Influence of fine process particles enriched with metals and metalloids on Lactuca sativa L. leaf fatty acid composition following air and/or soil-plant field exposure

Spraying or fertigation? looking for the better method in terms of the lower concentration of Pb and Ni in greenhouse cucumber

This study was conducted to investigate the status of Lead (Pb) and Nickel (Ni) in greenhouse cucumber affected by fertigation and spraying as a factorial split plot arrangement based on a randomized complete block design (RCBD) with three replications at Soil and Water Research Institute, Karaj, Iran in 2023. The main and sub-plots were respectively fertigation and spraying that was applied in two levels [the minimum permissible concentration of these metals in granular triple super phosphate fertilizer (five ppm Pb and five ppm Ni) as the control treatment, and the maximum permissible concentration of Pb and Ni in granular triple super phosphate fertilizer (50 ppm Pb and 100 ppm Ni)]. Spraying was done in three modes (spraying leaves, leaves + fruit, and fruit). Based on the results, the highest concentration of Pb in the fruit (fruit peel + fruit flesh) (0.295 mg/kg DW) was recorded in the fertigation + spraying with the maximum permissible concentrations of Pb and Ni treatments. A general comparison between the two fertilization methods showed that the spraying method accumulated a higher concentration of Pb in the fruit (i.e., peel + flesh) than the fertigation method. The reverse of this status happened for Ni, so the fertigation method accumulated a higher concentration of Ni in the fruit (skin + flesh) compared to the spraying method. On average, the order of Pb concentration in different organs was as follows: leaf (0.765 mg/kg) > fruit peel (0.232 mg/kg) > fruit peel + flesh (0.174 mg/kg) > fruit flesh (0.129 mg/kg). This order for Ni was as follows: fruit flesh (0.597 mg/kg) > fruit peel + flesh (0.345 mg/kg) > leaf (0.3 mg/kg) > fruit peel (0.175 mg/kg). These orders show that the status of the heavy metals in plant tissues is related to the nature of the metal, the type of the organ, and the method of fertilization.

Flooding by sea and brackish waters enhances mobility of Cd, Zn and Pb from airborne dusts in coastal soils

Sea level rise and extreme weather conditions caused by climatic changes enhance the frequency and length of submersion events in coastal soils, causing deposited airborne dusts to get in contact with marine salts. The behaviour of Cd, Zn and Pb from pedogenetic minerals and from dusts from mining and smelting activities, added to two soils under different agricultural management (arable and grassland) was examined after soil flooding for 1, 7 and 30 days with waters of increasing salinities (0, 4.37, 8.75, 17.25 and 34.5 g L-1). A rain water event following 1 d flooding released an extra amount of metals. Concentration of potentially toxic elements (PTE), pH, dissolved inorganic and organic C were measured in solutions collected by gravity from soil columns. Speciation distribution of leached metals and oversaturation parameters were calculated by Visual Minteq 3.0 and showed that complexation by chloride ions for Cd and fulvic acids for Pb were the drivers of solubilisation, while Zn interacted with both. Results showed that marine salts enhance up to 300 times leaching of Cd, and several times that of Zn and Pb from contaminated soils and that airborne toxic elements are much more mobilized than pedogenic ones. Smelter exhaust metals, particularly Pb, were made more mobile than those in mine tailings (up to 55 against 0.7 ng μg-1 Pb). Soil management strongly also influence mobilization by saline water: much lower amounts were leached from the grassland soil. Soil organic matter quality (DOC and humification) affects the extent of mobilization. The length of the flooding period did not result in coherent time trend patterns for the three metals, probably because of the multiple changes in solution parameters, but leached metals were always highly linearly correlated negatively with pH and positively with DOC.

Integrated morphological, physiological and transcriptomic analyses reveal response mechanisms of rice under different cadmium exposure routes

Rice (Oryza sativa) is one of the major cereal crops and takes up cadmium (Cd) more readily than other crops. Understanding the mechanism of Cd uptake and defense in rice can help us avoid Cd in the food chain. However, studies comparing Cd uptake, toxicity, and detoxification mechanisms of leaf and root Cd exposure at the morphological, physiological, and transcriptional levels are still lacking. Therefore, experiments were conducted in this study and found that root Cd exposure resulted in more severe oxidative and photosynthetic damage, lower plant biomass, higher Cd accumulation, and transcriptional changes in rice than leaf Cd exposure. The activation of phenylpropanoids biosynthesis in both root and leaf tissues under different Cd exposure routes suggests that increased lignin is the response mechanism of rice under Cd stress. Moreover, the roots of rice are more sensitive to Cd stress and their adaptation responses are more pronounced than those of leaves. Quantitative PCR revealed that OsPOX, OsCAD, OsPAL and OsCCR play important roles in the response to Cd stress, which further emphasize the importance of lignin. Therefore, this study provides theoretical evidence for future chemical and genetic regulation of lignin biosynthesis in crop plants to reduce Cd accumulation.

