Compost-assisted revegetation of highly phytotoxic sulfidic tailings with Medicago sativa L. plants grown from the seed to seedpod stage under greenhouse experimental mesocosms conditions.

The revegetation of highly phytotoxic sulfidic tailings is a challenging task which may often be successfully accomplished only following the addition of soil amendments. This study evaluated the use of green compost at increasing rates (10, 25 and 50% v/v) for the revegetation of extremely acidic sulfidic tailings of the North Mathiatis mine, Cyprus, with the use of alfalfa (Medicago sativa L.) plants, under greenhouse conditions. Alfalfa seeds were successfully germinated in tailings amended either with 25% or 50% (v/v) compost (52 and 85%, respectively). Plants managed to complete their life cycle and produce seeds only in the tailings amended with 50% (v/v) compost, since plants grown in tailings amended with lower rates of compost (i.e., 10 or 25% v/v) showed severe symptoms of phytotoxicity and eventually died. The amendment of tailings with 50% (v/v) green compost resulted in increased pH values, water holding capacity and organic content levels, soil respiration rates, as well as changes in soil elemental composition compared with tailings alone treatment, which in turn facilitated the growth and development of alfalfa plants during the whole experimental period (140 days). Plants managed to reach the late seedpod growth stage, indicating their potential regeneration and continual existence to the amended tailings, simultaneously uncovering the development of favorable conditions in the rhizosphere for the successful revegetation of studied tailings.

Occurrence and Distribution of Hexavalent Chromium in Ground and Surface Waters in Cyprus.

The origin and distribution of hexavalent chromium, Cr (VI) over four seasonal cycles was investigated through a conceptual model that included three aquifer systems in Cyprus. An extensive water sampling grid covered two sea water intruded coastal aquifers, namely the Kokkinochoria (A1) and Kiti-Pervolia (A2) aquifers and the Troodos massif (A3). Analytical results give a first insight to the presence of Cr (VI) in Cyprus ground and surface waters. The highest Cr (VI) value of 26 µg L-1 is observed in the Troodos area (A3) where Cr(VI) is detected in all sampled water systems (surface and ground/spring). Nonetheless, the highest median values of 4.6 and 4.5 µg L-1 are observed in the Kokkinochoria (A1) and Kiti-Pervolia (A2) study areas respectively, where the local aquifers are under increased pressure from agriculture, urbanization and seawater intrusion. Stable isotopes were used to discern the effect of return irrigation and seawater intrusion. Stable isotope analyses from Troodos samples show two distinct groups of meteoric and near meteoric waters whereas isotopically enriched water is shown to correspond to the Kiti and Kokkinochoria area.

Ranking of crop plants according to their potential to uptake and accumulate contaminants of emerging concern.

The reuse of treated wastewater (TWW) for irrigation and the use of biosolids and manures as soil amendment constitute significant pathways for the introduction of the contaminants of emerging concern (CECs) to the agricultural environment. Consequently, CECs are routinely detected in TWW-irrigated agricultural soils and runoff from such sites, in biosolids- and manure-amended soils, and in surface and groundwater systems and sediments receiving TWW. Crop plants grown in such contaminated agricultural environments have been found to uptake and accumulate CECs in their tissues, constituting possible vectors of introducing CECs into the food chain; an issue that is presently considered of high priority, thus needing intensive investigation. This review paper aims at highlighting the responsible mechanisms for the uptake of CECs by plants and the ability of each crop plant species to uptake and accumulate CECs in its edible tissues, thus providing tools for mitigating the introduction of these contaminants into the food chain. Both biotic (e.g. plants' genotype and physiological state, soil fauna) and abiotic factors (e.g. soil pore water chemistry, physico-chemical properties of CECs, environmental perturbations) have been proven to influence the ability of crop plants to uptake and accumulate CECs. According to authors' estimates, based on the thorough elaboration of knowledge produced by existing relevant studies, the ability of crop plants to uptake and accumulate CECs decrease in the order of leafy vegetables > root vegetables > cereals and fodder crops > fruit vegetables; though, the uptake of CECs by important crop plants, such as fruit trees, is not yet evaluated. Overall, further studies must be performed to estimate the potential of crop plants to uptake and accumulate CECs in their edible tissues, and to characterize the risk for human health represented by their presence in human and livestock food products.

