Transfer of heavy metals in fruits and vegetables grown in greenhouse cultivation systems and their health risks in Northwest China

Temporal variations in absorption and translocation of heavy metal(loid)s in pak choi (Brassica rapa L.) under open-field and greenhouse cultivation

Elucidating the absorption and translocation of heavy metal(loid)s by common vegetables across different growth environments and stages is crucial for conducting accurate environmental risk assessments and for associated control. This study investigated temporal variations in the absorption and translocation capacities of pak choi (Brassica rapa L.) for As, Cd, Cr, Cu, Pb, and Zn in polluted soils during the plant growth cycle under greenhouse and open-field cultivation modes. Results showed high root metal(loid) bioconcentration factors and root-to-shoot translocation factors for Cd (0.25 and 1.44, respectively) and Zn (0.26 and 1.01), but low values for As (0.06 and 0.88) and Pb (0.06 and 0.87). The Cd concentration in the aerial edible parts peaked during the early slow growth period, whereas other heavy metal(loid)s peaked during the later stable maturity period. Root bioconcentration and root-to-shoot translocation factors did not significantly differ between cultivation modes. However, greenhouse cultivation exhibited lower average Cd and Zn concentrations in the edible parts and cumulative uptake amounts of most metal(loid)s than open-field cultivation during the typical harvest period spanning days 60 and 90. Short-term transitioning from open-field to greenhouse cultivation may reduce health risks associated with heavy metal(loid) intake via pak choi consumption. These findings facilitate sustainable agricultural practices and food safety management.

Analyzing heavy metal contamination for one of the high-rate consumption fruits in Iran: A probabilistic health risk assessment

Good health and well-being is one of the sustainable development goals (SDGs) that can be achieved through fruit consumption. This study measured cucumber (Cucumis sativus L.) heavy metal concentrations. Inductively coupled plasma-mass spectrometry (ICP-OES) was used to analyze the samples for heavy metal content. The uncertainty and sensitivity analyses of carcinogenic and non-carcinogenic heavy metal intake via cucumber (Cucumis sativus L.) consumption were assessed by Monte Carlo simulation. The mean ± SD levels of Cu, Pb, Zn, Cd, and As were determined to be 157.87 ± 128.54, 33.81 ± 6.27, 288.46 ± 114.59, 35.22 ± 18.67, and 33.6 ± 18.1 μg/kg, respectively. The 95th percentile of HI related to heavy metal intake via cucumber (Cucumis sativus L.) among children and adults were 2.64 and 1.75, respectively. Also, the 95th percentile of ELCR related to heavy metal were 8.26E-4 and 4.14E-3 among children and adults, respectively. The 95th percentile of LTCR of As among adults and As, Cd, and Pb among children were in the WHO target range (1E-04 to 1E-06) so reducing the concentration of them can help to reduce overall LTCR. When HQ and LTCR are below the cut limits, reducing heavy metals in high-consumption meals is a good way to lower them. In general, due to the wide consumption of various fruits, such as cucumber (Cucumis sativus L.), the concentration of environmental pollutants in their edible tissues should be monitored regularly, and the concentration of pollutants in these tissues should be minimized by proper planning.

Metal distribution and human health risk assessment in legumes crops (chickpea, lentils and peas) from Belesa districts, Ethiopia

Accumulation of heavy metals in food is a major concern for humans' health. This study was aimed at determining the levels of Cu, Fe, Mn, Ni and Zn in chickpea, lentil and pea samples and evaluating the health risk for consumers. The concentrations (in mg/kg) of Cu, Fe, Mn, Zn, and Ni were varied from 23.6-48, 67.7-132.3, 15-26.5, 37.6-68.2, and 25.5-33.3 in chickpea, 39.8-80.5, 116.1-180.5, 12.1-21.6, 36.4-57.2, and 25.4-34.1 for lentil and 32-64.2, 51.6-100.0, 6.3-15, 25.3-42.5, and 25.5-48.5 for peas, respectively. Pearson correlation verified that strong positive correlations were observed between Cu and Zn in lentils, Ni and Mn, Fe with Cu and Mn in peas. Target hazard quotients (THQ) except Ni in all samples, Cu in lentil and pea were < 1 and the hazard index (HI) values of all heavy metals were greater than 1, thus an appropriate strategy is required to reduce exposure to heavy metals.

Review of the Terminology, Approaches, and Formulations Used in the Guidelines on Quantitative Risk Assessment of Chemical Hazards in Food

This paper reviews the published terminology, mathematical models, and the possible approaches used to characterise the risk of foodborne chemical hazards, particularly pesticides, metals, mycotoxins, acrylamide, and polycyclic aromatic hydrocarbons (PAHs). The results confirmed the wide variability of the nomenclature used, e.g., 28 different ways of referencing exposure, 13 of cancer risk, or 9 of slope factor. On the other hand, a total of 16 equations were identified to formulate all the risk characterisation parameters of interest. Therefore, the present study proposes a terminology and formulation for some risk characterisation parameters based on the guidelines of international organisations and the literature review. The mathematical model used for non-genotoxic hazards is a ratio in all cases. However, the authors used the probability of cancer or different ratios, such as the margin of exposure (MOE) for genotoxic hazards. For each effect studied per hazard, the non-genotoxic effect was mostly studied in pesticides (79.73%), the genotoxic effect was mostly studied in PAHs (71.15%), and both effects were mainly studied in metals (59.4%). The authors of the works reviewed generally opted for a deterministic approach, although most of those who assessed the risk for mycotoxins or the ratio and risk for acrylamide used the probabilistic approach.

