Foliar uptake and metal(loid) bioaccessibility in vegetables exposed to particulate matter

Foliar uptake screening: A promising strategy for identifying wheat varieties with low lead accumulation

Lead (Pb) contamination in wheat grain is of great concern, especially in North China. Atmospheric deposition is a major contributor to Pb accumulation in wheat grain. Screening low Pb accumulating wheat varieties has been an effective method for addressing Pb contamination in wheat grain. However, identifying wheat varieties with low Pb accumulation based on foliar uptake of atmospheric Pb has been neglected. Therefore, two field trials with distinct atmospheric Pb deposition were conducted to screen for stable varieties with low Pb accumulation. It was verified that YB700 and CH58, which have high thousand-grain weights and stable low Pb accumulation in field 1 (0.19 and 0.13 mg kg-1) and field 2 (0.17 and 0.20 mg kg-1), respectively, were recommended for cultivation in atmospheric Pb contaminated farmlands in North China. Furthermore, indoor experiments were conducted to investigate Pb uptake by the roots and leaves of different wheat varieties. Our findings indicate that Pb accumulation in different wheat varieties is primarily influenced by foliar Pb uptake rather than root Pb uptake. Interestingly, there was a positive correlation (p < 0.05) between the Pb concentrations in leaves and the stomatal width and trichome length of the adaxial epidermal surface. Additionally, there is a positive correlation (p < 0.01) between the Pb concentration in the wheat grain and trichome length. In conclusion, the screening of wheat varieties with narrower stomatal widths or shorter trichomes based on foliar uptake pathways is an effective strategy for ensuring food safety in areas contaminated by atmospheric Pb.

Characteristics and evaluation of heavy metal pollution in a soil-wheat system of an arid oasis city in northwest China

In this paper, the Cu and Ni accumulation and contamination levels in agricultural soils and wheat around a smelter in Jinchang City in northwest China were investigated with a combination of field investigations and indoor analytical tests, using a soil-wheat system as the study area. The average Cu and Ni contents in the soil were 119.50 mg kg-1 and 123.40 mg kg-1, respectively, both of which exceeded the local soil background values. The Cu and Ni contents in 46.15% o and 26.92% of sampling sites, respectively, exceeded the screening values for soil contamination risk in agricultural land in China. The average Cu content in different parts of wheat was in the order of roots (24.22 mg kg-1) > leaves (20.11 mg kg-1) > husks (5.51 mg kg-1) > grains (4.05 mg kg-1) > stalks (3.74 mg kg-1). Furthermore, the average Ni content ranked as leaves (24.64 mg kg-1) > roots (21.12 mg kg-1) > husks (6.95 mg kg-1) > stalks (1.75 mg kg-1) > grains (0.38 mg kg-1). The health risk evaluation showed that with average hazard index values of 0.88 for adults and 1.04 for children for Cu and Ni in wheat grain, wheat in this region is unlikely to pose a health risk to adults but may pose a lesser health risk to children. The Ni bio-concentration and translocation factors in the husk and leaves of wheat were greater than those of Cu and smaller than those of Cu in the other parts of wheat. The results of this study provide basic data for the remediation of heavy metal contamination in local agricultural soils.

Exploring the mechanism of Cd uptake and translocation in rice: Future perspectives of rice safety

Cadmium (Cd) contamination in rice fields has been recognized as a severe global agro-environmental issue. To reach the goal of controlling Cd risk, we must pay more attention and obtain an in-depth understanding of the environmental behavior, uptake and translocation of Cd in soil-rice systems. However, to date, these aspects still lack sufficient exploration and summary. Here, we critically reviewed (i) the processes and transfer proteins of Cd uptake/transport in the soil-rice system, (ii) a series of soil and other environmental factors affecting the bioavailability of Cd in paddies, and (iii) the latest advances in regard to remediation strategies while producing rice. We propose that the correlation between the bioavailability of Cd and environmental factors must be further explored to develop low Cd accumulation and efficient remediation strategies in the future. Second, the mechanism of Cd uptake in rice mediated by elevated CO2 also needs to be given more attention. Meanwhile, more scientific planting methods (direct seeding and intercropping) and suitable rice with low Cd accumulation are important measures to ensure the safety of rice consumption. In addition, the relevant Cd efflux transporters in rice have yet to be revealed, which will promote molecular breeding techniques to address the current Cd-contaminated soil-rice system. The potential for efficient, durable, and low-cost soil remediation technologies and foliar amendments to limit Cd uptake by rice needs to be examined in the future. Conventional breeding procedures combined with molecular marker techniques for screening rice varieties with low Cd accumulation could be a more practical approach to select for desirable agronomic traits with low risk.

Emergence of toxic trace elements in plant environment: Insights into potential of silica nanoparticles for mitigation of metal toxicity in plants

Emergence of trace elements at potentially toxic concentrations in the environment has become a global issue in recent times. Owing to the rapid population growth, unregulated industrialisation, intensive farming practices and excessive mining activities, these elements are accumulating in environment at high toxic concentrations. The exposure of plants to metal-contaminated environments severely influences their reproductive and vegetative growth, eventually affecting crop performance and production. Hence, it is crucial to find alternatives to mitigate the stress caused by toxic elements, in plants of agricultural importance. In this context, silicon (Si) has been widely recognized to alleviate metal toxicity and promote plant growth during various stress conditions. Amending soil with silicates has shown to ameliorate the lethal effects of metals and stimulates crop development. However, in comparison to silicon in bulk form, nano-sized silica particles (SiNPs) have been demonstrated to be more efficient in their beneficial roles. SiNPs can be used for various technological applications, viz. Improving soil fertility, agricultural yield, and remediating heavy metal-polluted soil. The research outcomes of studies focussing on role of silica nanoparticles to specifically mitigate the metal toxicity in plants have not been reviewed earlier in depth. The aim of this review is to explore the potential of SiNPs in alleviating metal stress and improving plant growth. The benefits of nano-silica over bulk-Si fertilizers in farming, their performance in diverse plant varieties, and the possible mechanisms to mitigate metal toxicity in plants have been discussed in detail. Further, research gaps are identified and future prospects are envisioned for advanced investigations in this field. The growing interest towards nano-silica related research will facilitate exploration of the true prospective of these nanoparticles for mitigation of metal stress in crops and in other fields of agriculture as well.

Foliar cadmium uptake, transfer, and redistribution in Chili: A comparison of foliar and root uptake, metabolomic, and contribution

Atmospheric deposition is an essential cadmium (Cd) pollution source in agricultural ecosystems, entering crops via roots and leaves. In this study, atmospherically deposited Cd was simulated using cadmium sulfide nanoparticles (CdS_N), and chili (Capsicum frutescens L.) was used to conduct a comparative foliar and root experiment. Root and foliar uptake significantly increased the Cd content of chili tissues as well as the subcellular Cd content. Scanning electron microscopy and high-resolution secondary ion mass spectrometry showed that Cd that entered the leaves via stomata was fixed in leaf cells, and the rest was mainly through phloem transport to the other organs. In leaf, stem, and root cell walls, Cd signal intensities were 47.4%, 72.2%, and 90.0%, respectively. Foliar Cd uptake significantly downregulated purine metabolism in leaves, whereas root Cd uptake inhibited stilbenoid, diarylheptanoid, and gingerol biosynthesis in roots. Root uptake contributed 90.4% Cd in fruits under simultaneous root and foliar uptake conditions attributed to xylem and phloem involvement in Cd translocation. Moreover, root uptake had a more significant effect on fruit metabolic pathways than foliar uptake. These findings are critical for choosing pollution control technologies and ensuring food security.

Detoxifying the heavy metals: a multipronged study of tolerance strategies against heavy metals toxicity in plants

Heavy metal concentrations exceeding permissible limits threaten human life, plant life, and all other life forms. Different natural and anthropogenic activities emit toxic heavy metals in the soil, air, and water. Plants consume toxic heavy metals from their roots and foliar part inside the plant. Heavy metals may interfere with various aspects of the plants, such as biochemistry, bio-molecules, and physiological processes, which usually translate into morphological and anatomical changes. They use various strategies to deal with the toxic effects of heavy metal contamination. Some of these strategies include restricting heavy metals to the cell wall, vascular sequestration, and synthesis of various biochemical compounds, such as phyto-chelators and organic acids, to bind the free moving heavy metal ions so that the toxic effects are minimized. This review focuses on several aspects of genetics, molecular, and cell signaling levels, which integrate to produce a coordinated response to heavy metal toxicity and interpret the exact strategies behind the tolerance of heavy metals stress. It is suggested that various aspects of some model plant species must be thoroughly studied to comprehend the approaches of heavy metal tolerance to put that knowledge into practical use.