Accumulation and distribution characteristics of rare earth elements (REEs) in the naturally grown marigold (Tagetes erecta L.) from the soil

Rare earth elements (REEs) are considered environmental pollutants that have received extensive attention recently. The accumulation of REEs in plants is important because REEs can eventually enter the human body via the food chain. Marigolds are widely utilized as medicinal and commercial plants in medicine, feed, and therapeutics. Due to the extremely high demand for marigold in global, it is urgent to investigate the accumulation and distribution of REEs in marigold plants to reduce human and animal health risks. Marigold leaves tended to bioaccumulate the highest amounts of REEs from soil compared with other tissues. The distribution patterns of REEs in marigold were similar to those in the rhizosphere soil, which was enriched in light rare earth elements. Cerium accumulated most in marigold and soil, accounting for nearly 50% of ΣREEs, followed by lanthanum, neodymium, and yttrium. Roots were the most susceptible tissue affected by soil REE concentration, and a significant positive correlation was observed for REEs in the roots of marigold and soils (R = 0.87), while no significant correlation was observed for REEs in soils and other tissues. REEs were poorly transferred from soil to marigold, with bioaccumulation factor values for all tissues of marigold less than one. Additionally, REEs exhibited a positive correlation with Al and Fe in the roots, stems, leaves, and flowers of marigold. The present research revealed the biological interactions between marigold and soil and the distribution of REEs in various parts of marigold. It provides a reference for large-scale commercial cultivation and potential environmental risk in the future.

Association mapping uncovers maize ZmbZIP107 regulating root system architecture and lead absorption under lead stress

Lead (Pb) is a highly toxic contaminant to living organisms and the environment. Excessive Pb in soils affects crop yield and quality, thus threatening human health via the food chain. Herein, we investigated Pb tolerance among a maize association panel using root bushiness (BSH) under Pb treatment as an indicator. Through a genome-wide association study of relative BSH, we identified four single nucleotide polymorphisms (SNPs) and 30 candidate genes associated with Pb tolerance in maize seedlings. Transcriptome analysis showed that four of the 30 genes were differentially responsive to Pb treatment between two maize lines with contrasting Pb tolerance. Among these, the ZmbZIP107 transcription factor was confirmed as the key gene controlling maize tolerance to Pb by using gene-based association studies. Two 5' UTR_variants in ZmbZIP107 affected its expression level and Pb tolerance among different maize lines. ZmbZIP107 protein was specifically targeted to the nucleus and ZmbZIP107 mRNA showed the highest expression in maize seedling roots among different tissues. Heterologous expression of ZmbZIP107 enhanced rice tolerance to Pb stress and decreased Pb absorption in the roots. Our study provided the basis for revelation of the molecular mechanism underlying Pb tolerance and contributed to cultivation of Pb-tolerant varieties in maize.

Recent advances in physiological and molecular mechanisms of heavy metal accumulation in plants

Among abiotic stress, the toxicity of metals impacts negatively on plants' growth and productivity. This toxicity promotes various perturbations in plants at different levels. To withstand stress, plants involve efficient mechanisms through the implication of various signaling pathways. These pathways enhance the expression of many target genes among them gene coding for metal transporters. Various metal transporters which are localized at the plasma membrane and/or at the tonoplast are crucial in metal stress response. Furthermore, metal detoxification is provided by metal-binding proteins like phytochelatins and metallothioneins. The understanding of the molecular basis of metal toxicities signaling pathways and tolerance mechanisms is crucial for genetic engineering to produce transgenic plants that enhance phytoremediation. This review presents an overview of the recent advances in our understanding of metal stress response. Firstly, we described the effect of metal stress on plants. Then, we highlight the mechanisms involved in metal detoxification and the importance of the regulation in the response to heavy metal stress. Finally, we mentioned the importance of genetic engineering for enhancing the phytoremediation technique. In the end, the response to heavy metal stress is complex and implicates various components. Thus, further studies are needed to better understand the mechanisms involved in response to this abiotic stress.

Biochemical and Metabolic Plant Responses toward Polycyclic Aromatic Hydrocarbons and Heavy Metals Present in Atmospheric Pollution

Heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) are toxic components of atmospheric particles. These pollutants induce a wide variety of responses in plants, leading to tolerance or toxicity. Their effects on plants depend on many different environmental conditions, not only the type and concentration of contaminant, temperature or soil pH, but also on the physiological or genetic status of the plant. The main detoxification process in plants is the accumulation of the contaminant in vacuoles or cell walls. PAHs are normally transformed by enzymatic plant machinery prior to conjugation and immobilization; heavy metals are frequently chelated by some molecules, with glutathione, phytochelatins and metallothioneins being the main players in heavy metal detoxification. Besides these detoxification mechanisms, the presence of contaminants leads to the production of the reactive oxygen species (ROS) and the dynamic of ROS production and detoxification renders different outcomes in different scenarios, from cellular death to the induction of stress resistances. ROS responses have been extensively studied; the complexity of the ROS response and the subsequent cascade of effects on phytohormones and metabolic changes, which depend on local concentrations in different organelles and on the lifetime of each ROS species, allow the plant to modulate its responses to different environmental clues. Basic knowledge of plant responses toward pollutants is key to improving phytoremediation technologies.

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.