Co-exposure to UV-aged microplastics and cadmium induces intestinal toxicity and metabolic responses in earthworms

Aged microplastics (MPs) alter the interaction with heavy metals due to changes in surface properties. However, the combined toxicological effects of aged MPs on heavy metals in soil remain poorly understood. In this study, earthworms were employed as model animals to investigate the effects of aged MPs on the biotoxicity of cadmium (Cd) by simulating the exposure patterns of original and UV-aged MPs (polylactic acid (PLA) and polyethylene (PE)) with Cd. The results showed that UV-aging decreased the zeta potential and increased the specific surface area of the MPs, which enhanced the bioaccumulation of Cd and caused more severe oxidative stress to earthworms. Meanwhile, the earthworm intestines exhibited increased tissue damage, including chloragogenous tissue congestion lesions, and typhlosole damage. Furthermore, the combined exposure to UV-aged MPs and Cd enhanced the complexity of the microbial network in the earthworm gut and interfered with endocrine disruption, membrane structure, and energy metabolic pathways in earthworms. The results emphasized the need to consider the degradation of MPs in the environment. Hence, we recommend that future toxicological studies use aged MPs that are more representative of the actual environmental conditions, with the results being important for the risk assessment and management of MPs.

Foliar spraying of lanthanum activates endocytosis in lettuce (Lactuca sativa L.) root cells, increasing Cd and Pb accumulation and their bioaccessibility

Cadmium (Cd) and lead (Pb) accumulate easily in leafy vegetables and can harm human health. Lanthanum (La) have been used to improve agricultural yield and quality, but the effect of La application on Cd/Pb enrichment in leafy vegetables remains incomplete currently. A previous study reported that the endocytosis in lettuce leaf cells can be activated by La, leading to an increase in Pb accumulation in lettuce leaves. However, it has not been investigated whether foliar application of La enhances root cellular endocytosis and promotes its uptake of Cd and Pb. In this study, the influence of La on the uptake of Cd and Pb, Cd bioaccessibility, and the safety risks of cultivating lettuce under Cd and Pb stress were explored. It was found that La increased Cd (16-30 % in shoot, 16-34 % in root) and Pb (25-29 % in shoot, 17-23 % in root) accumulation in lettuce. The increased accumulation of Cd and Pb could be attributed to La-enhanced endocytosis. Meanwhile, La enhanced the toxicity of both Cd and Pb, inhibited lettuce growth, and aggravated the damage to the photosynthetic and antioxidant systems. Finally, gastrointestinal simulation experiments showed that La increased the Cd bioaccessibility in both gastric and intestinal phase by 7-108 % and 9-87 %, respectively. These results offer valuable insights into the safety of REEs for agricultural applications.

Zinc and nano zinc mediated alleviation of heavy metals and metalloids in plants: an overview

Heavy metals and metalloids (HMs) contamination in the environment has heightened recently due to increasing global concern for food safety and human livability. Zinc (Zn2+ ) is an important nutrient required for the normal development of plants. It is an essential cofactor for the vital enzymes involved in various biological mechanisms of plants. Interestingly, Zn2+ has an additional role in the detoxification of HMs in plants due to its unique biochemical-mediating role in several soil and plant processes. During any exposure to high levels of HMs, the application of Zn2+ would confer greater plant resilience by decreasing oxidative stress, maintaining uptake of nutrients, photosynthesis productivity and optimising osmolytes concentration. Zn2+ also has an important role in ameliorating HMs toxicity by regulating metal uptake through the expression of certain metal transporter genes, targeted chelation and translocation from roots to shoots. This review examined the vital roles of Zn2+ and nano Zn in plants and described their involvement in alleviating HMs toxicity in plants. Moving forward, a broad understanding of uptake, transport, signalling and tolerance mechanisms of Zn2+ /zinc and its nanoparticles in alleviating HMs toxicity of plants will be the first step towards a wider incorporation of Zn2+ into agricultural practices.