Melatonin systemically ameliorates drought stress-induced damage in Medicago sativa plants by modulating nitro-oxidative homeostasis and proline metabolism.

Recent reports have uncovered the multifunctional role of melatonin in plant physiological responses under optimal and suboptimal environmental conditions. In this study, we explored whether melatonin pretreatment could provoke priming effects in alfalfa (Medicago sativa L.) plants subsequently exposed to prolonged drought stress (7 days), by withholding watering. Results revealed that the rhizospheric application of melatonin (10 µmol L-1 ) remarkably enhanced the drought tolerance of alfalfa plants, as evidenced by the observed plant tolerant phenotype, as well as by the higher levels of chlorophyll fluorescence and stomatal conductance, compared with nontreated drought-stressed plants. In addition, lower levels of lipid peroxidation (MDA content) as well as of both H2 O2 and NO contents in primed compared with nonprimed stressed plants suggest that melatonin pretreatment resulted in the systemic mitigation of drought-induced nitro-oxidative stress. Nitro-oxidative homeostasis was achieved by melatonin through the regulation of reactive oxygen (SOD, GR, CAT, APX) and nitrogen species (NR, NADHde) metabolic enzymes at the enzymatic and/or transcript level. Moreover, melatonin pretreatment resulted in the limitation of cellular redox disruption through the regulation of the mRNA levels of antioxidant and redox-related components (ADH, AOX, GST7, GST17), as well via osmoprotection through the regulation of proline homeostasis, at both the enzymatic (P5CS) and gene expression level (P5CS, P5CR). Overall, novel results highlight the importance of melatonin as a promising priming agent for the enhancement of plant tolerance to drought conditions through the regulation of nitro-oxidative and osmoprotective homeostasis.

Sodium hydrosulfide induces systemic thermotolerance to strawberry plants through transcriptional regulation of heat shock proteins and aquaporin.

BACKGROUND: Temperature extremes represent an important limiting factor to plant growth and productivity. The present study evaluated the effect of hydroponic pretreatment of strawberry (Fragaria x ananassa cv. 'Camarosa') roots with an H2S donor, sodium hydrosulfide (NaHS; 100 µM for 48 h), on the response of plants to acute heat shock treatment (42°C, 8 h). RESULTS: Heat stress-induced phenotypic damage was ameliorated in NaHS-pretreated plants, which managed to preserve higher maximum photochemical PSII quantum yields than stressed plants. Apparent mitigating effects of H2S pretreatment were registered regarding oxidative and nitrosative secondary stress, since malondialdehyde (MDA), H2O2 and nitric oxide (NO) were quantified in lower amounts than in heat-stressed plants. In addition, NaHS pretreatment preserved ascorbate/glutathione homeostasis, as evidenced by lower ASC and GSH pool redox disturbances and enhanced transcription of ASC (GDH) and GSH biosynthetic enzymes (GS, GCS), 8 h after heat stress imposition. Furthermore, NaHS root pretreatment resulted in induction of gene expression levels of an array of protective molecules, such as enzymatic antioxidants (cAPX, CAT, MnSOD, GR), heat shock proteins (HSP70, HSP80, HSP90) and aquaporins (PIP). CONCLUSION: Overall, we propose that H2S root pretreatment activates a coordinated network of heat shock defense-related pathways at a transcriptional level and systemically protects strawberry plants from heat shock-induced damage.

Polyamines reprogram oxidative and nitrosative status and the proteome of citrus plants exposed to salinity stress.