Assessment of lettuces grown in urban areas for human consumption and as bioindicators of atmospheric pollution

This study proposes using the network of urban gardens to grow vegetables and to monitor air quality, and it also evaluates whether food grown on a clean substrate in an urban environment is safe for consumption. For this purpose, lettuces were exposed to different degrees of air pollution in five locations in the city of Copenhagen, plus a reference site. Six specimens were placed at each site and, after the exposure period, half of each sample was washed. Subsamples were then digested by a total extraction method and a bioaccessible extraction method, and the concentration of 23 elements subsequently measured by ICP-MS. The results showed that exposed samples in areas of higher atmospheric pollution accumulated a larger amount of trace elements associated with typical urban sources. They also highlighted the importance of washing food to remove particles that adhere to their surface. However, bioaccessibility testing demonstrated the importance of including bioaccessibility in risk analyses and how this factor varies depending on the type of matrix. In this case, bioaccessibility was higher for plant tissue than for particulate matter. Lastly, metal concentrations in lettuce were compared with legal values and an analysis of daily intake showed that the levels in Copenhagen were within limits for the protection of human health.

Managing health risks in urban agriculture: The effect of vegetable washing for reducing exposure to metal contaminants

A common, yet poorly evaluated, advice to remove contaminants from urban vegetables is to wash the produce before consumption. This study is based on 63 samples of chard, kale, lettuce and parsley that have grown near a heavily trafficked road in the third largest city in Sweden, with one portion of each sample being analysed without first being washed, and the other portion being subjected to common household washing. Concentrations of 71 elements were analysed by ICP-SFMS after a sample digestion that dissolves both the plant tissues and all potentially adhering particles. The results show that the washing effect, or the fraction removed upon washing, varies significantly between elements: from approximately 0 % for K to 68 % for the ∑REEs. Considering traditional metal contaminants, the efficiency decreased from Pb (on average 56 % lost) to Co (56 %) > Cr (55 %) > As (45 %) > Sb (35 %) > Ni (33 %) > Cu (13 %) > Zn (7 %) > Cd (7 %), and Ba (5 %). A clear negative correlation between the washing effect and the different elements' bioconcentration factors shows that the elements' accessibility for plant uptake is a key controlling factor for the degree to which they are removed upon washing. Based on the average washing efficiencies seen in this study, the average daily intake of Pb would increase by 130 % if vegetables are not washed prior to consumption. For the other contaminant metals this increase corresponds to 126 % (Co), 121 % (Cr), 82 % (As), 55 % (Sb), 50 % (Ni), 16 % (Cu), 8 % (Zn), 7 % (Cd) and 5 % (Ba). The advice to wash vegetables is therefore, for many elements, highly motivated for reducing exposure and health risks. For elements which are only slightly reduced when the vegetables are washed, however, advising should rather focus on reducing levels of contamination in the soil itself.

Air quality in post-mining towns: tracking potentially toxic elements using tree leaves

In this study, leaves of the evergreen holm oak Quercus ilex were used to assess airborne contamination of potentially toxic elements (PTEs) at five towns located on the slopes of the Mt. Amiata (central Italy), an area with a long history of mining and, more recently, an important district for the industrial exploitation of geothermal energy. PTE composition and covariance of washed and unwashed Q. ilex leaves of three different ages (6, 12 and 24 month-old) were used to identify atmospheric inputs of PTEs at residential areas, evaluate long-term adsorption and retention of PTEs by the leaves, thus providing an indication of potential human exposure. Moreover, the determination of foliar concentrations of major elements (C, N, S and P) allowed an assessment of the nutritional status of the investigated urban tree stands which excluded the existence of stress condition caused by air pollution or other disturbances. Results indicated that overall Pb, Cu, and Cd concentration were low in the investigated urban sites, if compared with similar studies conducted in larger Italian cities, denoting a low contribution of vehicular traffic to the atmospheric pathway. The five urban settlements were characterized by a specific profile of elements (Al, Ba, Hg and Sb) enriched in unwashed leaves, resulting from the distinct geochemical characteristics of the area and from diffuse (i.e., urban activity) and point sources of PTEs emission (i.e., brownfields, geothermal power plants). The latter sources primarily govern the distribution of Hg, whose contamination was found to be very localized close to a major abandoned mining area. Our data provided quantitative evidence of the spectrum of PTEs potentially impacting resident population and may prove useful in support of follow-up instrumental monitoring campaigns of air quality, as well as for human health and ecological risk assessments.

Heavy metals accumulation in wheat (Triticum aestivum L.) roots and shoots grown in calcareous soils treated with non-spiked and spiked sewage sludge

With growing urbanization and agriculture, the quantity of sewage sludge production increases every year. For the purpose of risk management, it is crucial to figure out how much heavy metals are transported to different parts of plants when sewage sludge is used. A greenhouse experiment was carried out to investigate the accumulation of heavy metals in wheat (Triticum aestivum L.) grown in 30 calcareous soils. The soils in this study were subjected to three different treatments: soils treated with sewage sludge at a rate of 2.5%, soils treated with sewage sludge at a rate of 2.5% and enriched with heavy metals, and control soils that received neither sewage sludge nor heavy metals. Wheat grown in sewage sludge-treated soils had the highest mean dry matter, and was 2.11 and 1.25 times greater than wheat grown in control and spiked-sewage sludge-treated soils, respectively. In all treatments, wheat roots had greater heavy metal levels than wheat shoots. Among all the heavy metals examined, Pb and Cu had the highest bioconcentration factors for roots and shoots (BCF_Roots and BCF_Shoots) in control and sewage sludge-treated soils, followed by Cd in spiked-sewage sludge-treated soils, and Co and Ni had the lowest BCF_Roots and BCF_Shoots across all treatments. In spiked-sewage sludge-treated soils, the root restriction for heavy metals translocation was more important for Co, Cu, and Ni than for Pb and Zn, indicating that wheat can be grown safely in a variety of calcareous soils amended with sewage sludge with high content of Cd, Co, Cu, and Ni. Reducing the transfer of Pb and Zn from soils to wheat in soils treated with sewage sludge yet having high concentrations of these heavy metals should be considered as a top priority strategy for preserving wheat products. Since a wide range of calcareous soils was used in this study and because calcareous soils make up the majority of soils in the Middle East, the findings are relevant for all of the countries in this region.

Convolutional graph neural networks-based research on estimating heavy metal concentrations in a soil-rice system

Estimating heavy metal concentrations in soil-rice systems is of great significance to identify the factors controlling heavy metal transfer in soil-crop ecosystems. Recent research utilizes the advantage of convolutional calculations to extract and learn complicated information from 17 environmental covariates in rice and achieve promising results. However, as the complexity and interconnectivity in soil-crop ecosystem, just relying on convolutional calculations and a deep network structure is far from enough. The data processed by traditional deep learning technologies even with convolutional calculations are limited to Euclidean space; these architectures do not have the ability to extract information from the relationships in graph structures, which may contain rich information. Thus, in this paper, we try to integrate graph information into convolutional calculations for heavy metal prediction and propose a model named ConvGNN-HM. ConvGNN-HM combines the advantages of graph learning and convolutional calculations to predict heavy metal concentrations in a soil-rice system with analysis of 17 environmental factors. For comparison, we conduct an experiment to compare ConvGNN-HM with techniques with convolutional neural networks, multilayer perceptron, back-propagation neural networks, support vector machine, random forest, Bayesian ridge regression, and multiple linear regression. The experimental results illustrate that ConvGNN-HM got the best prediction values; the R² values of ConvGNN-HM for cadmium (Cd), plumbum (Pb), chromium (Cr), arsenic (As), and hydrargyrum (Hg) in rice were 0.84, 0.75, 0.79, 0.49, and 0.83, respectively, and the MAE values were also acceptable. We further conduct sensitivity analysis to demonstrate the stability and robustness of ConvGNN-HM. This study demonstrates the usefulness of combining graph learning and convolutional calculations in the prediction of heavy metal concentrations and provides a new perspective to build multidimensional and multi-scale complex ecosystem models.