Combination of intercropping maize and soybean with root exudate additions reduces metal mobility in soil-plant system under wastewater irrigation

The effects of root exudates and irrigation with treated wastewater on heavy metal mobility and soil bacterial composition under intercropping remain poorly understood. We conducted a pot experiment with maize and soybean grown in monocultures or intercultures, irrigated with either groundwater or treated wastewater. In addition, the pre-collected root exudates from hydroponic culture with mono- or inter-cropped maize and soybean were applied to the soil at four levels (0 %, 16 %, 32 % and 64 %). The results showed that application of root exudates increased plant growth and soil nutrient content. The analysis of "Technique for Order of Preference by Similarity to Ideal Solution" for higher plant biomass and lower soil Cd and Pb concentrations indicated that the best performance of soybean under treated wastewater irrigation was recorded under intercropping applied with 64 % of exudates, with a performance score of 0.926 and 0.953 for Cd and Pb, respectively. The second-best performance of maize under treated wastewater irrigation was also observed under intercropping applied with 64 % of exudates. Root exudate application reduced heavy metals migration in the soil-plant system, with a greater impact in intercropping than in monocropping. In addition, certain soil microorganisms were also increased with root exudate application, regardless of irrigation water. This study suggests that appropriate application of root exudates could potentially improve plant growth and soil health, and reduce toxic heavy metal concentrations in soils and plants irrigated with treated wastewater.

Elevated CO2 may increase the health risks of consuming leafy vegetables cultivated in flooded soils contaminated with Cd and Pb

Elevated CO₂ levels threat the crop quality by altering the environmental behavior of heavy metals (HMs) in soils. In reality, multiple HMs often co-exist in field, while details regarding coexisting HMs migration in flooded soil at elevated CO₂ levels remain unclear. A pot experiment in open-top chambers (CO₂ at 400 and 600 μmol mol^-1) was conducted to explore the uptake and transfer of cadmium (Cd) and lead (Pb) in water dropwort (Oenanthe javanica DC.) grown in flooded soils contaminated with Cd and Pb. Results showed that elevated CO₂ significantly reduced soil pH, promoting the release of Cd and Pb (by 63.64-106.90% and 10.66-30.99%, respectively) into soil porewater. In the harvested O. javanica, elevated CO₂ decreased the root uptake of Cd but promoted that of Pb. Further mechanism analysis showed that elevated CO₂ promoted the formation of iron plaque on root surface by 44.60-139.57%, with lower adsorption capacity to HMs (0-34.93% and 63.61-67.69% for Cd and Pb, respectively). Meanwhile, Pb showed lower adsorbability in iron plaque but higher transfer capacity when compared with Cd. Ultimately, elevated CO₂ increased the target hazard quotient values of Pb in O. javanica. These findings provide new insights on the effects of elevated CO₂ on the transfer of coexisting HMs in soil-plant system, and the risk of HMs pollution under climate changes needs to be more fully assessed.

A comprehensive assessment of heavy metal(loid) contamination in leafy vegetables grown in two mining areas in Yunnan, China-a focus on bioaccumulation of cadmium in Malabar spinach

Contamination of leafy vegetables grown in heavy metal(loid)-polluted mining areas pose serious health risks. This study aimed to explore the heavy metal(loid) contamination of leafy vegetables near two mining areas, by collecting samples from 14 different leafy vegetable species in Yunnan Province, China. The lead (Pb), cadmium (Cd), arsenic (As), and copper (Cu) contents of the samples were determined, and risks to human health were calculated using the hazard quotient and hazard index (HI). Moreover, Malabar spinach was identified as a leafy vegetable that exhibits low accumulation of heavy metal(loid)s. The accumulation capacity of different Malabar spinach varieties was verified, and a Cd soil safety threshold was determined using a pot experiment. Overall, Pb and Cd were the main soil and vegetable contaminants found in both study sites. The HI values for all leafy vegetables, apart from Malabar spinach, were greater than 1, indicating the presence of risks to human health; moreover, the health risks were greater for children than adults. The Malabar spinach pot experiment results showed that only some Cd forms exceeded China's maximum permissible standards. Furthermore, Malabar spinach varieties A (instant Malabar spinach), C (extra-large leaf green vine Malabar spinach), and F (large leaf Malabar spinach) displayed the lowest Cd accumulation. We calculated Cd total and bioavailable soil safety thresholds of 4.75 and 0.77 mg kg-1, respectively. However, further research is required to validate soil heavy metal safety thresholds for different vegetables. Ultimately, the heavy metal(loid) contamination of leafy vegetables described here was more serious than anticipated. Finally, the results of this study can inform residents living near these mining areas of a low-risk leafy vegetable, which will reduce the harm caused by heavy metal(loid) contamination in the area.

Impact of Vanadium-Containing Stone Coal Smelting on Trace Metals in an Agricultural Soil-Vegetable System: Accumulation, Transfer, and Health Risks

Dietary exposure to trace metals (TMs) through vegetable consumption has been identified as a potential risk to human health. Fifty-one paired agricultural soil and leaf vegetable samples were collected around V-containing stone coal smelting sites in Hunan Province, China, to study the contamination and transfer characteristics of TMs (Cd, Cr, Cu, Pb, V, and Zn) in the soil-vegetable system. The health risk to local residents through vegetable ingestion was evaluated using Monte Carlo simulations. The results showed that 96.2%, 23.1%, 53.8%, 30.8%, 96.2%, and 69.2% of the soil samples had Cd, Cr, Cu, Pb, V, and Zn contents exceeding their related maximum allowable values, respectively. Cadmium and V were the primary pollutants based on the I_geo values. Moreover, 46.9% and 48.4% of vegetable samples exceeded the maximum permissible levels for Cd and Pb, respectively. There was a negative correlation between the bioaccumulation factors for Cd and V of the vegetable and soil physicochemical properties, including pH, organic matter, and free Fe₂O₃ content. Ingestion of garland chrysanthemum and pak choi posed high health risks, and Cd, V, and Pb were the primary contributors. These findings will help design strategies to minimize contamination and human exposure to soil-vegetable systems caused by V-containing stone coal smelting.