Impact of salicylic acid on the growth and physiological activities of parsley plants under lead toxicity

Impact of spraying 50 µM salicylic acid (SA), lead nitrate soil treatments [1 and 2 mM Pb (NO₃)₂] and their combinations on parsley leaves (Petroselinum crispum L.) for 3 weeks was studied to evaluate leaf symptoms, photosynthetic pigments, anthocyanin, ultrastructure, malondialdehyde (MDA), soluble proteins, phenolic compounds, and guaiacol peroxidase activity (GPOX). Under Pb effect, parsley leaves showed chlorosis and decline in the content of photosynthetic pigments chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenoid (Car) with increasing Pb treatments compared to the control. SA spraying helped to reduce chlorosis and increase photosynthetic pigments of Pb-treated plants compared to that of Pb treatment alone. Leaf anthocyanin content of SA-sprayed plants significantly increased compared to the control. On contrast, the anthocyanin content of Pb-treated plants with or without SA treatment decreased compared to the control. Parsley leaf chloroplasts were characterized by many and large starch grains. Deformations of chloroplast shape, increasing formation of plastoglobules and degeneration of chloroplast grana thylakoids were observed in Pb-treated plants. MDA and total phenolic compound contents increased in Pb-treated plants compared to the control. In contrast, soluble protein content decreased in Pb-treated plants. The decrease in leaf photosynthetic pigments and increase MDA contents was Pb-concentration dependent. The results as indicated by increasing lipid peroxidation confirmed Pb treatments generated reactive oxygen species (ROS) which caused oxidative stress. In contrast, SA application declined the extent of detrimental and harmful influence of Pb toxicity as indicated by the decrease MDA content, and increase in photosynthetic pigments, anthocyanin and phenolic compound contents of parsley leaves.

Assessment of Foliar Uptake and Accumulation of Airborne Polyaromatic Hydrocarbons Under Laboratory Conditions

Urban horticulture and community gardening have become more and more popular in the past years, however, the risk of bioaccumulation of atmospheric polyaromatic hydrocarbons (PAHs) in vegetables grown in polluted areas cannot be neglected. In our study, the No. 227 OECD GUIDELINE FOR THE TESTING OF CHEMICALS: Terrestrial Plant Test: Vegetative Vigour Test was followed to assess foliar uptake of PAHs from aqueous extract of an urban aerosol. Using lettuce (Lactuca sativa) as a test organism, significant accumulation was experienced. The highest bioconcentration factors (BCFs) were experienced for naphthalene and for anthracene, pyrene and fluoranthene showed the lowest bioaccumulation potential. BCF of each PAH showed strong correlation with molecular weight. The standard protocol defined by the Guideline made it possible to assess bioaccumulation pattern under controlled laboratory conditions.

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.

Enantioselective Phytotoxic Disturbances of Fatty Acids in Arabidopsis thaliana by Dichlorprop

Plant fatty acids have indispensable physiological functions and nutritional value. However, the overuse of herbicides may cause phytotoxic disturbances of fatty acids in nontarget plants while spraying for weeds. Evidence has shown that the herbicide dichlorprop can inhibit the activity of acetyl-CoA carboxylase (ACCase), a key enzyme involved in fatty acid synthesis. However, the enantioselective phytotoxic effects of dichlorprop enantiomers ((R)-dichlorprop and (S)-dichlorprop) on fatty acids and their related mechanisms remain unclear. To solve this issue, the enantioselective phytotoxicity of dichlorprop in the model plant species Arabidopsis thaliana (A. thaliana) with a focus on fatty acids was evaluated for the first time. The results indicated a significant difference in enantioselectivity and that exposure to (R)-dichlorprop can cause marked fatty acid disturbances in nontarget plant species. Specifically, (R)-dichlorprop decreased the content of three fatty acids by more than 50% by inhibiting the activity of ACCase. In addition, increased malondialdehyde (MDA) and lipid hydroperoxides (LOOHs) contents and membrane permeability reflected herbicide-induced lipid peroxidation, which decreased the unsaturation of fatty acids in membranes and further influenced membrane composition and function. Moreover, an increased level of glutathione peroxidase (GPX) and cytochrome P450 (CYP450) reflected a plant stress-induced response. To summarize, fatty acids represent a new perspective for evaluating the toxicity of chiral pesticides, contributing to a better understanding of the enantioselective phytotoxicity and mechanisms of dichlorprop, and providing evidence for herbicide security and risk assessments.

Foliar uptake of arsenic nanoparticles by spinach: an assessment of physiological and human health risk implications

Atmospheric contamination by heavy metal(loid)-enriched particulate matter (metal-PM) is highly topical these days because of its high persistence, toxic nature, and health risks. Globally, foliar uptake of metal(loid)s occurs for vegetables/crops grown in the vicinity of industrial or urban areas with a metal-PM-contaminated atmosphere. The current study evaluated the foliar uptake of arsenic (As), accumulation of As in different plant organs, its toxicity (in terms of ROS generation, chlorophyll degradation, and lipid peroxidation), and its defensive mechanism (antioxidant enzymes) in spinach (Spinacia oleracea) after foliar application of As in the form of nanoparticles (As-NPs). The As-NPs were prepared using a chemical method. Results indicate that spinach can absorb As via foliar pathways (0.50 to 0.73 mg/kg in leaves) and can translocate it towards root tissues (0.35 to 0.68 mg/kg). However, health risk assessment parameters showed that the As level in the edible parts of spinach was below the critical limit (hazard quotient < 1). Despite low tissue level, As-NP exposure caused phytotoxicity in terms of a decrease in plant dry biomass (up to 84%) and pigment contents (up to 38%). Furthermore, several-fold higher activities of antioxidant enzymes were observed under metal stress than control. However, no significant variation was observed in the level of hydrogen peroxide (H₂O₂), which can be its possible transformation to other forms of reactive oxygen species (ROS). It is proposed that As can be absorbed by spinach via foliar pathway and then disturbs the plant metabolism. Therefore, air quality needs to be considered and monitored continuously for the human health risk assessment and quality of vegetables cultivated on polluted soils (roadside and industrial vicinity). Graphical abstract ᅟ.