Insights into site-specific influences of emission sources on accumulation of heavy metal(loid)s in soils by wheat grains

Excessive accumulation of heavy metal(loid)s in agricultural environment usually originates from anthropogenic activities. Both large diversities of emission sources and complexity of plant accumulation challenge the understanding of the site-specific effects of emission sources on heavy metal(loid)s in wheat grains. Herein, both soil samples and wheat grain samples (n = 80) were collected from the farmland of Jiyuan City, China. Soil and grain burdens of heavy metal(loid)s were determined by inductively coupled plasma mass spectrometry (ICP-MS) and/or X-ray fluorescence spectrometry (XRF). The quotients (Q) were developed to indicate relative impacts of industrial plants and traffic to soil sites. Principal component analysis-absolute principal component scores-multivariate linear regression (PCA-APCS-MLR) analysis was conducted to reveal the source contributions to heavy metal(loid)s in grains, considering Q values, soil, and wheat grain data. Results showed that contributions of main sources and factors drastically varied with soil sites, and usually overlapped to different extents. For grain Cd and grain Pb, natural soil silicate (0.066/0.104 mg/kg) and iron-bearing minerals (- 0.044/ - 0.174 mg/kg) contributed to high extents, while metal smelting activities (0.018/0.019 mg/kg) and agronomic activities (- 0.017/ - 0.019 mg/kg) unexpectedly posed low or moderate contributions. The pH-mediated availability of soil Cd (0.035 mg/kg) and the sand-dust weather (0.028 mg/kg) also made considerable contributions to grain Cd. For grain As, both natural soil iron-bearing (- 0.048 mg/kg) and silicate minerals (- 0.013 mg/kg) made negative contributions. The results benefit to the decision-making of pollution remediation of farmland soils in the regional scales.

Foliar uptake, accumulation, and distribution of cadmium in rice (Oryza sativa L.) at different stages in wet deposition conditions

Atmospheric deposition of cadmium (Cd) in rice (Oryza sativa L.) has become a major global concern. Foliar uptake allows vegetables to accumulate heavy metals from the atmosphere, but this has rarely been studied in rice. Therefore, this study investigated the Cd accumulation in rice growing at different exposure periods (the tillering, booting, heading, and maturity stages) under a wet deposition of CdCl₂·2.5H₂O solution through pot experiments. The Cd concentrations in leaves, roots, husk, brown rice, and leaf structures were analyzed to explore foliar uptake, accumulation, and distribution of Cd in rice tissues at different growth stages. The results showed that wet deposited Cd can be absorbed on the rice leaf surface and remains on the leaves for a long time. The sequence of Cd accumulation in rice tissues was: leaves > brown rice > husk > roots, with leaves accounting for greater than 71.78% of the total accumulation. The accumulation of wet deposited Cd in leaves, husk, and brown rice had large temporal variations between the four typical stages. There was no significant variations in Cd content in roots between different growth stages. Correspondingly, the foliar uptake of Cd was rarely transported from the leaves via the phloem to roots. Conversely, the foliar uptake of Cd was transported upwards to grains. The accumulation of Cd fluctuated with each growth stage, initially increasing and then decreasing at the heading stage and finally reaching a peak at the maturity stage. The highest total accumulation of Cd in both the high and low wet deposition conditions occurred at maturity, resulting in 15.53 and 11.23 μg plant^-1, respectively. These results provide theoretical support for further research into identifying efficient foliar control measures to reduce Cd accumulation and maintain food safety.

Convolutional neural network-based applied research on the enrichment of heavy metals in the soil-rice system in China

The enrichment of heavy metals in the soil-rice system is affected by various factors, which hampers the prediction of heavy metal concentrations. In this research, a prediction model (CNN-HM) of heavy metal concentrations in rice was constructed based on convolutional neural network (CNN) technology and 17 environmental factors. For comparison, other machine learning models, such as multiple linear regression, Bayesian ridge regression, support vector machine, and backpropagation neural networks, were applied. Furthermore, the LH-OAT method was used to evaluate the sensitivity of CNN-HM to each environmental factor. The results showed that the R² values of CNN-HM for Cd, Pb, Cr, As, and Hg were 0.818, 0.709, 0.688, 0.462, and 0.816, respectively, and both the MAE and RMAE values were acceptable. The sensitivity analysis showed that the concentrations of Cd and Pb, mechanical composition, soil pH, and altitude were the main sensitive features for CNN-HM. Compared with CNN-HM based on all input features, the performance of the quick prediction model that was based on the sensitive features did not degrade significantly, thereby indicating that CNN-HM has stronger stability and robustness. The quick prediction model has extensive application value for timely prediction of the enrichment of heavy metals in emergencies. This study demonstrated the effectiveness and practicability of CNNs in predicting heavy metal enrichment in the soil-rice system and provided a new perspective and solution for heavy metal prediction.

Leaf fitness and stress response after the application of contaminated soil dust particulate matter

In this study, we observed the effect of the application of soil dust enriched with risk elements (Cd, Pb, As and Zn) to leaf surfaces of lettuce (Lactuca sativa var. capitata) while it was grown under hydroponic conditions. This study aimed to determine how low soil dust particulate matter (PM) doses affected the activity of or damaged the photosynthetic apparatus and how the uptake of risk elements was associated with both epigenetic changes (5-methylcytosine content, i.e., 5mC) and stress metabolism. During the study, we obtained many results pertaining to risk element contents and biochemical (total phenolic content (TPC), malondialdehyde (MDA) content and the amount of free amino acids (AAs)) and physiological (photosynthesis parameters: net photosynthetic rate, transpiration rate, intercellular CO2 concentration, stomatal conductance, instantaneous water-use efficiency, maximum quantum yield of PSII, chlorophyll and carotenoid contents, and leaf water potential (WP)) plant features. The results showed an increase in MDA and 5mC. However, the transpiration rate, WP and free AAs decreased. In conclusion, contamination by very low doses of soil dust PM had no direct or significant effect on plant fitness, as shown by the TPC and 5mC content, which indicates that plants can overcome the oxidative stress caused by the accumulation of risk elements. From the above, we propose the use of epigenetic changes as biomarkers of potential changes in the activation of plant metabolism under stress caused by environmental pollution.

Spatiotemporal Differences and Ecological Risk Assessment of Heavy Metal Pollution of Roadside Plant Leaves in Baoji City, China

The concentration of heavy metals in plants’ leaves can effectively indicate the spatiotemporal differences of environmental pollution, providing a scientific basis for the monitoring of urban air quality. The concentration of Ni, Cu, Cd, Pb and Zn in the leaves of five different species (Ophiopogon japonicus, Ligustrum vicaryi, Platanus acerifolia, Sophora japonicaand Cedrusdeodara) were measured, which were from I, II, III, IV (0.05 m, 0.25 m, 1 m, 4 m) at different times (May and November) in the green belt of Baoji city. The degree of heavy metal pollution and potential ec ological risk were analyzed. The results revealed that the concentration of Zn, Cu and Pb in roadside plant leaves was relatively high. In May, the heavy metal concentration was the highest in the leaves of C.deodara, whereas this was the case for S. japonica in November. Arbors were more effective at capturing particles from the atmosphere than low plants. At the same height, areas with high levels of heavy metal pollution in May were basically the same as that in November, and areas with high levels of pollution were affected by traffic and industry. The pollution index and the comprehensive index of potential ecological risk of element Cd were the highest, indicating that the potential harm of Cd to the environment should receive more attention from the Government.

Concentrations and transportation of metal and organochlorine pollutants in vegetables and risk assessment of human exposure in rural, urban and industrial environments (Bouches-du-Rhône, France)

The bioaccumulation of metals (As, Cd, Co, Cr, Cu, Ni, Pb, Sb, V, Zn, Al, Fe) and organochlorine compounds (PCDD-Fs and PCBs) was assessed in soils and vegetables of 3 sites of contrasted anthropogenic influence (rural and industrial-urban areas). Cultivated soils in industrial areas exhibited diffuse pollution in organochlorine pollutants (PCBs and PCDD-Fs). The pollutant levels encountered in vegetables were always lower than the EU regulatory or recommended values. However, the contents measured in vegetables cultivated near industrialized areas were significantly higher than those observed in rural areas. This was notably the case for Co, Cd, Cr, Ni, Pb, V, NDL- and DL-PCB, PCDD, and PCDF. The leaf pathway appeared as the main absorption pathway for many contaminants. The results suggested that population exposure to pollutants was mainly caused by vegetable ingestion. In the vegetables and soils, the toxicity was mainly caused by the V, Co, Cd, and Pb contents to which can be added As and PCDD-Fs for soils. Therefore, the proximity of vegetable crops to highly anthropised areas has led to long-term exposure of vegetables and soils to air pollutants, leading to an accumulation in the food chain and thus a risk for human health.

