Uptake and distribution of minerals and heavy metals in commonly grown leafy vegetable species irrigated with sewage water

Assessment of heavy metal contamination in leafy vegetables: implications for public health and regulatory measures

Heavy metal contamination in leafy vegetables poses significant health risks, highlighting the urgent need for stringent monitoring and intervention measures to ensure food safety and mitigate potential adverse effects on public health. This study investigates the levels of heavy metals, including cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb), zinc (Zn), and copper (Cu), in locally grown and commercially available leafy vegetables, comparing them to the safety limits established by WHO/FAO. The results revealed that levels of Cd, Cr, Ni, and Pb in the vegetables exceeded WHO/FAO limits, while Zn and Cu remained within permissible bounds. Marketed vegetables exhibited higher metal concentrations than those from nearby farms. For Cu (0.114-0.289 mg/kg) and Zn (0.005-0.574 mg/kg), the daily intake of metals (DIM) was below the dietary intake (DI) and upper limit (UL). Cd's DIM (0.031-0.062 mg/kg) remained below the UL but exceeded the DI. Marketed kale and mint surpassed both DI and UL limits for Ni, while local produce only exceeded the DI. All vegetables had DIM below the DI, except for mint and kale. For Pb, every vegetable exceeded DI limits, with market samples contributing significantly. Cr's DIM ranged from 0.028 to 1.335 mg/kg, for which no set maximum daily intake exists. The health risk index (HRI) values for Zn, Cd, Cu, Ni, and Pb suggested potential health risks associated with leafy greens, while Cr's HRI was below 1. The study underscores the need for stringent monitoring and intervention measures to mitigate the health risks posed by heavy metal contamination in leafy vegetables. These findings suggest that consuming these leafy greens may put consumers at considerable risk for health problems related to Cd, Cu, Ni, Pb, and Zn exposure.

A critical analysis of wastewater use in agriculture and associated health risks in Pakistan

Freshwater shortage and its contamination with various types of pollutants are becoming the most alarming issues worldwide due to impacts on socioeconomic values. Considering an increasing freshwater scarcity, it is imperative for the growers, particularly in semiarid and arid areas, to use wastewater for crop production. Wastewaters generally contain numerous essential inorganic and organic nutrients which are considered necessary for plant metabolism. Besides, this practice provokes various hygienic, ecological and health concerns due to the occurrence of toxic substances such as heavy metals. Pakistan nowadays faces a severe freshwater scarcity. Consequently, untreated wastewater is used routinely in the agriculture sector. In this review, we have highlighted the negative and positive affectivity of wastewater on the chemical characteristics of the soil. This review critically delineates toxic metal accumulation in soil and their possible soil-plant-human transfer. We have also estimated and deliberated possible health hazards linked with the utilization of untreated city waste effluents for the cultivation of food/vegetable crops. Moreover, we carried out a multivariate analysis of data (144 studies of wastewater crop irrigation in Pakistan) to trace out common trends in published data. We have also compared the limit values of toxic metals in irrigation water, soil and plants. Furthermore, some viable solutions and future viewpoints are anticipated taking into account the on-ground situation in Pakistan-such as planning and sanitary matters, remedial/management technologies, awareness among local habitants (especially farmers) and the role of the government, NGOs and pertinent stakeholders. The data are supported by 13 tables and 7 figures.

Phytomanagement of trace element polluted fields with aromatic plants: supporting circular bio-economies

Trace elements pollution of soils became a global concern because of their persistence in the environment which can lead to accumulation in food chains up to toxic levels. At the same time, there is a shortage of arable land for growing food, fodder and industrial crops, which highlights the need for remediation/use of polluted land. Restoration of degraded lands has been included as a vital component of UN Sustainable Development Goals (SDGs). We summarize various sources of entry of important trace elements in the environment, available biological reclamation and management strategies and their limitations. Recent advances in phytomanagement approaches using aromatic crops to obtain economically valuable products such as essential oils and revalorize such polluted areas are reviewed. The worldwide application of this strategy in the last 10 years is illustrated through a choropleth map. Finally, the emerging concept of phytomanagement as a restorative and regenerative circular bio-economy is also discussed.

Mixing tannery effluent had fertilizing effect on growth, nutrient accumulation, and photosynthetic capacity of some cucurbitaceous vegetables: A little help from foe

Tannery effluent contains a number of organic and inorganic elements as pollutants which reduce plant growth. To overcome shortage of water, use of diluted industrial wastewater such as tannery effluent can be a viable strategy for improving crop growth and yield. A pot experiment was conducted to determine the effects of tannery effluent and its various dilutions on physiological and biochemical characteristics of five cucurbitaceous vegetables. Tannery effluent was applied 0, 25, 50, 75 and 100% to 3-week-old plants of five cucurbitaceous vegetables (Cucurbita maxima, Luffa cylindrica, Citrullus vulgaris, Cucumis melo, and Praecitrullus fistulosus) for 4 weeks. Tannery effluent reduced the growth of all five cucrbitaceous vegetables. Diluted tannery effluent (25%) improved the growth of Cucurbita maxima, Citrullus vulgaris, and Cucumis melo. Moderately diluted (50%) did not affect the growth of Citrullus vulgaris and Cucumis melo. Toxic effects of tannery effluent were associated with high accumulation of heavy metals Cr, Cd, Mn, and Fe in leaves and roots. High accumulation of heavy metals in leaves reduced the accumulation of nutrients in leaves (N, P, K) and reduced photosynthetic pigments and photosynthetic rate. Changes in photosynthetic rates of all vegetable species due to tannery effluent were not associated with stomatal limitations (stomatal conductance, transpiration rate, internal CO₂). Toxic effects of tannery effluent on plants also include changes in N-metabolism (amino acid and protein). However, extent of these adverse effects of tannery effluent on vegetables was species specific. It is suggested that Cucurbita maxima can be grown by supplying 25% tannery effluent, whereas Citrullus vulgaris and Cucumis melo can be grown with moderately diluted (50%) tannery effluent.

