of mobility and stability; Cr, As, Hg, and Pb were stable, while Ni, Cd, Cu, and Zn showed higher mobility. The results of the principal component analysis reveal that heavy metals primarily originate from industrial and agricultural waste. Finally, the geoaccumulation index of the metals indicated that Cu, Zn, Cd, and Pb exhibited severe contamination. Most importantly, Cd posed the greatest environmental risk as it has the highest effective content, bioavailability, and mobility. This study provides a scientific foundation for mitigating heavy metal pollution in the humus soil of landfill sites.

&amp;lt;p&amp;gt;Conservation of agriculture soils is a topic of major concern, namely through the increase of soil organic matter. SoilCare project (https://www.soilcare-project.eu/) aims to enhance the quality of agricultural soils in Europe, through the implementation and testing of Soil Improving Cropping Systems in 16 study sites. In Portugal, the application of urban sewage sludge amendments in agriculture soils has been investigated. However, this application is a sensitive topic, due to the risk of long term accumulation of heavy metals and consequent contamination of the soil. The recent Portuguese legislation (Decret-Law 103/2015) is more restrictive than the precedent one (Decret-Law 276/2009) in terms of maximum concentrations of heavy metals in agricultural soils. The analytical quantification of heavy metals, however, raises some methodological questions associated with soil sample pre-treatment, due to some imprecisions in standard analytical methods. For example, the ISO 11466 regarding the extraction in Aqua Regia provides two pre-treatment options: (i) sieve the soil sample with a 2 mm mesh (but if mass for analyses is &amp;lt;2g, mill and sieve the sample &amp;lt;250&amp;amp;#181;m is required), or (ii) mill and sieve the soil sample through a 150&amp;amp;#181;m mesh. On the other hand, the EN 13650 requests soil samples to be sieved at 500&amp;amp;#181;m. Since heavy metals in the soil are usually associated with finer particles, the mesh size used during the pre-treatment of soil samples may affect their quantification.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;This study aims to assess the impact of soil particle size on total heavy metal concentrations in the soil. Soil samples were collected at 0-30cm depth in an agricultural field with sandy loam texture, fertilized with urban sludge amendment for 3 years. These samples were then divided in four subsamples and sieved with 2mm, 500&amp;amp;#181;m, 250&amp;amp;#181;m and 106&amp;amp;#181;m meshes (soil aggregates were broken softly but soil wasn&amp;amp;#8217;t milled). Finer and coarser fractions were weighted and analyzed separately. Heavy metals were extracted with Aqua Regia method, using a mass for analyze of 3g, and quantified by atomic absorption spectrophotometer with graphite furnace (Cd) and flame (Cu, Ni, Pb, Zn and Cr).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Except for Cu, heavy metals concentrations increase linearly with the decline of the coarser fraction. This means that analyzing heavy metals content only in the finest fractions of the soil leads to an over estimation of their concentrations in the total soil. Results also show that coarser fractions of soil comprise lower, but not negligible, concentrations of heavy metals. Calculating heavy metal concentrations in the soil based on the weighted average of both fine and coarse fractions and associated concentrations, provide similar results to those driven by the analyses of heavy metals in the &amp;lt;2mm fraction. This indicates that milling and analyzing finer fractions of the soil did not influence the quantification of heavy metals in total soil. Clearer indications on analytical procedures should be provided in analytical standards, in order to properly assess heavy metal concentrations and compare the results with soil quality standards legislated. &amp;amp;#160;&amp;lt;/p&amp;gt;

This study attempts to evaluate the spatial variability characteristic of soil heavy metals in different industrial types. Therefore, concentrations of heavy metals in soils with different distances from solid, liquid and gas point source and nonpoint source were measured in Yixing, an area with intensive industrialization in Yangtze River Delta of China. The results show that 1) the enrichment of heavy metals in soils around point source is strong and concentrations of heavy metals in soils around solid point source are the highest, followed by liquid, and gas is relatively low. The types of enrichment element depend on the types of point source. Concentrations of heavy metals in soils with distance are significantly decreased. And affected by the prevailing wind, the area influenced by gas point source is the largest, followed by solid, and liquid is relatively small; 2) compared with point source, the enrichment of heavy metals in soils around nonpoint source is relatively weak, but its element types are complex. There are no significant changes of concentrations of heavy metals in soils with distance, but the influenced area is larger; and 3) affected not only by the prevailing wind direction, but also by industry layout, concentrations of soil heavy metals around nonpoint source are of difference in different directions. Due to the complexity of the enrichment element's types of soil heavy metals and their combined effect in nonpoint source, the spatial variability is more complex. It means that taking effective measures to control nonpoint source is especially difficult.