The interplay among polyamines (PAs) and reactive oxygen and nitrogen species (RNS and ROS) is emerging as a key issue in plant responses to salinity. To address this question, we analysed the impact of exogenous PAs [putrescine (Put), spermidine (Spd) and spermine (Spm)] on the oxidative and nitrosative status in citrus plants exposed to salinity. PAs partially reversed the NaCl-induced phenotypic and physiological disturbances. The expression of PA biosynthesis (ADC, SAMDC, SPDS and SPMS) and catabolism (DAO and PAO) genes was systematically up-regulated by PAs. In addition, PAs altered the oxidative status in salt-stressed plants as inferred by changes in ROS production and redox status accompanied by regulation of transcript expression and activities of various antioxidant enzymes. Furthermore, NaCl-induced up-regulation of NO-associated genes, such as NR, NADde, NOS-like and AOX, along with S-nitrosoglutathione reductase and nitrate reductase activities, was partially restored by PAs. Protein carbonylation and tyrosine nitration are depressed by specific PAs whereas protein S-nitrosylation was elicited by all PAs. Furthermore, we identified 271 S-nitrosylated proteins that were commonly or preferentially targeted by salinity and individual PAs. This work helps improve our knowledge on the plant's response to environmental challenge.

Assessment of long-term wastewater irrigation impacts on the soil geochemical properties and the bioaccumulation of heavy metals to the agricultural products.

An extensive field survey was employed for assessing the impacts of long-term wastewater irrigation of forage crops and orange orchards in three suburban agricultural areas in Cyprus (areas I, II, and III), as compared to rainfed agriculture, on the soil geochemical properties and the bioaccumulation of heavy metals (Zn, Ni, Mn, Cu, Co) to the agricultural products. Both ryegrass fields and orange orchards in areas I and II were continuously wastewater irrigated for 10 years, whereas clover fields in area III for 0.5, 4, and 8 years. The results revealed that wastewater reuse for irrigation caused a slight increase in soil salinity and Cl(-) content in areas I and II, and a remarkable increase, having strong correlation with the period in which wastewater irrigation was practiced, in area III. Soil salinization in area III was due to the high electrical conductivity (EC) of the wastewater applied for irrigation, attributed to the influx of seawater to the sewage collection network in area III. In addition, the wastewater irrigation practice resulted in a slight decrease of the soil pH values in area III, while a subtle impact was identified regarding the CaCO3, Fe, and heavy metal content in the three areas surveyed. The heavy metal content quantified in the forage plants' above-ground parts was below the critical levels of phytotoxicity and the maximum acceptable concentration in dairy feed, whereas heavy metals quantified in orange fruit pulp were below the maximum permissible levels (MPLs). Heavy metal phytoavailability was confined due to soil properties (high pH and clay content), as evidenced by the calculated low transfer factor (TF).

Linking the use of reclaimed water to indicators of crop stress by metabolomic and transcriptomic analyses. A tool to compare water irrigation quality.

The occurrence of contaminants of emerging concern (CECs) or heavy metals in reclaimed water used for agricultural irrigation may affect crop morphology and physiology. Here, we analyzed lettuce (Lactuca sativa) grown in outdoor lysimeters and irrigated with either tap water, used as a control, or reclaimed water: CAS-reclaimed water, an effluent from a conventional activated sludge system (CAS) followed by chlorination and sand filtration, or MBR-reclaimed water, an effluent from a membrane biological reactor (MBR). Chemical analyses identified seven CECs in the reclaimed waters, but only two of them were detected in lettuce (carbamazepine and azithromycin). Metabolomic and transcriptomic analyses revealed that irrigation with reclaimed water increased the concentrations of several crop metabolites (5-oxoproline, leucine, isoleucine, and fumarate) and of transcripts codifying for the plant stress-related genes Heat-Shock Protein 70 (HSP70) and Manganese Superoxide Dismutase (MnSOD). In both cases, MBR-water elicited the strongest response in lettuce, perhaps related to its comparatively high sodium adsorption ratio (4.5), rather than to its content in CECs or heavy metals. Our study indicates that crop metabolomic and transcriptomic profiles depend on the composition of irrigating water and that they could be used for testing the impact of water quality in agriculture.