Optimizing textile dyeing wastewater for tomato irrigation through physiochemical, plant nutrient uses and pollution load index of irrigated soil

Reuse of wastewater for vegetable cultivation is becoming popular in order to augment the inadequate irrigation supplies and meet the growing demands of ground water for agriculture and industries production in different regions of the world. This study was investigated to optimize different stages of textile dyeing wastewater (TDW) for irrigation focusing on their effect on growth, yield and physiochemical attributes of tomato, plant nutrient use, heavy metals enrichment and pollution load of the irrigated soil. Textile wastewater were collected from the seven stages of (second wash after scouring and bleaching T2; enzyme treated water T3; second wash after bath drain T4; neutralization treatment T5; second wash after soaping T6; fixing treatment water T7; mixed effluent T8) of a dyeing process for physiochemical characterization and evaluation their irrigation feasibility for tomato cultivation in compare with the ground water (T1). The pot experiment consists of eight irrigation treatments was laid out following a completely randomized block design with three replications. Results showed the presence of plant nutrients and heavy metals in all the studied samples where T8 (mixed effluent) exceeded the limit of agricultural standard for almost all physiological parameters such as TDS, TSS, EC, BOD, COD affording the highest value. T8 also delivered the highest Cl- and heavy metals like Cd, Ni, Cr followed by T4 < T7. As a consequence, these provided comparatively higher enrichment factor (EF), pollution load index (PLI) and sodium absorption ratio (SAR) to transform fresh soil into the category of severe and slightly to moderate saline. Therefore, the yield and physiochemical attributes of tomato were dramatically reduced with T8 and T4 treatment. On the other hand, T2, T3 and T6 treatment had significant positive impact on growth and yield of tomato due to having higher N, P, K, S and lower heavy metals (Cu, Zn, Fe, Pb, Cd, Ni, Cr) than the recommended guideline. These features were contributed to cause minimum EF and PLI in the soil irrigated with T2, T3 and T6 stages of TDW. Correlation matrix demonstrated that EF and PLI of heavy metals (except Cd, Ni) were negatively related to yield, while positively related to SAR and fruit abortion. Although T6 (2nd wash after soaping) performed better in respect to growth, yield, yield attributes and nutrient use efficiency, principal component analysis revealed that T2 (2nd wash after scouring and bleaching) and T3 (enzyme treated water) were also belong to the same group of T6 and T1 (ground water). Thus, it may be suggested that T2, T3 and T6 stages of textile dyeing wastewater could be used profitably without ETP for vegetable cultivation and would effectively supplement not only the nutrient requirement of the crop but may also act as the alternate source of irrigation water. Although, further research is needed to sort out the health risk assessment through the heavy metals’ accumulation in the plant parts after irrigation with different stages of textile dyeing wastewater.

The Salicornia europaea potential for phytoremediation of heavy metals in the soils under different times of wastewater irrigation in northwestern Iran

The use of wastewater for irrigation usually leads to the buildup of potentially toxic elements (PTEs) in soils. The objective of this study was to assess the capacity of Salicornia europaea L. to uptake heavy metal when irrigated with wastewater at the vegetative, flowering, and reproductive stages of S. europaea for 2 and 4 days (in each stage) in the coastal saline area of Lake Urmia. The concentrations of heavy metals were detected in irrigated water, soil, and plant samples, while transfer factor (TF), bioconcentration factor (BCF), and bioaccumulation factor (BAF) were calculated. The results revealed that metal concentrations in the wastewater were above the permissible limits. The wastewater irrigation caused higher shoot biomass despite the high uptake of PTEs. Levels of Fe and Cu in plants were higher when irrigated with wastewater at the reproductive stage as compared to flowering and vegetative stages. The TF of wastewater-irrigated plants was higher at the flowering stage. TF of different metals at the flowering stage were in order of Zn > Pb > Ni > Cd > Cu, while the BCF increased in the order Cd > Cu > Zn > Ni > Pb. The BAF of the investigated PTEs at the flowering stage increased in the order Cd > Pb > Ni > Zn > Cu. In conclusion, higher Pb and Zn in the shoot indicated that the plant exhibited the phytoextraction mechanism, while Salicornia used a phytostabilization mechanism for roots-Cu, Ni, and Cd.

Bacteria Isolated from Wastewater Irrigated Agricultural Soils Adapt to Heavy Metal Toxicity While Maintaining Their Plant Growth Promoting Traits

The present study explored the plant growth promotion and bioremediation potential of bacteria inhabiting wastewater irrigated agricultural soils. Thirty out of 75 bacterial isolates (40%), 29/75 (39%) and 28/75 (37%) solubilized Zn, K and PO4 during plate essays respectively. Fifty-six percent of the isolates produced siderophores, while 30% released protease in vitro. Seventy-four percent of bacteria resisted Pb, Ni and Cd at various concentrations added to the culture media plates. Sixteen out of 75 (26%) isolates were able to fix N in Nbf medium. Among these 16 N fixers, N fixing nifH, nifD and nifK genes was detected through PCR in 8, 7 and 1 strain respectively using gene specific primers designed in the study with Enterobacter sp. having all three (nifHKD) genes. Isolated bacteria showed resemblance to diverse genera such as Bacillus, Pseudomonas, Enterobacter, Citrobacter, Acinetobacter, Serratia, Klebsiella and Enterococcus based on 16S rRNA gene sequence analysis. In addition to showing the best mineral solubilization and metal resistance potential, Citrobacter sp. and Enterobacter sp. also removed 87%, 79% and 43% and 86%, 78% and 51% of Ni, Cd and Pb, respectively, from aqueous solution. These potent bacteria may be exploited both for bioremediation and biofertilization of wastewater irrigated soils leading to sustainable agriculture.

Nickel in terrestrial biota: Comprehensive review on contamination, toxicity, tolerance and its remediation approaches

Nickel (Ni) has been a subject of interest for environmental, physiological, biological scientists due to its dual effect (toxicity and essentiality) in terrestrial biota. In general, the safer limit of Ni is 1.5 μg g^-1 in plants and 75-150 μg g^-1 in soil. Litreature review indicates that Ni concentrations have been estimated up to 26 g kg^-1 in terrestrial, and 0.2 mg L^-1 in aquatic resources. In case of vegetables and fruits, mean Ni content has been reported in the range of 0.08-0.26 and 0.03-0.16 mg kg^-1. Considering, Ni toxicity and its potential health hazards, there is an urgent need to find out the suitable remedial approaches. Plant vascular (>80%) and cortical (<20%) tissues are the major sequestration site (cation exchange) of absorbed Ni. Deciphering molecular mechanisms in transgenic plants have immense potential for enhancing Ni phytoremediation and microbial remediation efficiency. Further, it has been suggested that integrated bioremediation approaches have a potential futuristic path for Ni decontamination in natural resources. This systematic review provides insight on Ni effects on terrestrial biota including human and further explores its transportation, bioaccumulation through food chain contamination, human health hazards, and possible Ni remediation approaches.