Heavy metals in daily meals and food ingredients in the Yangtze River Delta and their probabilistic health risk assessment

Heavy metal exposure via food consumption is inadequately investigated and deserves considerable attention. We collected hundreds of food ingredients and daily meals and assessed their probabilistic health risk using a Monte Carlo simulation based on an ingestion rate investigation. The detected concentrations of four heavy metals (Cr, Cd, Pb, and Hg) in all daily meal samples were within the limits stipulated in the National Food Safety Standard (GB 2762-2017), while that for As level was excessive in 0.3 % of daily meal samples. The same results were also observed in most food ingredient samples, and a standard-exceeding ratio of 23 % of As was observed in aquatic food or products, especially seafood, which was with the highest concentration reaching 1.24 mg/kg. Combining the detected heavy metal amounts with the ingestion rate investigation, the hazard quotients (HQs) of As, Cr, Cd, Pb, and Hg in daily meals and food ingredients were all calculated as lower than 1 (no obvious harm), while the incremental lifetime cancer risk (ILCR) of As and Cr (>1 × 10-4), indicating that the residual As posed potential health effects to human health. It was noteworthy that the proportion of aquatic foods only accounted for 6.3 % of daily meals, but they occupied 41.1 % of the heavy metal exposure, which could be attributed to the high amounts of heavy metals in aquatic foods. This study not only provided basic data of heavy metal exposure and potential health risks through daily oral dietary intake, but also illuminated the contribution of different kinds of food ingredients. Specifically, the study highlighted the contamination of aquatic foods with As, especially seafood such as shellfish and bivalves.

Rhizosphere bacteria regulated arsenic bioavailability and accumulation in the soil-Chinese cabbage system

The accumulation of arsenic (As) in Chinese cabbage (Brassica rapa ssp. pekinensis) has recently been a source of concern for a potential risk to human health. It is unknown whether natural variations of As accumulation in different genotypes of Chinese cabbage are related to rhizobacterial characteristics. Experiments were conducted to investigate the mechanisms of rhizobacteria involving in As fates in a soil-Chinese cabbage system using various genotypes using high-throughput sequencing and quantitative PCR. There were significant differences in As accumulation in cabbage leaves between 32 genotypes, and genotypes of low-As-accumulation (LSA) and high-As-accumulation (HSA) were identified. The As concentrations in the shoots of LSA were 23.25 %, 24.19 %, 15.05 %, and 70.69 % lower than those of HSA in seedling stage (SS), rosette stage (RS), heading stage (HS), and mature stage (MS), respectively. Meanwhile, the relative abundances of phyla Patescibacteria (in RS), Acidobacteria and Rokubacteria (in HS) in the rhizosphere of LSA were 60.18 %, 28.19 %, and 45.38 % less than those of HSA, respectively. Additionally, both shoot-As and As translocation factor had significantly positive or negative correlations with the relative abundances of Rokubacteria or Actinobacteria. In LSA rhizosphere, the relative abundances of genera Flavobacterium (in SS), Ellin6055 and Sphingomonas (in HS) were 128.12 %, 83.69 % and 79.50 % higher than those of HSA, respectively. This demonstrated that rhizobacteria contribute to the accumulation and translocation of As in HSA and LSA. Furthermore, the gene copies of aioA and arsM in LSA rhizosphere were 25.54 % and 16.13 % higher than those of HSA, respectively, whereas the gene copies of arsC in LSA rhizosphere were 26.36 % less than those of HSA in MS, indicating that rhizobacteria are involved in As biotransformation in the soil. These results provide a comprehensive understanding of the relationship between characteristics of rhizobacterial communities and As variations in Chinese cabbage genotypes.