Hydrogen sulfide induces systemic tolerance to salinity and non-ionic osmotic stress in strawberry plants through modification of reactive species biosynthesis and transcriptional regulation of multiple defence pathways.

Hydrogen sulfide (H2S) has been recently found to act as a potent priming agent. This study explored the hypothesis that hydroponic pretreatment of strawberry (Fragaria × ananassa cv. Camarosa) roots with a H2S donor, sodium hydrosulfide (NaHS; 100 µM for 48 h), could induce long-lasting priming effects and tolerance to subsequent exposure to 100mM NaCI or 10% (w/v) PEG-6000 for 7 d. Hydrogen sulfide pretreatment of roots resulted in increased leaf chlorophyll fluorescence, stomatal conductance and leaf relative water content as well as lower lipid peroxidation levels in comparison with plants directly subjected to salt and non-ionic osmotic stress, thus suggesting a systemic mitigating effect of H2S pretreatment to cellular damage derived from abiotic stress factors. In addition, root pretreatment with NaHS resulted in the minimization of oxidative and nitrosative stress in strawberry plants, manifested via lower levels of synthesis of NO and H(2)O(2) in leaves and the maintenance of high ascorbate and glutathione redox states, following subsequent salt and non-ionic osmotic stresses. Quantitative real-time RT-PCR gene expression analysis of key antioxidant (cAPX, CAT, MnSOD, GR), ascorbate and glutathione biosynthesis (GCS, GDH, GS), transcription factor (DREB), and salt overly sensitive (SOS) pathway (SOS2-like, SOS3-like, SOS4) genes suggests that H2S plays a pivotal role in the coordinated regulation of multiple transcriptional pathways. The ameliorative effects of H2S were more pronounced in strawberry plants subjected to both stress conditions immediately after NaHS root pretreatment, rather than in plants subjected to stress conditions 3 d after root pretreatment. Overall, H2S-pretreated plants managed to overcome the deleterious effects of salt and non-ionic osmotic stress by controlling oxidative and nitrosative cellular damage through increased performance of antioxidant mechanisms and the coordinated regulation of the SOS pathway, thus proposing a novel role for H2S in plant priming, and in particular in a fruit crop such as strawberry.

Looking into the effects of co-contamination by micro(nano)plastics in the presence of other pollutants on irrigated edible plants.

To address water shortage challenges, treated wastewater is used to meet the demand for irrigation water in several countries worldwide. Considering the presence of pollutants in treated wastewater, its use for land irrigation might have an impact in the environment. This review article focuses on the combined effects (or potential joint toxicity) of microplastics (MPs)/nanoplastics (NPs) and other environmental contaminants present in treated wastewater on edible plants after irrigation. Initially, the concentrations of MPs/NPs in wastewater treatment plant effluents and surface waters are summarized, indicating the presence of MPs/NPs in both water matrices (i.e., wastewater after receiving treatment and lakes/rivers). Then, the results of 19 studies related to joint toxicity of MPs/NPs and co-contaminants (e.g., heavy metals and pharmaceuticals) on edible plants, are reviewed and discussed. This concurrent presence may result in several combined effects on edible plants, e.g., rapid root growth, increase in antioxidant enzymes, decrease in photosynthetic rate and increased production of ROS. These effects, as discussed in the various studies on which this review is based, can generate antagonistic or even neutral impact on plants, depending on the size of MPs/NPs and their mixing ratio with the co-contaminants. However, a combined exposure of edible plants to MPs/NPs and co-contaminants can also lead to hormetic adaptive responses. The data reviewed and discussed herein may relieve overlooked environmental impacts of treated wastewater reuse and may be useful to address challenges related to the combined effects of MPs/NPs and co-contaminants on edible plants after irrigation. The conclusions drawn in this review article are relevant to both direct (i.e., treated wastewater irrigation) and indirect (i.e., discharging treated wastewater in surface waters used for irrigation purposes) reuse, and may contribute to the implementation of the European Regulation 2020/741 on the minimum requirements for water reuse.