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.

Forest Canopy Can Efficiently Filter Trace Metals in Deposited Precipitation in a Subalpine Spruce Plantation

Trace metals can enter natural regions with low human disturbance through atmospheric circulation; however, little information is available regarding the filtering efficiency of trace metals by forest canopies. In this study, a representative subalpine spruce plantation was selected to investigate the net throughfall fluxes of eight trace metals (Fe, Mn, Cu, Zn, Al, Pb, Cd and Cr) under a closed canopy and gap-edge canopy from August 2015 to July 2016. Over the one-year observation, the annual fluxes of Al, Zn, Fe, Mn, Cu, Cd, Cr and Pb in the deposited precipitation were 7.29 kg·ha−1, 2.30 kg·ha−1, 7.02 kg·ha−1, 0.16 kg·ha−1, 0.19 kg·ha−1, 0.06 kg·ha−1, 0.56 kg·ha−1 and 0.24 kg·ha−1, respectively. The annual net throughfall fluxes of these trace metals were −1.73 kg·ha−1, −0.90 kg·ha−1, −1.68 kg·ha−1, 0.03 kg·ha−1, −0.03 kg·ha−1, −0.02 kg·ha−1, −0.09 kg·ha−1 and −0.08 kg·ha−1, respectively, under the gap-edge canopy and 1.59 kg·ha−1, −1.13 kg·ha−1, −1.65 kg·ha−1, 0.10 kg·ha−1, −0.04 kg·ha−1, −0.03 kg·ha−1, −0.26 kg·ha−1 and −0.15 kg·ha−1, respectively, under the closed canopy. The closed canopy displayed a greater filtering effect of the trace metals from precipitation than the gap-edge canopy in this subalpine forest. In the rainy season, the net filtering ratio of trace metals ranged from −66.01% to 89.05% for the closed canopy and from −52.32% to 33.09% for the gap-edge canopy. In contrast, the net filtering ratio of all trace metals exceeded 50.00% for the closed canopy in the snowy season. The results suggest that most of the trace metals moving through the forest canopy are filtered by canopy in the subalpine forest.

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.

Using multi-medium factors analysis to assess heavy metal health risks along the Yangtze River in Nanjing, Southeast China

In the environmental ecosystem, there are no absolutely isolated risks. Each risk might be influenced by multiple environmental factors and the factors' interaction within the specific system. Hence, health risk assessments of heavy metal contamination must consider multiple environmental media and their transfer processes from one medium to another. Integrated assessments provide a new perspective for evaluating many factors, such as the potential ecological risks of soils, sediments, plants, and the transportation of heavy metals in these media, which influences the health risks. In this study, the main influencing factors for human health risk from heavy metals along the Yangtze River in Nanjing, Southeast China, were explored. The contents of five heavy metals were measured in sediment-soil-plant, including cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), and chromium (Cr). The Cd displayed the highest potential ecological risk in soils and sediments, as it possessed high bioaccessibility (BA; 0.17 ± 0.211) and bioaccumulation factor (BCF; 0.35 ± 0.33). The 5.97% of the target hazard quotient (THQ) of Cd were higher than 1, indicating a potential health risk in plant consumption. Based on the geodetector model, determinant power (DP) valves for factors influencing health risk strongly suggest that plant types (0.479) has a highest effect, followed by soil organic matter (SOM; 0.292), and the BA of heavy metals (0.107). The results also indicate that pollution from the upper reaches of the river, and agricultural activities, had a greater impact on health risk than did industrial activities in the study area. Thus, regular monitoring and source control for Cd, along with integrated agricultural management practices should be implemented to control and reduce heavy metal inputs and improve the safety of cultivated plants.

Spectrochemical analysis of sycamore (Acer pseudoplatanus) leaves for environmental health monitoring

Terrestrial plants are ideal sentinels of environmental pollution, due to their sedentary nature, abundance and sensitivity to atmospheric changes. However, reliable and sensitive biomarkers of exposure have hitherto been difficult to characterise. Biospectroscopy offers a novel approach to the derivation of biomarkers in the form of discrete molecular alterations detectable within a biochemical fingerprint. We investigated the application of this approach for the identification of biomarkers for pollution exposure using the common sycamore (Acer pseudoplatanus) as a sentinel species. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy was used to interrogate leaf tissue collected from three sites exposed to different levels of vehicle exhaust emissions. Following multivariate analysis of acquired spectra, significant biochemical alterations were detected between comparable leaves from different sites that may constitute putative biomarkers for pollution-induced stress. These included differences in carbohydrate and nucleic acid conformations, which may be indicative of sub-lethal exposure effects. We also observed several corresponding spectral alterations in both the leaves of A. pseudoplatanus exposed to ozone pollution under controlled environmental conditions and in leaves infected with the fungal pathogen Rhytisma acerinum, indicating that some stress-induced changes are conserved between different stress signatures. These similarities may be indicative of stress-induced reactive oxygen species (ROS) generation, although further work is needed to verify the precise identity of infrared biomarkers and to identify those that are specific to pollution exposure. Taken together, our data clearly demonstrate that biospectroscopy presents an effective toolkit for the utilisation of higher plants, such as A. pseudoplatanus, as sentinels of environmental pollution.