Cadmium, lead, mercury, and arsenic in fresh fruits and fruit products intended for human consumption in the Republic of Serbia, 2015-2017

The European Commission has established legislation for toxic metals in certain foodstuffs in order to protect public health already in 1993. After several amendments, new maximum levels for cadmium and lead in certain foods were set as per 30 and 31 August 2021 for lead and cadmium, respectively. The new Serbian Regulation on "maximum levels of certain contaminants in food" is fully harmonised with this European legislation. The concentrations of cadmium (Cd), lead (Pb), mercury (Hg), and arsenic (As) were determined in 832 samples of 39 species of fruits and processed fruits, collected during the period January 2015 to December 2017. Fruits and fruit products originated from 45 countries, including Serbia. Samples were analysed by inductively coupled plasma - optical emission spectrometry (ICP-OES). Concentrations of cadmium, lead, mercury, and arsenic in fruits and fruit products were compared to these maximum levels (MLs). Overall, measurable Cd, Pb, Hg, and As were found in 377 samples (45.3%). According to the former regulations, the maximum levels of Cd and Pb for analysed fruits and fruit products were exceeded in only 10 samples (1.20%; n = 832): Cd in 6 and Pb in 4 samples, but according to the latest regulations, the maximum levels of Cd and Pb for fruits were exceeded in 196 of the samples (23.9%; n = 820): Cd in 191 and Pb in 5 samples. The increase of ML exceedances shows that attention needs to be paid for compliance of food to the recent MLs for these metals.

Anthropogenic activities affecting metal transfer and health risk in plastic-shed soil-vegetable-human system via changing soil pH and metal contents

Accumulation and concomitant risk of metals in plastic-shed soil (PSS)-vegetable system around industrial areas have attracted growing public concern recently, while limited studies have focused on human bioaccessible metals in various plastic-shed vegetables and health risk calculated using bioaccessible metals. Previous studies showed that intensive farming and industrial activities could prominently affect metal migration from PSS to vegetables via altering PSS pH, total and bioavailable metal contents. In contrast, whether changes in PSS pH and metal contents control bioaccessible metals in vegetables and health risk is still unknown. For PSS management and sustainable plastic-shed vegetable production in the areas with rapid industrialization, 41 PSS and 32 plastic-shed vegetable samples were sampled from the industrial areas of Yangtze River Delta, China to systematically clarify the specific connections among anthropogenic activities, soil pH and metal contents, and metal transfer and health risk in PSS-vegetable-human system. The results indicated that Cr and Cd contents in 15.6% and 9.38% of vegetable samples exceeded the allowable limits in China. Tolerable cancer risk existed and was mainly induced by bioaccessible Cr in vegetables. Decreased PSS pH mainly caused by heavy use of nitrogen fertilizers increased bioavailable Ni, Cd, Zn, Pb, and Cu in PSS and subsequently enhanced their total and bioaccessible contents in vegetables. Prominent Cr accumulation in PSS induced by industrial wastewater irrigation exacerbated Cr uptake by vegetables, which increased bioaccessible Cr in vegetables and contributed greatly to cancer risk. To reduce transfer and health risk especially of Cd and Cr in the food chain, some appropriate measures related to source control and remediation should be proposed for preventing and mitigating PSS acidification and Cr accumulation.

Risk assessment and early warning of the presence of heavy metal pollution in strawberries

Heavy metal pollution is a major threat to agricultural produce and it can pose potential ecological risks which subsequently impacts on human health. Strawberries are an economically important produce of China. The intrinsic link of heavy metal pollution risk in the soil-strawberry ecosystem is of concern. In this study, the pollution index of heavy metal pollutants in farmlands of different provinces were evaluated, and the results showed significantly high levels of cadmium. In addition, Nemerow integrated pollution index analysis showed that low-pollution farmlands only accounted for 14.07% of the total arable land area. Then, the transfer factors were used to calculate the migration of heavy metals from the soil into strawberries. The results showed that cadmium and nickel were relatively high in strawberries from the Guangxi province. Similar results were found for mercury in Jiangxi Province. The pollution index of single food pollution also showed that mercury in strawberries from Jiangxi Province was at a moderate pollution level. The comprehensive pollution index indicated that heavy metal pollution in strawberries in Central China may be severe. In addition, spatial clustering analysis showed that cadmium, chromium, lead, arsenic and zinc in strawberries had significant hotspot clustering in central, south and southwest China. Finally, our studies also suggested that the risk of carcinogenic and non-carcinogenic diseases was higher in the (2, 4] years age group than in other age groups. People in Yunnan Province were also found to have a higher non-carcinogenic risk than those in other provinces and cities in China. This study provides a comprehensive view of the potential risks of heavy metal contamination in strawberries, which could provide assistance in the design of regulatory and risk management programs for chemical pollutants in strawberries, thus ensuring the safety of consumption of these edible fruits.

Closed-loop evaluation on potential of three oil crops in remediation of Cd-contaminated soil

Cd-contaminated farmlands threaten food security and safety by inhibiting crop growth and Cd accumulating in edible parts. Phytoremediation is a promising option to remove Cd from farmland soil. An ideal option is to remediate Cd and produce crops simultaneously on the contaminated soil. Therefore, we chose widely planted oil crops (soybean, sunflower and rape) as experimental materials, cultured in pots filled with soils contaminated with different concentrations (10, 20, 50, and 100 mg kg^-1) Cd till harvest, and then took a closed-loop method to evaluate the remediation potential of the three oil crops, including the remediating ability, yield, and quality of seeds and environmental risk of pyrolytic biochar. The results show that the order of Cd accumulation capacity in the three oil crops was sunflower > rape > soybean. The yield and quality of the three oil crops were decreased by being treated with different concentrations of Cd. In addition, the order for a decreased degree in yield of the three oil crops was sunflower < rape < soybean, and the order for a decreased degree in protein and fat content was sunflower < soybean < rape. The potential risk of seeds of the three oil crops as food/feed was sunflower/soybean < soybean/sunflower < rape. After pyrolysis of harvested three oil crops, the order for leaching toxicity/leaching potential was sunflower-biochar < soybean-biochar/rape-biochar < rape-biochar/soybean-biochar. All three oil crops could remediate Cd-contaminated soils, and their seeds could generate economic value. Closed-loop evaluation of sunflower proved it might be a good option for removing Cd from farmland soil.