Performance and retention mechanisms of corn silk to atmospheric heavy metal lead

Atmospheric heavy metals are seriously harmful, and porous materials have unique advantages in the control of air pollutants. However, the direct use of plant porous materials to purify atmospheric heavy metals are rare. So agricultural waste corn silk with porous structures was selected to analyze the retention capability and mechanism to the atmospheric lead. The results show that the corn silk can effectively retain atmospheric lead in natural growing state or fixed experimental conditions. The analysis of a total of 765 corn silk samples from 17 different regions in Shandong province, China, shows that atmospheric lead is the main source of lead in the corn silk, and corn silk can be used for biological monitoring of atmospheric lead to some extent. Based on the analysis with different techniques including scanning electron microscope (SEM), energy spectrum dispersive X-ray spectrometer (EDS), Fourier infrared spectrometer (FTIR) and Zeta potential, the effective retention of lead by corn silk is due to a variety of mechanisms, including physical adsorption, electrostatic adsorption, complexation, chelation and ion exchange. So agricultural waste corn silk has great potential in the application of biosorption or preparation of porous materials in purification of atmospheric heavy metals.

Phyllosphere microbiome: Diversity and functions

Phyllosphere or aerial surface of plants represents the globally largest and peculiar microbial habitat that inhabits diverse and rich communities of bacteria, fungi, viruses, cyanobacteria, actinobacteria, nematodes, and protozoans. These hyperdiverse microbial communities are related to the host's specific functional traits and influence the host's physiology and the ecosystem's functioning. In the last few years, significant advances have been made in unravelling several aspects of phyllosphere microbiology, including diversity and microbial community composition, dynamics, and functional interactions. This review highlights the current knowledge about the assembly, structure, and composition of phyllosphere microbial communities across spatio-temporal scales, besides functional significance of different microbial communities to the plant host and the surrounding environment. The knowledge will help develop strategies for modelling and manipulating these highly beneficial microbial consortia for furthering scientific inquiry into their interactions with the host plants and also for their useful and economic utilization.

Effectiveness of plants and green infrastructure utilization in ambient particulate matter removal

Air pollution is regarded as an increasingly threatening, major environmental risk for human health. Seven million deaths are attributed to air pollution each year, 91% of which is due to particulate matter. Vegetation is a xenobiotic means of removing particulate matter. This review presents the mechanisms of PM capture by plants and factors that influence PM reduction in the atmosphere. Vegetation is ubiquitously approved as a PM removal solution in cities, taking various forms of green infrastructure. This review also refers to the effectiveness of plant exploitation in GI: trees, grasslands, green roofs, living walls, water reservoirs, and urban farming. Finally, methods of increasing the PM removal by plants, such as species selection, biodiversity increase, PAH-degrading phyllospheric endophytes, transgenic plants and microorganisms, are presented.

Adsorption of nanoparticles suspended in a drop on a leaf surface of Perilla frutescens and their infiltration through stomatal pathway

Particulate matter (PM) has become a severe environmental issue, and ultrafine PM particles such as PM2.5 or PM1 can cause various complications and respiratory diseases to human beings. In particular, heavy metals contained in PM particles can contaminate edible plants; for example, plant leaves are exposed to PM particle-laden raindrops. The contaminated edible plants can injure the human health by ingestion, so a detailed understanding on the accumulation of PM particles inside edible plants is essential. In this study, we investigate the infiltration of PM particles in plant tissues with a hypothesis that ultrafine PM particles are absorbed through stomatal pathways. As an edible test plant, Perilla frutescens is selected. Drops of gold nanoparticle (AuNP) suspension are deposited on a leaf of P. frutescens to simulate the scenario where PM particle-laden raindrops fall on patulous stomata of the test plant. To examine AuNP adsorption on the P. frutescens foliar surface and diffusional AuNP absorption through stomatal apertures, we investigate three physical dynamics of AuNPs suspended in a sessile drop: sedimentation, evaporation-driven convective flow, and shrinkage of the drop interface. Quantitative information on the 3D spatial distribution of AuNPs in plant tissues was measured by X-ray imaging and two-photon excitation microscopy.

Impact of particulate matter on primary leaves of Vigna radiata (L.) R. Wilczek

Particulate matter (PM) pollution is of great concern for human health and vegetation. In this study, we investigated the impact of PM on primary (unifoliate) leaves of Vigna radiata (L.) R.Wilczek by exposing leaves' adaxial surface to PM. Leaves exposed to PM showed accumulation of various metal(loid)s even after removal of epicuticular wax (EW) revealing that the metals/metalloids could penetrate through the cuticular barrier. Scanning electron microscopic studies revealed that even after thorough washing with water, a significant amount (~55%) of particles were retained on the leaf surface. Leaves did not show any particles on their surface post EW removal, revealing that particles adhered to EW. Exposing primary leaves to PM did not alter their size but gave rise to smaller sized trifoliate leaves. A decline in Chl a/b of PM-exposed primary leaves suggested that PM cause a shading effect on leaves. PM-exposed primary leaves also showed a decline in sugar levels. However, the trifoliate leaves did not show any variation in Chl a/b as well as sugar levels. Our findings furnish evidence for the negative effects of PM on plants and a probable dietary exposure of humans to PMs, warranting more in-depth studies on the potential risks of PMs in agricultural sector.

Foliar uptake, biotransformation, and impact of CuO nanoparticles in Lactuca sativa L. var. ramosa Hort

Plant leaves can intercept and directly absorb nanoparticles (NPs) that deposit on their surface, which can lead severe phytotoxicity. However, there is a large blind spot when it comes to the fate and phytotoxicity of NPs after leaf exposure, even though foliar uptake is likely to occur. In this study, lettuce leaves (Lactuca sativa L. var. ramosa Hort.) were exposed to different concentrations of copper-oxide NPs (CuO-NPs, 0, 100, and 1000 mg L-1) for 5, 10, and 15 days. Foliar uptake, subcellular distribution, chemical forms, and impact of CuO-NPs on nutrient status, antioxidant systems, and lettuce growth were examined. Substantially elevated Cu levels were observed in lettuce leaves (up to 6350 mg kg-1), which was one magnitude greater than that in the roots (up to 525 mg kg-1). Cu translocation factors from leaves to roots ranged from 1.80 to 15.6%. The application of CuO-NPs severely inhibited lettuce growth and altered the nutrient status in plants (especially Mn, K, and Ca). Moreover, CuO-NPs increased H2O2 generation, malonaldehyde level (on the 5th and 10th day of exposure), and catalase activity (on the 15th day of exposure) in lettuce leaves. The Cu concentrations in subcellular fractions were ranked: cell wall ≈ organelles > soluble fraction in lettuce leaves, and organelles > cell wall > soluble fraction in lettuce roots. Undissolved Cu forms were predominant in lettuce, which may have helped to reduce the Cu's mobility and phytotoxicity in the plant. The findings of this study will be of great interest in areas with high levels of metal-NPs in the atmosphere.

Ecotoxicology of Heavy Metal(loid)-Enriched Particulate Matter: Foliar Accumulation by Plants and Health Impacts

Atmospheric contamination by heavy metal-enriched particulate matter (metal-PM) is highly topical nowadays because of its high persistence and toxic nature. Metal-PMs are emitted to the atmosphere by various natural and anthropogenic activities, the latter being the major source. After being released into the atmosphere, metal-PM can travel over a long distance and can deposit on the buildings, water, soil, and plant canopy. In this way, these metal-PMs can contaminate different parts of the ecosystem. In addition, metal-PMs can be directly inhaled by humans and induce several health effects. Therefore, it is of great importance to understand the fate and behavior of these metal-PMs in the environment. In this review, we highlighted the atmospheric contamination by metal-PMs, possible sources, speciation, transport over a long distance, and deposition on soil, plants, and buildings. This review also describes the foliar deposition and uptake of metal-PMs by plants. Moreover, the inhalation of these metal-PMs by humans and the associated health risks have been critically discussed. Finally, the article proposed some key management strategies and future perspectives along with the summary of the entire review. The abovementioned facts about the biogeochemical behavior of metal-PMs in the ecosystem have been supported with well-summarized tables (total 14) and figures (4), which make this review article highly informative and useful for researchers, scientists, students, policymakers, and the organizations involved in development and management. It is proposed that management strategies should be developed and adapted to cope with atmospheric release and contamination of metal-PM.