Lead contamination of soils, sediments, and vegetation in a shooting range and adjacent terrestrial and aquatic ecosystems: A holistic approach for evaluating potential risks.

It is well accepted that shooting ranges constitute hotspots of Pb contamination. This study evaluated the degree of Pb contamination of soils, sediments and vegetation within the boundaries of a highly visited shooting range, as well as the fluvial transport and dispersal of Pb, and therefore the contamination of adjacent river and water reservoir. Soils in the shooting range were severely contaminated with Pb, as indicated by the values of enrichment and contamination factor. The concentration of Pb in these soils ranged from 791 mg kg-1 to 7265 mg kg-1, being several dozens or even hundreds of times higher compared with control background samples. A temporary stream being in close proximity was also polluted, though to a much lesser extent. The degree of Pb contamination was negatively correlated with the distance from the shooting range. To this effect, the degree of contamination of the river and the water reservoir being in the vicinity of the shooting range was negligible, as sediments and water samples preserved similar Pb concentrations with control samples. However, cultivated (olives) and wild native plant species grown in the area of the shooting range were found to uptake and accumulate high concentrations of Pb in their tissues (even 50 times higher compared with control samples). The severe contamination of soils, sediments and vegetation in the studied shooting range can provoke very high ecological risks. Overall, results suggest that management measures should be undertaken within the boundaries of the studied shooting range.

Uptake of hexavalent chromium by Lactuca sativa and Triticum aestivum plants and mediated effects on their performance, linked with associated public health risks.

Plants exposed to toxic Cr(VI) concentrations show reduced biomass production and yield. The present study examined (1) the impacts of increasing Cr(VI) exposure (0.05, 0.5, 1, 5 and 10 mg L-1 K2Cr2O7 in irrigation water) on the growth and development, yield, and stress physiology of two important crop species, such as wheat (Triticum aestivum L.) and lettuce (Lactuca sativa L.), and (2) the associated human health risks due to the consumption of these commodities. Plants in all Cr(VI) treatments preserved similar growth rates and phenotypes with control, untreated plants, with no remarkable modulations in biomass yield (fresh/dry weight, plant height, straw/grain weight). Grains harvested from plants exposed to all Cr(VI) treatments had increased size and 1000 grain weight, partially suggesting hormetic effect. Elevated K2Cr2O7 concentrations (5 and 10 mg L-1) resulted in increased photosynthetic pigments' levels in lettuce leaves. Lipid peroxidation and H2O2 content also revealed the absence of oxidative stress in lettuce plants. Non-carcinogenic (target hazard quotient) and carcinogenic risks from the consumption of these commodities grown under the conditions described in this study were found de minimis. However, more studies are needed in order to obtain more solid information on the safety of Cr(VI)-contaminated water irrigation.

Systems biology reveals key tissue-specific metabolic and transcriptional signatures involved in the response of Medicago truncatula plant genotypes to salt stress.

Salt stress is an important factor limiting plant productivity by affecting plant physiology and metabolism. To explore salt tolerance adaptive mechanisms in the model legume Medicago truncatula, we used three genotypes with differential salt-sensitivity: TN6.18 (highly sensitive), Jemalong A17 (moderately sensitive), and TN1.11 (tolerant). Cellular damage was monitored in roots and leaves 48 h after 200 mM NaCl treatment by measuring lipid peroxidation, nitric oxide, and hydrogen peroxide contents, further supported by leaf stomatal conductance and chlorophyll readings. The salt-tolerant genotype TN1.11 displayed the lowest level of oxidative damage, in contrast to the salt sensitive TN6.18, which showed the highest responses. Metabolite profiling was employed to explore the differential genotype-related responses to stress at the molecular level. The metabolic data in the salt tolerant TN1.11 roots revealed an accumulation of metabolites related to the raffinose pathway. To further investigate the sensitivity to salinity, global transcriptomic profiling using microarray analysis was carried out on the salt-stressed sensitive genotypes. In TN6.18, the transcriptomic analysis identified a lower expression of many genes related to stress signalling, not previously linked to salinity, and corresponding to the TIR-NBS-LRR gene class. Overall, this global approach contributes to gaining significant new insights into the complexity of stress adaptive mechanisms and to the identification of potential targets for crop improvement.