Copper Oxide Nanoparticle Foliar Uptake, Phytotoxicity, and Consequences for Sustainable Urban Agriculture

Throughout the world, urban agriculture supplies fresh local vegetables to city populations. However, the increasing anthropogenic uses of metal-containing nanoparticles (NPs) such as CuO-NPs in urban areas may contaminate vegetables through foliar uptake. This study focused on the CuO-NP transfer processes in leafy edible vegetables (i.e., lettuce and cabbage) to assess their potential phytotoxicity. Vegetables were exposed via leaves for 5, 10, or 15 days to various concentrations of CuO-NPs (0, 10, or 250 mg per plant). Biomass and gas exchange values were determined in relation to the Cu uptake rate, localization, and Cu speciation within the plant tissues. High foliar Cu uptake occurred after exposure for 15 days for lettuce [3773 mg (kg of dry weight)-1] and cabbage [4448 mg (kg of dry weight)-1], along with (i) decreased plant weight, net photosynthesis level, and water content and (ii) necrotic Cu-rich areas near deformed stomata containing CuO-NPs observed by scanning electron microscopy and energy dispersive X-ray microanalysis. Analysis of the CuO-NP transfer rate (7.8-242 μg day-1), translocation of Cu from leaves to roots and Cu speciation biotransformation in leaf tissues using electron paramagnetic resonance, suggests the involvement of plant Cu regulation processes. Finally, a potential health risk associated with consumption of vegetables contaminated with CuO-NPs was highlighted.

Nature of fly ash amendments differently influences oxidative stress alleviation in four forest tree species and metal trace element phytostabilization in aged contaminated soil: A long-term field experiment

Aided phytostabilization using coal fly ashes (CFAs) is an interesting technique to clean-up polluted soils and valorizing industrial wastes. In this context, our work aims to study the effect of two CFAs: silico-aluminous (CFA1) and sulfo-calcic (CFA2) ones, 10 years after their addition, on the phytostabilization of a highly Cd (cadmium), Pb (lead) and Zn (zinc) contaminated agricultural soil, with four forest tree species: Robinia pseudoacacia, Alnus glutinosa, Acer pseudoplatanus and Salix alba. To assess the effect of CFAs on trees, leaf fatty acid composition, malondialdehyde (MDA), oxidized and reduced glutathione contents ratio (GSSG: GSH), 8-hydroxy-2'-deoxyguanosine (8-OHdG), Peroxidase (PO) and Superoxide dismutase (SOD) activities were examined. Our results showed that CFA amendments decreased the CaCl_2-extractable fraction of Cd and Zn from the soil. However, no significant effect was observed on metal trace element (MTE) concentrations in leaves. Fatty acid percentages were only affected by the addition of sulfo-calcic CFA. The most affected species were A. glutinosa and R. pseudoacacia in which C16:0, C18:0 and C18:2 percentages increased significantly whereas the C18:3 decreased. The addition of sulfo-calcic CFA induced the antioxidant systems response in tree leaves. An increase of SOD and POD activities in leaves of trees planted on the CFA2-amended plot was recorded. Conversely, silico-aluminous CFA generated a reduction of lipid and DNA oxidation associated with the absence or low induction of anti-oxidative processes. Our study evidenced oxidative stress alleviation in tree leaves due to CFA amendments. MTE mobility in contaminated soil and their accumulation in leaves differed with the nature of CFA amendments and the selected tree species.

Foliar heavy metal uptake, toxicity and detoxification in plants: A comparison of foliar and root metal uptake

Anthropologic activities have transformed global biogeochemical cycling of heavy metals by emitting considerable quantities of these metals into the atmosphere from diverse sources. In spite of substantial and progressive developments in industrial processes and techniques to reduce environmental emissions, atmospheric contamination by toxic heavy metals and associated ecological and health risks are still newsworthy. Atmospheric heavy metals may be absorbed via foliar organs of plants after wet or dry deposition of atmospheric fallouts on plant canopy. Unlike root metal transfer, which has been largely studied, little is known about heavy metal uptake by plant leaves from the atmosphere. To the best of our understanding, significant research gaps exist regarding foliar heavy metal uptake. This is the first review regarding biogeochemical behaviour of heavy metals in atmosphere-plant system. The review summarizes the mechanisms involved in foliar heavy metal uptake, transfer, compartmentation, toxicity and in plant detoxification. We have described the biological and environmental factors that affect foliar uptake of heavy metals and compared the biogeochemical behaviour (uptake, translocation, compartmentation, toxicity and detoxification) of heavy metals for root and foliar uptake. The possible health risks associated with the consumption of heavy metal-laced food are also discussed.