Phytohormonal Roles in Plant Responses to Heavy Metal Stress: Implications for Using Macrophytes in Phytoremediation of Aquatic Ecosystems

Heavy metals can represent a threat to the health of aquatic ecosystems. Unlike organic chemicals, heavy metals cannot be eliminated by natural processes such as their degradation into less toxic compounds, and this creates unique challenges for their remediation from soil, water, and air. Phytoremediation, defined as the use of plants for the removal of environmental contaminants, has many benefits compared to other pollution-reducing methods. Phytoremediation is simple, efficient, cost-effective, and environmentally friendly because it can be carried out at the polluted site, which simplifies logistics and minimizes exposure to humans and wildlife. Macrophytes represent a unique tool to remediate diverse environmental media because they can accumulate heavy metals from contaminated sediment via roots, from water via submerged leaves, and from air via emergent shoots. In this review, a synopsis is presented about how plants, especially macrophytes, respond to heavy metal stress; and we propose potential roles that phytohormones can play in the alleviation of metal toxicity in the aquatic environment. We focus on the uptake, translocation, and accumulation mechanisms of heavy metals in organs of macrophytes and give examples of how phytohormones interact with plant defense systems under heavy metal exposure. We advocate for a more in-depth understanding of these processes to inform more effective metal remediation techniques from metal-polluted water bodies. Environ Toxicol Chem 2021;40:7-22. © 2020 SETAC.

Particulate Matter Accumulation on Apples and Plums: Roads Do Not Represent the Greatest Threat

Particulate matter (PM) is a mixture of solid and liquid substances of organic and inorganic character suspended in air. Plants are used as biological filters of air. However, PM can be deposited on their edible parts, with a negative effect on people’s health. The aim of this study was to document the PM accumulation on apples and plums harvested from orchards located alongside roads with differing amounts of traffic. Plums accumulated more PM than apples. The deposition of PM on apples increased during fruit development and was highest at harvest. The impact of road type, traffic intensity, and distance from the road on PM accumulation on fruit was small. The least PM was adsorbed by apples harvested from an orchard located close to a road with the highest traffic, while in the case of plums, no effect of the road on PM deposition was recorded. The amount of PM accumulated on fruits depended on the species (fruit morphology, harvest period), activities undertaken in the orchard (early pruning exposes fruits to PM, ecological preparations increase fruit viscosity), and sources of pollution other than the roads located close to the orchard. Washing fruits with water removed half of the accumulated PM.

Foliar application of lead and arsenic solutions to Spinacia oleracea: biophysiochemical analysis and risk assessment

Atmospheric contamination by heavy metal(loid)s is a widespread global issue. Recent studies have shown foliar pathway of heavy metal(loid) uptake by plants, thus menacing plant productivity and threatening health risks. In contrast to root uptake of heavy metal(loid)s, there is scarce data available on heavy metal(loid) foliar uptake, accumulation in different plant parts, changes in growth and other biophysiochemical processes/reactions, detoxification mechanisms and associated health risks due to the consumption of contaminated vegetables. This study evaluated the effect of foliar application of two potentially toxic metal(loid)s (arsenic (As) and lead (Pb)) on their uptake by Spinacia oleracea, plant growth, pigment contents, physiological changes, and activation of antioxidative enzymes. Results revealed that S. oleracea seedlings can accumulate both the metal(loid)s in their leaves via foliar pathway. Arsenic was transferred from the leaves towards the roots, while Pb was mainly sequestered in S. oleracea leaves. Both the metal(loid)s significantly decreased plant growth and pigment contents, As being more toxic than Pb. Foliar application of As and Pb did not cause lipid peroxidation and overproduction of reactive oxygen species (ROS). However, both the metal(loid)s enhanced the activities of antioxidative enzymes. We also calculated possible health risks (both non-carcinogenic and carcinogenic) due to As and Pb accumulation in the edible parts for both the adults and children. It was observed that As can induce non-carcinogenic effects (HQ > 1) in children only, while both As and Pb can cause carcinogenic hazards in both adults and children under their all applied foliar levels. Therefore, it is proposed that As and Pb contents in the atmosphere must be monitored continuously for their possible foliar uptake and accumulation in edible plant parts to avoid cancer risks. Moreover, multivariate analysis traced weak-strong correlations between metal(loid) treatments and plant response variables.

Urban kitchen gardens: Effect of the soil contamination and parameters on the trace element accumulation in vegetables - A review

Trace element contaminants in kitchen garden soils can contribute to human exposure through the consumption of homegrown vegetables. In urban areas, these soils can be contaminated to various degrees by trace element (TE). They are characterized by a great variability in their physicochemical parameters due to the high anthropization level, the wide variety and combination of disturbance sources, as well as the diversity of cultivation practices and the large range of contamination levels. Pollutants can be taken up by vegetables cultivated in these soils and be concentrated in their edible parts. In this review, the behavior of vegetables cultivated in contaminated kitchen gardens is assessed through six examples of the most widely cultivated vegetables (lettuce, tomato, bean, carrot, radish, potato). The role of soil parameters that could influence the uptake of As, Cd, Cr, Ni, Pb, and Zn by these vegetables is also discussed.

Estimating the contribution of atmosphere on heavy metals accumulation in the aboveground wheat tissues induced by anthropogenic forcing

The influence of atmosphere pollution on human health is receiving more and more concerns as strengthened anthropogenic activity had brought excessive pollutant into the atmosphere. To date, the quantitative estimation about the contribution of atmosphere on the accumulation of heavy metal in the edible cereal parts induced by anthropogenic forcing is scarce. Taking the Yangtze River Delta area, China as an example, this study estimates quantitatively the influence of atmosphere on the concentration of heavy metal in the aboveground wheat tissues induced by anthropogenic industrial activity at the regional scale. The results show that the aboveground wheat tissues in the southern Yangtze River Delta area accumulated much more heavy metals than that in the northern area, although there is no significant difference in the geological and climate conditions, soil types, agricultural manages, wheat cultivar and soil heavy metals concentrations (even heavy metals concentrations in wheat root) between the southern area and northern area. The mean concentrations of Pb, Zn, Cu and Cd in wheat grain in southern area have exceeded the thresholds of contamination levels. The present study suggests that the influence of atmosphere on the accumulation of Hg, Cd, Pb, Zn, Cu, Ni and Cr in the aboveground wheat tissues is greatly significant when high amounts of pollutant are measured in the atmosphere. Based on translocation coefficient of the element, it is estimated that atmospheric pollution induced by anthropogenic forcing might lead to the concentration of heavy metals in wheat straw and grain increase by approximately 100% and 354% (Hg), 64% and 293% (Pb), 122% and 160% (Cr), 50% and 38% (Cd) and 14% and 41% (Cu), respectively.

Foliar uptake and transport of atmospheric trace metals bounded on particulate matters in epiphytic Tillandsia brachycaulos

Epiphytic Tillandsia species are uniquely suitable for the study of foliar uptake of atmospheric trace metals (ATM) because these plants can only rely on their leaves for this purpose. Therefore, we analyzed the uptake and transport of different metals (Fe, Al, Zn, Mn, Ba, Ti, Cu, Ni, Cr, Sn, Pb, Co, As, and Se) bounded on atmospheric particulate matters (APM) in Tillandsia brachycaulos Schltdl. The results showed that the metal contents inside leaves significantly (p < .05) increased after APM exposure. There was a significant (p < .05) positive correlation between the content of 14 trace metals accumulated on the leaf surface and inside the leaf, which indicated that APM is the main source of ATM uptake. The subcellular analysis showed that the Pb, Cu, Ni, Zn, and Cr absorbed by T. brachycaulos were stored primarily in the cell walls and organelles. After the removal of foliar trichomes of T. brachycaulos, the metal contents on the leaf surface decreased, whereas the contents of most metals inside the leaf increased. This is an evidence that foliar trichomes serve a protective function by intercepting ATM onto the leaf surface.Novelty statementsThere was a significant positive correlation between the contents of 14 trace metals accumulated on the leaf surface and in the leaf of T. brachycaulos, which indicated that atmospheric particulate matters are the main source of trace metals in the leaves.After the removal of foliar trichomes of T. brachycaulos, the trace metal contents on the leaf surface decreased, whereas the contents of most trace metals inside the leaf increased. This is an evidence that foliar trichomes serve a protective function by intercepting atmospheric trace metals onto the leaf surface.