Contamination of stream waters, sediments, and agricultural soil in the surroundings of an abandoned copper mine by potentially toxic elements and associated environmental and potential human health-derived risks: a case study from Agrokipia, Cyprus.

Abandoned mining areas have left a legacy of environmental damage with potential public health implications. The present study aimed at (1) assessing the level of contamination of the sites surrounding the Agrokipia abandoned copper mine in Cyprus through the mobilization of potentially toxic elements (PTEs), (2) correlating results with the mineralogy of the area, (3) discussing potential ecological and human health risks, and (4) proposing regeneration strategies. To this effect, the levels of 22 PTEs and other major elements were assessed in the acidic water of pit lakes, the tailings, the waters, and sediments of several streams originating from the mining site and flowing through the village of Agrokipia, and from agricultural soil from an impacted adjacent olive orchard. The pH values of water (pH < 2.7) in the pit lakes uncovered the acidic and oxidizing conditions that prevailed in the area. The acidity and the examined PTE concentrations in stream waters followed a decreasing trend with increasing distance from the tailing, reaching background values in a distance of 1500 m. The tailing spoil-heap was significantly enriched with Cu, Zn, Pb, Cd, Cr, and Ag (e.g., enrichment factor values up to 29 for Cu and 120 for Ag). Stream sediments and agricultural soil were contaminated with PTEs (mainly Cu, Zn, Pb, Cd, Cr, Ag, and Li), as evident by several contamination indices (i.e., enrichment and contamination factor). The level of contamination was correlated with the reported mineralogy of the site. The values of the degree of contamination (Cdeg = 62) and pollution load index (PLI = 2.4) indicated contamination of the sediments of the Voulgarides stream flowing through the village, suggesting potential public health implications to the local community. In addition, the values of the ecological risk factor suggested that the studied streams pose moderate ecological risks, mainly mediated by Cd and Cu. Overall, the results highlighted the need for undertaking regeneration measures for safeguarding environmental sustainability and public health.

Exploring the Potential of Nitric Oxide and Hydrogen Sulfide (NOSH)-Releasing Synthetic Compounds as Novel Priming Agents against Drought Stress in Medicago sativa Plants.

Land plants are continuously exposed to multiple abiotic stress factors like drought, heat, and salinity. Nitric oxide (NO) and hydrogen sulfide (H2S) are two well-examined signaling molecules that act as priming agents, regulating the response of plants to stressful conditions. Several chemical donors exist that provide plants with NO and H2S separately. NOSH is a remarkable novel donor as it can donate NO and H2S simultaneously to plants, while NOSH-aspirin additionally provides the pharmaceutical molecule acetylsalicylic acid. The current study aimed to investigate the potential synergistic effect of these molecules in drought-stressed Medicago sativa L. plants by following a pharmacological approach. Plants were initially pre-treated with both donors (NOSH and NOSH-aspirin) via foliar spraying, and were then subsequently exposed to a moderate water deficit while NO and H2S inhibitors (cPTIO and HA, respectively) were also employed. Phenotypic and physiological data showed that pre-treatment with NOSH synthetic compounds induced acclimation to subsequent drought stress and improved the recovery following rewatering. This was accompanied by modified reactive-oxygen and nitrogen-species signaling and metabolism, as well as attenuation of cellular damage, as evidenced by altered lipid peroxidation and proline accumulation levels. Furthermore, real-time RT-qPCR analysis revealed the differential regulation of multiple defense-related transcripts, including antioxidant enzymes. Overall, the present study proposed a novel role for NOSH compounds as efficient plant priming agents against environmental constraints through the coordinated regulation of multiple defense components, thus opening new horizons in the field of chemical priming research toward the use of target-selected compounds for stress tolerance enhancement.