Impacts of Long- and Short-Term of Irrigation with Treated Wastewater and Synthetic Fertilizers on the Growth, Biomass, Heavy Metal Content, and Energy Traits of Three Potential Bioenergy Crops in Arid Regions

The availability of suitable water is an important factor for increasing the cultivated areas and sustainability in arid (i.e., less than 200 mm precipitation per year) and semiarid regions (i.e., 200–700 mm precipitation per year). Therefore, this study aimed to analyze the impact of treated wastewater (TWW) and groundwater (GW) as well as synthetic fertilizers (50% and 100% of the recommended NPK dose; 150–150–60 kg N–P2O5–K2O ha−1) on the growth, biomass, energy traits, and macro and trace elements of maize (Zea mays L.), sorghum (Sorghum bicolor L.), and pearl millet (Pennisetum glaucum L) grown in old cultivated (first location; L1) and virgin soil (L2 and L3) as potential bioenergy crops. The soil in L1 has been irrigated with treated wastewater for the last 15 years and continued to be irrigated with treated wastewater in this investigation. The virgin soil was divided into two parts: the first part was irrigated with TWW, and the second part was irrigated with GW. The experiments were laid out in a split-plot with a randomized complete block design with water treatments (TWW in old and virgin soil, and GW in virgin soil) in main plots, and the two treatments of fertilization (50% and 100% of the recommended NPK dose) were distributed randomly in subplots. Compared with the crops irrigated with GW, the crops irrigated with TWW, whether grown on old or virgin soil, showed higher plant height, total chlorophyll content, leaf area per plant, total biomass, energy content, and gross energy with low ash. They also contained higher (but lower than permissible limits) concentrations of macro-elements (NPK) and trace elements (Fe, Mn, Cu, Zn, Cd, Pb, Ni, and Co). In addition, the application of a 50% recommended dose of NPK with TWW showed equivalent results to a 100% recommended dose of NPK on all measured parameters with few exceptions. In conclusion, the TWW can be used to irrigate field crops allocated for bioenergy production in arid regions because it does not harm the plants and environment. In addition, the 50% recommended dose of NPK fertilizer exerted no negative effects on the growth and energy production of field crops, thereby protecting the environment and reducing the leaching of excessive fertilizers into GW.

Heavy metal accumulation by roadside vegetation and implications for pollution control

Vehicular emissions cause heavy metal pollution and exert negative impacts on environment and roadside vegetation. Wild plants growing along roadsides are capable of absorbing considerable amounts of heavy metals; thus, could be helpful in reducing heavy metal pollution. Therefore, current study inferred heavy metal absorbance capacity of some wild plant species growing along roadside. Four different wild plant species, i.e., Acacia nilotica L., Calotropis procera L., Ricinus communis L., and Ziziphus mauritiana L. were selected for the study. Leaf samples of these species were collected from four different sites, i.e., Control, New Lahore, Nawababad and Fatehabad. Leaf samples were analyzed to determine Pb2+, Zn2+, Ni2+, Mn2+ and Fe3+ accumulation. The A. nilotica, Z. mauritiana and C. procera accumulated significant amount of Pb at New Lahore site. Similarly, R. communis and A. nilotica accumulated higher amounts of Mn, Zn and Fe at Nawababad and New Lahore sites compared to the rest of the species. Nonetheless, Z. mauritiana accumulated higher amounts of Ni at all sites compared with the other species included in the study. Soil surface contributed towards the uptake of heavy metals in leaves; therefore, wild plant species should be grown near the roadsides to control heavy metals pollution. Results revealed that wild plants growing along roadsides accumulate significant amounts of heavy metals. Therefore, these species could be used to halt the vehicular pollution along roadsides and other polluted areas.

Cadmium stress suppresses the tillering of perennial ryegrass and is associated with the transcriptional regulation of genes controlling axillary bud outgrowth

Perennial ryegrass (Lolium perenne L.), a grass species with superior tillering capacity, plays a potential role in the phytoremediation of cadmium (Cd)-contaminated soils. Tiller production is inhibited in response to serious Cd stress. However, the regulatory mechanism of Cd stress-induced inhibition of tiller development is not well documented. To address this issue, we investigated the phenotype, the expression levels of genes involved in axillary bud initiation and bud outgrowth, and endogenous hormone biosynthesis and signaling pathways in seedlings of perennial ryegrass under Cd stress. The results showed that the number of tillers and axillary buds in the Cd-treated seedlings decreased by 67% and 21%, respectively. The suppression of tiller production in the Cd-treated seedlings was more closely associated with the inhibition of axillary bud outgrowth than with bud initiation. Cd stress upregulated the expression level of genes related to axillary bud dormancy and downregulated bud activity genes. Additionally, genes involved in strigolactone biosynthesis and signaling, auxin transport and signaling, and cytokinin degradation were upregulated in Cd-treated seedlings, and cytokinin biosynthesis gene expression were decreased by Cd stress. The content of zeatin in the Cd-treated pants was significantly reduced by 69~85% compared to the control plants. The content of indole-3-acetic acid (IAA) remains constant under Cd stress. Overall, Cd stress induced axillary bud dormancy and subsequently inhibited axillary bud outgrowth. The decrease of zeatin content and upregulation of genes involved in strigolactone signaling and bud dormancy might be responsible for the inhibition of axillary bud outgrowth.