Effect of industrial wastewater on wheat germination, growth, yield, nutrients and bioaccumulation of lead

Due to fresh water scarcity, farmers are using polluted water for irrigation. This research was conducted to study the bioaccumulation of Pb in wheat (Cv. Shafaq-2006). The experiment was comprised of seven treatments of lead i.e. 0–1,000 mg Pb/kg. The results revealed that lead severely reduces germination (− 30%), seedling fresh weight (− 74%), seedling dry weight (− 77%), vigor index (− 89%), tolerance index (− 84%), plant height (− 33%), number of leaves (− 41%), root fresh weight (− 50%), shoot fresh weight (− 62%), root dry weight (− 63%), shoot dry weight (− 71%), and root length (− 45%). The physiological parameters also respond negatively like stomatal conductance (− 82%), transpiration rate (− 72%) and photosynthetic rate (− 74%). Similarly, biochemical parameters also showed negative impacts, like carotenoids (− 41), total chlorophyll (− 43), chlorophyll a (− 42) and chlorophyll b (− 53). Yield parameters like the number of seed/plant, seed weight/plant, 1,000 seed weight and harvest index were reduced by 90%, 88%, 44% and 61%, respectively in T₆. In addition, protein contents (− 81%), phosphorous (− 60%) and potassium (− 55%) were highly effected in the highest lead concentration (T₆). Lead accumulation was extremely higher in seeds (119%) as compared to control plants. Lead bio-accumulation above threshold concentrations in crop parts is a serious human health concern.

Risk assessment and biophysiochemical responses of spinach to foliar application of lead oxide nanoparticles: A multivariate analysis

Despite extensive research progress in the recent past, the data regarding foliar uptake of heavy metals, associated biophysiochemical changes inside plants and possible health hazards are limited. This study determined the effect of foliar application of lead oxide nanoparticles (PbO-NPs) on lead (Pb) accumulation, physiological and biochemical changes inside spinach plants and associated health risks. A green method was used to prepare PbO-NPs using coconut water. Scanning electron microscopy (SEM) showed the preparation of smooth, unwrinkled, granular and spherical PbO-NPs. Spinach leaves were exposed via foliar application to three concentrations of PbO-NPs (0, 10 and 50 mg/plant). Foliar PbO-NPs application resulted in a significant accumulation of Pb in leaves (42.25 μg g^-1), with limited translocation towards root tissues (4.46 μg g^-1). This revealed that spinach can accumulate considerable amount of Pb via foliar uptake. Lead accumulation inside spinach caused a significant decrease in pigment contents (38%) and dry weight (67%). After foliar uptake, Pb caused several-fold increase in the activities of catalase and peroxidase. However, foliar PbO-NPs did not induce significant changes in H₂O₂ production, lipid peroxidation and superoxide dismutase activity. Application of PbO-NPs (50 mg/plant) showed possible health risks (non-carcinogenic) due to ingesting Pb-contaminated leaves of spinach. It is proposed that atmospheric contamination and foliar deposition of metal-PM can seriously affect vegetable growth and can provoke health issues due to ingestion of metal-enriched vegetables. Therefore, atmospheric levels of heavy metals need to be monitored on a regular basis to avoid their food chain contamination and possible human exposure.

Changes in heavy metal accumulation in some edible landscape plants depending on traffic density

Food scarcity is one of global issues that our world faces today. A significant portion of the world's population has no access to adequate food, and it is stated that approximately 830 million people suffer from chronic famine. This predicament is estimated to grow even further. Many attempts have been made to solve the food problem. Some examples are using new resources which have not been used for dietary purposes up to this point, planting new areas to produce food products, and increasing the potential harvest per an area unit. One of the solution proposals, which has come up recently within this scope, is the term of "edible landscaping", which means the use of edible plants in the landscaping works, and thus maximizing the potential for food security. However, edible landscaping poses a considerable risk. Heavy metal accumulation in plants grown in urban centers can reach to high levels, and consuming these plants will allow these heavy metals a direct access into the human body and wreak havoc to the public health. But since this subject has not been sufficiently studied yet, the extent of such a risk is not accurately determined yet. This study aims to determine the changes of Ni, Co and Mn concentrations depending on traffic density in the leaves, branches, barks and fruits of cherry, plum, mulberry and apple trees growing in areas with dense traffic, low-density traffic and no-traffic zones in Kastamonu province. The results showed that the concentrations of Ni and Co elements increased in many organelles depending on traffic density, and that the heavy metal concentrations in fruits could be very high. This situation indicates that fruit and vegetables grown in industrial zones and urban centers, where heavy metal pollution may be high, can be harmful to the public health if consumed as crops.

Determination of Pb and Mg accumulation in some of the landscape plants in shrub forms

Heavy metals have a separate precaution in the air pollution components as they are not easily deteriorated in nature, they tend to bioaccumulate, they are carcinogenic or poisonous, and they can be toxic even at low concentrations. Therefore, monitoring of heavy metal pollution is of great importance. Plants are frequently used as biomonitors to monitor the heavy metal pollution. However, the heavy metal accumulation capacities of plants can vary considerably depending on the plant species, as well as on the organelle basis and the amount of particulate matter in the environment. It is also very important to determine how much of the heavy metal concentrations found in plants are derived from the plant species and how much from the particulate matter on the organ. In this study, it was aimed to determine the change of heavy metal accumulation in some landscape plants grown in the city center of Kastamonu depending on plant type, plant organism, washing status, and traffic density. For this purpose, leaf and branch samples were collected from individuals of Ligustrum vulgare L., Euonymus japonica Thunb., Biota orientalis L., Juniperus sabina L., Berberis thunbergii DC, Mahonia aquifolium (Pursh) Nutt., and Buxus sempervirens L., which are frequently used in urban landscape designs growing in areas with heavy, low dense, and no traffic. Some of the collected samples were washed, and heavy metal analyses were conducted to determine the amount of Pb and Mg concentrations. It was remarkable that Pb concentration was higher in branches than in the leaves for all the species. And the alteration depending on traffic density on the base of the factors studied was in different proportion depending on the metals.

Impacts of atmospheric particulate matter pollution on environmental biogeochemistry of trace metals in soil-plant system: A review

Atmospheric particulate matter (PM) pollution and soil trace metal (TM) contamination are binary environmental issues harming ecosystems and human health, especially in the developing China with rapid urbanization and industrialization. Since PMs contain TMs, the air-soil nexus should be investigated synthetically. Although the PMs and airborne TMs are mainly emitted from urban or industrial areas, they can reach the rural and remote mountain areas owing to the ability of long-range transport. After dry or wet deposition, they will participate in the terrestrial biogeochemical cycles of TMs in various soil-plant systems, including urban soil-greening trees, agricultural soil-food crops, and mountain soil-natural forest systems. Besides the well-known root uptake, the pathway of leaf deposition and foliar absorption contribute significantly to the plant TM accumulation. Moreover, the aerosols can also exert climatic effects by absorption and scattering of solar radiation and by the cloud condensation nuclei activity, thereby indirectly impact plant growth and probably crop TM accumulation through photosynthesis, and then threat health. In particular, this systematic review summarizes the interactions of PMs-TMs in soil-plant systems including the deposition, transfer, accumulation, toxicity, and mechanisms among them. Finally, current knowledge gaps and prospective are proposed for future research agendas. These analyses would be conducive to improving urban air quality and managing the agricultural and ecological risks of airborne metals.