Natural field freeze-thaw process leads to different performances of soil amendments towards Cd immobilization and enrichment

Cadmium (Cd) soil pollution is a global issue affecting crop production and food safety. Remediation methods involving in-situ Cd immobilization have been developed, but their effectiveness can diminish under seasonal freeze-thaw aging processes. In this study, we assessed the field performance of four soil treatments at a seasonally frozen rice paddy. Amendments were applied at 2 wt%, including: (i) sepiolite (a 2:1 clay mineral), (ii) superphosphate, (iii) biochar (produced by rice husk at 500 °C for 2 h), and (iv) joint application of biochar & superphosphate (1:1 mixture by weight). Immobilization performance was determined as DTPA extractable Cd and plant uptake in various organs. Overall, the four treatments significantly reduced Cd bioavailability during the plant growth period, with average DTPA-extractable concentrations decreasing by 43%, 34%, 39% and 45% for the four treatments, respectively, relative to untreated soil (control). Rice grain yields from the superphosphate and the joint application treatments increased by 8.0% and 11.8%, respectively, and Cd accumulation within those grains reduced by 14.3% and 48.9%, respectively. During the winter non-growth period, freeze-thaw aging facilitated Cd mobilization, with DTPA-extractable Cd increasing by 16.9% in the control soil, relative to the initial period. However, this reduced to 10.9%, 14.4%, 7.6% and 5.0%, for the sepiolite, superphosphate, biochar and joint application treatments, respectively. Overall, the joint application of biochar and superphosphate provided the best performance in terms of both long-term Cd immobilization and rice production enhancement, offering a green remediation option for risk management at Cd contaminated rice paddies in seasonally frozen regions.

Heavy element contents of vegetables and health-risk assessment in China

This study analyzed five heavy elements (HEs), including cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb), and arsenic (As), in fresh vegetables (i.e., legume, rhizome and potato, gourd, bulb, solanaceous fruit, leafy, and brassica; total: 7214) collected from 31 provinces in China from 2016 to the first half of 2017. By analyzing the concentration level of the five HEs in seven regions (the Northeast, North China, East China, South China, Central China, the Northwest, and the Southwest), except for As, average HEs concentrations were higher in the Southwest than that in the other six regions. According to the maximum permissible limit (MPL), the highest rate of HEs concentration above the MPL was found in the Southwest (11.038%). Analysis of variance (ANOVA) showed varying degrees of variability between regions and categories. By using principal component analysis (PCA), it was found that two principal components account for 73.79% of the total variance in the data. Together with hierarchical cluster analysis (HCA), concluded that Tibet was significantly different from the other 30 provinces. By calculating estimated daily intake (EDI) and the target hazard quotient (THQ), the EDI of Cr in the Southwest was the highest, with results of 1.2119 μg/kg/day for children and 0.8073 μg/kg/day for adults. North China had the highest total target hazard quotient (TTHQ) for HEs in vegetables ingested by children, with a result of 0.933.

Introducing melatonin to the horticultural industry: physiological roles, potential applications, and challenges

Melatonin (N-acetyl-5-methoxytryptamine) is an emerging biomolecule that influences horticultural crop growth, flowering, fruit ripening, postharvest preservation, and stress protection. It functions as a plant growth regulator, preservative and antimicrobial agent to promote seed germination, regulate root system architecture, influence flowering and pollen germination, promote fruit production, ensure postharvest preservation, and increase resistance to abiotic and biotic stresses. Here, we highlight the potential applications of melatonin in multiple aspects of horticulture, including molecular breeding, vegetative reproduction, production of virus-free plants, food safety, and horticultural crop processing. We also discuss its effects on parthenocarpy, autophagy, and arbuscular mycorrhizal symbiosis. Together, these many features contribute to the promise of melatonin for improving horticultural crop production and food safety. Effective translation of melatonin to the horticultural industry requires an understanding of the challenges associated with its uses, including the development of economically viable sources.

Residue, dissipation and dietary intake risk assessment of tolfenpyrad in four leafy green vegetables under greenhouse conditions

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A QuEChERS-GC–MS/MS method was used to detect tolfenpyrad in leafy green vegetables.

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Half-lives of tolfenpyrad were 2.0–6.8 d in greenhouse-grown leafy green vegetables.

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PHI of tolfenpyrad was suggested as 21 d in BCL and 28 d in BBL, SOL and LSL.