Rising Metals Concentration in the Environment: A Response to Effluents of Leather Industries in Sialkot

Many leather processing industries in Sialkot, Pakistan, discharge their wastes freely into the environment which then enters nearby water bodies. Irrigation practices with these polluted waters pose a great threat to the soil quality. Hence, the soils and effluent waters of five famous leather processing sites were evaluated for the presence of As, Cr, Cd, Ni, Zn, Mn, Mg, Na, K, and Ca. High mean concentrations of As (112.6 mg kg^-1), Cr (45.9 mg kg^-1), Cd (2.0 mg kg^-1), Ni (58.2 mg kg^-1), Zn (117.6 mg kg^-1), Mn (12.8 mg kg^-1), Mg (34,511 mg kg^-1), Na (16,292 mg kg^-1), K (1765 mg kg^-1), and Ca (4387 mg kg^-1) were found in soils at our study sites. Effluents were found to be highly acidic with high TDS content and high EC values. Index of Geoaccumulation (Igeo) confirmed the extremely toxic nature of these soils. Plants growing at these sites also showed high concentrations of As, Cr, and Cd in their leaves.

Accumulation of heavy metals and bacteriological indicators in spinach irrigated with further treated secondary wastewater

Shortage of water for agriculture has resulted in the need to explore the use of wastewater for irrigation, however this can pose a health problem to the people emanating from the produced food as a result of the accumulation of pollutants. The purpose of this research was to investigate the accumulation of some heavy metals and bacteriological indicators in the different parts of spinach vegetable irrigated with secondary wastewater effluent treated through a pilot filtration system. There was a variation of heavy metals accumulation in the roots, stem and leafy parts of the vegetable. Bioaccumulation factors of some metals were greater than 1 in the roots and stems but not in the leaves. Three heavy metals being copper, iron and zinc revealed high translocation factors in the stems than leaves; whereas arsenic, chromium, nickel, manganese and lead had high translocation factors in the leaves than stems. Health index coefficients in the stem during the first, second and third months were 2.33, 0.18 and 3.57 respectively, and corresponding values in the leaves were 0.68, 0.09 and 6.75 if consumed by adults. The health index values greater than 1 in children were 2.68 in the stem during the first month and then 4.1 and 7.76 in the stem and leaves during the third month for spinach consumed by children. There was no bacteriological indicators detected in the aboveground parts of the vegetable. To conclude, irrigation of vegetables should be practiced using secondary treated wastewater and monitoring over time intervals in order to safe guard human health.

Cadmium uptake from soil and transport by leafy vegetables: A meta-analysis

Cadmium (Cd) pollution in soil is a serious problem affecting environmental safety and human health, and the majority of Cd in human body comes from edible vegetables, especially leafy vegetables. Therefore, it is necessary to understand the absorption and transport of Cd soil by leafy vegetables. In this study, the meta-analysis method was firstly employed to study the relationship of Cd in leafy vegetables and soil systems. The results showed that different kinds of leafy vegetables have different abilities of Cd accumulation (measured by bioconcentration factor (BCF)) and transportation (measured by translocation factor (TF)): Brassica juncea (BCF = 5.10) and Brassica pekinensis (BCF = 1.90) had significantly higher ability to absorb cadmium in soil among the 19 studied species, Brassica pekinensis (TF = 2.52), Coriandrum sativum (TF = 2.18) had significantly higher cadmium transport capacity than other 11 species. To further clarify the influence of the three main factors of soil pH, Cd content and leafy vegetable species on the Cd enrichment ability of leafy vegetables, the regression equation was obtained by meta-regression analysis. BCF is affected by species, soil pH, soil cadmium content in the order from high to low. It was found that the estimated range of SOM for safe production of leafy vegetables is 20-30 g/kg. It could also be observed that soil cation exchange capacity (CEC) had a negative correlation with BCF, while soil salinity had a strong positive correlation with BCF. This study can provide a reliable reference for leafy vegetable security production in the Cd polluted field and aids in selecting species suitable for avoiding the absorption of heavy metals from polluted soil.

Evaluation of inorganic contaminants emitted from automobiles and dynamics in soil, dust, and vegetations from major highways in Pakistan

The deposition of toxic metals in the ecosystem contributes to the exposure and bioaccumulation of metals in the food chain, thus affecting human health. This study aimed to access the distribution of metal pollution emitted from automobiles in the dust, soil, and plant samples collected from the roadsides of national highways. Furthermore, metals were also determined in fuels and vehicular emissions. High contents of Pb, Cd, Cr, Cu, Fe, Mn, and Zn were found in roadsides as compared to control (35 km away from roads). The comparison among plants indicated that Calotropis procera and Rumex dentatus contained significantly higher metals than other plants. The concentrations of Pb, Cd, Cr, and Fe in plants were above the safe limits of the WHO/FAO. Significant and positive correlations were found between Cr, Cu, Fe, Pb, and Zn in the dust and soil samples and Cd and Cr in dust and plants. According to the results of the PCA analysis, all metals formed the first two components explaining 89.5% of the total variance. The source of these metals was attributed to automobile exhaust and dust depositions. The findings of the present study suggest that roadside plants are heavily infested with heavy metals due to vehicular smoke pollution, so the consumption of vegetation facing vehicular pollution may lead to certain physiological disorders and diseases. Graphical abstract.

Lead Toxicity: Health Hazards, Influence on Food Chain, and Sustainable Remediation Approaches

Lead (Pb) toxicity has been a subject of interest for environmental scientists due to its toxic effect on plants, animals, and humans. An increase in several Pb related industrial activities and use of Pb containing products such as agrochemicals, oil and paint, mining, etc. can lead to Pb contamination in the environment and thereby, can enter the food chain. Being one of the most toxic heavy metals, Pb ingestion via the food chain has proven to be a potential health hazard for plants and humans. The current review aims to summarize the research updates on Pb toxicity and its effects on plants, soil, and human health. Relevant literature from the past 20 years encompassing comprehensive details on Pb toxicity has been considered with key issues such as i) Pb bioavailability in soil, ii) Pb biomagnification, and iii) Pb- remediation, which has been addressed in detail through physical, chemical, and biological lenses. In the review, among different Pb-remediation approaches, we have highlighted certain advanced approaches such as microbial assisted phytoremediation which could possibly minimize the Pb load from the resources in a sustainable manner and would be a viable option to ensure a safe food production system.