Potential of indigenous plant species for phytoremediation of metal(loid)-contaminated soil in the Baoshan mining area, China

A field survey was conducted to investigate metal(loid) concentration in soils and native plants in the Baoshan mining area for potential application in phytoremediation. Total concentrations of arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn) in soil varied from 125 to 6656, 5.10 to 1061, 568 to 49294, and 241 to 17296 mg kg^-1, respectively, showing severe contamination. Among 20 species native to this area, Pteris ensiformis accumulated 1091 mg kg^-1 As in the shoot, and its translocation factor (TF) was greater than 1, suggesting potential capacity for As phytoextraction. Boehmeria nivea, Aster prorerus, and Hydrocotyle sibthorpioides showed potential for phytoextraction of Cd due to their high accumulation of Cd in shoots (490.3, 175.4, and 128.5 mg kg^-1, respectively) and high TFs (92.0, 22.1, and 6.7, respectively). Eleusine indica and P. ensiformis were found to contain high concentrations of Pb (7474 mg kg^-1) and Zn (1662 mg kg^-1) in roots, but with low TFs for Pb (0.4) and Zn (0.2), suggesting potential capability for phytostabilization. There was a positive correlation (p < 0.01, N = 25) of TFs between the metal(loid)s, indicating a synergic interaction in the uptake of metal(loid)s by these plants. According to metal(loid) concentrations in shoots, bioconcentration factors (BFs), and TFs, as well as the botanical features such as wide occurrence, high biomass yield, and rapid growth of the plants, the five native species identified above have the potential for phytoremediation in the Baoshan mining area.

Vermicompost addition influences symbiotic fungi communities associated with leek cultivated in metal-rich soils

In the context of urban agriculture, where soils are frequently contaminated with metal(loid)s (TM), we studied the influence of vermicompost amendments on symbiotic fungal communities associated with plants grown in two metal-rich soils. Leek (Allium porrum L.) plants were grown with or without vermicompost in two metal-rich soils characterized by either geogenic or anthropogenic TM sources, to assess the influence of pollutant origin on soil-plant transfer. Fungal communities associated with the leek roots were identified by high throughput Illumina MiSeq and TM contents were measured using mass spectrometry. Vermicompost addition led to a dramatic change in the fungal community with a loss of diversity in the two tested soils. This effect could partially explain the changes in metal transfer at the soil-AMF-plant interface. Our results suggest being careful while using composts when growing edibles in contaminated soils. More generally, this study highlights the need for further research in the field of fungal communities to refine practical recommendations to gardeners. Graphical abstract.

Influence of earthworm bioturbation on metals phytoavailability and human gastric bioaccessibility

At the global scale, urban agriculture is increasingly developing in cities due to demographic growth and sustainable food concerns. But, urban soils are frequently polluted with metals. In urban gardens, organic matter is also commonly added both to valorize organic household waste and to promote biophysicochemical fertility. As earthworms promote the decomposition and the recycling of soil organic matter, they can also influence the biogeochemical cycle of metals in urban polluted soils. In order to produce safe vegetables in urban areas, it is crucial to highlight the mechanisms involved in complex soil-earthworm-plant ecosystems. An experiment was set up to examine these relationships using lettuce cultivated in controlled conditions with RHIZOtest® devices. Thanks to the RHIZOtest® devices, metal transfer and bioaccessibility were for the first time compared for urban polluted soil without (1-urban soil polluted with Pb, Cd, Cu, and Zn: essential or toxic metals currently found in environment, SNB) and with bioturbation (2-this metal-polluted soil subjected to earthworm bioturbation, SB) and earthworm casts (3-earthworm casts produced in this polluted soil and naturally enriched in organic matter and microorganisms, T). Metal concentration, phytoavailability, and human gastric bioaccessibility were determined in the different samples. Results showed that earthworm bioturbation increased the phytoavailability of all the metals. For the experimental condition SB, the phytoavailability of metals was increased up to 75% compared to SNB. In addition, surprisingly, metal phytoavailability was always superior in SB compared to earthworm casts (T). Moreover, earthworms led to an increase in Zn gastric bioaccessibility up to 10% in the soils in the same way as for phytoavailability, meaning Zn bioaccessibility in SB > T > SNB, whereas it remained unchanged in the lettuces. These data are important to promote sustainable agriculture activities in urban areas; actually, databases concerning different experimental conditions are needed to develop decision support tools.

The role of epicuticular waxes on foliar metal transfer and phytotoxicity in edible vegetables: case of Brassica oleracea species exposed to manufactured particles

The rapid industrialization and urbanization of intra- and peri-urban areas at the world scale are responsible for the degradation of the quality of edible crops, because of their contamination with airborne pollutants. Their consumption could lead to serious health risks. In this work, we aim to investigate the phytotoxicity induced by foliar transfer of atmospheric particles of industrial/urban origin. Leaves of cabbage plants (Brassica oleracea var. Prover) were contaminated with metal-rich particles (PbSO₄ CuO and CdO) of micrometer size. A trichloroacetic acid (TCA) treatment was used to inhibit the synthesis of the epicuticular waxes in order to investigate their protective role against metallic particles toxicity. Besides the location of the particles on/in the leaves by microscopic techniques, photosynthetic activity measurements, genotoxicity assessment, and quantification of the gene expression have been studied for several durations of exposure (5, 10, and 15 days). The results show that the depletion of epicuticular waxes has a limited effect on the particle penetration in the leaf tissues. The stomatal openings appear to be the main pathway of particles entry inside the leaf tissues, as demonstrated by the overexpression of the BolC.CHLI1 gene. The effects of particles on the photosynthetic activity are limited, considering only the photosynthetic F_v/F_m parameter. The genotoxic effects were significant for the contaminated TCA-treated plants, especially after 10 days of exposure. Still, the cabbage plants are able to implement repair mechanisms quickly, and to thwart the physiological effects induced by the particles. Finally, the foliar contamination by metallic particles induces no serious damage to DNA, as observed by monitoring the BolC.OGG1 gene.

Airborne foliar transfer of particular metals in Lactuca sativa L.: translocation, phytotoxicity, and bioaccessibility

The uptake, translocation, and human bioaccessibility of metals originating from atmospheric fine particulate matters (PM) after foliar exposure is not well understood. Lettuce (Lactuca sativa L.) plants were exposed to micronic PbO, CuO, and CdO particulate matters (PMs) by the foliar pathway and mature plants (6 weeks old) were analyzed in terms of: (1) metal accumulation and localization on plant leaf surface, and metal translocation factor (TF) and global enrichment factor (GEF) in the plants; (2) shoot growth, plant dry weight (DW), net photosynthesis (Pn), stomatal conductance (Gs), and fatty acid ratio; (3) metal bioaccessibility in the plants and soil; and (4) the hazard quotient (HQ) associated with consumption of contaminated plants. Substantial levels of metals were observed in the directly exposed edible leaves and newly formed leaves of lettuce, highlighting both the possible metal transfers throughout the plant and the potential for human exposure after plant ingestion. No significant changes were observed in plant biomass after exposure to PbO, CuO, and CdO-PMs. The Gs and fatty acid ratio were increased in leaves after metal exposure. A dilution effect after foliar uptake was suggested which could alleviate metal phytotoxicity to some degree. However, plant shoot growth and Pn were inhibited when the plants are exposed to PbO, and necrosis enriched with Cd was observed on the leaf surface. Gastric bioaccessibility of plant leaves is ranked: Cd > Cu > Pb. Our results highlight a serious health risk of PbO, CuO, and CdO-PMs associated with consumption of vegetables exposed to these metals, even in newly formed leaves in the case of PbO and CdO exposure. Finally, the study highlights the fate and toxicity of metal rich-PMs, especially in the highly populated urban areas which are increasingly cultivated to promote local food.

Dual Role of Metallic Trace Elements in Stress Biology-From Negative to Beneficial Impact on Plants

Heavy metals are an interesting group of trace elements (TEs). Some of them are minutely required for normal plant growth and development, while others have unknown biological actions. They may cause injury when they are applied in an elevated concentration, regardless of the importance for the plant functioning. On the other hand, their application may help to alleviate various abiotic stresses. In this review, both the deleterious and beneficial effects of metallic trace elements from their uptake by roots and leaves, through toxicity, up to the regulation of physiological and molecular mechanisms that are associated with plant protection against stress conditions have been briefly discussed. We have highlighted the involvement of metallic ions in mitigating oxidative stress by the activation of various antioxidant enzymes and emphasized the phenomenon of low-dose stimulation that is caused by non-essential, potentially poisonous elements called hormesis, which is recently one of the most studied issues. Finally, we have described the evolutionary consequences of long-term exposure to metallic elements, resulting in the development of unique assemblages of vegetation, classified as metallophytes, which constitute excellent model systems for research on metal accumulation and tolerance. Taken together, the paper can provide a novel insight into the toxicity concept, since both dose- and genotype-dependent response to the presence of metallic trace elements has been comprehensively explained.