Effects of prescription antibiotics on soil- and root-associated microbiomes and resistomes in an agricultural context.

The use of treated wastewater for crop irrigation is rapidly increasing to respond to the ever-growing demands for water and food resources. However, this practice may contribute to the spread of antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) in agricultural settings. To evaluate this potential risk, we analyzed microbiomes and resistomes of soil and Lactuca sativa L. (lettuce) root samples from pots irrigated with tap water spiked with 0, 20, or 100 µg L-1 of a mixture of three antibiotics (Trimethoprim, Ofloxacin, Sulfamethoxazole). The presence of antibiotics induced changes in bacterial populations, particularly in soil, as revealed by 16S rDNA sequence analysis. Parallel shotgun sequencing identified a total of 56 different ARGs conferring resistance against 14 antibiotic families. Antibiotic -treated samples showed increased loads of ARGs implicated in mutidrug resistance or in both direct and indirect acquired resistance. These changes correlated with the prevalence of Xantomonadales species in the root microbiomes. We interpret these data as indicating different strategies of soil and root microbiomes to cope with the presence of antibiotics, and as a warning that their presence may increase the loads of ARBs and ARGs in edible plant parts, therefore constituting a potential risk for human consumers.

Hexavalent chromium leads to differential hormetic or damaging effects in alfalfa (Medicago sativa L.) plants in a concentration-dependent manner by regulating nitro-oxidative and proline metabolism.

Chromium has been proven to be extremely phytotoxic. This study explored the impacts of increasing Cr(VI) exposure (up to 10 mg L-1 K2Cr2O7) on the growth and development of alfalfa plants and adaptation responses employed, in an environmentally relevant context. The threshold concentration of K2Cr2O7 in irrigation water beyond which stress responses are initiated is 1 mg L-1. Lower Cr(VI) exposure (0.5 mg L-1 K2Cr2O7) induced hormesis, evident through increased biomass and larger leaves, likely mediated by increased NO content (supported by elevated NR enzymatic activity and overexpression of NR and ndh genes). Elevated Cr(VI) exposure (5 and 10 mg L-1 K2Cr2O7) resulted in reduced biomass and smaller leaves, and lower levels of photosynthetic pigment (10 mg L-1 K2Cr2O7). Higher levels of lipid peroxidation, H2O2 and NO contents in these plants suggested nitro-oxidative stress. Stress responses included increased SOD and CAT enzymatic activities, further supported to some extent by MnSOD, FeSOD, Cu/ZnSOD and CAT transcripts levels. GST7 and GST17 gene expression patterns, as well as proline content, P5CS enzymatic activity and corresponding P5CS and P5CR gene expression levels emphasized the role of proline and GSTs in the adaptation responses. Results highlight the importance of managing Cr(VI) levels in irrigation water.

Uptake and bioaccumulation of three widely prescribed pharmaceutically active compounds in tomato fruits and mediated effects on fruit quality attributes.