Interactive effect of drought and cadmium stress on soybean root morphology and gene expression

Recent climatic changes and low water availability due to unpredictable precipitation have reduced the productivity of soybean (Glycine max [L.] Merr.) cultivars. Limited information is available on how drought affects the accumulation and translocation of cadmium (Cd) by affecting soybean root. In this study, we investigated the effect of polyethylene glycol (PEG; 5% and 10%)-induced drought and Cd (0.2 and 0.5 mg L-1) stresses on soybean root morphology, Cd uptake and gene expression; plants not exposed to these stress (0% PEG and 0 mg L-1 Cd) served as a control. The results showed that drought affected roots morphology and Cd uptake. The reduction in root length, root area and root diameter and increase in catalase activity was less prominent in drought tolerant cultivars (Shennong20 and Liaodou32) than in drought sensitive cultivars (Liaodou3 and Liaodou10). Genes involved in abscisic acid (ABA) degradation, gibberellin and salicylic acid biosynthesis, hydrogen peroxide (H2O2) production and Cd transport were up-regulated, while those involved in zeatinriboside (ZR), indole 3-acetic acid (IAA) and methyl jasmonate (MeJA) biosynthesis were down-regulated under Cd and drought stress. Biosynthesis genes of gibberellin (Glyma03G019800.1), IAA (Glyma02G037600), ZR (XM_003550461.3) and MeJA (Glyma11G007600) were expressed to higher levels in drought tolerant cultivars than in drought sensitive cultivars. These genes represent potential candidates for the development of drought and Cd tolerant soybean cultivars.

The concentration of potentially toxic elements (PTEs) in the onion and tomato irrigated by wastewater: A systematic review; meta-analysis and health risk assessment

Nowadays, vegetable irrigation with wastewater in developing countries has become a serious issue. In this regard, the current investigation was performed to collect the related data regarding the concentration of potentially toxic elements (PTEs) including Fe, Zn, Cu, Cr, Pb, Ni, and Cd in onion and tomato samples irrigated with wastewater by the aid of a systematic review among the Scopus, Medline and Embase databases between 1/January/1983 to 31/January/2019. Also, the health risk assessment for consumers due to PTEs ingestion via the consumption of onion and tomato was estimated by using target hazard quotient (THQ). In this context, 35 articles with 64 studies out of 779 retrieved citations were included in the meta-analysis. The ranking of different parts of tomato based on Pb, Cd, and Cu concentration was shoot > root > leave > edible part; Fe, leave > shoot > root > edible part; Cr, root > leave > shoot > edible part; Zn, shoot > leave > root > edible part; and Ni, leave > edible part > root > shoot. Moreover, the ratio concentration of Pb, Cd, Cu, Fe, Cr, Zn and Ni in the edible part to leave of onion was 2.92, 6.01, 1.29, 4.17, 0.84, and 3.55, 10.10, respectively. According to findings, the rank order of PTEs in the onion was Fe (43.09 mg/kg-dry weight) > Zn (34.3 mg/ kg-dry weight) > Pb (18.54 mg/ kg-dry weight) > Cu (14.9 mg/ kg-dry weight) > Ni (11.92 mg/ kg-dry weight) > Cr (7.24 mg/ kg-dry weight) > Cd (0.23 mg/ kg-dry weight) and tomato; Fe (139.12 mg/ kg-dry weight) > Zn (29.81 mg/ kg-dry weight) > Cu (25.04 mg/ kg-dry weight) > Cr (14.28 mg/ kg-dry weight) > Pb (9.58 mg/ kg-dry weight) > Ni (9.23 mg/ kg-dry weight) > Cd (4.64 mg/kg-dry weight). However, the concentration of PTEs investigated in the edible part of onion was higher than leaves; their concentrations in the edible part of the tomato were lower than other parts. The health risk assessment indicated that consumers groups are at significant non-carcinogenic risk due to the ingestion of PTEs via consumption of the onion and tomato vegetable wastewater irrigated (THQ > 1). Therefore, the irrigation of vegetables with wastewater should be monitored and controlled by some prevention plans.

Chelators induced uptake of cadmium and modulation of water relation, antioxidants, and photosynthetic traits of maize

The present study was aimed to reveal the effect of cadmium (Cd)-polluted soil on the activation of antioxidant enzymes, photosynthesis, pigments, water relation, and other biochemical traits and comparative effect of synthetic and organic chelators. A pot experiment was conducted using two maize varieties grown in Cd-contaminated (15 and 30 mg kg^-1) soil and chelators (1 mM EDTA, and 1 mM citric acid). Cd decreased biomass and photosynthetic traits while increased malondialdehyde (MDA) contents, total proteins, and antioxidant enzyme activities. Addition of EDTA enhanced Cd uptake, antioxidative enzyme, and total proteins; however, it reduced the water, osmotic, and turgor potential as compared to Cd alone. Addition of citric acid has lessened the antioxidant enzyme activities and MDA contents and enhanced the plant biomass as compared to Cd alone. Increases in antioxidants and MDA content were found to be positively related to the Cd contents in shoot and root. The application of citric acid significantly alleviated the Cd-induced toxic effects, showing remarkable improvement in biomass. These results indicated that EDTA was more effective for mobilizing Cd from soil to the root and shoot than citric acid; however, the physiological traits and plant biomass were more strongly inhibited by EDTA than by the Cd. Our study implies that citric acid ameliorated the negative effect of Cd on physiological traits and biomass, and hence could be used effectively for Cd phytoextraction.

Sewage waste water application improves the productivity of diverse wheat (Triticum aestivum L.) cultivars on a sandy loam soil