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The potential health risk of tolfenpyrad was acceptable in leafy green vegetables.

A novel and accurate analytical method for the determination of tolfenpyrad in four leafy green vegetables, Brassica bara L., Spinacia oleracea L., Lactuca sativa L. and Brassica chinensis L., was developed and applied to investigate the residue distribution and dietary risk under greenhouse conditions. The established approach was determined to be adequate, with recoveries of 79.2%–92.9% and relative standard deviations < 8%. Tolfenpyrad dissipated relatively rapidly in four leafy green vegetables. Terminal residues of tolfenpyrad were below 0.5 mg/kg (maximum residue limit for Brassica bara L. set by China) in leafy green vegetables collected 28 d after the last application. Due to risk quotient values < 100%, the residue levels of tolfenpyrad in leafy green vegetables collected 21 days after the last application were deemed safe for consumers. The results provide field data for the reasonable use and dietary risk assessment of tolfenpyrad in leafy green vegetables.

BrpNAC895 and BrpABI449 coregulate the transcription of the afflux-type Cd transporter BrpHMA2 in Brassica parachinensis

Brassica parachinensis is a popular leafy vegetable. It is able to accumulate high concentration of Cd, however, the molecular mechanism of Cd accumulation is unknown. This study investigated the function and regulatory mechanism of the Cd-responsive metal ion transporter gene BrpHMA2. BrpHMA2 was induced by Cd stress and specifically expressed in vascular tissues, and the protein was localized in the plasma membrane. Heterologous expression of BrpHMA2 enhanced Cd accumulation and Cd sensitivity in transgenic Arabidopsis and yeast. After Cd stress, the transcriptional factors BrpNAC895 and BrpABI449, which may recognize the ABREs in the BrpHMA2 promoter, were also differentially expressed. The transcriptional regulation of BrpHMA2 was further investigated using ChIP-qPCR, EMSA and LUC reporter activity analysis employing the transient expression system of Brassica parachinensis protoplasts and tobacco leaves and the E. coli expression system. By binding to the promoter, BrpNAC895 induced the transcription of BrpHMA2. BrpABI449 might bind to the BrpHMA2 promoter or interact with BrpNAC895 to interfere with the action of BrpNAC895. The findings suggest that BrpHMA2 is a membrane-based afflux-type Cd transporter involved in the Cd2+ uptake and long-distance transport in plants. BrpNAC895 and BrpABI449, which function as the transcription activator and repressor respectively, coregulate BrpHMA2 expression.

Toxic element contents and associated multi-medium health risk assessment in an area under continuous agricultural use

Soils and contaminated plants are in the group of significant environmental pathways of human exposure to toxic elements (TEs). This study aimed to assess the soil-to-plant transfer of TEs (Pb, As, Cd, Hg), as well as the plausible health risks via different exposure pathways in the Armavir region of Armenia. The contents of TEs were determined in soil, fruit and vegetable samples using X-ray fluorescence and atomic absorption spectroscopy, respectively, and the soil-to-plant transfer of TEs and induced chronic non-carcinogenic risks were evaluated. The detected TE contents did not exceed the available national and international regulatory levels. Moreover, the evaluated soil-to-plant transfer of these TEs was negligible. The obtained results indicated the absence of a single-element non-carcinogenic risk via one single ingestion pathway. Meanwhile, in the case of multi-food and multi-soil ingestion, the combined non-carcinogenic risk estimates for Pb and As exceeded the precautionary level of 0.1 indicating a low health risk. Similarly, the multi-element hazard index (HI) showed a low level of non-carcinogenic risk through a multi-pathway ingestion. Thus, the outcomes highlighted that there was a need for precautionary measures to prevent plausible health issues for the adult population in Armavir.

Metal accumulation and health risk assessment in wastewater used for irrigation around the Agra Canal in Faridabad, India

Wastewater application for irrigation is a traditional and economic tool in developing nations. Yet prolonged use of wastewater for agricultural activities contributes to the accumulation of metals in both soil and vegetables. This study investigated the accumulation and contamination of vegetables with heavy metals ensuing from the application of wastewater from the Agra Canal and the associated risks posed to human health. Three sites across the Agra canal were selected for sampling (CW-1, CW-2, and CW-3), where untreated wastewater is being used to irrigate vegetables (spinach, coriander, radish, and garlic crops), for which tube-well water (TW) from a village served as the control site. Water, soil, and vegetable samples were collected from all sites. The presence in them of various metals, such as As, Pb, Cr, Mn, Cu, Zn, and Ni, was detected at all four sites. The greatest content of Mn was found in CW-1's water (7.91 mg/L), soil (633.77 mg/kg), and in spinach 368.12 (mg/kg) grown there. Significantly higher metal concentrations were observed in vegetables irrigated with wastewater than in tube-well-irrigated vegetables, with the metals ranked in accumulation as follows Mn > Zn > Ni > Cu > Cr > Pb > As. Our results also revealed that metal bioaccumulation varied enormously between foliar and non-foliar vegetables, as well as among the four sites. Daily metal intake (DMI) and health risk index (HRI) analyses suggested that children consuming contaminated vegetables are at higher risk than adults. The HRI for Mn, Ni, and Pb was above 1, which indicated significant health hazards to humans consuming the wastewater-irrigated vegetables. Moreover, the control site where tube-well water was used had an HRI below 1, signifying a negligible health risk for its consumption. Therefore, we may conclude that the extensive application of contaminated water for a longer duration would likely further increase metal accumulation in soil and vegetables that may be hazardous to living organisms.