Evaluation of historical atmospheric pollution in an industrial area by dendrochemical approaches

We conducted a dendrochemical study in order to evaluate the exposure of territories and populations to different types of pollutants and to characterise the history of pollution in one of the most intensely industrialised areas of Europe: the industrial port zone of Fos, also heavily urbanised. To perform the study, two tree species have been selected, Pinus halepensis and Populus nigra, on a rural plot located roughly 20 km away from the industrial harbour, an urban plot located in the city of Fos-sur-Mer and an industrial plot. Our study indicated that poplar was a more relevant model for the dendrochemical studies, exhibiting a higher bioaccumulation capacity than pine except for Hg, Sb and Mn. Moreover, thanks to this work, we observed significant exposure of the trees in the urban and industrial areas to As, Cd, Co, Cu, Mo, Sb, Zn, Al, Ca, and Mg, highlighting the exposure of the territory and populations living in the vicinity of the industrial harbour. The temporal variability of the concentrations measured in the tree rings corresponds to the increasing industrialisation of the territory as well as to the evolution of the industrial processes. Thus, this project highlighted the exposure of the Gulf of Fos to atmospheric emissions (industrial, road and urban) of the industrial harbour as well as the changes over time. It also pointed out the relevance of using dendrochemistry to measure atmospheric exposure of metals and metalloids and its temporal variability.

Heavy metals in food crops: Health risks, fate, mechanisms, and management

Food security is a high-priority issue for sustainable global development both quantitatively and qualitatively. In recent decades, adverse effects of unexpected contaminants on crop quality have threatened both food security and human health. Heavy metals and metalloids (e.g., Hg, As, Pb, Cd, and Cr) can disturb human metabolomics, contributing to morbidity and even mortality. Therefore, this review focuses on and describes heavy metal contamination in soil-food crop subsystems with respect to human health risks. It also explores the possible geographical pathways of heavy metals in such subsystems. In-depth discussion is further offered on physiological/molecular translocation mechanisms involved in the uptake of metallic contaminants inside food crops. Finally, management strategies are proposed to regain sustainability in soil-food subsystems.

Trace elements in soil-vegetables interface: Translocation, bioaccumulation, toxicity and amelioration - A review

The contamination of soil and vegetables with trace elements is one of the most severe ecological problems in developing industrialized countries. Trace elements are released into the environment from natural and anthropogenic activities and accumulated in soil and vegetables through various pathways which ultimately affects the human health. The present review aimed at 1) discussing the anthropogenic sources in detail, 2) describing the bioaccumulation, absorption, and transportation of trace elements, 3) exploring the options to reduce the health risk due to consumption of contaminated vegetables, 4) identifying the research and policy gaps related to soil and vegetables contamination with trace elements. Besides these objectives, the present review also detailed the several factors which affect the rate of accumulation, toxicity mechanism, and effects of trace elements on vegetables and humans. Various toxicity indices for health risk assessment have also been described. It is suggested to evaluate the trace metals concentration in irrigation water and soil prior to plant the vegetable to minimize the possible contamination.

Atmo-ecometabolomics: a novel atmospheric particle chemical characterization methodology for ecological research

Aerosol particles play important roles in processes controlling the composition of the atmosphere and function of ecosystems. A better understanding of the composition of aerosol particles is beginning to be recognized as critical for ecological research to further comprehend the link between aerosols and ecosystems. While chemical characterization of aerosols has been practiced in the atmospheric science community, detailed methodology tailored to the needs of ecological research does not exist yet. In this study, we describe an efficient methodology (atmo-ecometabolomics), in step-by-step details, from the sampling to the data analyses, to characterize the chemical composition of aerosol particles, namely atmo-metabolome. This method employs mass spectrometry platforms such as liquid and gas chromatography mass spectrometries (MS) and Fourier transform ion cyclotron resonance MS (FT-ICR-MS). For methodology evaluation, we analyzed aerosol particles collected during two different seasons (spring and summer) in a low-biological-activity ecosystem. Additionally, to further validate our methodology, we analyzed aerosol particles collected in a more biologically active ecosystem during the pollination peaks of three different representative tree species. Our statistical results showed that our sampling and extraction methods are suitable for characterizing the atmo-ecometabolomes in these two distinct ecosystems with any of the analytical platforms. Datasets obtained from each mass spectrometry instrument showed overall significant differences of the atmo-ecometabolomes between spring and summer as well as between the three pollination peak periods. Furthermore, we have identified several metabolites that can be attributed to pollen and other plant-related aerosol particles. We additionally provide a basic guide of the potential use ecometabolomic techniques on different mass spectrometry platforms to accurately analyze the atmo-ecometabolomes for ecological studies. Our method represents an advanced novel approach for future studies in the impact of aerosol particle chemical compositions on ecosystem structure and function and biogeochemistry.

Study of the bioavailability of heavy metals from atmospheric deposition on the soil-pakchoi (Brassica chinensis L.) system

The objective of this study was to investigate the bioavailability of heavy metals from atmospheric deposition on the soil-pakchoi (Brassica chinensis L.) system near a smelter. Soil reciprocal translocation experiment was conducted with seven groups of pot culture (filled with soils of gradient levels of heavy metals) in three sites of gradient atmospheric heavy metal depositions. Results showed that the newly deposited heavy metals (Cu and Cd) were preferential retention in topsoil (0-4 cm) and presented as higher bioavailable fractions compared to those in original soils. Atmospheric depositions contributed to 20-85% of shoot Cu and Cd in high deposition site, which were likely resulted not only from the direct transfer of contaminants from atmosphere to foliar but also from the atmosphere-soil-root transfer. However, the 52-62% of Pb in shoot from atmospheric depositions was mainly resulted from foliar direct uptake. The increasing atmospheric heavy metal depositions significantly decreased the photosynthetic parameters of pakchoi. Additionally, the potential health risks associated with the consumption of pakchoi were elevated in high deposition site and the bioaccessibility values were observed up to 56-81%. This study will provide useful reference information for the newly deposited heavy metal dynamics in the surface environment.

Individual heavy metal exposure and birth outcomes in Shenqiu county along the Huai River Basin in China

Background: Exposure to heavy metals during pregnancy is an important risk factor for adverse birth outcomes. We aimed to investigate the current heavy metal exposure levels in cord blood from healthy pregnant women residing in the Huaihe River Basin, China, and examined the association between heavy metal levels and dietary habits and lifestyle factors. In this study, we measured the exposure levels of five heavy metals in the umbilical cord blood from 350 healthy pregnant women and administered 350 self-reported questionnaires regarding the general characteristics and dietary habits of those women. Methods: This study was undertaken in Shenqiu county, Henan province, which is in the area of the Huai River Basin, in a cohort of pregnant women and newborn babies in 2013-2014. We recruited a sample of 1000 pregnant women among those receiving prenatal examination, measured the real individual newborn exposure to heavy metals in serum by ICP-MS, collected information regarding the pregnant women with a questionnaire survey and obtained data on environmental quality from environmental protection agencies and the available literature. We estimated the daily individual exposure to heavy metals of all the 1000 participants throughout the pregnancy and recorded their birth outcomes after delivery. Then we analyzed the association between birth outcome and individual exposure to heavy metals. Results: 54 newborn children had birth defects. The geometric means of cord blood levels of As, Cd, Cr, Pb and Hg were measured at 0.92 ± 1.01 ng mL-1, 0.11 ± 0.17 ng mL-1, 4.57 ± 5.02 ng mL-1, 3.37 ± 3.81 ng mL-1 and 0.89 ± 1.69 ng mL-1 for subjects (n = 54) who gave birth to infants with birth defects and 0.43 ± 0.88 ng mL-1, 0.52 ± 3.86 ng mL-1, 1.94 ± 2.92 ng mL-1, 4.38 ± 4.96 ng mL-1 and 0.43 ± 0.91 ng mL-1 for subjects (n = 296) with healthy infants, respectively. The contents of all five heavy metals in the whole blood of both of these two groups were higher than the reference values of the Chinese general population (P < 0.001). Conclusions: The occurrence of birth defects was 15.4% in this cohort, and was correlated to exposure of parents to environments containing heavy metal contaminants in Shenqiu county in the Huai River Basin. The heavy metal exposure situation of the investigated population had serious effects in terms of reproductive defects in children. The specific link between newborn defects and environmental heavy metal contaminants suggested that contamination in pregnant women persisted over time, and that the exposure may have a long term effect.