Water stress due to climate change is an emerging threat to wheat (Triticum aestivum L.) productivity in the arid regions of the world which will impact the future food security. In this scenario, the investigations are needed to check the feasibility of alternate sources of irrigation water to fulfill the irrigation demands of the crops in the arid regions. This 2-year study was aimed to investigate the influence of three irrigation sources (sewage water, canal water, and underground water) on the productivity of 10 wheat cultivars under an arid climate of Layyah, Pakistan. The results indicated that the number of fertile tillers, grains per spike, 1000-grain weight, and grain yield varied from 114 to 168 m^-2, 34.8 to 53.3, 33.4 to 38.4 g, and 2.68 to 4.05 Mg ha^-1, respectively in various wheat cultivars. The highest fertile tillers (168 m^-2) were recorded in cultivar Gold-2016 followed by Aas-2011 (155 cm), AARI-2011 (153 m^-2), and Ujala-2016 (150 m^-2). The highest 1000-grain weight of 38.4 g was recorded in cultivar NARC-2016. The grains per spike (53.3) were the highest in cultivar Ujala-2016. The grain yields were the highest in cultivars Ujala-2016 (4.05 Mg ha^-1) and Gold-2016 (3.91 Mg ha^-1). The highest grain yield of 3.71 Mg ha^-1 was recorded with sewage water irrigation against the grain yield of 3.18 and 2.91 Mg ha^-1 in canal and underground water irrigation, respectively. There existed a strong co-relation of fertile tillers and grains per spike with the grain yield of wheat. Application of sewage water also enhanced the total nitrogen, extractable potassium, and available phosphorous in soil. In crux, the cultivation of recently bread wheat cultivars (viz. Ujala-2016, Gold-2016) and the irrigation of field with sewage water in the absence of canal water might be a viable option to boost wheat productivity under arid regions. A range of genetic variability existed for different traits in the cultivars; therefore, these can be used to breed wheat cultivars to be used for sewage water cultivation.

Chronic exposure to low doses of Pb induces hepatotoxicity at the physiological, biochemical, and transcriptomic levels of mice

Lead (Pb), a non-essential heavy metal, is a major global environmental contaminant with serious toxicological consequences. In the present study, the effects on hepatotoxicity of mice with chronic exposure to low doses of Pb were evaluated. While oral exposure to 0.03 or 0.1 mg/L Pb for 15 weeks in male adult mice had no significant effect on body weights, Pb exposure resulted in liver histopathological effects and increase of hepatic activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP). In addition, hepatic reactive oxygen species (ROS) and malondialdehyde (MDA) significantly accumulated after treatment. Conversely, glutathione (GSH) decreased significantly in both 0.03 and 0.1 mg/L Pb-treated groups. Moreover, the hepatic activities of superoxide dismutase 1 (SOD) and catalase (CAT) increased significantly following treatment with 0.1 mg/L Pb for 15 weeks, concomitant with increases in transcriptions of hepatic Sod, Cat, and Gpx. Furthermore, transcriptions of hepatic metallothionein (MT), zinc transporter 5 (Znt5) and copper transporter 1 (Ctr1), and subsequent protein levels were also increased in liver of mice when exposed to 0.1 mg/L Pb for 15 weeks. In addition, the transcriptome data showed that Pb has substantial influence on several pathways, including PPAR signaling pathways, AMPK signaling pathways, fatty acid metabolism, and drug metabolism. Our data suggested that chronic Pb exposure could induce hepatotoxicity at the physiological, biochemical, and transcriptomic levels in mice.

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

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

Composting of municipal solid waste by different methods improved the growth of vegetables and reduced the health risks of cadmium and lead

Reutilization of putrescible municipal solid wastes (MSW) in agriculture can provide valuable plant nutrients. However, it may pose serious noncarcinogenic health risks for a human when contaminants, especially the heavy metals in MSW, end up in plants through the waste-soil-plant continuum. This study examined the effects of composting methods viz. aerobically (AC), anaerobically (ANC), and aerobic-anaerobically (AANC) composted MSW material on (i) fertilizer value: vegetable yield, nitrogen (N) mineralization, and apparent N recovery (ANR); and (ii) associated health risks: selected heavy metal concentration, daily intake of metals (DIM), health risk index (HRI), hazard index (HI), and target hazard quotient (THQ) when applied to a loamy soil. All the aforementioned compost materials were incorporated into the sandy loam soil filled in pots and carrot and spinach were cultivated for 85 and 90 days, respectively. After soil application, between 51 and 56% of the applied organic N was mineralized from ANC material, while the values in case of AC and AANC were 26-31% and 34-40%, respectively. Consequently, dry matter yield and vegetable N uptake from composts were in the order ANC > AANC > AC (P < 0.05). Further, vegetable ANR was the highest from ANC (56 and 56%) than AANC (42 and 45%), and AC (30 and 33%) for spinach and carrot, respectively (P < 0.05). Interestingly, plant uptake of lead and cadmium was lowest from ANC as compared to AC or AANC (P < 0.05), irrespective of the vegetable type. Consequently, DIM, HRI, and THQ for these metals were substantially lower in the former as compared to the latter compost materials. Further, HI from ANC material was 50% lower over the unfertilized control indicating the absence of noncarcinogenic human health risks via vegetable intake. This all indicates that from viewpoint of sustainable waste recycling in agriculture, anaerobic composting is superior to the other composting methods.

Suitability of aromatic plants for phytoremediation of heavy metal contaminated areas: a review

This review briefly elucidates the research undertaken and benefits of using aromatic plants for remediation of heavy metal polluted sites. A sustainable approach to mitigate heavy metal contamination of environment is need of the hour. Phytoremediation has emerged to be one of the most preferable choices for combating the metal pollution problem. Aromatic plants can be used for remediation of contaminated sites as they are non-food crops thus minimizing the risk of food chain contamination. Most promising aromatic plants for phytoremediation of heavy metal contaminated sites have been identified from families - Poaceae, Lamiaceae, Asteraceae, and Geraniaceae. They act as potential phytostabilisers, hyper accumulators, bio-monitors, and facultative metallophytes. Being high value economic crops, monetary benefits can be obtained by growing them in tainted areas instead of food crops. It has been observed that heavy metal stress enhances the essential oil percentage of certain aromatic crops. Research conducted on some major aromatic plants in this context has been highlighted in the present review which suggests that aromatic plants hold a great potential for phytoremediation. It has been reported that essential oil from aromatic crops is not contaminated by heavy metals significantly. Thus, aromatic plants are emerging as an ideal candidate for phytoremediation. Highlights • Aromatic plants hold a great potential for phytoremediation of heavy metal contaminated sites. • Being high value economic crops, monetary benefits can be obtained by growing them in contaminated areas instead of food crops. • Research done on some major aromatic plants in this context has been highlighted in the present review.