Comprehensive Risk Assessment of Applying Biogas Slurry in Peanut Cultivation

Biogas slurry, a byproduct of biogas plants, is considered a high-quality bio-organic fertilizer. Despite providing nutrients to crops, biogas slurry may contain a high concentration of heavy metals, leading to food safety problems and endangering human health if such metals are absorbed by plants. Therefore, biogas slurry should undergo systematic risk assessment prior to direct use on farmland to ensure its safety for soils and crops. In this study, the risk of applying biogas slurry in peanut cultivation was comprehensively evaluated. Based on nitrogen contents, different concentrations of biogas slurry were applied in peanut cultivation. The results achieved herein showed that the application of biogas slurry as a nutrient supplier in peanut cultivation would significantly affect the physical and chemical properties of soil and characteristics of the plant and the quality of peanuts. Although the heavy metal content of biogas slurry was within the permitted range, it had potential risks to human health and the environment. Principal component analysis (PCA) showed that biogas slurry was the primary source of heavy metals in soil. After the application of biogas slurry, the contents of As and Hg in the soil increased significantly, which were 11.12 and 26.67 times higher than those in the control soil. The contents of Cu, Zn, Pb, Cd, and As in peanut kernel samples under different levels of biogas slurry application were all lower than the maximum permissible limit set by the Standardization Administration of China. In contrast, the content of Hg in peanut kernels was higher than the maximum permissible limit value of 0.02 mg/kg. Peanut had a higher enrichment capacity of Cd and Zn and a higher migration capacity of Pb. The health risk assessment showed that the long-term consumption of peanuts grown with a high dosage of biogas slurry would be harmful to the health of children aged 2–6 years with a large consumption level.

Ecological-health risks assessment and source identification of heavy metals in typical greenhouse vegetable production systems in Northwest China

Due to the high cropping index and substantial agricultural inputs in greenhouse vegetable production systems (GVP), the environmental problems caused by heavy metals in GVP are becoming increasingly serious. A systematic investigation of heavy metals accumulation was carried out in GVP located in Jingyang, Shaanxi, China. The accumulation of Cd and Hg was assessed to be more significant than that of other elements in these GVP soils. The pollution load index (PLI) confirmed that 98.9% of the soil samples showed a moderate level of pollution. Additionally, the potential ecological risk index (RI) values indicated that 63.7 and 14.3% of the area was at moderate and high ecological risk, respectively. In assessing the human health risks associated with vegetable consumption, the highest target hazard quotient (THQ) was that for As, followed by Cu > Cd > Zn > Pb > Hg > Cr. Although the hazard index (HI) values were below 1 except for three sample sites in the study area, the 95% quantile of forecasted HI values was 1.22. More attention should be devoted to heavy metal pollution in GVP products. Positive matrix factorization (PMF) was used to identify the sources of the heavy metals. Cu and Zn accumulation were the results of fertilizer overuse; the parent material was the primary source of the As, Pb, and Cr; and the sources of Cd and Hg were inorganic fertilization and industrial emissions, respectively. Effective measures should be implemented to reduce future ecological and health risks in GVP.

Effects of Long-Term Freeze-Thaw Cycles on the Properties of Stabilized/Solidified Lead-Zinc-Cadmium Composite-Contaminated Soil

Lead, zinc, and cadmium were used to prepare a composite-contaminated soil to replicate common situations, in which soil is usually simultaneously contaminated by multiple metals. To examine the long-term durability of stabilized/solidified (S/S) contaminated soil, specimens were subjected to a series of freeze–thaw (F-T) cycles, up to ninety times (one day per cycle), prior to testing. Triaxial compression tests, soil column leaching tests, and X-ray diffraction analysis were then employed to study the mechanical properties, environmental influences, and micro-mechanisms of the S/S lead-zinc-cadmium composite-contaminated soils after long-term F-T. The results showed that triaxial compressive strength increases within three F-T cycles, then decreases before slightly increasing or stabilizing after thirty F-T cycles. The stage of decreased cohesion thus occurs between three and fourteen F-T cycles, with variation in other factors similar to that of the triaxial compressive strength. The cohesion mainly increases between three and seven cycles. The soil column leaching test showed that the permeability of soil is more than four times higher than that of soil not subject to freeze–thaw cycles after ninety F-T cycles. XRD tests further revealed that the chemical composition of S/S contaminated soil and the occurrence of each heavy metal (HM) remained unchanged under F-T treatment.