Treated wastewater phytotoxicity assessment using Lactuca sativa: Focus on germination and root elongation test parameters

Sensitive and simple ecotoxicological bioassays like seed germination and root elongation tests are commonly used to evaluate the phytotoxicity of waste and industrial discharge waters. Although the tests are performed following national and international standards, various parameters such as the number of seeds per dish, the test duration or the type of support used remain variable. To be able to make a correct comparison of results from different studies, it is crucial to know which parameter(s) could affect ecotoxicological diagnosis. We tested four different control waters and three seed densities. No significant differences on either germination rate or root elongation endpoints were shown. Nevertheless, we found that the four lettuce cultivars (Appia, batavia dorée de printemps, grosse blonde paresseuse, and Kinemontepas) showed significantly different responses when watered with the same and different metal-loaded industrial discharge water. From the comparison, it is clear that a differential sensitivity scale occurs among not just species but cultivars.

Cadmium Bioavailability, Uptake, Toxicity and Detoxification in Soil-Plant System

This review summarizes the findings of the most recent studies, published from 2000 to 2016, which focus on the biogeochemical behavior of Cd in soil-plant systems and its impact on the ecosystem. For animals and people not subjected to a Cd-contaminated environment, consumption of Cd contaminated food (vegetables, cereals, pulses and legumes) is the main source of Cd exposure. As Cd does not have any known biological function, and can further cause serious deleterious effects both in plants and mammalian consumers, cycling of Cd within the soil-plant system is of high global relevance.The main source of Cd in soil is that which originates as emissions from various industrial processes. Within soil, Cd occurs in various chemical forms which differ greatly with respect to their lability and phytoavailability. Cadmium has a high phytoaccumulation index because of its low adsorption coefficient and high soil-plant mobility and thereby may enter the food chain. Plant uptake of Cd is believed to occur mainly via roots by specific and non-specific transporters of essential nutrients, as no Cd-specific transporter has yet been identified. Within plants, Cd causes phytotoxicity by decreasing nutrient uptake, inhibiting photosynthesis, plant growth and respiration, inducing lipid peroxidation and altering the antioxidant system and functioning of membranes. Plants tackle Cd toxicity via different defense strategies such as decreased Cd uptake or sequestration into vacuoles. In addition, various antioxidants combat Cd-induced overproduction of ROS. Other mechanisms involve the induction of phytochelatins, glutathione and salicylic acid.

Measurement of metal bioaccessibility in vegetables to improve human exposure assessments: field study of soil-plant-atmosphere transfers in urban areas, South China

The quality of cultivated consumed vegetables in relation to environmental pollution is a crucial issue for urban and peri-urban areas, which host the majority of people at the global scale. In order to evaluate the fate of metals in urban soil-plant-atmosphere systems and their consequences on human exposure, a field study was conducted at two different sites near a waste incinerator (site A) and a highway (site B). Metal concentrations were measured in the soil, settled atmospheric particulate matter (PM) and vegetables. A risk assessment was performed using both total and bioaccessible metal concentrations in vegetables. Total metal concentrations in PM were (mg kg^-1): (site A) 417 Cr, 354 Cu, 931 Zn, 6.3 Cd and 168 Pb; (site B) 145 Cr, 444 Cu, 3289 Zn, 2.9 Cd and 396 Pb. Several total soil Cd and Pb concentrations exceeded China's Environmental Quality Standards. At both sites, there was significant metal enrichment from the atmosphere to the leafy vegetables (correlation between Pb concentrations in PM and leaves: r = 0.52, p < 0.05) which depended on the plant species. Total Cr, Cd and Pb concentrations in vegetables were therefore above or just under the maximum limit levels for foodstuffs according to Chinese and European Commission regulations. High metal bioaccessibility in the vegetables (60-79 %, with maximum value for Cd) was also observed. The bioaccessible hazard index was only above 1 for site B, due to moderate Pb and Cd pollution from the highway. In contrast, site A was considered as relatively safe for urban agriculture.

Kinetic study of phytotoxicity induced by foliar lead uptake for vegetables exposed to fine particles and implications for sustainable urban agriculture

At the global scale, foliar metal transfer occurs for consumed vegetables cultivated in numerous urban or industrial areas with a polluted atmosphere. However, the kinetics of metal uptake, translocation and involved phytotoxicity was never jointly studied with vegetables exposed to micronic and sub-micronic particles (PM). Different leafy vegetables (lettuces and cabbages) cultivated in RHIZOtest® devices were, therefore, exposed in a greenhouse for 5, 10 and 15days to various PbO PM doses. The kinetics of transfer and phytotoxicity was assessed in relation to lead concentration and exposure duration. A significant Pb accumulation in leaves (up to 7392mg/kg dry weight (DW) in lettuce) with translocation to roots was observed. Lead foliar exposure resulted in significant phytotoxicity, lipid composition change, a decrease of plant shoot growth (up to 68.2% in lettuce) and net photosynthesis (up to 58% in lettuce). The phytotoxicity results indicated plant adaptation to Pb and a higher sensitivity of lettuce in comparison with cabbage. Air quality needs, therefore, to be considered for the health and quality of vegetables grown in polluted areas, such as certain megacities (in China, Pakistan, Europe, etc.) and furthermore, to assess the health risks associated with their consumption.