Assessing cadmium exposure risks of vegetables with plant uptake factor and soil property

Plant uptake factors (PUFs) are of great importance in human cadmium (Cd) exposure risk assessment while it has been often treated in a generic way. We collected 1077 pairs of vegetable-soil samples from production fields to characterize Cd PUFs and demonstrated their utility in assessing Cd exposure risks to consumers of locally grown vegetables. The Cd PUFs varied with plant species and pH and organic matter content of soils. Once normalized PUFs against soil parameters, the PUFs distributions were log-normal in nature. In this manner, the PUFs were represented by definable probability distributions instead of a deterministic figure. The Cd exposure risks were then assessed using the normalized PUF based on the Monte Carlo simulation algorithm. Factors affecting the extent of Cd exposures were isolated through sensitivity analyses. Normalized PUF would illustrate the outcomes for uncontaminated and slightly contaminated soils. Among the vegetables, lettuce was potentially hazardous for residents due to its high Cd accumulation but low Zn concentration. To protect 95% of the lettuce production from causing excessive Cd exposure risks, pH of soils needed to be 5.9 and above.

Farmyard manure alone and combined with immobilizing amendments reduced cadmium accumulation in wheat and rice grains grown in field irrigated with raw effluents

Cadmium (Cd) stress is a serious concern in agricultural soils worldwide whereas little is known about the impact of farmyard manure (FYM) alone or combined with limestone, lignite and biochar on Cd concentrations in plants. Wheat was grown in Cd-contaminated field amended with control (T₁), FYM @ 0.1% (T₂), FYM + limestone @ 0.05% each (T₃), FYM + lignite @ 0.05% each (T₄), FYM + biochar @ 0.05% each (T₅) and subsequent rice was grown without additional use of amendments. Soil application of amendments increased straw and grain yield and thousand grain weight being maximum in FYM + limestone treatment. Wheat and rice straw yield increased by 19% and 10% in T₃ than control respectively. Photosynthetic pigments increased with the supply of amendments than control. Amendments decreased Cd concentration, total Cd uptake in straw and grains and Cd harvest index of both crops and the maximum reduction in these parameters was recorded with where FYM + limestone (T₃). Cd concentration in wheat and rice straw decreased by 78.5% and 65% in T₃ than control, respectively. The highest benefit to cost ratio was obtained in FYM + limestone (T₃). Ammonium bicarbonate - diethylenetriamine penta acetic acid (AB-DTPA) extractable Cd of the post-harvest soil reduced whereas Cd immobilization index and soil pH increased with the supply of all treatments than control being maximum in T_3. The present study revealed that field management with FYM + limestone increased plant yield and reduced Cd concentrations in grains.

Heavy metal accumulation, risk assessment and integrated biomarker responses of local vegetables: A case study along the Le'an river

In this research, Ganzhou Chinese Cabbage (Brassica rapa pekinensis), Native Purple Garlic (Allium sativum L) and Leping Radish (Raphanus sativus L) widely planted and distributed along the Le'an River were chosen in the present study. Soil physical-chemical properties, nutrients contents as well as heavy metals elements accumulated in both soils and vegetables collected from 24 sites were analyzed by lab analysis combined with statistical method which was also used for calculation of contamination factor, pollution indexes and hazardous index. Heavy metals accumulation in soils were revealed with higher level, and copper and cadmium exceeded the background values by 8.82 and 16.73 times on average, which were also significantly related with the distribution of nonferrous metal processing enterprises. Heavy metal elements accumulated in vegetables were fully consistent with the finding of pollution characteristics in soils. Peroxidase biomarkers in vegetables, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), reduced glutathione (GSH) and lipoperoxidation (as TBARS), as well as integrated biomarker responses (IBR) were determined to give a reliable response after exposing of contaminants. Heavy metals accumulation ability and biomarker responses for three vegetables were usually determined in the following decrease trend: Ganzhou Chinese Cabbage > Native Purple Garlic > Leping Radish. Compared with peroxidase biomarkers activities or contents of control site, all the measured biomarkers in polluted sites showed significantly responses, indicating potential relationship between pollutants stresses and biomarker responses. This study also revealed that the IBR values were coordinated well with the pollutants concentrations.

Management of tannery wastewater for improving growth attributes and reducing chromium uptake in spinach through citric acid application

The use of chromium (Cr)-contaminated tannery wastewater for irrigation is a common practice, especially in developing countries like Pakistan. This practice is due to the shortage of good quality irrigation water for crop growth as well as the issue of tannery wastewater disposal. The current study was done to evaluate the effect of citric acid (CA) (0, 1.0, and 2.0 mM) on the growth and Cr uptake by spinach irrigated with different mixtures of tap water and tannery wastewater (100:0, 50:50, and 0:100 tap water to wastewater ratio). Plants were grown for 8 weeks under ambient conditions. Results showed that 50:50% tap water and wastewater increased plant height, dry weights of shoots and roots, total chlorophyll contents, and gas exchange attributes than the plants treated with only tap water or only wastewater. Increasing wastewater ratio increased electrolyte leakage (EL) in plants and enhanced the leaf key antioxidant enzyme activities as well as increased Cr contents. Foliar application of CA increased the plant dry weights, photosynthesis, and enzyme activities, whereas reduced the EL and Cr concentrations in plants than respective treatments without CA application. It can be concluded that 50:50 tap water and wastewater irrigation along with foliar CA application might be an effective strategy for increasing vegetable growth with reduced metal concentrations.

Beryllium Stress-Induced Modifications in Antioxidant Machinery and Plant Ultrastructure in the Seedlings of Black and Yellow Seeded Oilseed Rape

Beryllium (Be) could be a threatening heavy metal pollutant in the agroecosystem that may severely affect the performance of crops. The present study was conducted to evaluate the toxic effects of Be (0, 100, 200, and 400 μM) on physiological, ultrastructure, and biochemical attributes in hydroponically grown six-day-old seedlings of two cultivars of Brassica napus L., one tolerant (ZS 758, black seeded) and one sensitive (Zheda 622, yellow seeded). Higher Be concentrations reduced the plant growth, biomass production, chlorophyll contents, and the total soluble protein contents. A significant accumulation of ROS (H₂O₂, OH⁻) and MDA contents was observed in a dose-dependent manner. Antioxidant enzymatic activities including SOD, POD, GR, APX, and GSH (except CAT) were enhanced with the increase in Be concentrations in both cultivars. Relative transcript gene expression of above-mentioned antioxidant enzymes further confirmed the alterations induced by Be as depicted from higher involvement in the least susceptible cultivar ZS 758 as compared to Zheda 622. The electron microscopic study showed that higher level of Be (400 μM) greatly damaged the leaf mesophyll and root tip cells. More damage was observed in cultivar Zheda 622 as compared to ZS 758. The damage in leaf mesophyll cells was highlighted as the disruption in cell wall, immature nucleus, damaged mitochondria, and chloroplast structures. In root tip cells, disruption in Golgi bodies and damage in cell wall were clearly noticed. As a whole, the present study confirmed that more inhibitory effects were recorded in yellow seeded Zheda 622 as compared to black seeded ZS 758 cultivar, which is regarded as more sensitive cultivar.