Pharmaceutically active compounds (PhACs) released in agroecosystems have been found to be taken up by and accumulated in the edible parts of crop plants. By employing simulated hydroponic cultivation under controlled conditions, the present study aimed at evaluating 1) the uptake and bioaccumulation of three common PhACs (diclofenac, DCF; sulfamethoxazole, SMX; trimethoprim, TMP), either applied individually (10 µg L-1) or as mixture (10 µg L-1 each), in tomato fruits harvested from the first three fruit sets, and 2) the PhACs-mediated effects on fruit quality attributes. DCF was not detected in tomato fruits, whereas both SMX and TMP were detected in varying concentrations in fruits, depending on the time of harvest, the mode of application and the allocation of plants in the greenhouse. The studied PhACs applied at environmentally relevant concentrations did not significantly affect plant productivity. Nevertheless, important fruit quality attributes, such as soluble solids and carbohydrate (fructose, glucose, sucrose, total sugars) content were significantly impacted by all studied PhACs applied individually, suggesting that for DCF, potentially its transformation products (TPs) (not examined in this study) may exert significant effects on fruits quality attributes. In addition, no additive or synergistic effects of the mixture of PhACs on studied fruits quality attributes were revealed. Gene expression analysis showed that the PhACs-mediated effects on the carbohydrate content of fruits can be attributed, at least to some extent, to the significant modulation of the abundance of transcripts related to the biosynthesis and catabolism of sucrose, such as SlSuSys, SlLin5 and SlLin7. To our knowledge, this is the first report highlighting the potential effects of PhACs released in agroecosystems on the quality of widely consumed agricultural products. In any case, further studies are warranted for the overall assessment of the potential impacts of PhACs on the quality of agricultural products under conventional agricultural conditions.

Can the pharmaceutically active compounds released in agroecosystems be considered as emerging plant stressors?

Pharmaceutically active compounds (PhACs) entering agroecosystems as a result of various human activities may be taken up by and accumulated within crop plants, with potential human health implications. Despite their extensive metabolism by a sophisticated enzyme-based detoxification system in plant cells, PhACs and their transformation products (TPs) may result in adverse effects on plants' physiology. PhACs-mediated phytotoxic effects, as well as plants' defense responses have been depicted on plants exposed to individual or low number of PhACs under controlled conditions. We highlight the need to consider the cocktails effects and synergistic interactions of PhACs present in mixtures in actual agroecosystems, towards phytotoxicity and agricultural sustainability in general. Considering PhACs as emerging plant stressors will better facilitate the understanding of their phytotoxic effects.

Long-term wastewater irrigation of vegetables in real agricultural systems: Concentration of pharmaceuticals in soil, uptake and bioaccumulation in tomato fruits and human health risk assessment.

Wastewater (WW) reuse for vegetable crops irrigation is regularly applied worldwide. Such a practice has been found to allow the uptake of pharmaceutical active compounds (PhACs) by plants and their subsequent entrance to the food web, representing an important alternative pathway for the exposure of humans to PhACs, with potential health implications. Herein we report the impacts of the long-term (three consecutive years) WW irrigation of a tomato crop with two differently treated effluents under real agricultural conditions, on (1) the soil concentration of selected PhACs (i.e. diclofenac, DCF; sulfamethoxazole, SMX; trimethoprim, TMP), (2) the bioaccumulation of these PhACs in tomato fruits, and (3) the human risks associated with the consumption of WW-irrigated fruits. Results revealed that the concentration of the studied PhACs in both the soil and tomato fruits varied depending on the qualitative characteristics of the treated effluent applied and the duration of WW irrigation. The PhAC with the highest soil concentration throughout the studied period was SMX (0.98 µg kg-1), followed by TMP (0.62 µg kg-1) and DCF (0.35 µg kg-1). DCF was not found in tomato fruits harvested from WW-irrigated plants during the first year of the study. However, DCF displayed the highest fruit concentration (11.63 µg kg-1) throughout the study (as a result of prolonged WW irrigation), followed by SMX (5.26 µg kg-1) and TMP (3.40 µg kg-1). The calculated fruit bioconcentration factors (BCFF) were extremely high for DCF in the 2nd (108) and 3rd year (132) of the experimental period, with the respective values for SMX (0.5-5.4) and TMP (0.2-6.4) being significantly lower. The estimated threshold of toxicity concern (TTC) and hazard quotients (HQ) values revealed that the consumption of fruits harvested from tomato plants irrigated for long period with the WW applied for irrigation under field conditions in this study represent a de minimis risk to human health. However, more studies need to be performed in order to obtain more solid information on the safety of WW reuse for irrigation.