Potential of Opuntia ficus-indica for air pollution biomonitoring: a lead isotopic study

Opuntia ficus-indica (Ofi) is a long-domesticated cactus that is widespread throughout arid and semiarid regions. Ofi is grown for both its fruits and edible cladodes, which are flattened photosynthetic stems. Young cladodes develop from mother cladodes, thus forming series of cladodes of different ages. Therefore, successive cladodes may hold some potential for biomonitoring over several years the local atmospheric pollution. In this study, cladodes, roots, dust deposited onto the cladodes, and soil samples were collected in the vicinity of three heavily polluted sites, i.e., a fertilizer industry, the road side of a highway, and mine tailings. The lead content was analyzed using atomic absorption spectroscopy (AAS) and inductively coupled plasma-mass spectrometry (ICP-MS). Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) was used to characterize the cladode surfaces and the nature of dust deposit, and the lead isotopes were analyzed to identify the origin of Pb. The results show that (i) Ofi readily bioaccumulates Pb, (ii) the lead isotopic composition of cladodes evidences a foliar pathway of lead into Ofi and identifies the relative contributions of local Pb sources, and (iii) an evolution of air quality is recorded with successive cladodes, which makes Ofi a potential biomonitor to be used in environmental and health studies.

Concentration and transportation of heavy metals in vegetables and risk assessment of human exposure to bioaccessible heavy metals in soil near a waste-incinerator site, South China

There is limited study focusing on the bioaccumulation of heavy metals in vegetables and human exposure to bioaccessible heavy metals in soil. In the present study, heavy metal concentrations (Cr, Ni, Cu, Pb and Cd) were measured in five types of vegetables, soil, root, and settled air particle samples from two sites (at a domestic waste incinerator and at 20km away from the incinerator) in Guangzhou, South China. Heavy metal concentrations in soil were greater than those in aerial parts of vegetables and roots, which indicated that vegetables bioaccumulated low amount of heavy metals from soil. The similar pattern of heavy metal (Cr, Cd) was found in the settled air particle samples and aerial parts of vegetables from two sites, which may suggest that foliar uptake may be an important pathway of heavy metal from the environment to vegetables. The highest levels of heavy metals were found in leaf lettuce (125.52μg/g, dry weight) and bitter lettuce (71.2μg/g) for sites A and B, respectively, followed by bitter lettuce and leaf lettuce for sites A and B, respectively. Swamp morning glory accumulated the lowest amount of heavy metals (81.02μg/g for site A and 53.2μg/g for site B) at both sites. The bioaccessibility of heavy metals in soil ranged from Cr (2%) to Cu (71.78%). Risk assessment showed that Cd and Pb in soil samples resulted in the highest non-cancer risk and Cd would result in unacceptable cancer risk for children and risk. The non-dietary intake of soil was the most important exposure pathway, when the bioaccessibility of heavy metals was taken into account.

Antimony bioavailability: knowledge and research perspectives for sustainable agricultures

The increasing interest in urban agriculture highlights the crucial question of crop quality. The main objectives for environmental sustainability are a decrease in chemical inputs, a reduction in the level of pollutants, and an improvement in the soil's biological activity. Among inorganic pollutants emitted by vehicle traffic and some industrial processes in urban areas, antimony (Sb) is observed on a global scale. While this metalloid is known to be potentially toxic, it can transfer from the soil or the atmosphere to plants, and accumulate in their edible parts. Urban agriculture is developing worldwide, and could therefore increasingly expose populations to Sb. The objective of this review was in consequences to gather and interpret actual knowledge of Sb uptake and bioaccumulation by crops, to reveal investigative fields on which to focus. While there is still no legal maximal value for Sb in plants and soils, light has to be shed on its accumulation and the factors affecting it. A relative absence of data exists about the role of soil flora and fauna in the transfer, speciation and compartmentation of Sb in vegetables. Moreover, little information exists on Sb ecotoxicity for terrestrial ecosystems. A human risk assessment has finally been reviewed, with particular focus on Sb bioaccessibility.

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

At the global scale, high concentrations of particulate matter (PM) enriched with metal(loid)s are currently observed in the atmosphere of urban areas. Foliar lead uptake was demonstrated for vegetables exposed to airborne PM. Our main objective here was to highlight the health risk associated with the consumption of vegetables exposed to foliar deposits of PM enriched with the various metal(loid)s frequently observed in the atmosphere of urban areas (Cd, Sb, Zn and Pb). Leaves of mature cabbage and spinach were exposed to manufactured mono-metallic oxide particles (CdO, Sb2O3 and ZnO) or to complex process PM mainly enriched with lead. Total and bioaccessible metal(loid) concentrations were then measured for polluted vegetables and the various PM used as sources. Finally, scanning electronic microscopy coupled with energy dispersive X-ray microanalysis was used to study PM-phyllosphere interactions. High quantities of Cd, Sb, Zn and Pb were taken up by the plant leaves. These levels depended on both the plant species and nature of the PM, highlighting the interest of acquiring data for different plants and sources of exposure in order to better identify and manage health risks. A maximum of 2% of the leaf surfaces were covered with the PM. However, particles appeared to be enriched in stomatal openings, with up to 12% of their area occupied. Metal(loid) bioaccessibility was significantly higher for vegetables compared to PM sources, certainly due to chemical speciation changes. Taken together, these results confirm the importance of taking atmospheric PM into account when assessing the health risks associated with ingestion of vegetables grown in urban vegetable crops or kitchen gardens.