Contrasting Effects of Organic and Inorganic Amendments on Reducing Lead Toxicity in Wheat

Contamination of agricultural soils with lead (Pb) is a widespread problem which is mainly due to anthropogenic activities. The present study investigated the effect of organic and inorganic amendments on wheat growth and reducing Pb concentration in the plant. A greenhouse experiment was conducted on Pb spiked soil (500 mg kg^-1 of soil) with the application of farmyard manure, poultry manure, gypsum and di-ammonium phosphate (DAP). Plants were harvested after 120 days of growth and analyzed for Pb concentration in different plant parts. Under Pb stress, amendments significantly (p < 0.05) increased grain yield and root dry weights compared to the control. Grain yield and dry weights of shoots and roots were maximum with DAP compared to the control and other amendments. Amendments increased transpiration rate, stomatal conductance, chlorophyll contents and photosynthetic rate. The lowest Pb concentration was found in DAP treated plants which were about 88%, 84%, and 85% lower in root, shoots and grains than control respectively. DAP fertilizer was the most effective in improving these parameters than control and other amendments and can be used to reduce Pb concentration in wheat and probably other crops.

Citric acid assisted phytoextraction of chromium by sunflower; morpho-physiological and biochemical alterations in plants

Soil and water contamination from heavy metals and metalloids is one of the most discussed and burning global issues due to its potential to cause the scarcity of healthy food and safe water. The scientific community is proposing a range of lab and field based physical, chemical and biological solutions to remedy metals and metalloids contaminated soils and water. The present study finds out a possibility of Chromium (Cr) extraction by sunflower from spiked soil under chelating role of citric acid (CA). The sunflower plants were grown under different concentrations of Cr (0, 5, 10 & 20mgkg^-1) and CA (0, 2.5 & 5mM). Growth, biomass, gas exchange, photosynthesis, electrolyte leakage (EL), reactive oxygen species (ROS; malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and the activities of antioxidant enzymes such as, superoxide dismutase (SOD), guaiacole values peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT) were measured. The results depicted a clear decline in plant height, root length, leaf area, number of leaves and flowers per plant along with fresh and dry biomass of all parts of plant with increasing concentration of Cr in soil. Similar reduction was observed in chlorophyll a and b, total chlorophyll, carotenoids, soluble protein, gas exchange attributes and SPAD. The increasing concentration of Cr also enhanced the Cr uptake and accumulation in plant roots, stem and leaves along with the production of ROS and EL. The activities of antioxidant enzymes increased with increasing Cr concentration from 0 to 10mg, but decreased at 20mgkg^-1 soil. The CA application significantly alleviated Cr-induced inhibition of plant growth, biomass, photosynthesis, gas exchange, soluble proteins and SPAD value. Presence of CA also enhanced the activities of all antioxidant enzymes and reduced the production of ROS and EL. The chelating potential of CA increased the concentration and accumulation of Cr in plant roots, stem and leaves. It is concluded that the sunflower can be a potential candidate for the remediation of Cr under CA treatment, while the possibility may vary with genotype, Cr level and CA concentration.

A critical review on effects, tolerance mechanisms and management of cadmium in vegetables

Cadmium (Cd) accumulation in vegetables is an important environmental issue that threatens human health globally. Understanding the response of vegetables to Cd stress and applying management strategies may help to reduce the Cd uptake by vegetables. The aim of the present review is to summarize the knowledge concerning the uptake and toxic effects of Cd in vegetables and the different management strategies to combat Cd stress in vegetables. Leafy vegetables grown in Cd contaminated soils potentially accumulate higher concentrations of Cd, posing a threat to food commodities. The Cd toxicity decreases seed germination, growth, biomass and quality of vegetables. This reduces the photosynthesis, stomatal conductance and alteration in mineral nutrition. Toxicity of Cd toxicity also interferes with vegetable biochemistry causing oxidative stress and resulting in decreased antioxidant enzyme activities. Several management options have been employed for the reduction of Cd uptake and toxicity in vegetables. The exogenous application of plant growth regulators, proper mineral nutrition, and the use of organic and inorganic amendments might be useful for reducing Cd toxicity in vegetables. The use of low Cd accumulating vegetable cultivars in conjunction with insolubilizing amendments and proper agricultural practices might be a useful technique for reducing Cd exposure in the food chain.

Impact of chelator-induced phytoextraction of cadmium on yield and ionic uptake of maize

Enhanced phytoextraction uses soil chelators to increase the bioavailability of heavy metals. This study tested the effectiveness of ethylenediaminetetraacetic acid (EDTA) and citric acid in enhancing cadmium (Cd) phytoextraction and their effects on the growth, yield, and ionic uptake of maize (Zea mays). Maize seeds of two cultivars were sown in pots treated with 15 (Cd₁₅) or 30 mg Cd kg^-1 soil (Cd₃₀). EDTA and citric acid at 0.5 g kg^-1 each were applied 2 weeks after germination. Results demonstrated that the growth, yield per plant, and total grain weight were reduced by exposure to Cd. EDTA increased the uptake of Cd in shoots, roots, and grains of both maize varieties. Citric acid did not enhance the uptake of Cd, rather it ameliorated the toxicity of Cd, as shown by increased shoot and root length and biomass. Cadmium toxicity reduced the number of grains, rather than the grain size. The maize cultivar Sahiwal-2002 extracted 1.6% and 3.6% of Cd from soil in both Cd+ EDTA treatments. Hence, our study implies that maize can be used to successfully phytoremediate Cd from soil using EDTA, without reducing plant biomass or yield.