Lead and cadmium phytoavailability and human bioaccessibility for vegetables exposed to soil or atmospheric pollution by process ultrafine particles

When plants are exposed to airborne particles, they can accumulate metals in their edible portions through root or foliar transfer. There is a lack of knowledge on the influence of plant exposure conditions on human bioaccessibility of metals, which is of particular concern with the increase in urban gardening activities. Lettuce, radish, and parsley were exposed to metal-rich ultrafine particles from a recycling factory via field atmospheric fallouts or polluted soil. Total lead (Pb) and cadmium (Cd) concentrations in of the edible plant parts and their human bioaccessibility were measured, and Pb translocation through the plants was studied using Pb isotopic analysis. The Pb and Cd bioaccessibility measured for consumed parts of the different polluted plants was significantly higher for root exposure (70% for Pb and 89% for Cd in lettuce) in comparison to foliar exposure (40% for Pb and 69% for Cd in lettuce). The difference in metal bioaccessibility could be linked to the metal compartmentalization and speciation changes in relation to exposure conditions. Metal nature strongly influences the measured bioaccessibility: Cd presents higher bioaccessibility in comparison to Pb. In the case of foliar exposure, a significant translocation of Pb from leaves toward the roots was observed. To conclude, the type of pollutant and the method of exposure significantly influences the phytoavailability and human bioaccessibility of metals, especially in relation to the contrasting phenomena involved in the rhizosphere and phyllosphere. The conditions of plant exposure must therefore be taken into account for environmental and health risk assessment.

Earthworm bioturbation influences the phytoavailability of metals released by particles in cultivated soils

The influence of earthworm activity on soil-to-plant metal transfer was studied by carrying out six weeks mesocosms experiments with or without lettuce and/or earthworms in soil with a gradient of metal concentrations due to particles fallouts. Soil characteristics, metal concentrations in lettuce and earthworms were measured and soil porosity in the mesocosms was determined. Earthworms increased the soil pH, macroporosity and soil organic matter content due to the burying of wheat straw provided as food. Earthworm activities increased the metals concentrations in lettuce leaves. Pb and Cd concentrations in lettuce leaves can increase up to 46% with earthworm activities … These results and the low correlation between estimated by CaCl2 and EDTA and measured pollutant phytoavailability suggest that earthworm bioturbation was the main cause of the increase. Bioturbation could affect the proximity of pollutants to the roots and soil organic matter.

Foliar or root exposures to smelter particles: consequences for lead compartmentalization and speciation in plant leaves

In urban areas with high fallout of airborne particles, metal uptake by plants mainly occurs by foliar pathways and can strongly impact crop quality. However, there is a lack of knowledge on metal localization and speciation in plants after pollution exposure, especially in the case of foliar uptake. In this study, two contrasting crops, lettuce (Lactuca sativa L.) and rye-grass (Lolium perenne L.), were exposed to Pb-rich particles emitted by a Pb-recycling factory via either atmospheric or soil application. Pb accumulation in plant leaves was observed for both ways of exposure. The mechanisms involved in Pb uptake were investigated using a combination of microscopic and spectroscopic techniques (electron microscopy, laser ablation, Raman microspectroscopy, and X-ray absorption spectroscopy). The results show that Pb localization and speciation are strongly influenced by the type of exposure (root or shoot pathway) and the plant species. Foliar exposure is the main pathway of uptake, involving the highest concentrations in plant tissues. Under atmospheric fallouts, Pb-rich particles were strongly adsorbed on the leaf surface of both plant species. In lettuce, stomata contained Pb-rich particles in their apertures, with some deformations of guard cells. In addition to PbO and PbSO4, chemical forms that were also observed in pristine particles, new species were identified: organic compounds (minimum 20%) and hexagonal platy crystals of PbCO3. In rye-grass, the changes in Pb speciation were even more egregious: Pb-cell wall and Pb-organic acid complexes were the major species observed. For root exposure, identified here as a minor pathway of Pb transfer compared to foliar uptake, another secondary species, pyromorphite, was identified in rye-grass leaves. Finally, combining bulk and spatially resolved spectroscopic techniques permitted both the overall speciation and the minor but possibly highly reactive lead species to be determined in order to better assess the health risks involved.

Green manure plants for remediation of soils polluted by metals and metalloids: ecotoxicity and human bioavailability assessment

Borage, white mustard and phacelia, green manure plants currently used in agriculture to improve soil properties were cultivated for 10 wk on various polluted soils with metal(loid) concentrations representative of urban brownfields or polluted kitchen gardens. Metal(loid) bioavailability and ecotoxicity were measured in relation to soil characteristics before and after treatment. All the plants efficiently grow on the various polluted soils. But borage and mustard only are able to modify the soil characteristics and metal(loid) impact: soil respiration increased while ecotoxicity, bioaccessible lead and total metal(loid) quantities in soils can be decreased respectively by phytostabilization and phytoextraction mechanisms. These two plants could therefore be used for urban polluted soil refunctionalization. However, plant efficiency to improve soil quality strongly depends on soil characteristics.